Rewrite generator pipeline

Services/PostsSource.cs

@@ -0,0 +1,43 @@
+namespace QuestReader.Services;
+
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+public class PostsSource
+{
+    public List<ThreadPost> Posts { get; set; }
+
+    public List<ThreadPost> Accepted { get; set; }
+
+    public Metadata Metadata { get; set; }
+
+    public PostsSource(string questName, string basePath)
+    {
+        var options = new JsonSerializerOptions
+        {
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
+        };
+
+        using var fileStream = File.OpenRead(Path.Combine(basePath, "metadata.json"));
+        Metadata = JsonSerializer.Deserialize<Metadata>(fileStream, options)
+                ?? throw new InvalidDataException("Empty deserialisation result for quest metadata");
+        fileStream.Dispose();
+
+        Console.Out.WriteLine($"Loaded metadata: {Metadata}");
+        Posts = Metadata.Threads.SelectMany(tId => {
+            using var fileStream = File.OpenRead(Path.Combine(basePath, $"thread_{tId}.json"));
+            var threadData = JsonSerializer.Deserialize<List<ThreadPost>>(fileStream, options)
+                ?? throw new InvalidDataException("Empty deserialisation result for thread data");
+            fileStream.Dispose();
+
+            return threadData;
+        }).ToList();
+
+        using var postsListStream = File.OpenRead(Path.Combine(basePath, "accepted.json"));
+        var ids = JsonSerializer.Deserialize<List<int>>(postsListStream, options)
+                ?? throw new InvalidDataException("Empty deserialisation result for quest metadata");
+        Accepted = Posts.Where(p => ids.Contains(p.Id)).ToList();
+        Console.Out.WriteLine($"Loaded a list of {Accepted.Count} posts, referencing {Accepted.Where(a => a.File is not null).Count()} files");
+    }
+}