feat: add skip habit endpoint

src/Orbit.Api/Controllers/HabitsController.cs

@@ -205,6 +205,19 @@ public async Task<IActionResult> LogHabit(
             : BadRequest(new { error = result.Error });
     }
 
+    [HttpPost("{id:guid}/skip")]
+    public async Task<IActionResult> SkipHabit(
+        Guid id,
+        CancellationToken cancellationToken)
+    {
+        var command = new SkipHabitCommand(HttpContext.GetUserId(), id);
+        var result = await mediator.Send(command, cancellationToken);
+
+        return result.IsSuccess
+            ? NoContent()
+            : BadRequest(new { error = result.Error });
+    }
+
     [HttpPut("{id:guid}")]
     public async Task<IActionResult> UpdateHabit(
         Guid id,

src/Orbit.Application/Habits/Commands/SkipHabitCommand.cs

@@ -0,0 +1,49 @@
+using MediatR;
+using Microsoft.Extensions.Caching.Memory;
+using Orbit.Application.Common;
+using Orbit.Domain.Common;
+using Orbit.Domain.Entities;
+using Orbit.Domain.Interfaces;
+
+namespace Orbit.Application.Habits.Commands;
+
+public record SkipHabitCommand(Guid UserId, Guid HabitId) : IRequest<Result>;
+
+public class SkipHabitCommandHandler(
+    IGenericRepository<Habit> habitRepository,
+    IUserDateService userDateService,
+    IUnitOfWork unitOfWork,
+    IMemoryCache cache) : IRequestHandler<SkipHabitCommand, Result>
+{
+    public async Task<Result> Handle(SkipHabitCommand request, CancellationToken cancellationToken)
+    {
+        var habit = await habitRepository.FindOneTrackedAsync(
+            h => h.Id == request.HabitId,
+            cancellationToken: cancellationToken);
+
+        if (habit is null)
+            return Result.Failure(ErrorMessages.HabitNotFound);
+
+        if (habit.UserId != request.UserId)
+            return Result.Failure(ErrorMessages.HabitNotOwned);
+
+        if (habit.IsCompleted)
+            return Result.Failure("Cannot skip a completed habit.");
+
+        if (habit.FrequencyUnit is null)
+            return Result.Failure("Cannot skip a one-time task.");
+
+        var today = await userDateService.GetUserTodayAsync(request.UserId, cancellationToken);
+
+        if (habit.DueDate > today)
+            return Result.Failure("Cannot skip a habit that is not yet due.");
+
+        habit.AdvanceDueDate(today);
+
+        await unitOfWork.SaveChangesAsync(cancellationToken);
+
+        CacheInvalidationHelper.InvalidateSummaryCache(cache, habit.UserId);
+
+        return Result.Success();
+    }
+}

src/Orbit.Application/Habits/Validators/SkipHabitCommandValidator.cs

@@ -0,0 +1,16 @@
+using FluentValidation;
+using Orbit.Application.Habits.Commands;
+
+namespace Orbit.Application.Habits.Validators;
+
+public class SkipHabitCommandValidator : AbstractValidator<SkipHabitCommand>
+{
+    public SkipHabitCommandValidator()
+    {
+        RuleFor(x => x.UserId)
+            .NotEmpty();
+
+        RuleFor(x => x.HabitId)
+            .NotEmpty();
+    }
+}