add initial implementation of LDtk importer with data models and scene builder

addons/csharp_ldtk_importer/LdtkResourceImporter.cs

@@ -0,0 +1,95 @@
+using System.Text.Json;
+using CSharpLdtkImporter.Models;
+using Godot;
+using Godot.Collections;
+
+namespace CSharpLdtkImporter;
+
+[Tool]
+public partial class LdtkResourceImporter : EditorImportPlugin
+{
+    public override string _GetImporterName() => "ldtk.importer";
+    public override string _GetVisibleName() => "LDtk Level Importer";
+    public override string[] _GetRecognizedExtensions() => new string[] { "ldtk" };
+    public override string _GetResourceType() => "PackedScene";
+    public override string _GetSaveExtension() => "tscn";
+    public override int _GetPresetCount() => 0;
+    public override float _GetPriority() => 1.0f;
+    
+    public override Error _Import(string sourceFile, string savePath, Godot.Collections.Dictionary options, Godot.Collections.Array<string> platformVariants, Godot.Collections.Array<string> genFiles)
+    {
+        // 1. Read the .ldtk file content
+        using var file = FileAccess.Open(sourceFile, FileAccess.ModeFlags.Read);
+        if (file == null)
+        {
+            GD.PushError($"Failed to open LDTK file: {sourceFile}");
+            return Error.CantOpen;
+        }
+        string jsonContent = file.GetAsText();
+
+        // 2. Deserialize the JSON into our C# data models
+        LdtkData ldtkData;
+        try
+        {
+            ldtkData = JsonSerializer.Deserialize<LdtkData>(jsonContent);
+        }
+        catch (JsonException e)
+        {
+            GD.PushError($"Failed to parse LDTK JSON: {e.Message}");
+            return Error.ParseError;
+        }
+
+        if (ldtkData == null)
+        {
+            GD.PushError("Parsed LDTK data is null.");
+            return Error.Failed;
+        }
+
+        // 3. Use the Scene Builder to generate the Godot scene
+        var builder = new LdtkSceneBuilder(ldtkData, sourceFile);
+        var rootNode = builder.BuildLdtkProjectRoot();
+
+        var scene = new PackedScene();
+        scene.Pack(rootNode);
+
+        var newSceneNodeCount = scene.GetState().GetNodeCount();
+        
+        GD.Print($"New scene node count: {newSceneNodeCount}, expected: {rootNode.GetChildCount() + 1} (including root)");
+
+        // 4. Save the generated scene
+        var destinationPath = $"{savePath}.{_GetSaveExtension()}";
+        var error = ResourceSaver.Save(scene, destinationPath);
+        if (error != Error.Ok)
+        {
+            GD.PushError($"Failed to save generated scene to {destinationPath}");
+        }
+
+        return error;
+    }
+
+    public override Array<Dictionary> _GetImportOptions(string path, int presetIndex)
+    {
+        var options = new Array<Dictionary>()
+        {
+            new()
+            {
+                { "name", "import_entities" },
+                { "default_value", true },
+                { "usage", (int)(PropertyUsageFlags.Default | PropertyUsageFlags.UpdateAllIfModified) }
+            },
+            new()
+            {
+                { "name", "import_tilemaps" },
+                { "default_value", true },
+                { "usage", (int)(PropertyUsageFlags.Default | PropertyUsageFlags.UpdateAllIfModified) }
+            }
+        };
+        
+        return options;
+    }
+
+    public override bool _GetOptionVisibility(string path, StringName optionName, Dictionary options)
+    {
+        return true;
+    }
+}