docs: copyright dates

docs: more code comments and minor style refactoring
fix: use URL to construct API requests
2026-06-30 10:52:41 +03:00 · 2026-05-24 08:30:01 +00:00 · 2026-05-24 08:28:09 +00:00 · 2026-05-24 08:27:00 +00:00 · 2026-05-23 07:04:29 +00:00 · 2026-05-22 09:53:27 +00:00
42 changed files with 2627 additions and 2487 deletions
@@ -6,7 +6,7 @@
 	"image": "mcr.microsoft.com/devcontainers/dotnet:1-10.0",
 	// Features to add to the dev container. More info: https://containers.dev/features.
 	"features": {
-		"ghcr.io/devcontainers/features/node:1": {
+		"ghcr.io/devcontainers/features/node:2": {
 			"version": "lts",
 			"pnpmVersion": "none",
 			"nvmVersion": "latest"
@@ -48,7 +48,10 @@ updates:
    schedule:
      interval: monthly
    rebase-strategy: disabled
-    open-pull-requests-limit: 20
+    groups:
+      all:
+        patterns:
+          - "*"

  - package-ecosystem: "github-actions"
    directory: "/"
@@ -58,7 +61,10 @@ updates:
    schedule:
      interval: monthly
    rebase-strategy: disabled
-    open-pull-requests-limit: 20
+    groups:
+      all:
+        patterns:
+          - "*"

  - package-ecosystem: "devcontainers"
    directory: "/"
@@ -68,7 +74,10 @@ updates:
    schedule:
      interval: monthly
    rebase-strategy: disabled
-    open-pull-requests-limit: 20
+    groups:
+      all:
+        patterns:
+          - "*"

  - package-ecosystem: "docker"
    directories:
@@ -80,4 +89,7 @@ updates:
    schedule:
      interval: monthly
    rebase-strategy: disabled
-    open-pull-requests-limit: 20
+    groups:
+      all:
+        patterns:
+          - "*"
@@ -31,16 +31,16 @@ jobs:
    runs-on: ubuntu-latest

    steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6

-      - uses: docker/build-push-action@v6
+      - uses: docker/build-push-action@v7
        with:
          context: ./api
          tags: ${{ github.repository }}-api:ci

      - run: docker save ${{ github.repository }}:ci | gzip > api_image.tar.gz

-      - uses: actions/upload-artifact@v5
+      - uses: actions/upload-artifact@v7
        with:
          name: api-image
          path: api_image.tar.gz
@@ -49,16 +49,16 @@ jobs:
    runs-on: ubuntu-latest

    steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6

-      - uses: docker/build-push-action@v6
+      - uses: docker/build-push-action@v7
        with:
          context: ./app
          tags: ${{ github.repository }}-app:ci

      - run: docker save ${{ github.repository }}:ci | gzip > app_image.tar.gz

-      - uses: actions/upload-artifact@v5
+      - uses: actions/upload-artifact@v7
        with:
          name: app-image
          path: app_image.tar.gz
@@ -68,7 +68,7 @@ jobs:
    container: node:latest

    steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6

      - run: npm install
        working-directory: ./app
@@ -82,7 +82,7 @@ jobs:
      - run: npm audit --audit-level=moderate --json > audit_report.json
        working-directory: ./app

-      - uses: actions/upload-artifact@v5
+      - uses: actions/upload-artifact@v7
        with:
          name: app-audit-report
          path: ./app/audit_report.json
@@ -13,9 +13,9 @@ jobs:
    runs-on: ubuntu-latest

    steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6

-      - uses: docker/metadata-action@v5
+      - uses: docker/metadata-action@v6
        id: meta
        with:
          images: |
@@ -26,19 +26,19 @@ jobs:
            ${{ github.ref_name }}

      - name: "Login to Docker Hub"
-        uses: docker/login-action@v3
+        uses: docker/login-action@v4
        with:
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: "Login to GitHub Container Registry"
-        uses: docker/login-action@v3
+        uses: docker/login-action@v4
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GITHUB_TOKEN }}

-      - uses: docker/build-push-action@v6
+      - uses: docker/build-push-action@v7
        with:
          context: ./api
          push: true
@@ -48,9 +48,9 @@ jobs:
    runs-on: ubuntu-latest

    steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6

-      - uses: docker/metadata-action@v5
+      - uses: docker/metadata-action@v6
        id: meta
        with:
          images: |
@@ -61,19 +61,19 @@ jobs:
            ${{ github.ref_name }}

      - name: "Login to Docker Hub"
-        uses: docker/login-action@v3
+        uses: docker/login-action@v4
        with:
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: "Login to GitHub Container Registry"
-        uses: docker/login-action@v3
+        uses: docker/login-action@v4
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GITHUB_TOKEN }}

-      - uses: docker/build-push-action@v6
+      - uses: docker/build-push-action@v7
        with:
          context: ./app
          push: true
@@ -93,7 +93,7 @@ jobs:
      url: ${{ steps.deployment.outputs.page_url }}

    steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6

      - run: npm install
        working-directory: ./app
@@ -104,12 +104,12 @@ jobs:
        working-directory: ./app

      - name: Setup Pages
-        uses: actions/configure-pages@v5
+        uses: actions/configure-pages@v6

-      - uses: actions/upload-pages-artifact@v4
+      - uses: actions/upload-pages-artifact@v5
        with:
          path: "./app/dist"

      - name: Deploy to GitHub Pages
        id: deployment
-        uses: actions/deploy-pages@v4
+        uses: actions/deploy-pages@v5
@@ -1,6 +1,6 @@
 MIT License

-Copyright (c) 2025 Eugene Fox
+Copyright (c) 2026 Eugene Fox

 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -14,7 +14,7 @@ This is my farewell gift to the university.

 ## Demo

-<!-- TODO: put demo here -->
+![Demo](/assets/demo.gif)

 ## Q&A

@@ -45,4 +45,4 @@ If you're interested in becoming a maintainer, please reach out to me via email
 [![GitHub](https://img.shields.io/badge/%40xfox111-GitHub?logo=github&logoColor=%23181717&label=GitHub&labelColor=white&color=%23181717)](https://github.com/xfox111)
 [![Buy Me a Coffee](https://img.shields.io/badge/%40xfox111-BMC?logo=buymeacoffee&logoColor=black&label=Buy%20me%20a%20coffee&labelColor=white&color=%23FFDD00)](https://buymeacoffee.com/xfox111)

-> ©2025 Eugene Fox. Licensed under [MIT license](https://github.com/XFox111/bonch-calendar/blob/main/LICENSE)
+> ©2026 Eugene Fox. Licensed under [MIT license](https://github.com/XFox111/bonch-calendar/blob/main/LICENSE)
@@ -3,6 +3,10 @@
 ##
 ## Get latest from `dotnet new gitignore`

+# Solution files
+*.sln
+*.slnx
+
 # dotenv files
 .env

@@ -480,3 +480,5 @@ $RECYCLE.BIN/

 # Vim temporary swap files
 *.swp
+
+core
@@ -0,0 +1,18 @@
+using System.Text.Json.Serialization;
+using BonchCalendar.Health;
+
+namespace BonchCalendar;
+
+/// <summary>
+/// Custom JSON serializer context for static serialization/deserialization of requests and responses
+/// </summary>
+[JsonSerializable(typeof(string))]
+[JsonSerializable(typeof(string[]))]
+[JsonSerializable(typeof(int))]
+[JsonSerializable(typeof(bool))]
+[JsonSerializable(typeof(StatsResponse))]
+[JsonSerializable(typeof(Dictionary<int, string>))]
+[JsonSerializable(typeof(HealthResponse))]
+internal partial class AppJsonSerializerContext : JsonSerializerContext
+{
+}
@@ -4,13 +4,13 @@
 		<TargetFramework>net10.0</TargetFramework>
 		<Nullable>enable</Nullable>
 		<ImplicitUsings>enable</ImplicitUsings>
+		<PublishAot>true</PublishAot>
 	</PropertyGroup>

 	<ItemGroup>
 		<PackageReference Include="AngleSharp" Version="1.4.0" />
-		<PackageReference Include="AspNetCore.HealthChecks.UI.Client" Version="9.0.0" />
-		<PackageReference Include="Ical.Net" Version="5.1.2" />
-		<PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="10.0.0" />
+		<PackageReference Include="Ical.Net" Version="5.2.2" />
+		<PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="10.0.8" />
 	</ItemGroup>

 </Project>
@@ -5,6 +5,11 @@ Accept: application/json

 ###

+GET {{Host}}/stats
+Accept: application/json
+
+###
+
 GET {{Host}}/faculties
 Accept: application/json

@@ -12,7 +17,7 @@ Accept: application/json

 GET {{Host}}/groups
 	?facultyId=56682
-	&course=2
+	&year=2
 Accept: application/json

 ###
@@ -20,4 +25,10 @@ Accept: application/json
@groupId = 56606
@facultyId = 50029
 GET {{Host}}/timetable/{{facultyId}}/{{groupId}}
+	?id=download
 Accept: text/calendar
+
+# id parameter changes behavior for the calendar:
+# - If set to "download", nothing changes
+# - If not present, an additional event will be appended to the calendar (see Program.cs)
+# - If set to any other value, this request will be counted in active users stats (only once per ID until the next restart)
@@ -1,34 +0,0 @@
-
-Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio Version 17
-VisualStudioVersion = 17.0.31903.59
-MinimumVisualStudioVersion = 10.0.40219.1
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BonchCalendar", "BonchCalendar.csproj", "{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}"
-EndProject
-Global
-	GlobalSection(SolutionConfigurationPlatforms) = preSolution
-		Debug|Any CPU = Debug|Any CPU
-		Debug|x64 = Debug|x64
-		Debug|x86 = Debug|x86
-		Release|Any CPU = Release|Any CPU
-		Release|x64 = Release|x64
-		Release|x86 = Release|x86
-	EndGlobalSection
-	GlobalSection(ProjectConfigurationPlatforms) = postSolution
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Debug|x64.ActiveCfg = Debug|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Debug|x64.Build.0 = Debug|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Debug|x86.ActiveCfg = Debug|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Debug|x86.Build.0 = Debug|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Release|Any CPU.Build.0 = Release|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Release|x64.ActiveCfg = Release|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Release|x64.Build.0 = Release|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Release|x86.ActiveCfg = Release|Any CPU
-		{811C13A0-E5FC-452C-8628-AD36B9A8A7E2}.Release|x86.Build.0 = Release|Any CPU
-	EndGlobalSection
-	GlobalSection(SolutionProperties) = preSolution
-		HideSolutionNode = FALSE
-	EndGlobalSection
-EndGlobal
@@ -0,0 +1,3 @@
+<Solution>
+	<Project Path="BonchCalendar.csproj" />
+</Solution>
@@ -1,15 +1,21 @@
-FROM mcr.microsoft.com/dotnet/sdk:10.0-alpine AS build
+FROM mcr.microsoft.com/dotnet/sdk:10.0-alpine-aot AS build
 WORKDIR /build

-ADD *.csproj .
-RUN dotnet restore
+ADD --link . .
+RUN --mount=type=cache,target=/root/.nuget \
+	--mount=type=cache,target=/source/bin \
+	--mount=type=cache,target=/source/obj \
+	dotnet publish --output /out BonchCalendar.csproj \
+	&& rm /out/*.dbg /out/*.Development.json

-ADD . ./
-RUN dotnet publish --no-restore --configuration Release --output /out
-
-FROM mcr.microsoft.com/dotnet/aspnet:10.0-alpine AS prod
+FROM mcr.microsoft.com/dotnet/runtime-deps:10.0-alpine AS prod
 WORKDIR /app

-COPY --from=build /out/* .
+COPY --link --from=build /out/* .
+USER $APP_UID

-ENTRYPOINT [ "dotnet", "BonchCalendar.dll" ]
+HEALTHCHECK --interval=60s --retries=3 --start-period=5s --timeout=10s \
+	CMD wget --no-verbose --tries 1 --spider http://localhost:8080/health || exit 1
+
+EXPOSE 8080
+ENTRYPOINT [ "./BonchCalendar" ]
@@ -0,0 +1,8 @@
+// This file is used by Code Analysis to maintain SuppressMessage
+// attributes that are applied to this project.
+// Project-level suppressions either have no target or are given
+// a specific target and scoped to a namespace, type, member, etc.
+
+using System.Diagnostics.CodeAnalysis;
+
+[assembly: SuppressMessage("Performance", "CA1873:Avoid potentially expensive logging", Justification = "The cost is negligible on current setup.")]
@@ -3,24 +3,24 @@ using Microsoft.Extensions.Diagnostics.HealthChecks;

 namespace BonchCalendar.Health;

-public class ApiHealthCheck(ApiService groupService) : IHealthCheck
+/// <summary>
+/// Healthcheck service for sut.ru API.
+/// </summary>
+public class ApiHealthCheck(IssueTrackingService trackingService) : IHealthCheck
 {
 	public async Task<HealthCheckResult> CheckHealthAsync(
 		HealthCheckContext context, CancellationToken cancellationToken = default
 	)
 	{
-		try
-		{
-			Dictionary<int, string> faculties = await groupService.GetFacultiesListAsync();
+		Dictionary<string, object> report = trackingService.GetReport();

-			if (faculties.Count > 0)
-				return HealthCheckResult.Healthy();
+		// We deem service "unhealthy" if any of the last requests to the API were unsuccessful.
+		if (report.Count > 0)
+			return HealthCheckResult.Unhealthy(
+				description: "We're having issues with fetching data from the timetable website.",
+				data: report
+			);

-			return HealthCheckResult.Degraded(description: "Timetable website looks to be up, but returned an empty list of faculties.");
-		}
-		catch (Exception ex)
-		{
-			return HealthCheckResult.Unhealthy(description: "Timetable website appears to be down.", exception: ex);
-		}
+		return HealthCheckResult.Healthy();
 	}
 }
@@ -0,0 +1,80 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+
+namespace BonchCalendar.Health;
+
+public static class HealthCheckWriter
+{
+	private static readonly byte[] _emptyResponse = [ (byte)'{', (byte)'}' ];
+	private static readonly JsonSerializerContext _jsonContext = CreateSerializerContext();
+
+	public static async Task WriteHealthCheckResponse(HttpContext context, HealthReport report)
+	{
+		if (report is null)
+		{
+			// Just in case, but this should not ever happen.
+			await context.Response.BodyWriter.WriteAsync(_emptyResponse).ConfigureAwait(false);
+			return;
+		}
+
+		// Create DTO from the report.
+		HealthResponse response = new(
+			Status: report.Status,
+			TotalDuration: report.TotalDuration,
+			Entries: report.Entries.ToDictionary(
+				e => e.Key,
+				e => new HealthResponseEntry(
+					Status: e.Value.Status,
+					Description: e.Value.Description,
+					Duration: e.Value.Duration,
+					Data: e.Value.Data
+				)
+			)
+		);
+
+		// Write DTO to the response body.
+		context.Response.ContentType = "application/json; charset=utf-8";
+		await JsonSerializer.SerializeAsync(context.Response.Body, response, typeof(HealthResponse), _jsonContext).ConfigureAwait(false);
+	}
+
+	private static AppJsonSerializerContext CreateSerializerContext()
+	{
+		JsonSerializerOptions options = new()
+		{
+			PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+			DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+		};
+
+		options.Converters.Add(new JsonStringEnumConverter<HealthStatus>(options.PropertyNamingPolicy));
+		options.TypeInfoResolverChain.Insert(0, AppJsonSerializerContext.Default);
+
+		return new AppJsonSerializerContext(options);
+	}
+}
+
+/// <summary>
+/// Response body for /health endpoint.
+/// </summary>
+/// <param name="Status">Overall status of the application.</param>
+/// <param name="TotalDuration">Total time it took to complete the health check.</param>
+/// <param name="Entries">List of subcomponent healthcheck reports.</param>
+public record HealthResponse(
+	HealthStatus Status,
+	TimeSpan TotalDuration,
+	IReadOnlyDictionary<string, HealthResponseEntry> Entries
+);
+
+/// <summary>
+/// Healthcheck report for a subcomponent.
+/// </summary>
+/// <param name="Status">Status of the subcomponent.</param>
+/// <param name="Description">Report remarks.</param>
+/// <param name="Duration">Time it took to complete health check for this subcomponent.</param>
+/// <param name="Data">Addtional report data.</param>
+public record HealthResponseEntry(
+	HealthStatus Status,
+	string? Description,
+	TimeSpan Duration,
+	IReadOnlyDictionary<string, object> Data
+);
@@ -4,19 +4,23 @@ using BonchCalendar;
 using BonchCalendar.Health;
 using BonchCalendar.Services;
 using BonchCalendar.Utils;
-using HealthChecks.UI.Client;
-using Ical.Net;
-using Ical.Net.CalendarComponents;
-using Ical.Net.Serialization;
+using Ical.Net.DataTypes;
 using Microsoft.AspNetCore.Diagnostics.HealthChecks;
 using Microsoft.AspNetCore.Mvc;

-WebApplicationBuilder builder = WebApplication.CreateBuilder(args);
+WebApplicationBuilder builder = WebApplication.CreateSlimBuilder(args);
+
+// Adding static JSON serializer since we're running in Native AOT
+builder.Services.ConfigureHttpJsonOptions(options =>
+	options.SerializerOptions.TypeInfoResolverChain.Insert(0, AppJsonSerializerContext.Default)
+);

 // Add services to the container.
 // Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
-builder.Services.AddOpenApi();
-builder.Services.AddValidation();
+builder.Services.AddOpenApi();      // OpenAPI specification generator
+builder.Services.AddValidation();   // Request validation
+
+// Customizing non-200 responses to include trace identifier and a no-as-a-service reason
 builder.Services.AddProblemDetails(configure =>
 {
 	configure.CustomizeProblemDetails = context =>
@@ -27,104 +31,205 @@ builder.Services.AddProblemDetails(configure =>
 });

 builder.Services
-	.AddScoped<ApiService>()
-	.AddScoped<ParsingService>();
+	.AddSingleton<IssueTrackingService>()       // Service for tracking latest API request results
+	.AddScoped<TimetableService>()              // Service for generating a timetable
+	.AddScoped<ApiService>()                    // Service for making API calls to sut.ru API
+	.AddScoped<ParsingService>();               // Service for parsing timetable from sut.ru

 builder.Services.AddHealthChecks()
-	.AddCheck<ApiHealthCheck>("timetable_website");
+	.AddCheck<ApiHealthCheck>("timetable_website");     // Healthcheck service

+// Get ORIGIN_DOMAIN environmental variable
+string? corsDomain = Environment.GetEnvironmentVariable("ORIGIN_DOMAIN");
+
+// Configure defautl CORS policy
 builder.Services.AddCors(options =>
 	options.AddDefaultPolicy(policy =>
+	{
+		// Allow only GET requests with any headers
 		policy
 			.WithMethods(["GET"])
-			.AllowAnyOrigin()
-			.AllowAnyHeader()
-	)
+			.AllowAnyHeader();
+
+		// If ORIGIN_DOMAIN environmental variable is set, allow request only from this domain,
+		// otherwise allow request from any domains.
+		if (string.IsNullOrWhiteSpace(corsDomain))
+			policy.AllowAnyOrigin();
+		else
+			policy.WithOrigins(corsDomain);
+	})
 );

 WebApplication app = builder.Build();

-// Configure the HTTP request pipeline.
-app.UseCors();
-app.UseStatusCodePages();
-app.MapOpenApi();
+// Configure the HTTP request pipeline
+app.UseCors();                  // Enable CORS
+app.UseStatusCodePages();       // Enable default JSON response body for non-200 responses.
+app.MapOpenApi();               // Map OpenAPI sepcification. Available at /openapi/v1.json

+// Map healthcheck endpoint with custom response writer
+// Remark: /health and /openapi/v1.json endpoints are not present in OpenAPI specification.
 app.MapHealthChecks("/health", new HealthCheckOptions
 {
-	ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse
+	ResponseWriter = HealthCheckWriter.WriteHealthCheckResponse
 });

+// Request singleton services which will be used in subsequent endpoints
 ILogger<Program> logger = app.Services.GetRequiredService<ILogger<Program>>();
+IssueTrackingService tracker = app.Services.GetRequiredService<IssueTrackingService>();

+// List of identifiers for tracking unique visits to /timetable endpoint (essentially, for unique user counting).
+List<string> ids = [];
+
+// Statistics endpoint. Shows number of active users.
+app.MapGet("/stats", () => Results.Ok(new StatsResponse(ids.Count)))
+	.WithName("GetStats")
+	.WithDescription("Get basic usage statistics.")
+	.Produces<StatsResponse>(StatusCodes.Status200OK);
+
+// Retrieve list of faculties and their IDs from sut.ru API
 app.MapGet("/faculties", async ([FromServices] ApiService apiService) =>
 {
-	logger.LogInformation("Fetching faculties list.");
-	Dictionary<int, string> faculties = await apiService.GetFacultiesListAsync();
-	return Results.Ok(faculties);
+	try
+	{
+		Dictionary<int, string> faculties = await apiService.GetFacultiesListAsync();
+		logger.LogInformation("Fetched {Count} faculties.", faculties.Count);
+		tracker.TrackFacultyFetch(true);        // Record that last attempt to retrieve faculties was successful
+		return Results.Ok(faculties);
+	}
+	catch (Exception ex)
+	{
+		logger.LogError(ex, "Failed to fetch faculties list.");
+		tracker.TrackFacultyFetch(false);       // Record that last attempt to retrieve faculties was unsuccessful
+		return Results.Problem("Failed to fetch faculties list.", statusCode: StatusCodes.Status500InternalServerError);
+	}
 })
 	.WithName("GetFaculties")
 	.WithDescription("Gets the list of faculties.")
+	.ProducesProblem(StatusCodes.Status500InternalServerError)
 	.Produces<Dictionary<int, string>>(StatusCodes.Status200OK);

-app.MapGet("/groups", async ([FromServices] ApiService apiService, int facultyId, [Range(1, 5)] int course) =>
+// Retrieve list of groups for a chosen faculty and year.
+// Year can be in range from 1 to 5.
+// If year is not specified, all groups for chosen faculty will be retrieved.
+app.MapGet("/groups", async ([FromServices] ApiService apiService, int facultyId, [Range(1, 5)] int? year) =>
 {
-	logger.LogInformation("Fetching groups list for faculty {FacultyId} and course {Course}.", facultyId, course);
-	Dictionary<int, string> groups = await apiService.GetGroupsListAsync(facultyId, course);
-	return Results.Ok(groups);
+	year ??= 0;     // Setting year to 0 (show all groups) if not specified in the request.
+
+	try
+	{
+		Dictionary<int, string> groups = await apiService.GetGroupsListAsync(facultyId, year.Value);
+		logger.LogInformation("Fetched {Count} groups (facultyId: {FacultyId}, year: {Year}).", groups.Count, facultyId, year);
+		tracker.TrackGroupFetch(facultyId, year.Value, true);   // Track whether retrieving groups for this specific faculty and year was successul or not.
+		return Results.Ok(groups);
+	}
+	catch (Exception ex)
+	{
+		logger.LogError(ex, "Failed to fetch groups list (facultyId: {FacultyId}, year: {Year}).", facultyId, year);
+		tracker.TrackGroupFetch(facultyId, year.Value, false);  // Track whether retrieving groups for this specific faculty and year was successul or not.
+		return Results.Problem(
+			"Failed to fetch groups list.",
+			statusCode: StatusCodes.Status500InternalServerError,
+			extensions: new Dictionary<string, object?>
+			{
+				["facultyId"] = facultyId,
+				["year"] = year
+			}
+		);
+	}
 })
 	.WithName("GetGroups")
 	.WithDescription("Gets the list of groups for the specified faculty and course.")
 	.Produces<Dictionary<int, string>>(StatusCodes.Status200OK)
+	.ProducesProblem(StatusCodes.Status500InternalServerError)
 	.ProducesValidationProblem();

+// Retrieve timetable for specified group in form of iCal.
 app.MapGet("/timetable/{facultyId}/{groupId}", async (
-	int facultyId, int groupId,
-	[FromServices] ApiService apiService,
-	[FromServices] ParsingService parsingService
+	int facultyId, int groupId, string? id,
+	[FromServices] TimetableService timetableService
 ) =>
 {
-	logger.LogInformation("Generating timetable for group {GroupId} of faculty {FacultyId}.", groupId, facultyId);
-	string cacheFile = Path.Combine(Path.GetTempPath(), $"bonch_cal_{groupId}.ics");
+	string? content = await timetableService.TryGetTimetableFromCacheAsync(groupId);
+	bool hasId = !string.IsNullOrEmpty(id);

-	if (File.Exists(cacheFile) && (DateTime.UtcNow - File.GetLastWriteTimeUtc(cacheFile)).TotalHours < 6)
+	// If this is the first request with given id, we record it.
+	// "download" is a special "ID" that is used solely for downloading timetable as file.
+	if (hasId && id is not "download" && !ids.Contains(id!))
+		ids.Add(id!);
+
+	// If we have a valid cache, we serve it, instead of retrieving new timetable from sut.ru API
+	// We don't serve cache for requests with no ID, since they have a special behavior.
+	if (content is not null && hasId)
 	{
-		if (args.Contains("--no-cache"))
-			logger.LogWarning("Cache disabled via --no-cache, regenerating timetable for group {GroupId}.", groupId);
+		logger.LogInformation("Serving timetable for {FacultyId}/{GroupId} from cache.", facultyId, groupId);
+		return Results.Text(content, contentType: "text/calendar");
+	}
+
+	try
+	{
+		logger.LogInformation("Begin generating timetable for {FacultyId}/{GroupId}.", facultyId, groupId);
+
+		if (hasId)
+			content = await timetableService.GetTimetableAsync(facultyId, groupId, saveToCache: true);
 		else
 		{
-			logger.LogInformation("Serving timetable for group {GroupId} from cache.", groupId);
-			return Results.Text(await File.ReadAllTextAsync(cacheFile), contentType: "text/calendar");
+			// For requests with no ID we append an event at 7pm that asks users to update their calendar URL,
+			// since now all /timetable requests must have one.
+			// This is a temporary behavior that will be changed to just sending 4xx response instead later.
+			content = await timetableService.GetTimetableAsync(facultyId, groupId, saveToCache: false, transform: calendar =>
+				calendar.Events.Add(new()
+				{
+					Summary = "Важно: обновите календарь расписания",
+					Description = """
+					Ваша ссылка на календарь устарела. Пожалуйста, обновите ее чтобы продолжить пользоватся сервисом.
+
+					Новая ссылка позволит нам собирать статистику о количестве активных пользователей. Важно: мы НЕ собираем какие-либо персональные данные! Новая ссылка лишь позволит нам узнать точное количесво пользователей, что очень важно для продолжения работы сервиса.
+
+					Для того чтобы обновить ссылку:
+					1. Перейдите на сайт https://bonch.xfox111.net/
+					2. Повторите все действия что и при создании календаря
+					3. Удалите старый календарь
+
+					Просим прощения за доставленные неудобства.
+
+					Если возникнут вопросы – обращайтесь на почту feedback@xfox111.net
+
+					Это событие будет появляться каждый день в 19:00 до тех пор, пока ссылка не будет обновлена.
+					""",
+					Location = "https://bonch.xfox111.net",
+					Start = new CalDateTime((DateTime.Today + TimeSpan.FromHours(16)).ToUniversalTime()),
+					End = new CalDateTime((DateTime.Today + TimeSpan.FromHours(16) + TimeSpan.FromMinutes(15)).ToUniversalTime()),
+				})
+			);
+			logger.LogInformation("Deprecation notice appended to calendar {FacultyId}/{GroupId}.", facultyId, groupId);
 		}
+
+		logger.LogInformation("Fetched timetable for {FacultyId}/{GroupId}.", facultyId, groupId);
+		tracker.TrackTimetableFetch(facultyId, groupId, true);      // Track whether retrieving timetable for this specific group was successul or not.
+		return Results.Text(content, contentType: "text/calendar");
 	}
-
-	DateTime semesterStartDate = await apiService.GetSemesterStartDateAsync(groupId);
-	string groupName = (await apiService.GetGroupsListAsync(facultyId, 0))[groupId];
-
-	string classesRaw = await apiService.GetScheduleDocumentAsync(groupId, TimetableType.Classes);
-	List<CalendarEvent> timetable = [.. parsingService.ParseGeneralTimetable(classesRaw, semesterStartDate, groupName)];
-
-	TimetableType[] types = [TimetableType.Attestations, TimetableType.Exams, TimetableType.ExamsForExtramural];
-	foreach (TimetableType type in types)
+	catch (Exception ex)
 	{
-		classesRaw = await apiService.GetScheduleDocumentAsync(groupId, type);
-		timetable.AddRange(parsingService.ParseExamTimetable(classesRaw, groupName));
+		logger.LogError(ex, "Failed to generate timetable for {FacultyId}/{GroupId}.", facultyId, groupId);
+		tracker.TrackTimetableFetch(facultyId, groupId, false);     // Track whether retrieving timetable for this specific group was successul or not.
+
+		return Results.Problem(
+			"Failed to fetch timetable",
+			statusCode: StatusCodes.Status500InternalServerError,
+			extensions: new Dictionary<string, object?>
+			{
+				["facultyId"] = facultyId,
+				["groupId"] = groupId
+			}
+		);
 	}
-
-	Calendar calendar = new();
-	calendar.Properties.Add(new CalendarProperty("X-WR-CALNAME", groupName));
-	calendar.Properties.Add(new CalendarProperty("X-WR-TIMEZONE", "Europe/Moscow"));
-	calendar.Properties.Add(new CalendarProperty("REFRESH-INTERVAL;VALUE=DURATION", "PT6H"));
-	calendar.Events.AddRange(timetable);
-	calendar.AddTimeZone(new VTimeZone("Europe/Moscow"));
-	string serialized = new CalendarSerializer().SerializeToString(calendar)!;
-
-	await File.WriteAllTextAsync(cacheFile, serialized);
-	logger.LogInformation("Cached timetable for group {GroupId} to {CacheFile}.", groupId, cacheFile);
-	return Results.Text(serialized, contentType: "text/calendar");
 })
 	.WithName("GetTimetable")
 	.WithDescription("Gets the iCal timetable for the specified group.")
 	.Produces<string>(StatusCodes.Status200OK, "text/calendar")
+	.ProducesProblem(StatusCodes.Status500InternalServerError)
 	.ProducesValidationProblem();

+// Start the application.
 app.Run();
@@ -4,8 +4,19 @@ using BonchCalendar.Utils;

 namespace BonchCalendar.Services;

+// For better understanding of what is happening here,
+// I recommend visiting https://cabinet.sut.ru/raspisanie_all_new.php
+// and trying to send requests yourself.
+
+/// <summary>
+/// Service for calling sut.ru API.
+/// </summary>
 public class ApiService
 {
+	/// <summary>
+	/// Retrieve list of faculties and their IDs.
+	/// </summary>
+	/// <returns>A dictionary, where the key is faculty's ID and the value is faculty's name.</returns>
 	public async Task<Dictionary<int, string>> GetFacultiesListAsync() =>
 		ParseListResponse(await SendRequestAsync(new()
 		{
@@ -13,15 +24,30 @@ public class ApiService
 			["schet"] = GetCurrentSemesterId()
 		}));

-	public async Task<Dictionary<int, string>> GetGroupsListAsync(int facultyId, int course) =>
+	/// <summary>
+	/// Retrieve list of groups for specified faculty and year.
+	/// </summary>
+	/// <param name="facultyId">ID of selected faculty.</param>
+	/// <param name="year">An academic year. Should be from 0 to 5.</param>
+	/// <returns>A dictionary, where the key is group's ID and the value is group's name.</returns>
+	/// <remarks>
+	/// If <paramref name="year"/> is set to 0, all groups for the specified faculty will be retrieved instead.
+	/// </remarks>
+	public async Task<Dictionary<int, string>> GetGroupsListAsync(int facultyId, int year) =>
 		ParseListResponse(await SendRequestAsync(new()
 		{
 			["choice"] = "1",
 			["schet"] = GetCurrentSemesterId(),
 			["faculty"] = facultyId.ToString(), // Specifying faculty ID returns a list of groups
-			["kurs"] = course.ToString()        // Course number is actually optional, but filters out other groups. Can be set 0 to get all groups of the faculty.
+			["kurs"] = year.ToString()        // Course number is actually optional, but filters out other groups. Can be set 0 to get all groups of the faculty.
 		}));

+	/// <summary>
+	/// Retrieve timetable document for the specified group.
+	/// </summary>
+	/// <param name="groupId">ID of selected group.</param>
+	/// <param name="timetableType">Type of a timetable to retrieve.</param>
+	/// <returns>A string, represeting raw HTML document, that contains the timetable.</returns>
 	public async Task<string> GetScheduleDocumentAsync(int groupId, TimetableType timetableType) =>
 		await SendRequestAsync(new()
 		{
@@ -30,14 +56,34 @@ public class ApiService
 			["group"] = groupId.ToString()
 		});

+	/// <summary>
+	/// Retrieve current semester start date.
+	/// </summary>
+	/// <param name="groupId">ID of a group.</param>
+	/// <returns>A <see cref="DateTime"/> object, representing the first day of current semester.</returns>
+	/// <remarks>
+	/// <paramref name="groupId"/> can be any valid group ID. We only need it for retrieving a correct HTML document.
+	/// </remarks>
 	public async Task<DateTime> GetSemesterStartDateAsync(int groupId)
 	{
 		using HttpClient client = new();
+		// We go to this URL, since it has to contain current week number,
+		// which we can use to calculate the first day of the semester.
+		// If we don't specify group, we'll get a page listing all available groups,
+		// which doesn't contain current week number, thus, rendering it useless for us.
 		string content = await client.GetStringAsync($"https://www.sut.ru/studentu/raspisanie/raspisanie-zanyatiy-studentov-ochnoy-i-vecherney-form-obucheniya?group={groupId}");

 		using IHtmlDocument doc = new HtmlParser().ParseDocument(content);
+
+		// 1. Get <a> tag with id "rasp-prev"
+		// 2. Get it's neighbor <div> tag that is the second child of their parent tag
+		// 3. Get <span> tag inside the <div>
 		string labelText = doc.QuerySelector("a#rasp-prev + div:nth-child(2) > span")!.TextContent;
+
+		// Content of the <span> tag is supposed to be something like "Нечетная неделя (15)"
+		// So, we can use regular expressions to get the "15" part and parse it to an integer.
 		int weekNumber = int.Parse(ParserUtils.NumberRegex().Match(labelText).Value);
+
 		DateTime currentDate = DateTime.Today;
 		currentDate = currentDate
 			.AddDays(-(int)currentDate.DayOfWeek + 1) // Move to Monday
@@ -46,6 +92,8 @@ public class ApiService
 		return currentDate;
 	}

+	// Utility method that converts faculty or group list response into a dictionary.
+	// It expected the reponse to be in format: "1,Group 1;2,Group2;..."
 	private static Dictionary<int, string> ParseListResponse(string responseContent) =>
 		responseContent
 			.Split(';', StringSplitOptions.RemoveEmptyEntries)
@@ -55,7 +103,8 @@ public class ApiService
 				parts => parts[1]
 			);

-	public async Task<string> SendRequestAsync(Dictionary<string, string> formData)
+	// Utility method for sending request to sut.ru API.
+	private static async Task<string> SendRequestAsync(Dictionary<string, string> formData)
 	{
 		HttpRequestMessage request = new(HttpMethod.Post, "https://cabinet.sut.ru/raspisanie_all_new.php")
 		{
@@ -64,7 +113,8 @@ public class ApiService

 		using HttpClient client = new(new HttpClientHandler
 		{
-			// Sometimes Bonch being Bonch just doesn't renew its SSL certificates properly
+			// Sometimes Bonch being Bonch just doesn't renew its SSL certificates properly,
+			// so we just assume that we're in the right place.
 			ServerCertificateCustomValidationCallback = (sender, cert, chain, sslPolicyErrors) => true
 		});

@@ -81,11 +131,12 @@ public class ApiService
 			? 1         // August through January - first semester
 			: 2;        // Everything else - second

-		int termStartYear = now.Year - 2000;    // We need only last two digits (e.g. 25 for 2025)
+		int academicYearStartYear = now.Year - 2000;    // We need only last two digits (e.g. 25 for 2025)
+		// P.S. I am not a fun of this variable name either.

 		if (now.Month < 8)      // Before August means we are in the second semester of the previous academic year
-			termStartYear--;
+			academicYearStartYear--;

-		return $"205.{termStartYear}{termStartYear + 1}/{currentSemester}";
+		return $"205.{academicYearStartYear}{academicYearStartYear + 1}/{currentSemester}";
 	}
 }
@@ -0,0 +1,101 @@
+namespace BonchCalendar.Services;
+
+/// <summary>
+/// Service that tracks results of the most recent requests.
+/// </summary>
+public class IssueTrackingService
+{
+	private bool _isLastFacultyFetchSuccessful = true;
+
+	private readonly List<string> _unsuccessfulGroupFetches = [];
+
+	private readonly List<string> _unsuccessfulTimetableFetches = [];
+
+	/// <summary>
+	/// Record whether the last attempt to retrieve faculty list was successful.
+	/// </summary>
+	/// <param name="isSuccessful">Set <c>true</c> if the attempt was successful. Otherwise, set <c>false</c></param>
+	public void TrackFacultyFetch(bool isSuccessful) =>
+		_isLastFacultyFetchSuccessful = isSuccessful;
+
+	/// <summary>
+	/// Record whether the last attempt to retrieve groups for provided faculty and term year was successful.
+	/// </summary>
+	/// <param name="facultyId">ID of a faculty which was used to retrieve the group list.</param>
+	/// <param name="termYear">Term year which was used to retrieve the group list.</param>
+	/// <param name="isSuccessful">Set <c>true</c> if the attempt was successful. Otherwise, set <c>false</c></param>
+	public void TrackGroupFetch(int facultyId, int termYear, bool isSuccessful)
+	{
+		string key = $"{facultyId}/{termYear}";
+
+		if (!isSuccessful)
+		{
+			if (!_unsuccessfulGroupFetches.Contains(key))
+				_unsuccessfulGroupFetches.Add(key);
+		}
+		else
+			_unsuccessfulGroupFetches.Remove(key);
+	}
+
+	/// <summary>
+	/// Record whether the last attempt to retrieve timetable for provided group was successful.
+	/// </summary>
+	/// <param name="facultyId">ID of a faculty the group belongs to.</param>
+	/// <param name="groupId">ID of a group the timetable was retrieved for.</param>
+	/// <param name="isSuccessful">Set <c>true</c> if the attempt was successful. Otherwise, set <c>false</c></param>
+	public void TrackTimetableFetch(int facultyId, int groupId, bool isSuccessful)
+	{
+		string key = $"{facultyId}/{groupId}";
+
+		if (!isSuccessful)
+		{
+			if (!_unsuccessfulTimetableFetches.Contains(key))
+				_unsuccessfulTimetableFetches.Add(key);
+		}
+		else
+			_unsuccessfulTimetableFetches.Remove(key);
+	}
+
+	/// <summary>
+	/// Get report on the success of latest retrieval attempts.
+	/// </summary>
+	/// <returns>A dictionary for each of the tracked groups.</returns>
+	/// <remarks>
+	/// If the dictionary is empty, that means that there're no known issues.
+	/// </remarks>
+	public Dictionary<string, object> GetReport()
+	{
+		Dictionary<string, object> report = [];
+
+		if (!_isLastFacultyFetchSuccessful)
+			report.Add("/faculties", false);
+
+		if (_unsuccessfulGroupFetches.Count > 0)
+			report.Add("/groups", _unsuccessfulGroupFetches.ToArray());
+
+		if (_unsuccessfulTimetableFetches.Count > 0)
+			report.Add("/timetable", _unsuccessfulTimetableFetches.ToArray());
+
+		// No issues example:
+		/*
+		 * { }
+		 */
+
+		// Report example with issues:
+		/*
+		 * {
+		 *     "/faculties": false,
+		 *     "/groups": [
+		 *         "123/1",
+		 *         "321/3"
+		 *     ],
+		 *     "/timetable": [
+		 *         "123/321",
+		 *         "456/654"
+		 *     ],
+		 * }
+		 */
+
+		return report;
+	}
+}
@@ -11,6 +11,13 @@ namespace BonchCalendar.Services;

 public partial class ParsingService
 {
+	/// <summary>
+	/// Parse general timetable document.
+	/// </summary>
+	/// <param name="rawHtml">HTML document retrieved from the API.</param>
+	/// <param name="semesterStartDate"><see cref="DateTime"/> that represents the first day of current semester.</param>
+	/// <param name="groupName">Name of a group this timetable is for.</param>
+	/// <returns>An array of <see cref="CalendarEvent"/>s</returns>
 	public CalendarEvent[] ParseGeneralTimetable(string rawHtml, DateTime semesterStartDate, string groupName)
 	{
 		using IHtmlDocument doc = new HtmlParser().ParseDocument(rawHtml);
@@ -27,7 +34,7 @@ public partial class ParsingService
 			Match timeMatch = ParserUtils.TimeLabelRegex().Match(timeLabelText);
 			string number = timeMatch.Success ? timeMatch.Groups["number"].Value : timeLabelText;
 			(TimeSpan startTime, TimeSpan endTime) = !timeMatch.Success ?
-				ParserUtils.GetTimesFromLabel(timeLabelText) :
+				ParserUtils.GetTimesFromLabel(timeLabelText) : // If the label for some reason doesn't contain start and end time, we can infer it from class' number
 				(
 					TimeSpan.Parse(timeMatch.Groups["start"].Value),
 					TimeSpan.Parse(timeMatch.Groups["end"].Value)
@@ -44,16 +51,26 @@ public partial class ParsingService
 					.AddDays((week - 1) * 7)          // Move to the correct week
 					.AddDays(weekday - 1);            // Move to the correct weekday

-				classes.Add(GetEvent(
-					$"{number}. {className} ({classType})", auditorium,
-					GetDescription(groupName, professors, auditorium, weeks),
-					classDate, startTime, endTime));
+				classes.Add(CreateEvent(
+					title: $"{number}. {className} ({classType})",
+					location: auditorium,
+					description: CreateDescription(groupName, professors, auditorium, weeks),
+					date: classDate,
+					startTime,
+					endTime
+				));
 			}
 		}

 		return [.. classes];
 	}

+	/// <summary>
+	/// Parse exam timetable document.
+	/// </summary>
+	/// <param name="rawHtml">HTML document, retrieved from the API.</param>
+	/// <param name="groupName">Name of a group this timetable is for.</param>
+	/// <returns>An array of <see cref="CalendarEvent"/>s</returns>
 	public CalendarEvent[] ParseExamTimetable(string rawHtml, string groupName)
 	{
 		using IHtmlDocument doc = new HtmlParser().ParseDocument(rawHtml);
@@ -77,26 +94,32 @@ public partial class ParsingService
 			TimeSpan startTime = TimeSpan.Parse(timeMatch.Groups["start"].Value.Replace('.', ':'));
 			TimeSpan endTime = TimeSpan.Parse(timeMatch.Groups["end"].Value.Replace('.', ':'));

-			classes.Add(GetEvent(
-				$"{number}{className} ({classType})", auditorium,
-				GetDescription(groupName, professors, auditorium),
-				classDate, startTime, endTime));
+			classes.Add(CreateEvent(
+				title: $"{number}{className} ({classType})",
+				location: auditorium,
+				description: CreateDescription(groupName, professors, auditorium),
+				date: classDate,
+				startTime,
+				endTime
+			));
 		}

 		return [.. classes];
 	}

-	private static CalendarEvent GetEvent(string title, string auditorium, string description, DateTime date, TimeSpan startTime, TimeSpan endTime) =>
+	// Create a calendar event
+	private static CalendarEvent CreateEvent(string title, string location, string description, DateTime date, TimeSpan startTime, TimeSpan endTime) =>
 		new()
 		{
 			Summary = title,
 			Description = description,
 			Start = new CalDateTime(date.Add(startTime - TimeSpan.FromHours(3)).ToUniversalTime()),
 			End = new CalDateTime(date.Add(endTime - TimeSpan.FromHours(3)).ToUniversalTime()),
-			Location = auditorium
+			Location = location
 		};

-	private static string GetDescription(string groupName, string[] professors, string auditorium, int[]? weeks = null)
+	// Create event description
+	private static string CreateDescription(string groupName, string[] professors, string auditorium, int[]? weeks = null)
 	{
 		string str = $"""
 		Группа: {groupName}
@@ -107,31 +130,37 @@ public partial class ParsingService
 		if (weeks is not null && weeks.Length > 0)
 			str += $"\nНедели: {string.Join(", ", weeks)}";

+		// Attempt to recognize wing and room number
 		Match auditoriumMatch = ParserUtils.AuditoriumRegex().Match(auditorium);

 		if (!auditoriumMatch.Success)
 			auditoriumMatch = ParserUtils.AuditoriumAltRegex().Match(auditorium);

+		// If successful, we can add a nav.sut.ru map link
 		if (auditoriumMatch.Success)
 			str += "\n\n" + $"""
 			ГУТ.Навигатор:
 			https://nav.sut.ru/?cab=k{auditoriumMatch.Groups["wing"].Value}-{auditoriumMatch.Groups["room"].Value}
 			""";

+		// Some shameless self-promotion
+		str += "\n\n" + "Создано при помощи сервиса Бонч.Календарь: https://bonch.xfox111.net";
+
 		return str;
 	}

+	// Parse basic info for a class
 	private static (string className, string classType, string[] professors, string auditorium) ParseBaseInfo(IElement classElement)
 	{
-		string className = classElement.QuerySelector(".subect")!.TextContent;
-		string classType = classElement.QuerySelector(".type")!.TextContent
-			.Replace("(", string.Empty).Replace(")", string.Empty).Trim();
+		string className = classElement.QuerySelector(".subect")?.TextContent ?? string.Empty;
+		string classType = classElement.QuerySelector(".type")?.TextContent
+			.Replace("(", string.Empty).Replace(")", string.Empty).Trim() ?? string.Empty;

-		string[] professors = classElement.QuerySelector(".teacher[title]")!.GetAttribute("title")
-				!.Split(';', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+		string[] professors = classElement.QuerySelector(".teacher[title]")?.GetAttribute("title")
+				?.Split(';', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries) ?? [];

-		string auditorium = classElement.QuerySelector(".aud")!.TextContent
-			.Replace("ауд.:", string.Empty).Replace(';', ',').Trim();
+		string auditorium = classElement.QuerySelector(".aud")?.TextContent
+			.Replace("ауд.:", string.Empty).Replace(';', ',').Trim() ?? string.Empty;

 		return (className, classType, professors, auditorium);
 	}
@@ -0,0 +1,89 @@
+using Ical.Net;
+using Ical.Net.CalendarComponents;
+using Ical.Net.Serialization;
+
+namespace BonchCalendar.Services;
+
+/// <summary>
+/// Service for retrieving timetable.
+/// </summary>
+public class TimetableService(
+	ApiService apiService,
+	ParsingService parsingService,
+	ILogger<TimetableService> logger,
+	IHostEnvironment environment
+)
+{
+	/// <summary>
+	/// Try to retrieve timetable from application's cache.
+	/// </summary>
+	/// <param name="groupId">ID of a group to retrieve timetable for.</param>
+	/// <returns><c>null</c> if cache for this timetable is not present, or is older than 6 hours. Otherwise, timetable content in iCal format.</returns>
+	public async Task<string?> TryGetTimetableFromCacheAsync(int groupId)
+	{
+		string cacheFile = GetCachePath(groupId);
+
+		if (!File.Exists(cacheFile) || (DateTime.UtcNow - File.GetLastWriteTimeUtc(cacheFile)).TotalHours >= 6)
+			return null;
+
+		if (environment.IsDevelopment())
+		{
+			logger.LogWarning("Caching is disabled for development environment.");
+			return null;
+		}
+
+		logger.LogInformation("Calendar for group {GroupId} is present in cache ({CacheFile}).", groupId, cacheFile);
+
+		return await File.ReadAllTextAsync(cacheFile);
+	}
+
+	/// <summary>
+	/// Retrieve timetable for specified group from sut.ru API.
+	/// </summary>
+	/// <param name="saveToCache">If set to <c>true</c>, result timetable will be wirtten to cache for that group.</param>
+	/// <param name="transform">Action delegate that can be used to manipulate the result <see cref="Calendar"/> object, before converting it to iCal.</param>
+	/// <returns>A string that contains timetable in iCal format.</returns>
+	public async Task<string> GetTimetableAsync(int facultyId, int groupId, bool saveToCache = true, Action<Calendar>? transform = null)
+	{
+		// We need semester start date, since the regular timetable is represented on sut.ru semester week numbers.
+		DateTime semesterStartDate = await apiService.GetSemesterStartDateAsync(groupId);
+		string groupName = (await apiService.GetGroupsListAsync(facultyId, 0))[groupId];
+
+		// Retrieve and parse regular timetable first, since it's the only timetable that has different structure.
+		string classesRaw = await apiService.GetScheduleDocumentAsync(groupId, TimetableType.Classes);
+		List<CalendarEvent> timetable = [.. parsingService.ParseGeneralTimetable(classesRaw, semesterStartDate, groupName)];
+
+		// Retrieve and parse other timetables using a loop, since they all can be parsed using the same parser.
+		TimetableType[] types = [TimetableType.Attestations, TimetableType.Exams, TimetableType.ExamsForExtramural];
+		foreach (TimetableType type in types)
+		{
+			classesRaw = await apiService.GetScheduleDocumentAsync(groupId, type);
+			timetable.AddRange(parsingService.ParseExamTimetable(classesRaw, groupName));
+		}
+
+		// Create and configure the calendar.
+		Calendar calendar = new();
+		calendar.AddTimeZone(new VTimeZone("Europe/Moscow"));
+		calendar.Properties.Add(new CalendarProperty("X-WR-CALNAME", groupName));
+		calendar.Properties.Add(new CalendarProperty("X-WR-TIMEZONE", "Europe/Moscow"));
+		calendar.Properties.Add(new CalendarProperty("REFRESH-INTERVAL;VALUE=DURATION", "PT6H"));	// Specifies how often calendar client should poll for new timetable.
+		calendar.Events.AddRange(timetable);
+
+		transform?.Invoke(calendar);		// If transform delegate is not null, invoke it.
+
+		// Serialize calendar to iCal format.
+		string content = new CalendarSerializer().SerializeToString(calendar)!;
+
+		if (saveToCache)
+		{
+			string cacheFile = GetCachePath(groupId);
+			await File.WriteAllTextAsync(cacheFile, content);
+			logger.LogInformation("Cache updated: {CacheFile}", cacheFile);
+		}
+
+		return content;
+	}
+
+	private static string GetCachePath(int groupId) =>
+		Path.Combine(Path.GetTempPath(), $"bonch_cal_{groupId}.ics");
+}
@@ -0,0 +1,7 @@
+namespace BonchCalendar;
+
+/// <summary>
+/// Response body object for /stats endpoint.
+/// </summary>
+/// <param name="ActiveUsers">Number of active users.</param>
+public record StatsResponse(int ActiveUsers);
@@ -1,9 +1,27 @@
 namespace BonchCalendar;

+/// <summary>
+/// Types of timetable documents retrieved from sut.ru API.
+/// </summary>
 public enum TimetableType
 {
+	/// <summary>
+	/// Regular timetable document (Занятия).
+	/// </summary>
 	Classes = 1,
+
+	/// <summary>
+	/// Exams timetable document (Экзаменационная сессия).
+	/// </summary>
 	Exams = 2,
+
+	/// <summary>
+	/// Exams timetable for extramural students document (Сессия для заочников).
+	/// </summary>
 	ExamsForExtramural = 4,
+
+	/// <summary>
+	/// Attestations timetable document (Зачеты).
+	/// </summary>
 	Attestations = 14
 }
@@ -2,8 +2,20 @@ using System.Text.RegularExpressions;

 namespace BonchCalendar.Utils;

+/// <summary>
+/// Utility methods for timetable parser.
+/// </summary>
 public static partial class ParserUtils
 {
+	/// <summary>
+	/// Get class start and end times from class' number label.
+	/// </summary>
+	/// <param name="label">Class' number label.</param>
+	/// <returns>A tuple value of start and end times.</returns>
+	/// <remarks>
+	/// This method is only supposed to be used as a fallback method of determening class' time
+	/// </remarks>
+	/// <exception cref="NotImplementedException">Unknown label encountered.</exception>
 	public static (TimeSpan startTime, TimeSpan endTime) GetTimesFromLabel(string label)
 	{
 		(string startTime, string endTime) = label switch
@@ -1,8 +0,0 @@
-{
-  "Logging": {
-    "LogLevel": {
-      "Default": "Information",
-      "Microsoft.AspNetCore": "Warning"
-    }
-  }
-}
@@ -1,9 +1,9 @@
 {
-  "Logging": {
-    "LogLevel": {
-      "Default": "Information",
-      "Microsoft.AspNetCore": "Warning"
-    }
-  },
-  "AllowedHosts": "*"
+	"Logging": {
+		"LogLevel": {
+			"Default": "Information",
+			"Microsoft.AspNetCore": "Warning"
+		}
+	},
+	"AllowedHosts": "*"
 }
@@ -0,0 +1,69 @@
+### This file contains exampels of HTTP requests to sut.ru API.
+# You can use them for reference and better understanding of what I have to deal with.
+# You can use a vscode extension (like REST Client) to make this file interactive.
+
+# Current semester "ID" (must be updated before sending requests)
+@schet=205.2526/2
+
+# Breakdown:
+# "205." part is static
+# "2526" represents current academic year (2025-2026 in this case)
+# "/2" represents current semester. Can be either "/1" (first semester) or "/2" (second semester)
+# When making requests this ID must always point to current semester, otherwise you may get a broken response.
+
+# Tip:
+# From August through January is considered to be the first semester
+# Other months (February-July) are considered to be the second semester
+
+###
+
+# Get list of faculties
+POST https://cabinet.sut.ru/raspisanie_all_new.php
+Content-Type: application/x-www-form-urlencoded; charset=UTF-8
+
+choice=1&schet={{schet}}
+
+###
+
+# Get list of groups for faculty
+
+# Year filters out groups by the term year they are at.
+# Year should be an integer from 0 to 5, inclusive.
+# If year is set to 0, all groups for the chosen faculty will be received instead.
+
+@facultyId=50029
+@year=0
+POST https://cabinet.sut.ru/raspisanie_all_new.php
+Content-Type: application/x-www-form-urlencoded; charset=UTF-8
+
+choice=1&schet={{schet}}&faculty={{facultyId}}&kurs={{year}}
+
+###
+
+# Get timetable for selected group
+
+# Type here can be on of the following:
+# 1 - for regular timetable (Занятия)
+# 2 - for exams timetable (Экзаменационная сессия)
+# 4 - for exams timetable for extramural students (Сессия для заочников)
+# 14 - for attestations timetable (Зачеты)
+
+@type=1
+@groupId=55512
+POST https://cabinet.sut.ru/raspisanie_all_new.php
+Content-Type: application/x-www-form-urlencoded; charset=UTF-8
+
+schet={{schet}}&type_z={{type}}&group={{groupId}}
+
+###
+
+# Get page that contains current week number
+
+# We use this page because it's the only known page that contains publicly accessible semester week number.
+# Since regular timetable doesn't show normal dates for classes, and instead uses week numbers,
+# we need to know a date of the first day of current semester to calculate dates for them
+# (e.g. 3 week tuesday is = first day + 3 * 7 + 1)
+
+# Since we know current date and weekday, by knowing week number we can calculate date for the first day.
+
+GET https://www.sut.ru/studentu/raspisanie/raspisanie-zanyatiy-studentov-ochnoy-i-vecherney-form-obucheniya?group={{groupId}}
@@ -1 +1,2 @@
 VITE_BACKEND_HOST=https://api.bonch.xfox111.net
+VITE_BACKEND_HOST=http://localhost:8080
@@ -10,25 +10,26 @@
 		"preview": "vite preview"
 	},
 	"dependencies": {
-		"@fluentui/react-components": "^9.72.7",
-		"@fluentui/react-icons": "^2.0.315",
-		"@fluentui/react-motion-components-preview": "^0.14.1",
-		"react": "^19.2.0",
-		"react-dom": "^19.2.0",
-		"react-localization": "^2.0.6"
+		"@fluentui/react-components": "^9.73.8",
+		"@fluentui/react-icons": "^2.0.326",
+		"@fluentui/react-motion-components-preview": "^0.15.4",
+		"react": "^19.2.6",
+		"react-dom": "^19.2.6",
+		"react-localization": "^2.0.6",
+		"uuid": "^14.0.0"
 	},
 	"devDependencies": {
-		"@eslint/js": "^9.39.1",
-		"@types/node": "^24.10.1",
-		"@types/react": "^19.2.6",
+		"@eslint/js": "^10.0.1",
+		"@types/node": "^25.8.0",
+		"@types/react": "^19.2.14",
 		"@types/react-dom": "^19.2.3",
-		"@vitejs/plugin-react": "^5.1.1",
-		"eslint": "^9.39.1",
-		"eslint-plugin-react-hooks": "^7.0.1",
-		"eslint-plugin-react-refresh": "^0.4.24",
-		"globals": "^16.5.0",
-		"typescript": "~5.9.3",
-		"typescript-eslint": "^8.47.0",
-		"vite": "^7.2.2"
+		"@vitejs/plugin-react": "^6.0.2",
+		"eslint": "^10.4.0",
+		"eslint-plugin-react-hooks": "^7.1.1",
+		"eslint-plugin-react-refresh": "^0.5.2",
+		"globals": "^17.6.0",
+		"typescript": "~6.0.3",
+		"typescript-eslint": "^8.59.3",
+		"vite": "^8.0.13"
 	}
 }
@@ -5,6 +5,7 @@ import MainView from "./views/MainView";
 import FaqView from "./views/FaqView";
 import DedicatedView from "./views/DedicatedView";
 import FooterView from "./views/FooterView";
+import StatsView from "./views/StatsView";

 export default function App(): ReactElement
 {
@@ -15,6 +16,7 @@ export default function App(): ReactElement
 		<FluentProvider theme={ theme }>
 			<main className={ cls.root }>
 				<MainView />
+				<StatsView />
 				<FaqView />
 				<DedicatedView />
 				<FooterView />
@@ -16,6 +16,7 @@ const baseTheme: Partial<Theme> =
 	colorBrandBackground: "#f68b1f",
 	colorBrandBackgroundHover: "#c36e18",
 	colorNeutralForeground2BrandHover: "#c36e18",
+	colorNeutralForeground2BrandPressed: "#a95f15",
 	colorBrandBackgroundPressed: "#a95f15",
 	colorCompoundBrandStroke: "#f68b1f",
 	colorCompoundBrandStrokePressed: "#a95f15"
@@ -1,11 +1,63 @@
-export const fetchFaculties = async (): Promise<[string, string][]> =>
-{
-	const res = await fetch(import.meta.env.VITE_BACKEND_HOST + "/faculties");
-	return Object.entries(await res.json());
-};
+const timeout: number = 5000;

-export const fetchGroups = async (facultyId: string, course: number): Promise<[string, string][]> =>
+export const fetchFaculties = (): Promise<Record<string, string>> =>
+	fetchApi("/faculties", {});
+
+export const fetchGroups = (facultyId: string, year: number): Promise<Record<string, string>> =>
+	fetchApi(`/groups?facultyId=${facultyId}&year=${year}`, {});
+
+export const fetchStats = async (): Promise<StatsResponse> =>
+	fetchApi("/stats", {
+		activeUsers: 0
+	});
+
+export const fetchHealth = async (): Promise<HealthResponse> =>
+	fetchApi("/health", {} as HealthResponse, true);
+
+async function fetchApi<T>(path: string, defaultValue: T, alwaysReturnResponse: boolean = false): Promise<T>
 {
-	const res = await fetch(`${import.meta.env.VITE_BACKEND_HOST}/groups?facultyId=${facultyId}&course=${course}`);
-	return Object.entries(await res.json());
-};
+	try
+	{
+		const res = await fetch(new URL(path, import.meta.env.VITE_BACKEND_HOST), {
+			signal: AbortSignal.timeout(timeout)
+		});
+
+		if (!res.ok && !alwaysReturnResponse)
+			return defaultValue;
+
+		return await res.json();
+	}
+	catch
+	{
+		return defaultValue;
+	}
+}
+
+export type StatsResponse =
+	{
+		activeUsers: number;
+	};
+
+export type HealthResponse =
+	{
+		status: HealthStatus;
+		totalDuration: string;
+		entries: {
+			["timetable_website"]: TimetableHealthResponseEntry;
+		};
+	};
+
+export type HealthStatus = "healthy" | "unhealthy" | "degraded";
+
+export type TimetableHealthResponseEntry =
+	{
+		status: HealthStatus;
+		description?: string;
+		duration: string;
+		data:
+		{
+			"/faculties"?: false,
+			"/groups"?: string[],
+			"/timetable"?: string[];
+		};
+	};
@@ -9,15 +9,33 @@ const strings = new LocalizedStrings({
 		subtitle_p1: "Check your SPbSUT classes in {0} calendar",
 		subtitle_p2: "your",
 		pickFaculty: "1. Pick your faculty",
-		pickCourse: "2. Pick your course",
+		pickCourse: "2. Pick your year",
 		pickGroup: "3. Pick your group",
-		pickGroup_empty: "No groups are available for the selected course",
+		pickGroup_empty: "No groups are available for the selected year",
 		subscribe: "4. Subscribe to the calendar",
 		copy: "Copy link",
 		or: "or",
 		download: "Download .ics file",
 		cta: "Like the service? Tell your classmates!",

+		// StatsView.tsx
+		users: "Active users: {0}",
+		status_ok: "Status: Operational",
+		status_unhealthy: "Status: Degraded",
+		report_title: "Service status report",
+		report_close: "Close",
+		report_subtitle_ok: "Service operates normally",
+		report_subtitle_unhealthy: "Active issues: {0}",
+		report_issue_backend: "Unable to connect to service's backend application.",
+		report_issue_faculties: "Last attempt to fetch faculties list resulted in an error.",
+		report_issue_groups: "Last attempt to fetch groups for following faculties resulted in an error:",
+		report_issue_groups_item: "{0} ({1}), {2} year",
+		report_issue_groups_item_alt: "Faculty ID: {0}, {1} year",
+		report_issue_timetable: "Last attempt to fetch timetable for following groups resulted in an error:",
+		report_issue_timetable_item_alt1: "Group ID: {0}, {1} ({2})",
+		report_issue_timetable_item_alt2: "{0} ({1}), Faculty ID: {2}",
+		report_issue_timetable_item_alt3: "Group ID: {0}, Faculty ID: {1}",
+
 		// FaqView.tsx
 		faq_h2: "Frequently asked questions",
 		question1_h3: "How do I save timetable to my Outlook/Google calendar?",
@@ -77,6 +95,24 @@ const strings = new LocalizedStrings({
 		download: "Скачай .ics файл",
 		cta: "Понравился сервис? Расскажи одногруппникам!",

+		// StatsView.tsx
+		users: "Пользователей: {0}",
+		status_ok: "Статус сервиса",
+		status_unhealthy: "Статус сервиса",
+		report_title: "Состояние сервиса",
+		report_close: "Закрыть",
+		report_subtitle_ok: "Сервис работает в нормальном режиме",
+		report_subtitle_unhealthy: "Известных проблем: {0}",
+		report_issue_backend: "Ошибка при подключении к серверу приложения.",
+		report_issue_faculties: "Ошибка при попытке получить список факультетов.",
+		report_issue_groups: "Ошибка при попытке получить список групп для следующих факультетов:",
+		report_issue_groups_item: "{0} ({1}), {2} курс",
+		report_issue_groups_item_alt: "ID факультета: {0}, {1} курс",
+		report_issue_timetable: "Ошибка при попытке получить расписание для следующих групп:",
+		report_issue_timetable_item_alt1: "ID группы: {0}, {1} ({2})",
+		report_issue_timetable_item_alt2: "{0} ({1}), ID факультета: {2}",
+		report_issue_timetable_item_alt3: "ID группы: {0}, ID факультета: {1}",
+
 		// FaqView.tsx
 		faq_h2: "Часто задаваемые вопросы",
 		question1_h3: "Как сохранить расписание в Outlook/Google календарь?",
@@ -0,0 +1,67 @@
+import { type TimetableHealthResponseEntry, fetchFaculties, fetchGroups } from "./api";
+import strings from "./strings";
+
+export async function tryFormatNamesForReport(report?: TimetableHealthResponseEntry): Promise<TimetableHealthResponseEntry | undefined>
+{
+	if (report === undefined)
+		return report;
+
+	if (report.status === "healthy")
+		return report;
+
+	const isGroupsDown: boolean = report.data["/groups"] !== undefined;
+	const isTimetableDown: boolean = report.data["/timetable"] !== undefined;
+
+	if (!isGroupsDown && !isTimetableDown)
+		return report;
+
+	let faculties: Record<string, string> | undefined = undefined;
+
+	try { faculties = await fetchFaculties(); }
+	catch { /* empty */ }
+
+	const facultiesFormatted: string[] = [];
+
+	if (report.data["/groups"] !== undefined)
+		for (const faculty of report.data["/groups"])
+		{
+			const [facultyId, course] = faculty.split("/");
+
+			if (faculties?.[facultyId] === undefined)
+				facultiesFormatted.push(strings.formatString(strings.report_issue_groups_item_alt, facultyId, course) as string);
+
+			else
+				facultiesFormatted.push(strings.formatString(strings.report_issue_groups_item, faculties[facultyId], facultyId, course) as string);
+		}
+
+	const groups: Record<string, Record<string, string>> = {};
+	const groupsFormatted: string[] = [];
+
+	if (report.data["/timetable"] !== undefined)
+		for (const group of report.data["/timetable"])
+		{
+			const [facultyId, groupId] = group.split("/");
+
+			if (groups[facultyId] === undefined)
+				try { groups[facultyId] = await fetchGroups(facultyId, 0); }
+				catch { /* empty */ }
+
+			if (groups[facultyId]?.[groupId] !== undefined && faculties?.[facultyId] !== undefined)
+				groupsFormatted.push(`${groups[facultyId][groupId]} (${groupId}), ${faculties[facultyId]} (${facultyId})`);
+			else if (faculties?.[facultyId] !== undefined)
+				groupsFormatted.push(strings.formatString(strings.report_issue_timetable_item_alt1, groupId, faculties[facultyId], facultyId) as string)
+			else if (groups[facultyId]?.[groupId] !== undefined)
+				groupsFormatted.push(strings.formatString(strings.report_issue_timetable_item_alt2, groups[facultyId][groupId], groupId, facultyId) as string)
+			else
+				groupsFormatted.push(strings.formatString(strings.report_issue_timetable_item_alt3, groupId, facultyId) as string)
+		}
+
+	return {
+		...report,
+		data: {
+			...report.data,
+			["/groups"]: facultiesFormatted.length > 0 ? facultiesFormatted : undefined,
+			["/timetable"]: groupsFormatted.length > 0 ? groupsFormatted : undefined
+		}
+	};
+}
@@ -8,7 +8,7 @@ const useStyles_MainView = makeStyles({
 		flexFlow: "column",
 		gap: tokens.spacingVerticalXXXL,
 		justifyContent: "center",
-		minHeight: "90vh",
+		minHeight: "85vh",
 		alignItems: "center",
 		padding: `${tokens.spacingVerticalL} ${tokens.spacingHorizontalL}`,

@@ -8,8 +8,9 @@ import useTimeout from "../hooks/useTimeout";
 import useStyles_MainView from "./MainView.styles";
 import { fetchFaculties, fetchGroups } from "../utils/api";
 import strings from "../utils/strings";
+import { v7 as uuid7 } from "uuid";

-const facultiesPromise = fetchFaculties();
+const facultiesPromise = fetchFaculties().then(Object.entries);

 const getEntryOrEmpty = (entries: [string, string][], key: string): string =>
 	entries.find(i => i[0] === key)?.[1] ?? "";
@@ -25,6 +26,7 @@ export default function MainView(): ReactElement
 	const [groups, setGroups] = useState<[string, string][] | null>(null);
 	const [groupId, setGroupId] = useState<string>("");

+	const id = uuid7();
 	const icalUrl = useMemo(() => `${import.meta.env.VITE_BACKEND_HOST}/timetable/${facultyId}/${groupId}`, [groupId, facultyId]);

 	const [showCta, setShowCta] = useState<boolean>(false);
@@ -35,10 +37,10 @@ export default function MainView(): ReactElement

 	const copyLink = useCallback((): void =>
 	{
-		navigator.clipboard.writeText(icalUrl);
+		navigator.clipboard.writeText(icalUrl + "?id=" + id);
 		triggerCopy();
 		setShowCta(true);
-	}, [icalUrl, triggerCopy]);
+	}, [icalUrl, triggerCopy, id]);

 	const onFacultySelect = useCallback((_: SelectionEvents, data: OptionOnSelectData): void =>
 	{
@@ -59,7 +61,7 @@ export default function MainView(): ReactElement
 		setCourse(courseNumber);
 		setGroupId("");
 		setGroups(null);
-		fetchGroups(facultyId, courseNumber).then(setGroups);
+		fetchGroups(facultyId, courseNumber).then(Object.entries).then(setGroups);
 	}, [course, facultyId]);

 	return (
@@ -99,6 +101,7 @@ export default function MainView(): ReactElement
 								<Button key={ i }
 									className={ cls.courseButton }
 									appearance={ course === i ? "primary" : "secondary" }
+									disabled={ facultyId === "" }
 									onClick={ () => onCourseSelect(i) }>

 									{ i }
@@ -114,6 +117,7 @@ export default function MainView(): ReactElement
 							className={ cls.field }
 							positioning={ { pinned: true, position: "below" } }
 							value={ getEntryOrEmpty(groups ?? [], groupId) }
+							disabled={ course === 0 || groups === null }
 							onOptionSelect={ (_, e) => setGroupId(e.optionValue!) }>

 							{ groups?.map(([id, name]) =>
@@ -136,12 +140,13 @@ export default function MainView(): ReactElement
 								className={ mergeClasses(cls.field, copyActive && cls.copiedStyle) }
 								iconPosition="after"
 								title={ strings.copy }
+								disabled={ groupId === "" }
 								icon={ copyActive
 									? <Checkmark24Regular className={ cls.copyIcon } />
 									: <Copy24Regular className={ cls.copyIcon } />
 								}>

-								<span className={ cls.truncatedText }>{ icalUrl }</span>
+								<span className={ cls.truncatedText }>{ icalUrl + "?id=" + id }</span>
 							</Button>
 						</div>
 					</Slide>
@@ -151,7 +156,8 @@ export default function MainView(): ReactElement
 							<Button as="a"
 								appearance="subtle" icon={ <ArrowDownload24Regular /> }
 								onClick={ () => setShowCta(true) }
-								href={ icalUrl }>
+								disabled={ groupId === "" }
+								href={ icalUrl + "?id=download" }>

 								{ strings.download }
 							</Button>
@@ -0,0 +1,44 @@
+import { makeStyles, tokens } from "@fluentui/react-components";
+
+export const useStyles = makeStyles({
+	root:
+	{
+		display: "flex",
+		flexFlow: "column",
+		marginBottom: "80px"
+	},
+	container:
+	{
+		display: "flex",
+		padding: `${tokens.spacingVerticalS} ${tokens.spacingHorizontalMNudge}`,
+		gap: tokens.spacingHorizontalMNudge,
+		boxShadow: tokens.shadow4,
+		borderRadius: tokens.borderRadiusMedium
+	},
+	statsButton:
+	{
+		pointerEvents: "none"
+	},
+	statsButtonIcon:
+	{
+		color: tokens.colorBrandForeground1
+	},
+	statusIconHealthy:
+	{
+		color: tokens.colorStatusSuccessBorderActive,
+	},
+	statusIconUnhealthy:
+	{
+		color: tokens.colorStatusDangerBorderActive,
+	},
+	reportSubtitle:
+	{
+		display: "flex",
+		alignItems: "center",
+		gap: tokens.spacingHorizontalS
+	},
+	reportContent:
+	{
+		userSelect: "text"
+	}
+});
@@ -0,0 +1,129 @@
+import { Button, Dialog, DialogBody, DialogContent, DialogSurface, DialogTitle, DialogTrigger, Divider, Subtitle2 } from "@fluentui/react-components";
+import { ArrowTrendingLinesFilled, CheckmarkCircleFilled, Dismiss24Regular, WarningFilled } from "@fluentui/react-icons";
+import { use, useMemo, type ReactElement } from "react";
+import { fetchHealth, fetchStats, type StatsResponse, type TimetableHealthResponseEntry } from "../utils/api";
+import strings from "../utils/strings";
+import { tryFormatNamesForReport } from "../utils/tryFormatNamesForReport";
+import { useStyles } from "./StatsView.styles";
+
+const healthPromise = fetchHealth().then(i => i.entries?.["timetable_website"]).then(tryFormatNamesForReport);
+const statsPromise = fetchStats();
+
+export default function StatsView(): ReactElement
+{
+	const cls = useStyles();
+
+	const health: TimetableHealthResponseEntry | undefined = use(healthPromise);
+	const stats: StatsResponse = use(statsPromise);
+
+	const issueCounter: number = useMemo(() =>
+	{
+		let counter: number = 0;
+
+		if (health === undefined)
+			return 1;
+
+		if (health.data["/faculties"] !== undefined)
+			counter++;
+
+		counter += health.data["/groups"]?.length ?? 0;
+		counter += health.data["/timetable"]?.length ?? 0;
+
+		return counter;
+	}, [health]);
+
+	return (
+		<div className={ cls.root }>
+			<div className={ cls.container }>
+				{ stats.activeUsers > 3 &&
+					<>
+						<Button
+							className={ cls.statsButton } tabIndex={ -1 }
+							icon={ <ArrowTrendingLinesFilled className={ cls.statsButtonIcon } /> }
+							appearance="subtle"
+						>
+							{ strings.formatString(strings.users, stats.activeUsers) }
+						</Button>
+						<Divider vertical />
+					</>
+				}
+				<Dialog>
+					<DialogTrigger>
+						{ health?.status === "healthy" ?
+							<Button icon={ <CheckmarkCircleFilled className={ cls.statusIconHealthy } /> } appearance="subtle">
+								{ strings.status_ok }
+							</Button>
+							:
+							<Button icon={ <WarningFilled className={ cls.statusIconUnhealthy } /> } appearance="subtle">
+								{ strings.status_unhealthy }
+							</Button>
+						}
+					</DialogTrigger>
+
+					<DialogSurface>
+						<DialogBody>
+							<DialogTitle
+								action={
+									<DialogTrigger action="close">
+										<Button
+											appearance="subtle"
+											aria-label={ strings.report_close }
+											icon={ <Dismiss24Regular /> }
+										/>
+									</DialogTrigger>
+								}
+							>
+								{ strings.report_title }
+							</DialogTitle>
+							<DialogContent className={ cls.reportContent }>
+								{ health?.status === "healthy" ?
+									<div className={ cls.reportSubtitle }>
+										<CheckmarkCircleFilled className={ cls.statusIconHealthy } fontSize={ 24 } />
+										<Subtitle2>{ strings.report_subtitle_ok }</Subtitle2>
+									</div>
+									:
+									<div className={ cls.reportSubtitle }>
+										<WarningFilled className={ cls.statusIconUnhealthy } fontSize={ 24 } />
+										<Subtitle2>
+											{ strings.formatString(strings.report_subtitle_unhealthy, issueCounter) }
+										</Subtitle2>
+									</div>
+								}
+								{ health?.status !== "healthy" &&
+									<ul>
+										{ health === undefined &&
+											<li>{ strings.report_issue_backend }</li>
+										}
+										{ health?.data["/faculties"] !== undefined &&
+											<li>{ strings.report_issue_faculties }</li>
+										}
+										{ health?.data["/groups"] !== undefined &&
+											<li>
+												{ strings.report_issue_groups }
+												<ul>
+													{ health.data["/groups"].map((i, index) =>
+														<li key={ index }>{ i }</li>
+													) }
+												</ul>
+											</li>
+										}
+										{ health?.data["/timetable"] !== undefined &&
+											<li>
+												{ strings.report_issue_timetable }
+												<ul>
+													{ health.data["/timetable"].map((i, index) =>
+														<li key={ index }>{ i }</li>
+													) }
+												</ul>
+											</li>
+										}
+									</ul>
+								}
+							</DialogContent>
+						</DialogBody>
+					</DialogSurface>
+				</Dialog>
+			</div>
+		</div>
+	);
+}
@@ -3,6 +3,8 @@ services:
    image: xfox111/bonch-calendar-api:latest
    build:
      context: ./api
+    environment:
+      - ORIGIN_DOMAIN=localhost:8000
    ports:
      - 8080:8080