import type { ECharts } from 'echarts';

const TITLE_FONT = 'bold 32px "Microsoft YaHei","PingFang SC","Noto Sans SC",sans-serif';
const SUB_FONT = '22px "Microsoft YaHei","PingFang SC","Noto Sans SC",sans-serif';

type ChartShot = {
  title: string;
  instance: ECharts | undefined;
};

function loadImage(src: string): Promise<HTMLImageElement> {
  return new Promise((resolve, reject) => {
    const img = new Image();
    img.onload = () => resolve(img);
    img.onerror = () => reject(new Error('图表截图失败'));
    img.src = src;
  });
}

async function composePage(params: {
  chartPng: string;
  title: string;
  subtitle: string;
}): Promise<{ dataUrl: string; width: number; height: number }> {
  const img = await loadImage(params.chartPng);
  const header = 96;
  const canvas = document.createElement('canvas');
  canvas.width = img.width;
  canvas.height = img.height + header;
  const ctx = canvas.getContext('2d');
  if (!ctx) throw new Error('无法生成 PDF 画布');
  ctx.fillStyle = '#ffffff';
  ctx.fillRect(0, 0, canvas.width, canvas.height);
  ctx.textBaseline = 'top';
  ctx.fillStyle = '#1f1f1f';
  ctx.font = TITLE_FONT;
  ctx.fillText(params.title, 24, 16, canvas.width - 48);
  ctx.fillStyle = '#8c8c8c';
  ctx.font = SUB_FONT;
  ctx.fillText(params.subtitle, 24, 56, canvas.width - 48);
  ctx.drawImage(img, 0, header);
  return {
    dataUrl: canvas.toDataURL('image/jpeg', 0.92),
    width: canvas.width,
    height: canvas.height,
  };
}

/** 把当前已渲染折线图打成横向 A4 PDF（不含 KPI / 待办）。 */
export async function downloadDashboardChartsPdf(params: {
  filename: string;
  subtitle: string;
  charts: ChartShot[];
}): Promise<void> {
  const ready = params.charts.filter((c): c is { title: string; instance: ECharts } => !!c.instance);
  if (ready.length === 0) {
    throw new Error('暂无可下载的图');
  }
  if (ready.length !== params.charts.length) {
    throw new Error('图表尚未渲染完成，请稍后再试');
  }

  const { jsPDF } = await import('jspdf');
  const pdf = new jsPDF({ orientation: 'landscape', unit: 'mm', format: 'a4' });
  const pageW = pdf.internal.pageSize.getWidth();
  const pageH = pdf.internal.pageSize.getHeight();
  const margin = 10;

  for (let i = 0; i < ready.length; i += 1) {
    const chart = ready[i];
    const png = chart.instance.getDataURL({
      type: 'png',
      pixelRatio: 2,
      backgroundColor: '#ffffff',
    });
    const page = await composePage({
      chartPng: png,
      title: chart.title,
      subtitle: params.subtitle,
    });
    const maxW = pageW - margin * 2;
    const maxH = pageH - margin * 2;
    const ratio = Math.min(maxW / page.width, maxH / page.height);
    const w = page.width * ratio;
    const h = page.height * ratio;
    const x = (pageW - w) / 2;
    const y = margin + (maxH - h) / 2;
    if (i > 0) pdf.addPage();
    pdf.addImage(page.dataUrl, 'JPEG', x, y, w, h);
  }

  const filename = params.filename.endsWith('.pdf') ? params.filename : `${params.filename}.pdf`;
  pdf.save(filename);
}