import { PlaitBoard } from "@plait/core";

export type ImageExportOptions = {
  scale: 1 | 2 | 3;
  transparent: boolean;
  backgroundColor: string;
};

const textStyles = [
  "display",
  "box-sizing",
  "margin",
  "padding",
  "width",
  "height",
  "font-family",
  "font-size",
  "font-weight",
  "font-style",
  "line-height",
  "color",
  "background-color",
  "text-align",
  "text-decoration",
  "white-space",
  "word-break",
  "overflow-wrap",
  "border-radius",
  "vertical-align",
];

async function embedResource(url: string): Promise<string> {
  const response = await fetch(url, { signal: AbortSignal.timeout(15_000) });
  if (!response.ok) throw new Error("图片资源加载失败，请稍后重试");
  const blob = await response.blob();
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = () => resolve(String(reader.result));
    reader.onerror = () => reject(new Error("图片资源读取失败"));
    reader.readAsDataURL(blob);
  });
}

/** Render the complete content layer in board coordinates, independent of pan/zoom. */
export async function exportBoardImage(
  board: PlaitBoard,
  options: ImageExportOptions
) {
  if (!board.children.length) throw new Error("当前工作表没有可导出的内容");
  await document.fonts.ready;
  const host = PlaitBoard.getElementHost(board);
  const bounds = host.getBBox();
  const padding = 32;
  const width = Math.ceil(bounds.width + padding * 2);
  const height = Math.ceil(bounds.height + padding * 2);
  const pixelWidth = width * options.scale;
  const pixelHeight = height * options.scale;
  if (!bounds.width || !bounds.height)
    throw new Error("画布尚未准备好，请稍后重试");
  if (
    pixelWidth > 16_384 ||
    pixelHeight > 16_384 ||
    pixelWidth * pixelHeight > 64_000_000
  ) {
    throw new Error("图片尺寸过大，请降低清晰度或拆分工作表后导出");
  }
  const clone = host.cloneNode(true) as SVGGElement;
  clone.removeAttribute("transform");
  const sources = host.querySelectorAll("foreignObject *");
  const copies = clone.querySelectorAll("foreignObject *");
  sources.forEach((source, index) => {
    const copy = copies[index] as HTMLElement;
    const computed = getComputedStyle(source);
    for (const property of textStyles)
      copy.style.setProperty(property, computed.getPropertyValue(property));
    copy.removeAttribute("contenteditable");
  });
  const resources = new Map<string, Promise<string>>();
  await Promise.all(
    Array.from(clone.querySelectorAll("img, image")).map(async (node) => {
      const attribute = node.tagName.toLowerCase() === "img" ? "src" : "href";
      const url =
        node.getAttribute(attribute) ||
        node.getAttributeNS("http://www.w3.org/1999/xlink", "href");
      if (!url || url.startsWith("data:")) return;
      if (!resources.has(url)) resources.set(url, embedResource(url));
      node.setAttribute(attribute, await resources.get(url)!);
      node.removeAttributeNS("http://www.w3.org/1999/xlink", "href");
    })
  );
  const namespace = "http://www.w3.org/2000/svg";
  const svg = document.createElementNS(namespace, "svg");
  svg.setAttribute("width", String(width));
  svg.setAttribute("height", String(height));
  svg.setAttribute(
    "viewBox",
    `${bounds.x - padding} ${bounds.y - padding} ${width} ${height}`
  );
  for (const defs of PlaitBoard.getHost(board).querySelectorAll(
    ":scope > defs"
  ))
    svg.append(defs.cloneNode(true));
  const style = document.createElementNS(namespace, "style");
  const weights = [400, 500, 700, 800];
  const names = ["Regular", "Medium", "Bold", "Extrabold"];
  style.textContent = (
    await Promise.all(
      names.map(async (name, index) => {
        const data = await embedResource(`/fonts/xmind/NeverMind-${name}.ttf`);
        return `@font-face{font-family:NeverMind;src:url('${data}') format('truetype');font-weight:${weights[index]};}`;
      })
    )
  ).join("\n");
  svg.append(style, clone);
  const image = new Image();
  const svgData = new XMLSerializer().serializeToString(svg);
  // A self-contained data URI keeps foreignObject content safe to draw on canvas.
  image.src = `data:image/svg+xml;charset=utf-8,${encodeURIComponent(svgData)}`;
  await image.decode();
  const canvas = document.createElement("canvas");
  canvas.width = pixelWidth;
  canvas.height = pixelHeight;
  const context = canvas.getContext("2d");
  if (!context) throw new Error("浏览器无法生成图片");
  if (!options.transparent) {
    context.fillStyle = options.backgroundColor;
    context.fillRect(0, 0, pixelWidth, pixelHeight);
  }
  context.drawImage(image, 0, 0, pixelWidth, pixelHeight);
  const blob = await new Promise<Blob>((resolve, reject) =>
    canvas.toBlob(
      (value) => (value ? resolve(value) : reject(new Error("图片生成失败"))),
      "image/png"
    )
  );
  return { blob, width: pixelWidth, height: pixelHeight };
}