using System.IO;

public partial class Terrain
{
	// These mirror the modes / shapes in 'terrain_editing_controls.gd'.
	enum ToolMode { Height, Flatten, Paint, Erase }
	enum ToolShape { Corner, Circle, Square }

	// Set by the terrain editing plugin.
	// Enables access to the in-editor undo/redo system.
	public EditorUndoRedoManager EditorUndoRedo { get; set; }

	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   = (byte)(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.
		// FIXME: This causes FLATTEN to calculate the wrong height in some cases.
		if (isEven) hover.Position += hover.Corner switch {
			Corner.TopLeft     => (0, 0),
			Corner.TopRight    => (1, 0),
			Corner.BottomRight => (1, 1),
			Corner.BottomLeft  => (0, 1),
			_ => throw new InvalidOperationException(),
		};

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

		IEnumerable<TilePos> GetTilesInRadius() {
			var center = isEven ? (Vector2I)hover.Position
			                    : hover.Position.Center;
			var distanceSqr = Pow(radius + (isEven ? -1 : 1) * 0.25f, 2);
			return GetTilesInSquare().Where(tile =>
				center.DistanceSquaredTo(tile.Center) < distanceSqr);
		}

		// TODO: Allow click-dragging which doesn't affect already changed tiles / corners.
		// TODO: Use ArrayMesh instead of ImmediateMesh.
		// TODO: Support texture blending somehow.
		// TODO: Clear empty chunks.

		// Data structure for holding tiles to be modified.
		var tilesToChange = new Dictionary<TilePos, TileModification>();

		// Utility function to set 'Affected' for the specified position and corner.
		void SetCornerAffected((TilePos Position, Corner Corner) pair)
			=> tilesToChange.GetOrAddNew(pair.Position).Affected[pair.Corner] = true;

		// Utility function to get the height for the specified position and corner.
		short GetCornerHeight((TilePos Position, Corner Corner) pair)
			=> Data.GetTileOrDefault(pair.Position).Height[pair.Corner];

		if (toolMode is ToolMode.Paint or ToolMode.Erase) {
			// In PAINT or ERASE mode, only full tiles are ever affected.
			// So this makes populating 'tilesToChange' very straight-forward.

			var tiles = toolShape switch {
				// While in PAINT mode, the CORNER shape instead affects
				// a single tile, regardless of the current 'draw_size'.
				ToolShape.Corner => [ hover.Position ],
				ToolShape.Circle => GetTilesInRadius(),
				ToolShape.Square => GetTilesInSquare(),
				_ => throw new InvalidOperationException(),
			};

			foreach (var pos in tiles)
				tilesToChange.Add(pos, new(){ Affected = new(true) });

		} else if (toolShape == ToolShape.Corner) {
			// With the CORNER shape, only a single corner is affected.

			// Modify selected corner itself.
			SetCornerAffected(hover);

			// If the 'connected_toggle' button is active, move "connected" corners.
			// This is a simplified version of the code below that only affects the 3 neighboring corners.
			if (isConnected) {
				var height = GetCornerHeight(hover);
				foreach (var neighbor in GetNeighbors(hover.Position, hover.Corner))
					if (GetCornerHeight(neighbor) == height)
						SetCornerAffected(neighbor);
			}

		} else {

			var tiles = (toolShape switch {
				ToolShape.Circle => GetTilesInRadius(),
				ToolShape.Square => GetTilesInSquare(),
				_ => throw new InvalidOperationException(),
			}).ToHashSet();

			// Modify selected tiles themselves.
			foreach (var pos in tiles)
				tilesToChange.Add(pos, new(){ Affected = 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 = Data.GetTileOrDefault(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))
							if (GetCornerHeight(neighbor) == height)
								SetCornerAffected(neighbor);
				}
			}

		}

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

			// Fill with current tile data.
			foreach (var (pos, modified) in tilesToChange)
				modified.Original = modified.New = Data.GetTileOrDefault(pos);

			string action;
			if (toolMode == ToolMode.Paint) {
				action = "Paint terrain";
				foreach (var (_, modified) in tilesToChange)
					modified.New.TexturePrimary = texture;
			} else if (toolMode == ToolMode.Erase) {
				action = "Erase terrain";
				foreach (var (_, modified) in tilesToChange)
					modified.New = default;
			} else if (isFlatten) {
				action     = "Flatten terrain";
				var amount = GetCornerHeight(hover);
				foreach (var (_, modified) in tilesToChange) {
					ref var height = ref modified.New.Height;
					if (modified.Affected.TopLeft    ) height.TopLeft     = amount;
					if (modified.Affected.TopRight   ) height.TopRight    = amount;
					if (modified.Affected.BottomRight) height.BottomRight = amount;
					if (modified.Affected.BottomLeft ) height.BottomLeft  = amount;
				}
			} else {
				action     = isRaise ? "Raise terrain" : "Lower terrain";
				var amount = isRaise ?       (short)+1 :       (short)-1;
				foreach (var (_, modified) in tilesToChange) {
					ref var height = ref modified.New.Height;
					if (modified.Affected.TopLeft    ) height.TopLeft     += amount;
					if (modified.Affected.TopRight   ) height.TopRight    += amount;
					if (modified.Affected.BottomRight) height.BottomRight += amount;
					if (modified.Affected.BottomLeft ) height.BottomLeft  += amount;
				}
			}

			if (EditorUndoRedo is EditorUndoRedoManager undo) {
				undo.CreateAction(action, backwardUndoOps: false);

				var   doData = Pack(tilesToChange.Select(e => (e.Key, e.Value.New)));
				var undoData = Pack(tilesToChange.Select(e => (e.Key, e.Value.Original)));

				undo.AddDoMethod(this, nameof(DoModifyTerrain), doData);
				undo.AddDoMethod(this, nameof(UpdateMeshAndShape));
				undo.AddDoMethod(this, GodotObject.MethodName.NotifyPropertyListChanged);

				undo.AddUndoMethod(this, nameof(DoModifyTerrain), undoData);
				undo.AddUndoMethod(this, nameof(UpdateMeshAndShape));
				undo.AddUndoMethod(this, GodotObject.MethodName.NotifyPropertyListChanged);

				undo.CommitAction(true);
			}
		}

		UpdateEditToolMesh(tilesToChange.Select(e => (e.Key, e.Value.Affected)));
		return prevent_default;
	}

	class TileModification
	{
		public Corners<bool> Affected;
		public Tile Original;
		public Tile New;
	}

	public void EditorUnfocus()
		=> ClearEditToolMesh();

	public void DoModifyTerrain(byte[] data)
	{
		foreach (var (pos, tile) in Unpack(data))
			Data[pos] = tile;
	}


	void UpdateEditToolMesh(IEnumerable<(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 = ToPositions(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;
		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 ((TilePos)coord, corner);
	}

	static readonly Dictionary<Corner, (int X, int Z, 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.Z + e.Z), e.Opposite));


	static byte[] Pack(IEnumerable<(TilePos Position, Tile tile)> data)
	{
		using var stream = new MemoryStream();
		using var writer = new BinaryWriter(stream);
		foreach (var (pos, tile) in data) {
			writer.Write(pos.X);
			writer.Write(pos.Z);
			writer.Write(tile.Height.TopLeft);
			writer.Write(tile.Height.TopRight);
			writer.Write(tile.Height.BottomRight);
			writer.Write(tile.Height.BottomLeft);
			writer.Write(tile.TexturePrimary);
			writer.Write(tile.TextureSecondary);
			writer.Write(tile.TextureBlend);
		}
		return stream.ToArray();
	}

	static IEnumerable<(TilePos Position, Tile tile)> 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 height = new Corners<short>(
				reader.ReadInt16(), reader.ReadInt16(),
				reader.ReadInt16(), reader.ReadInt16());

			var texPrimary   = reader.ReadByte();
			var texSecondary = reader.ReadByte();
			var texBlend     = reader.ReadByte();

			yield return (new(x, y), new(){
				Height = height,
				TexturePrimary   = texPrimary,
				TextureSecondary = texSecondary,
				TextureBlend     = texBlend,
			});
		}
	}
}