feat: add quick stats

coffeecard/CoffeeCard.Library/Services/v2/IStatisticsService.cs

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+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CoffeeCard.Models.DataTransferObjects.v2.Statistics;
+using CoffeeCard.Models.Entities;
+
+namespace CoffeeCard.Library.Services.v2
+{
+    public interface IStatisticsService
+    {
+        Task<IEnumerable<QuickStatResponse>> GetQuickStatsAsync(User user);
+    }
+}

coffeecard/CoffeeCard.Library/Services/v2/StatisticsService.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using CoffeeCard.Library.Persistence;
+using CoffeeCard.Library.Utils;
+using CoffeeCard.Models.DataTransferObjects.v2.Statistics;
+using CoffeeCard.Models.Entities;
+using Microsoft.EntityFrameworkCore;
+
+namespace CoffeeCard.Library.Services.v2
+{
+    public class StatisticsService : IStatisticsService
+    {
+        private readonly CoffeeCardContext _context;
+        private readonly IDateTimeProvider _dateTimeProvider;
+
+        public StatisticsService(CoffeeCardContext context, IDateTimeProvider dateTimeProvider)
+        {
+            _context = context;
+            _dateTimeProvider = dateTimeProvider;
+        }
+
+        public async Task<IEnumerable<QuickStatResponse>> GetQuickStatsAsync(User user)
+        {
+            var utcNow = _dateTimeProvider.UtcNow();
+            var todayStart = utcNow.Date;
+            var todayEnd = todayStart.AddDays(1);
+            var weekStart = GetWeekStart(utcNow);
+            var weekEnd = weekStart.AddDays(7);
+
+            var totalDrinks = await _context.Tickets.CountAsync(ticket =>
+                ticket.OwnerId == user.Id && ticket.Status == TicketStatus.Used
+            );
+
+            var drinksToday = await _context.Tickets.CountAsync(ticket =>
+                ticket.Status == TicketStatus.Used
+                && ticket.DateUsed >= todayStart
+                && ticket.DateUsed < todayEnd
+            );
+
+            var favouriteDrink = await _context
+                .Tickets.Where(ticket =>
+                    ticket.OwnerId == user.Id
+                    && ticket.Status == TicketStatus.Used
+                    && ticket.UsedOnMenuItemId != null
+                )
+                .GroupBy(ticket => ticket.UsedOnMenuItem.Name)
+                .Select(group => new { MenuItemName = group.Key, Count = group.Count() })
+                .OrderByDescending(group => group.Count)
+                .ThenBy(group => group.MenuItemName)
+                .FirstOrDefaultAsync();
+
+            var drinksThisWeek = await _context.Tickets.CountAsync(ticket =>
+                ticket.OwnerId == user.Id
+                && ticket.Status == TicketStatus.Used
+                && ticket.DateUsed >= weekStart
+                && ticket.DateUsed < weekEnd
+            );
+
+            return new List<QuickStatResponse>
+            {
+                new QuickStatResponse
+                {
+                    Key = "total-drinks-user",
+                    Title = "Drinks consumed by you",
+                    Value = totalDrinks,
+                    SupportingText = null,
+                },
+                new QuickStatResponse
+                {
+                    Key = "global-drinks-today",
+                    Title = "Drinks consumed by ITU today",
+                    Value = drinksToday,
+                    SupportingText = null,
+                },
+                new QuickStatResponse
+                {
+                    Key = "favourite-drink",
+                    Title = "Your favourite drink",
+                    Value = favouriteDrink?.Count ?? 0,
+                    SupportingText = favouriteDrink?.MenuItemName ?? "No drinks yet",
+                },
+                new QuickStatResponse
+                {
+                    Key = "drinks-this-week-user",
+                    Title = "Drinks this week",
+                    Value = drinksThisWeek,
+                    SupportingText = null,
+                },
+            };
+        }
+
+        private static DateTime GetWeekStart(DateTime utcNow)
+        {
+            var daysSinceMonday = ((int)utcNow.DayOfWeek + 6) % 7;
+            return utcNow.Date.AddDays(-daysSinceMonday);
+        }
+    }
+}

coffeecard/CoffeeCard.Models/DataTransferObjects/v2/Statistics/QuickStatResponse.cs

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+using System.ComponentModel.DataAnnotations;
+
+namespace CoffeeCard.Models.DataTransferObjects.v2.Statistics
+{
+    /// <summary>
+    /// A small stat card used by the quick statistics endpoint.
+    /// </summary>
+    /// <example>
+    /// {
+    ///     "key": "favourite-drink",
+    ///     "title": "Your favourite drink",
+    ///     "value": "128",
+    ///     "supportingText": "Filter Coffee"
+    /// }
+    /// </example>
+    public class QuickStatResponse
+    {
+        /// <summary>
+        /// Stable stat identifier.
+        /// </summary>
+        [Required]
+        public required string Key { get; set; }
+
+        /// <summary>
+        /// Card title.
+        /// </summary>
+        [Required]
+        public required string Title { get; set; }
+
+        /// <summary>
+        /// Main value shown in the card.
+        /// </summary>
+        [Required]
+        public required int Value { get; set; }
+
+        /// <summary>
+        /// Smaller supporting text shown below the main value.
+        /// </summary>
+        [Required]
+        public required string? SupportingText { get; set; }
+    }
+}

coffeecard/CoffeeCard.Tests.Unit/Services/v2/StatisticsServiceTests.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using CoffeeCard.Common.Configuration;
+using CoffeeCard.Library.Persistence;
+using CoffeeCard.Library.Services.v2;
+using CoffeeCard.Library.Utils;
+using CoffeeCard.Models.DataTransferObjects.v2.Purchase;
+using CoffeeCard.Models.Entities;
+using CoffeeCard.Tests.Common.Builders;
+using Microsoft.EntityFrameworkCore;
+using Moq;
+using Xunit;
+
+namespace CoffeeCard.Tests.Unit.Services.v2
+{
+    public class StatisticsServiceTests
+    {
+        [Fact(DisplayName = "GetQuickStatsAsync returns the four quick stats")]
+        public async Task GetQuickStatsAsyncReturnsFourQuickStats()
+        {
+            // Arrange
+            var builder = new DbContextOptionsBuilder<CoffeeCardContext>().UseInMemoryDatabase(
+                nameof(GetQuickStatsAsyncReturnsFourQuickStats)
+            );
+
+            var databaseSettings = new DatabaseSettings { SchemaName = "test" };
+            var environmentSettings = new EnvironmentSettings()
+            {
+                EnvironmentType = EnvironmentType.Test,
+            };
+
+            await using var context = new CoffeeCardContext(
+                builder.Options,
+                databaseSettings,
+                environmentSettings
+            );
+
+            var user = UserBuilder.DefaultCustomer().WithId(1).Build();
+
+            var otherUser = UserBuilder.DefaultCustomer().WithId(2).Build();
+
+            context.Users.AddRange(user, otherUser);
+
+            var currentTime = new DateTime(2026, 5, 3, 12, 0, 0, DateTimeKind.Utc);
+
+            var latte = MenuItemBuilder.Simple().WithId(1).WithName("Latte").Build();
+            var americano = MenuItemBuilder.Simple().WithId(2).WithName("Americano").Build();
+            var espresso = MenuItemBuilder.Simple().WithId(3).WithName("Espresso").Build();
+
+            context.MenuItems.AddRange(latte, americano, espresso);
+
+            var largeProduct = ProductBuilder.Simple().WithId(1).WithName("Large").Build();
+            var smallProduct = ProductBuilder.Simple().WithId(2).WithName("Small").Build();
+            var fancyProduct = ProductBuilder.Simple().WithId(3).WithName("Fancy").Build();
+
+            context.Products.AddRange(largeProduct, smallProduct, fancyProduct);
+
+            var purchase1 = PurchaseBuilder
+                .Simple()
+                .WithId(1)
+                .WithProductName("Large")
+                .WithProductId(largeProduct.Id)
+                .WithProduct(largeProduct)
+                .WithPrice(20)
+                .WithNumberOfTickets(1)
+                .WithOrderId("order-1")
+                .WithStatus(PurchaseStatus.Completed)
+                .WithType(PurchaseType.Free)
+                .WithPurchasedById(user.Id)
+                .WithPurchasedBy(user)
+                .WithDateCreated(currentTime.AddDays(-1))
+                .Build();
+            var purchase2 = PurchaseBuilder
+                .Simple()
+                .WithId(2)
+                .WithProductName("Small")
+                .WithProductId(smallProduct.Id)
+                .WithProduct(smallProduct)
+                .WithPrice(20)
+                .WithNumberOfTickets(1)
+                .WithOrderId("order-2")
+                .WithStatus(PurchaseStatus.Completed)
+                .WithType(PurchaseType.Free)
+                .WithPurchasedById(user.Id)
+                .WithPurchasedBy(user)
+                .WithDateCreated(currentTime.AddDays(-2))
+                .Build();
+            var purchase3 = PurchaseBuilder
+                .Simple()
+                .WithId(3)
+                .WithProductName("Large")
+                .WithProductId(largeProduct.Id)
+                .WithProduct(largeProduct)
+                .WithPrice(20)
+                .WithNumberOfTickets(1)
+                .WithOrderId("order-3")
+                .WithStatus(PurchaseStatus.Completed)
+                .WithType(PurchaseType.Free)
+                .WithPurchasedById(user.Id)
+                .WithPurchasedBy(user)
+                .WithDateCreated(currentTime.AddDays(-3))
+                .Build();
+            var purchase4 = PurchaseBuilder
+                .Simple()
+                .WithId(4)
+                .WithProductName("Small")
+                .WithProductId(fancyProduct.Id)
+                .WithProduct(fancyProduct)
+                .WithPrice(20)
+                .WithNumberOfTickets(1)
+                .WithOrderId("order-4")
+                .WithStatus(PurchaseStatus.Completed)
+                .WithType(PurchaseType.Free)
+                .WithPurchasedById(otherUser.Id)
+                .WithPurchasedBy(otherUser)
+                .WithDateCreated(currentTime.AddDays(-1))
+                .Build();
+
+            var tickets = new List<Ticket>
+            {
+                TicketBuilder
+                    .Simple()
+                    .WithId(1)
+                    .WithDateCreated(currentTime.AddDays(-3))
+                    .WithDateUsed(currentTime.AddDays(-3))
+                    .WithProductId(largeProduct.Id)
+                    .WithStatus(TicketStatus.Used)
+                    .WithOwnerId(user.Id)
+                    .WithOwner(user)
+                    .WithPurchaseId(purchase1.Id)
+                    .WithPurchase(purchase1)
+                    .WithUsedOnMenuItemId(latte.Id)
+                    .WithUsedOnMenuItem(latte)
+                    .Build(),
+                TicketBuilder
+                    .Simple()
+                    .WithId(2)
+                    .WithDateCreated(currentTime.AddDays(-2))
+                    .WithDateUsed(currentTime.AddDays(-2))
+                    .WithProductId(smallProduct.Id)
+                    .WithStatus(TicketStatus.Used)
+                    .WithOwnerId(user.Id)
+                    .WithOwner(user)
+                    .WithPurchaseId(purchase2.Id)
+                    .WithPurchase(purchase2)
+                    .WithUsedOnMenuItemId(americano.Id)
+                    .WithUsedOnMenuItem(americano)
+                    .Build(),
+                TicketBuilder
+                    .Simple()
+                    .WithId(3)
+                    .WithDateCreated(currentTime.AddDays(-1))
+                    .WithDateUsed(currentTime.AddDays(-1))
+                    .WithProductId(largeProduct.Id)
+                    .WithStatus(TicketStatus.Used)
+                    .WithOwnerId(user.Id)
+                    .WithOwner(user)
+                    .WithPurchaseId(purchase3.Id)
+                    .WithPurchase(purchase3)
+                    .WithUsedOnMenuItemId(latte.Id)
+                    .WithUsedOnMenuItem(latte)
+                    .Build(),
+                TicketBuilder
+                    .Simple()
+                    .WithId(4)
+                    .WithDateCreated(currentTime)
+                    .WithDateUsed(currentTime)
+                    .WithProductId(fancyProduct.Id)
+                    .WithStatus(TicketStatus.Used)
+                    .WithOwnerId(otherUser.Id)
+                    .WithOwner(otherUser)
+                    .WithPurchaseId(purchase4.Id)
+                    .WithPurchase(purchase4)
+                    .WithUsedOnMenuItemId(espresso.Id)
+                    .WithUsedOnMenuItem(espresso)
+                    .Build(),
+                TicketBuilder
+                    .Simple()
+                    .WithId(5)
+                    .WithDateCreated(currentTime)
+                    .WithDateUsed(currentTime)
+                    .WithProductId(fancyProduct.Id)
+                    .WithStatus(TicketStatus.Used)
+                    .WithOwnerId(otherUser.Id)
+                    .WithOwner(otherUser)
+                    .WithPurchaseId(purchase4.Id)
+                    .WithPurchase(purchase4)
+                    .WithUsedOnMenuItemId(espresso.Id)
+                    .WithUsedOnMenuItem(espresso)
+                    .Build(),
+            };
+
+            context.Purchases.AddRange(purchase1, purchase2, purchase3, purchase4);
+            context.Tickets.AddRange(tickets);
+            await context.SaveChangesAsync();
+
+            var dateTimeProvider = new Mock<IDateTimeProvider>();
+            dateTimeProvider.Setup(provider => provider.UtcNow()).Returns(currentTime);
+
+            var statisticsService = new StatisticsService(context, dateTimeProvider.Object);
+
+            // Act
+            var result = (await statisticsService.GetQuickStatsAsync(user)).ToList();
+
+            // Assert
+            Assert.Equal(4, result.Count);
+
+            var totalDrinks = Assert.Single(result.Where(stat => stat.Key == "total-drinks-user"));
+            Assert.Equal(3, totalDrinks.Value);
+            Assert.Null(totalDrinks.SupportingText);
+
+            var drinksToday = Assert.Single(
+                result.Where(stat => stat.Key == "global-drinks-today")
+            );
+            Assert.Equal(2, drinksToday.Value);
+            Assert.Null(drinksToday.SupportingText);
+
+            var favouriteDrink = Assert.Single(result.Where(stat => stat.Key == "favourite-drink"));
+            Assert.Equal(2, favouriteDrink.Value);
+            Assert.Equal("Latte", favouriteDrink.SupportingText);
+
+            var drinksThisWeek = Assert.Single(
+                result.Where(stat => stat.Key == "drinks-this-week-user")
+            );
+            Assert.Equal(3, drinksThisWeek.Value);
+            Assert.Null(drinksThisWeek.SupportingText);
+        }
+    }
+}