Add broadcast scheduling features: implement Show and Channel entities, enhance AppDbContext and DependencyInjection for broadcasting, and update API routing. Include migration for new database schema and update documentation for broadcast-related functionalities.

backend/src/TeleWave.Application/Broadcast/AddChannelAd/AddChannelAdCommandHandler.cs

@@ -0,0 +1,35 @@
+using LiteCqrs;
+using Microsoft.EntityFrameworkCore;
+using TeleWave.Application.Common.Interfaces;
+using TeleWave.Application.Common.Models;
+
+namespace TeleWave.Application.Broadcast.AddChannelAd;
+
+public sealed class AddChannelAdCommandHandler(IAppDbContext dbContext)
+    : ICommandHandler<AddChannelAdCommand, Result<Guid>>
+{
+    public async Task<Result<Guid>> Handle(
+        AddChannelAdCommand command,
+        CancellationToken cancellationToken
+    )
+    {
+        var channel = await dbContext.Channels
+            .Include(c => c.Ads)
+            .FirstOrDefaultAsync(c => c.Id == command.ChannelId, cancellationToken);
+        if (channel is null)
+            return Result.Failure<Guid>(ChannelErrors.NotFound);
+
+        var assetExists = await dbContext.MediaAssets.AnyAsync(
+            a => a.Id == command.MediaAssetId,
+            cancellationToken
+        );
+        if (!assetExists)
+            return Result.Failure<Guid>(ChannelErrors.AssetNotFound);
+
+        if (channel.HasAd(command.MediaAssetId))
+            return Result.Failure<Guid>(ChannelErrors.AdAlreadyAdded);
+
+        var ad = channel.AddAd(command.MediaAssetId);
+        return Result.Success(ad.Id);
+    }
+}