using System.IO;
using System.Runtime.InteropServices;

public partial class Terrain
{
	enum ToolMode { Height, Flatten, Paint }
	enum ToolShape { Corner, Circle, Square }

	// Set by the terrain editing plugin.
	public EditorUndoRedoManager EditorUndoRedo { get; set; }

	// Dummy value to satisfy the overly careful compiler.
	static bool _dummy = false;

	Material _editToolMaterial;
	public override void _EnterTree()
	{
		_editToolMaterial = new StandardMaterial3D {
			VertexColorUseAsAlbedo = true,
			BlendMode     = BaseMaterial3D.BlendModeEnum.Mix,
			ShadingMode   = BaseMaterial3D.ShadingModeEnum.Unshaded,
			DepthDrawMode = BaseMaterial3D.DepthDrawModeEnum.Disabled,
			NoDepthTest   = true,
		};
	}

	Vector3 _lastPosition;
	public bool EditorInput(InputEvent ev, Control controls, Vector3 maybePos)
	{
		var prevent_default = false;

		// If 'maybePosition' is Vector3.Zero, use previous know position, otherwise update.
		var position = (maybePos == Vector3.Zero) ? _lastPosition : (_lastPosition = maybePos);

		var toolMode  = (ToolMode)(int)controls.Get("tool_mode");
		var toolShape = (ToolShape)(int)controls.Get("tool_shape");
		var texture   = (int)controls.Get("texture");
		var drawSize  = (int)controls.Get("draw_size");

		var isRaise     = (bool)controls.Get("is_raise");
		var isConnected = (bool)controls.Get("is_connected");
		var isFlatten   = toolMode  == ToolMode.Flatten;
		var isCorner    = toolShape == ToolShape.Corner;

		var hover = ToTilePos(position);
		if (isCorner) drawSize = 1;
		var isEven = (drawSize % 2) == 0;
		var radius = FloorToInt(drawSize / 2.0f);

		// Offset hover tile position by corner.
		if (isEven) hover.Position = hover.Corner switch {
			Corner.TopLeft     => hover.Position.Offset(0, 0),
			Corner.TopRight    => hover.Position.Offset(1, 0),
			Corner.BottomRight => hover.Position.Offset(1, 1),
			Corner.BottomLeft  => hover.Position.Offset(0, 1),
			_ => throw new InvalidOperationException(),
		};

		IEnumerable<TilePos> GetTilesInSquare() {
			var min = hover.Position.Offset(-radius, -radius);
			var max = hover.Position.Offset(+radius, +radius);
			if (isEven) max = max.Offset(-1, -1);
			for (var x = min.X; x <= max.X; x++)
				for (var y = min.Y; y <= max.Y; y++)
					yield return new(x, y);
		}

		IEnumerable<TilePos> GetTilesInRadius() {
			var center = isEven ? hover.Position.ToVector2I()
			                    : hover.Position.ToCenter();
			var distanceSqr = Pow(radius + 0.25f * (isEven ? -1 : 1), 2);
			return GetTilesInSquare().Where(tile =>
				center.DistanceSquaredTo(tile.ToCenter()) < distanceSqr);
		}

		// TODO: Handle different tool modes, such as painting.
		// TODO: Allow click-dragging which doesn't affect already changed tiles / corners.
		// TODO: Use ArrayMesh instead of ImmediateMesh.
		// TODO: Dynamically expand terrain instead of having it be a set size.

		// Holds onto all the tiles and which of their corners corners will be affected by this edit operation.
		var tilesToChange = new Dictionary<TilePos, Corners<bool>>();
		ref Corners<bool> GetTileToChange(TilePos position)
			// Don't look at this black magic. The Dictionary type should have this by default I swear!
			=> ref CollectionsMarshal.GetValueRefOrAddDefault(tilesToChange, position, out _dummy);

		if (toolShape == ToolShape.Corner) {
			// Modify selected corner itself.
			GetTileToChange(hover.Position)[hover.Corner] = true;

			if (isConnected) {
				var height = GetTile(hover.Position).Height[hover.Corner];
				foreach (var neighbor in GetNeighbors(hover.Position, hover.Corner)) {
					var neighborHeight = GetTile(neighbor.Position).Height[neighbor.Corner];
					if (neighborHeight != height) continue;
					GetTileToChange(neighbor.Position)[neighbor.Corner] = true;
				}
			}
		} else {
			var tiles = (toolShape switch {
				ToolShape.Circle => GetTilesInRadius(),
				ToolShape.Square => GetTilesInSquare(),
				_ => throw new InvalidOperationException(),
			}).ToHashSet();

			// Modify selected tiles themselves.
			foreach (var pos in tiles)
				GetTileToChange(pos) = new(true);

			// If the 'connected_toggle' button is active, move "connected" corners.
			// Connected corners are the ones that are at the same height as ones already being moved.
			if (isConnected) foreach (var pos in tiles) {
				var tile = GetTile(pos);
				foreach (var corner in Enum.GetValues<Corner>()) {
					var height = tile.Height[corner];
					foreach (var neighbor in GetNeighbors(pos, corner)) {
						if (tiles.Contains(neighbor.Position)) continue;
						var neighborHeight = GetTile(neighbor.Position).Height[neighbor.Corner];
						if (neighborHeight != height) continue;
						GetTileToChange(neighbor.Position)[neighbor.Corner] = true;
					}
				}
			}
		}

		// Raise / lower the terrain when left mouse button is pressed.
		if (ev is InputEventMouseButton { ButtonIndex: MouseButton.Left, Pressed: true }) {
			prevent_default = true;

			const float AdjustHeight = 0.5f;
			var amount = isFlatten ? GetTile(hover.Position).Height[hover.Corner]
			           : isRaise   ? AdjustHeight : -AdjustHeight;

			var tilesPrevious = new List<(TilePos, Corners<float>)>();
			var tilesChanged  = new List<(TilePos, Corners<float>)>();
			foreach (var (pos, corners) in tilesToChange) {
				var tile = GetTile(pos);
				tilesPrevious.Add((pos, tile.Height));

				var newHeight = tile.Height;
				if (corners.TopLeft    ) newHeight.TopLeft     = isFlatten ? amount : newHeight.TopLeft     + amount;
				if (corners.TopRight   ) newHeight.TopRight    = isFlatten ? amount : newHeight.TopRight    + amount;
				if (corners.BottomRight) newHeight.BottomRight = isFlatten ? amount : newHeight.BottomRight + amount;
				if (corners.BottomLeft ) newHeight.BottomLeft  = isFlatten ? amount : newHeight.BottomLeft  + amount;
				tilesChanged.Add((pos, newHeight));
			}

			if (EditorUndoRedo is EditorUndoRedoManager undo) {
				var name = "Modify terrain height"; // TODO: Change name depending on tool mode.
				undo.CreateAction(name, backwardUndoOps: false);

				undo.AddDoMethod(this, nameof(DoModifyTerrainHeight), Pack(tilesChanged));
				undo.AddDoMethod(this, nameof(UpdateMeshAndShape));
				undo.AddDoMethod(this, GodotObject.MethodName.NotifyPropertyListChanged);

				undo.AddUndoMethod(this, nameof(DoModifyTerrainHeight), Pack(tilesPrevious));
				undo.AddUndoMethod(this, nameof(UpdateMeshAndShape));
				undo.AddUndoMethod(this, GodotObject.MethodName.NotifyPropertyListChanged);

				undo.CommitAction(true);
			}
		}

		UpdateEditToolMesh(tilesToChange);
		return prevent_default;
	}

	public void EditorUnfocus()
		=> ClearEditToolMesh();

	public void DoModifyTerrainHeight(byte[] data)
	{
		foreach (var (pos, corners) in Unpack(data)) {
			var tile = GetTile(pos);
			tile.Height = corners;
			SetTile(pos, tile);
		}
	}


	void UpdateEditToolMesh(Dictionary<TilePos, Corners<bool>> tiles)
	{
		var mesh = GetOrCreateMesh("EditToolMesh");
		mesh.ClearSurfaces();
		mesh.SurfaceBegin(Mesh.PrimitiveType.Lines);

		void AddLine((Vector3 Position, bool Visible) start,
		             (Vector3 Position, bool Visible) end) {
			mesh.SurfaceSetColor(start.Visible ? Colors.Blue : Colors.Transparent);
			mesh.SurfaceAddVertex(start.Position);
			mesh.SurfaceSetColor(end.Visible ? Colors.Blue : Colors.Transparent);
			mesh.SurfaceAddVertex(end.Position);
		}

		foreach (var (tile, visible) in tiles) {
			var positions = GetTileCornerPositions(tile);
			foreach (var side in Enum.GetValues<Side>()) {
				var (corner1, corner2) = side.GetCorners();
				if (!visible[corner1] && !visible[corner2]) continue;
				AddLine((positions[corner1], visible[corner1]),
				        (positions[corner2], visible[corner2]));
			}
		}

		mesh.SurfaceEnd();
		mesh.SurfaceSetMaterial(0, _editToolMaterial);
	}

	void ClearEditToolMesh()
		=> GetNodeOrNull("EditToolMesh")?.QueueFree();


	(TilePos Position, Corner Corner) ToTilePos(Vector3 position)
	{
		var local  = ToLocal(position);
		var coord  = new Vector2(local.X, local.Z) / TileSize + (Size + Vector2.One) / 2;
		var pos    = TilePos.From(coord);
		var corner = coord.PosMod(1).RoundToVector2I() switch {
			(0, 0) => Corner.TopLeft,
			(1, 0) => Corner.TopRight,
			(1, 1) => Corner.BottomRight,
			(0, 1) => Corner.BottomLeft,
			_ => throw new InvalidOperationException(),
		};
		return (pos, corner);
	}

	static readonly Dictionary<Corner, (int X, int Y, Corner Opposite)[]> _offsetLookup = new(){
		[Corner.TopLeft    ] = [(-1, -1, Corner.BottomRight), (-1, 0, Corner.TopRight   ), (0, -1, Corner.BottomLeft )],
		[Corner.TopRight   ] = [(+1, -1, Corner.BottomLeft ), (+1, 0, Corner.TopLeft    ), (0, -1, Corner.BottomRight)],
		[Corner.BottomRight] = [(+1, +1, Corner.TopLeft    ), (+1, 0, Corner.BottomLeft ), (0, +1, Corner.TopRight   )],
		[Corner.BottomLeft ] = [(-1, +1, Corner.TopRight   ), (-1, 0, Corner.BottomRight), (0, +1, Corner.TopLeft    )],
	};
	static IEnumerable<(TilePos Position, Corner Corner)> GetNeighbors(TilePos pos, Corner corner)
		=> _offsetLookup[corner].Select(e => (new TilePos(pos.X + e.X, pos.Y + e.Y), e.Opposite));

	static byte[] Pack(IEnumerable<(TilePos Position, Corners<float> Corners)> data)
	{
		using var stream = new MemoryStream();
		using var writer = new BinaryWriter(stream);
		foreach (var (pos, corners) in data) {
			writer.Write(pos.X);
			writer.Write(pos.Y);
			writer.Write(corners.TopLeft);
			writer.Write(corners.TopRight);
			writer.Write(corners.BottomRight);
			writer.Write(corners.BottomLeft);
		}
		return stream.ToArray();
	}

	static IEnumerable<(TilePos Position, Corners<float> Corners)> Unpack(byte[] data)
	{
		using var stream = new MemoryStream(data);
		using var reader = new BinaryReader(stream);
		while (stream.Position < stream.Length) {
			var x = reader.ReadInt32();
			var y = reader.ReadInt32();
			var corners = new Corners<float>(
				reader.ReadSingle(), reader.ReadSingle(),
				reader.ReadSingle(), reader.ReadSingle());
			yield return (new(x, y), corners);
		}
	}
}