using System.Buffers;
using System.IO.Pipelines;
using Microsoft.AspNetCore.Http.Json;
using Microsoft.Extensions.Caching.Memory;
using NetVips;
using Oh.My.Stitcher;
using Validation;
using ZLogger;

WebApplicationBuilder builder = WebApplication.CreateSlimBuilder(args);
builder.Logging.ClearProviders().AddZLoggerConsole();
builder.Services.AddMemoryCache();
builder.Services.Configure<JsonOptions>(options =>
{
  options.SerializerOptions.TypeInfoResolver = StitchSerializerContext.Default;
});
WebApplication app = builder.Build();

ILoggerFactory loggerFactory = app.Services.GetRequiredService<ILoggerFactory>();
ILogger logger = loggerFactory.CreateLogger<Program>();

string? tilesDirectory = Environment.GetEnvironmentVariable("ASSET_PATH_RO");
string cacheDirectory = Path.Combine(Path.GetTempPath(), "oh-my-stitch");
Directory.CreateDirectory(cacheDirectory);

// sanity check
Assumes.NotNullOrEmpty(tilesDirectory);
Assumes.True(File.Exists(Path.Combine(tilesDirectory, "A1.png")));
Assumes.True(File.Exists(Path.Combine(tilesDirectory, "AE55.png")));


app.UseDefaultFiles();
app.UseStaticFiles();
app.MapPost("/api/image/generate", (Stitch request, IMemoryCache cache) =>
{
  Pipe pipe = new();
  _ = Task.Run(async () =>
  {
    Image? image = null;
    List<Image> images = [];
    try
    {
      bool created = Tile.TryCreate(in request, tilesDirectory, images, logger, cache, out image,
        out string? cacheKey, out string? cacheFile);
      if( !created && cacheFile != null )
      {
        logger.ZLogDebug($"cache hit key: {cacheKey}, file: {cacheFile}");
        await using FileStream cacheStream = new(cacheFile, FileMode.Open, FileAccess.Read, FileShare.Read);
        await cacheStream.CopyToAsync(pipe.Writer.AsStream());
        return;
      }

      if( cacheKey == null )
      {
        image?.WriteToStream(pipe.Writer.AsStream(), ".png");
        return;
      }

      Pipe innerPipe = new();
      _ = Task.Run(async () =>
      {
        string newCacheFile = Path.Combine(cacheDirectory, $"{cacheKey}.png");
        MemoryCacheEntryOptions cacheEntryOptions = new MemoryCacheEntryOptions()
          .SetSlidingExpiration(TimeSpan.FromMinutes(10))
          .RegisterPostEvictionCallback((_, value, _, _) =>
          {
            if( value is string path )
              File.Delete(path);
          });
        logger.ZLogDebug($"save cache key: {cacheKey}, file: {newCacheFile}");
        cache.Set(cacheKey!, newCacheFile, cacheEntryOptions);

        await using FileStream cacheStream = new(newCacheFile, FileMode.Create, FileAccess.Write, FileShare.Read);
        while( true )
        {
          ReadResult result = await innerPipe.Reader.ReadAsync();
          ReadOnlySequence<byte> buffer = result.Buffer;

          foreach( ReadOnlyMemory<byte> segment in buffer )
            await Task.WhenAll(pipe.Writer.WriteAsync(segment).AsTask(), cacheStream.WriteAsync(segment).AsTask());

          innerPipe.Reader.AdvanceTo(buffer.End);
          if( result.IsCompleted )
            break;
        }
      });
      image?.WriteToStream(innerPipe.Writer.AsStream(), ".png");
    }
    catch( Exception e )
    {
      logger.ZLogError(e, $"Error when generating image");
      using Image errorImage = Tile.CreateError(e);
      errorImage.WriteToStream(pipe.Writer.AsStream(), ".png");
    }
    finally
    {
      image?.Dispose();
      foreach( Image img in images )
        img.Dispose();
      await pipe.Writer.CompleteAsync();
    }
  });
  return Results.Stream(pipe.Reader.AsStream(), "image/png");
});

app.Run();