import type { ImageDocument } from "@core/document";
import type { EditorState } from "@editor/state";

export type RenderFrame = {
  document: ImageDocument;
  editor: EditorState;
};

export type ImageRenderer = {
  render(frame: RenderFrame): void;
  dispose(): void;
};

export type RendererBackend = "webgl";

export function createRenderer(canvas: HTMLCanvasElement, backend: RendererBackend = "webgl"): ImageRenderer {
  if (backend !== "webgl") {
    throw new Error(`Unsupported renderer backend: ${backend}`);
  }

  const context = canvas.getContext("webgl2");
  if (!context) {
    throw new Error("WebGL2 is not available");
  }

  const clearRect = (x: number, y: number, w: number, h: number, color: [number, number, number, number]) => {
    context.scissor(x, canvas.height - y - h, w, h);
    context.clearColor(...color);
    context.clear(context.COLOR_BUFFER_BIT);
  };

  return {
    render(frame) {
      const { w, h } = frame.editor.viewport.size;
      const { center, zoom } = frame.editor.viewport;

      if (canvas.width !== w) canvas.width = w;
      if (canvas.height !== h) canvas.height = h;

      context.viewport(0, 0, w, h);
      context.disable(context.SCISSOR_TEST);
      context.clearColor(0.18, 0.18, 0.2, 1);
      context.clear(context.COLOR_BUFFER_BIT);
      context.enable(context.SCISSOR_TEST);

      for (const artboard of frame.document.artboards) {
        const x = Math.round(w / 2 + (artboard.bounds.x - center.x) * zoom);
        const y = Math.round(h / 2 + (artboard.bounds.y - center.y) * zoom);
        const width = Math.max(0, Math.round(artboard.bounds.w * zoom));
        const height = Math.max(0, Math.round(artboard.bounds.h * zoom));

        if (artboard.backgroundColor === "transparent") {
          const squareSize = Math.max(4, Math.round(12 * zoom));
          for (let py = y; py < y + height; py += squareSize) {
            for (let px = x; px < x + width; px += squareSize) {
              const sx = Math.max(0, px);
              const sy = Math.max(0, py);
              const sw = Math.min(px + squareSize, x + width, w) - sx;
              const sh = Math.min(py + squareSize, y + height, h) - sy;
              if (sw <= 0 || sh <= 0) continue;

              const checker = (Math.floor((px - x) / squareSize) + Math.floor((py - y) / squareSize)) % 2 === 0;
              clearRect(sx, sy, sw, sh, checker ? [0.82, 0.82, 0.86, 1] : [0.94, 0.94, 0.97, 1]);
            }
          }
        }
      }

      context.disable(context.SCISSOR_TEST);
    },
    dispose() {},
  };
}