Refactor fluent download pipelines

Beam.Fluent/DownloadStage.cs

@@ -0,0 +1,44 @@
+using System.Collections.Concurrent;
+using System.Text.Json;
+using Beam.Models;
+
+namespace Beam.Fluent;
+
+internal sealed class DownloadStage<RawType, OutType>(DownloadEnumerable<OutType> download) : IDownloadStage<RawType, OutType> {
+    private IAsyncEnumerable<Ordered<OutType>> _download = download;
+
+    public DownloadEnumerable<OutType> AsAsyncEnumerable() {
+        return new DownloadEnumerable<OutType>(_download.GetAsyncEnumerator());
+    }
+
+    private async IAsyncEnumerable<Ordered<OutType>> _SaveToDirectory(string dir) {
+        Directory.CreateDirectory(dir);
+        await foreach (var download in _download) {
+            await System.IO.File.WriteAllTextAsync(
+                Path.Combine(dir, $"{Path.GetRandomFileName()}.{download.Order}.json"),
+                JsonSerializer.Serialize(dir));
+            yield return download;
+        }
+    }
+
+    public IDownloadStage<RawType, OutType> SaveToDirectory(string dir) {
+        _download = _SaveToDirectory(dir);
+        return this;
+    }
+
+    public IDownloadStage<RawType, OutType> SaveToFiles(IEnumerable<string> files) {
+        throw new NotImplementedException();
+    }
+
+    public IDownloadStage<RawType, OutType> SaveToMemory(ConcurrentBag<OutType> bag) {
+        throw new NotImplementedException();
+    }
+
+    public void WaitForDownload() {
+        throw new NotImplementedException();
+    }
+
+    public Task WaitForDownloadAsync() {
+        throw new NotImplementedException();
+    }
+}