Add backend to monitore the app in a desktop app

backend/Program.cs

@@ -0,0 +1,186 @@
+using DotNetEnv;
+using Google.Apis.AnalyticsData.v1beta;
+using Google.Apis.AnalyticsData.v1beta.Data;
+using Google.Apis.Auth.OAuth2;
+using Google.Apis.Services;
+using Microsoft.AspNetCore.Mvc;
+
+Env.Load();
+
+var builder = WebApplication.CreateBuilder(args);
+
+// Add services to the container.
+builder.Services.AddEndpointsApiExplorer();
+builder.Services.AddSwaggerGen();
+
+// Register Google Analytics Data Client
+builder.Services.AddSingleton<AnalyticsDataService>(sp =>
+{
+    GoogleCredential credential;
+    try 
+    {
+        // Tries to find credentials from GOOGLE_APPLICATION_CREDENTIALS environment variable
+        // or default cloud environment credentials.
+        credential = GoogleCredential.GetApplicationDefault();
+    }
+    catch (Exception)
+    {
+        // Fallback for local development if env var not set (User might need to run 'gcloud auth application-default login')
+        // Or we warn them. For now, we assume it's set up or will fail at runtime.
+         throw new InvalidOperationException("Could not load Google Credentials. Set GOOGLE_APPLICATION_CREDENTIALS or run 'gcloud auth application-default login'.");
+    }
+
+    if (credential.IsCreateScopedRequired)
+    {
+        credential = credential.CreateScoped(AnalyticsDataService.Scope.AnalyticsReadonly);
+    }
+
+    var service = new AnalyticsDataService(new BaseClientService.Initializer
+    {
+        HttpClientInitializer = credential,
+        ApplicationName = "TravelMate Backend",
+    });
+
+    return service;
+});
+
+var app = builder.Build();
+
+// Configure the HTTP request pipeline.
+if (app.Environment.IsDevelopment())
+{
+    app.UseSwagger();
+    app.UseSwaggerUI();
+}
+
+app.UseHttpsRedirection();
+
+string? ga4PropertyId = Environment.GetEnvironmentVariable("GA4_PROPERTY_ID");
+if (string.IsNullOrEmpty(ga4PropertyId))
+{
+    Console.WriteLine("Warning: GA4_PROPERTY_ID not set in .env");
+    // Default or error? Let's just hold it and fail in the endpoint if needed, or fail startup.
+    // For now, let's allow it to start but endpoint will likely fail.
+} 
+
+app.MapGet("/api/metrics/daily", async (
+    [FromServices] AnalyticsDataService service,
+    [FromQuery] string from, 
+    [FromQuery] string to) =>
+{
+    // Basic validation
+    // Basic validation: Check if it's a valid date OR a valid GA4 keyword
+    bool IsValidDate(string date)
+    {
+        return DateTime.TryParse(date, out _) || 
+               date == "today" || 
+               date == "yesterday" || 
+               date.EndsWith("daysAgo");
+    }
+
+    if (!IsValidDate(from) || !IsValidDate(to))
+    {
+        return Results.BadRequest(new { error = "Invalid date format. Use YYYY-MM-DD, 'today', 'yesterday', or 'NdaysAgo'." });
+    }
+
+    var request = new RunReportRequest
+    {
+        Property = $"properties/{ga4PropertyId}",
+        DateRanges = new List<DateRange>
+        {
+            new DateRange { StartDate = from, EndDate = to }
+        },
+        Dimensions = new List<Dimension>
+        {
+            new Dimension { Name = "date" }
+        },
+        Metrics = new List<Metric>
+        {
+            new Metric { Name = "activeUsers" } // equivalent to Daily Active Users in this context often
+            // Or strictly "activeUsers"
+        }
+    };
+
+    try
+    {
+        var response = await service.Properties.RunReport(request, $"properties/{ga4PropertyId}").ExecuteAsync();
+
+        var result = response.Rows?.Select(row => new
+        {
+            date = FormatDate(row.DimensionValues[0].Value), // GA4 returns date as YYYYMMDD string usually
+            dailyActiveUsers = int.Parse(row.MetricValues[0].Value)
+        }) ?? Enumerable.Empty<object>();
+
+        return Results.Ok(result);
+    }
+    catch (Exception ex)
+    {
+        Console.WriteLine($"Error: {ex}");
+        return Results.Problem($"Analytics API Error: {ex.Message}");
+    }
+})
+.WithName("GetDailyMetrics")
+.WithOpenApi();
+
+app.MapGet("/api/metrics/general", async (
+    [FromServices] AnalyticsDataService service) =>
+{
+    // "Global" means all time ideally, or a very long range.
+    // GA4 retention might limit this for user-level data, but aggregated metrics usually go back further.
+    var startDate = "2023-01-01"; // Arbitrary start date for the app
+    var endDate = "today";
+
+    var request = new RunReportRequest
+    {
+        Property = $"properties/{ga4PropertyId}",
+        DateRanges = new List<DateRange>
+        {
+            new DateRange { StartDate = startDate, EndDate = endDate }
+        },
+        Metrics = new List<Metric>
+        {
+            new Metric { Name = "totalUsers" }, // Proxy for "nb de comptes"
+            new Metric { Name = "eventCount" }  // Proxy for "nb de requètes"
+        }
+    };
+
+    try
+    {
+        var response = await service.Properties.RunReport(request, $"properties/{ga4PropertyId}").ExecuteAsync();
+
+        var totalUsers = 0;
+        var eventCount = 0;
+
+        if (response.Rows != null && response.Rows.Count > 0)
+        {
+            var row = response.Rows[0];
+            totalUsers = int.Parse(row.MetricValues[0].Value);
+            eventCount = int.Parse(row.MetricValues[1].Value);
+        }
+
+        return Results.Ok(new
+        {
+            totalAccounts = totalUsers,
+            totalRequests = eventCount
+        });
+    }
+    catch (Exception ex)
+    {
+        Console.WriteLine($"Error: {ex}");
+        return Results.Problem($"Analytics API Error: {ex.Message}");
+    }
+})
+.WithName("GetGeneralMetrics")
+.WithOpenApi();
+
+app.Run();
+
+// Helper to format GA4 YYYYMMDD to YYYY-MM-DD
+static string FormatDate(string gaDate)
+{
+    if (gaDate.Length == 8)
+    {
+        return $"{gaDate.Substring(0, 4)}-{gaDate.Substring(4, 2)}-{gaDate.Substring(6, 2)}";
+    }
+    return gaDate;
+}