feat: implement dashboard service and controller with tests (TDD)

src/AccountTracking.Api.Tests/DashboardServiceTests.cs

@@ -0,0 +1,161 @@
+using AccountTracking.Api.Data;
+using AccountTracking.Api.Models;
+using AccountTracking.Api.Services;
+using Microsoft.EntityFrameworkCore;
+
+namespace AccountTracking.Api.Tests;
+
+public class DashboardServiceTests
+{
+    private static AppDbContext CreateDb(params Transaction[] seed)
+    {
+        var opts = new DbContextOptionsBuilder<AppDbContext>()
+            .UseInMemoryDatabase(Guid.NewGuid().ToString())
+            .Options;
+        var db = new AppDbContext(opts);
+        db.Transactions.AddRange(seed);
+        db.SaveChanges();
+        return db;
+    }
+
+    private static Transaction Tx(string date, decimal amount, decimal balance,
+        string category = "Test", string txId = "") =>
+        new()
+        {
+            BookingDate = DateOnly.Parse(date),
+            Amount = amount,
+            Balance = balance,
+            Category = category,
+            TransactionId = txId == "" ? Guid.NewGuid().ToString() : txId,
+            Currency = "CZK",
+            AccountNumber = "test"
+        };
+
+    // ── Summary ──────────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task Summary_YearOnly_ReturnsTotalsForWholeYear()
+    {
+        using var db = CreateDb(
+            Tx("2025-01-10", -1000, 9000),
+            Tx("2025-06-15", -2000, 7000),
+            Tx("2025-03-01", 5000, 12000),
+            Tx("2024-12-31", -500, 9500) // different year — excluded
+        );
+        var svc = new DashboardService(db);
+
+        var result = await svc.GetSummaryAsync(2025, null);
+
+        Assert.Equal(3000m, result.TotalSpent);   // 1000 + 2000
+        Assert.Equal(5000m, result.TotalIncome);
+    }
+
+    [Fact]
+    public async Task Summary_YearAndMonth_ReturnsTotalsForMonth()
+    {
+        using var db = CreateDb(
+            Tx("2025-03-10", -1000, 9000),
+            Tx("2025-03-20", -500, 8500),
+            Tx("2025-04-01", -800, 7700) // different month — excluded
+        );
+        var svc = new DashboardService(db);
+
+        var result = await svc.GetSummaryAsync(2025, 3);
+
+        Assert.Equal(1500m, result.TotalSpent);
+        Assert.Equal(0m, result.TotalIncome);
+    }
+
+    // ── SpendingByCategory ───────────────────────────────────────────────────
+
+    [Fact]
+    public async Task SpendingByCategory_ReturnsAbsoluteValuesSortedDescending()
+    {
+        using var db = CreateDb(
+            Tx("2025-03-01", -100, 900, "A"),
+            Tx("2025-03-02", -300, 600, "B"),
+            Tx("2025-03-03", -200, 400, "A")
+        );
+        var svc = new DashboardService(db);
+
+        var result = await svc.GetSpendingByCategoryAsync(2025, 3);
+
+        Assert.Equal(2, result.Count);
+        Assert.Equal("A", result[0].Category);
+        Assert.Equal(300m, result[0].Total); // 100 + 200
+        Assert.Equal("B", result[1].Category);
+        Assert.Equal(300m, result[1].Total);
+    }
+
+    [Fact]
+    public async Task SpendingByCategory_ExcludesPositiveAmounts()
+    {
+        using var db = CreateDb(
+            Tx("2025-03-01", -500, 9500, "Potraviny"),
+            Tx("2025-03-02", 200, 9700, "Potraviny")  // refund — excluded
+        );
+        var svc = new DashboardService(db);
+
+        var result = await svc.GetSpendingByCategoryAsync(2025, 3);
+
+        Assert.Single(result);
+        Assert.Equal(500m, result[0].Total);
+    }
+
+    // ── MonthlyBalances ──────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task MonthlyBalances_ReturnsLastBalancePerMonth()
+    {
+        using var db = CreateDb(
+            Tx("2025-01-10", -100, 900),
+            Tx("2025-01-20", -200, 700),  // last in Jan — use this balance
+            Tx("2025-03-05", -150, 550)   // March — Feb omitted (no transactions)
+        );
+        var svc = new DashboardService(db);
+
+        var result = await svc.GetMonthlyBalancesAsync(2025);
+
+        Assert.Equal(2, result.Count);
+        Assert.Equal(1, result[0].Month);
+        Assert.Equal(700m, result[0].ClosingBalance);
+        Assert.Equal(3, result[1].Month);
+        Assert.Equal(550m, result[1].ClosingBalance);
+    }
+
+    // ── CumulativeSpending ───────────────────────────────────────────────────
+
+    [Fact]
+    public async Task CumulativeSpending_FillsGapsAndAccumulates()
+    {
+        using var db = CreateDb(
+            Tx("2025-03-01", -100, 900),
+            Tx("2025-03-03", -200, 700),  // gap on day 2
+            Tx("2025-03-03", -50, 650)    // two transactions on same day
+        );
+        var svc = new DashboardService(db);
+
+        var result = await svc.GetCumulativeSpendingAsync(2025, 3);
+
+        // Day 1: 100, Day 2: filled = 100, Day 3: 100 + 250 = 350
+        Assert.Equal(3, result.Count);
+        Assert.Equal(1, result[0].Day); Assert.Equal(100m, result[0].CumulativeSpent);
+        Assert.Equal(2, result[1].Day); Assert.Equal(100m, result[1].CumulativeSpent);
+        Assert.Equal(3, result[2].Day); Assert.Equal(350m, result[2].CumulativeSpent);
+    }
+
+    [Fact]
+    public async Task CumulativeSpending_ExcludesPositiveAmounts()
+    {
+        using var db = CreateDb(
+            Tx("2025-03-01", -100, 900),
+            Tx("2025-03-01", 500, 1400)   // income — not counted
+        );
+        var svc = new DashboardService(db);
+
+        var result = await svc.GetCumulativeSpendingAsync(2025, 3);
+
+        Assert.Single(result);
+        Assert.Equal(100m, result[0].CumulativeSpent);
+    }
+}

src/AccountTracking.Api/Controllers/DashboardController.cs

@@ -0,0 +1,30 @@
+using AccountTracking.Api.Services;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace AccountTracking.Api.Controllers;
+
+[ApiController]
+[Route("api/dashboard")]
+[Authorize]
+public class DashboardController : ControllerBase
+{
+    private readonly DashboardService _svc;
+    public DashboardController(DashboardService svc) => _svc = svc;
+
+    [HttpGet("summary")]
+    public async Task<IActionResult> Summary([FromQuery] int year, [FromQuery] int? month)
+        => Ok(await _svc.GetSummaryAsync(year, month));
+
+    [HttpGet("spending-by-category")]
+    public async Task<IActionResult> SpendingByCategory([FromQuery] int year, [FromQuery] int? month)
+        => Ok(await _svc.GetSpendingByCategoryAsync(year, month));
+
+    [HttpGet("monthly-balances")]
+    public async Task<IActionResult> MonthlyBalances([FromQuery] int year)
+        => Ok(await _svc.GetMonthlyBalancesAsync(year));
+
+    [HttpGet("cumulative-spending")]
+    public async Task<IActionResult> CumulativeSpending([FromQuery] int year, [FromQuery] int month)
+        => Ok(await _svc.GetCumulativeSpendingAsync(year, month));
+}

src/AccountTracking.Api/Services/DashboardService.cs

@@ -39,20 +39,20 @@ public class DashboardService(AppDbContext db)
 
     public async Task<List<MonthlyBalanceDto>> GetMonthlyBalancesAsync(int year)
     {
-        // For each month: get the balance of the transaction with the latest booking_date
-        // (highest id as tiebreaker for same-date rows)
+        // Fetch minimal columns, then group in memory to get closing balance per month
+        // (latest booking_date, highest id as tiebreaker)
         var rows = await db.Transactions
             .Where(t => t.BookingDate.Year == year)
+            .Select(t => new { t.BookingDate, t.Id, t.Balance })
+            .ToListAsync();
+
+        return rows
             .GroupBy(t => t.BookingDate.Month)
             .Select(g => new MonthlyBalanceDto(
                 g.Key,
-                g.OrderByDescending(t => t.BookingDate)
-                 .ThenByDescending(t => t.Id)
-                 .First().Balance))
+                g.OrderByDescending(t => t.BookingDate).ThenByDescending(t => t.Id).First().Balance))
             .OrderBy(r => r.Month)
-            .ToListAsync();
-
-        return rows;
+            .ToList();
     }
 
     public async Task<List<CumulativeSpendingDto>> GetCumulativeSpendingAsync(int year, int month)