import type { Artboard } from "@core/artboard";
import type { Asset } from "@core/asset";
import type { Layer } from "@core/layer";

export async function downloadArtboardPng(artboard: Artboard, assets: readonly Asset[]) {
  const width = Math.max(1, Math.round(artboard.bounds.w));
  const height = Math.max(1, Math.round(artboard.bounds.h));
  const canvas = document.createElement("canvas");
  canvas.width = width;
  canvas.height = height;

  const context = canvas.getContext("2d");
  if (!context) throw new Error("Canvas 2D is not available");

  if (artboard.backgroundColor !== "transparent") {
    context.fillStyle = artboard.backgroundColor;
    context.fillRect(0, 0, width, height);
  }

  context.save();
  context.translate(-artboard.bounds.x, -artboard.bounds.y);
  for (const layer of artboard.layers) await drawLayer(context, layer, assets);
  context.restore();

  const url = canvas.toDataURL("image/png");
  const link = document.createElement("a");
  link.href = url;
  link.download = `${safeFilename(artboard.name)}.png`;
  link.click();
}

async function drawLayer(context: CanvasRenderingContext2D, layer: Layer, assets: readonly Asset[]) {
  if (!layer.visible) return;

  context.save();
  context.globalAlpha *= layer.opacity;

  if (layer.type === "group") {
    for (const child of layer.children) await drawLayer(context, child, assets);
    context.restore();
    return;
  }

  const asset = assets.find((candidate) => candidate.id === layer.assetId);
  if (!asset) {
    context.restore();
    return;
  }

  const image = await loadImage(asset.source);
  context.drawImage(
    image,
    layer.transform.position.x,
    layer.transform.position.y,
    asset.intrinsicSize.w * layer.transform.scale.x,
    asset.intrinsicSize.h * layer.transform.scale.y,
  );
  context.restore();
}

function loadImage(source: string) {
  return new Promise<HTMLImageElement>((resolve, reject) => {
    const image = new Image();
    image.onload = () => resolve(image);
    image.onerror = () => reject(new Error("Failed to load image for export"));
    image.src = source;
  });
}

function safeFilename(name: string) {
  return name.trim().replace(/[^a-z0-9-_]+/gi, "-").replace(/^-+|-+$/g, "") || "artboard";
}