// frontend/utils/image-compositor.js
// 分享图离屏 canvas 合成(spec § 5.3)

import { BRAND_SLOGANS } from './brand-slogans.js';

const CANVAS_WIDTH = 750;
const CANVAS_HEIGHT = 1334;
const QR_SIZE = 240;
const AVATAR_SIZE = 240;
const COVER_HEIGHT = 1000;
const QR_Y = 960;
const AVATAR_Y = 720;
const SLOGAN_Y = 1200;

const FALLBACK_QRCODE = '/static/share/mock_qrcode.png';
const FALLBACK_AVATAR = '/static/square/gerenzhongxinkangpinkuang.png';

/**
 * 合成分享图(pure function — 不发起任何网络 IO)
 * @param {Object} opts
 * @param {string} opts.coverLocalPath - 本地封面临时路径(uni.downloadFile 后)
 * @param {string} opts.qrcodeLocalPath - 本地二维码临时路径(缺失时回退占位图)
 * @param {string} opts.avatarLocalPath - 本地头像临时路径(缺失时回退占位图)
 * @param {string} opts.nickname - 用户昵称(缺首字母时回退 'T')
 * @param {{brandLine: string, brandDesc: string}} [opts.slogan] - 品牌文案
 * @returns {Promise<{tempFilePath: string, width: number, height: number}>}
 */
export function composeShareImage(opts, componentThis) {
  return new Promise((resolve, reject) => {
    const {
      coverLocalPath,
      qrcodeLocalPath = FALLBACK_QRCODE,
      avatarLocalPath = FALLBACK_AVATAR,
      nickname = '',
      slogan = { brandLine: BRAND_SLOGANS[0].brandLine, brandDesc: BRAND_SLOGANS[0].brandDesc },
      canvasId = 'shareCanvas'
    } = opts;

    // app-plus 实测: 任何非 undefined 的 vm 参数都会触发 'reading ready' 错误。
    // 唯一稳的调用方式是只传 canvasId,完全省略第二参数(uni-app 默认在当前页找 canvas)
    // 重要:componentThis 参数保留兼容性但完全忽略
    const ctx = uni.createCanvasContext(canvasId);

    if (!ctx) {
      reject(new Error('canvas context unavailable on this platform'));
      return;
    }

    // L0: 白底(规避 iOS 离屏 canvas 黑底)
    ctx.setFillStyle('#FFFFFF');
    ctx.fillRect(0, 0, CANVAS_WIDTH, CANVAS_HEIGHT);

    // L1: 封面
    if (coverLocalPath) {
      ctx.drawImage(coverLocalPath, 0, 0, CANVAS_WIDTH, COVER_HEIGHT);
    }

    // L2: 头像 + nickname
    const avatarX = 60;
    const avatarYCenter = AVATAR_Y + AVATAR_SIZE / 2;
    ctx.save();
    ctx.beginPath();
    ctx.arc(avatarX + AVATAR_SIZE / 2, avatarYCenter, AVATAR_SIZE / 2, 0, 2 * Math.PI);
    ctx.clip();
    ctx.drawImage(avatarLocalPath, avatarX, AVATAR_Y, AVATAR_SIZE, AVATAR_SIZE);
    ctx.restore();

    ctx.setFillStyle('#FFFFFF');
    ctx.setFontSize(36);
    ctx.setTextAlign('left');
    ctx.fillText(nickname || 'T', avatarX + AVATAR_SIZE + 30, avatarYCenter + 12);

    // L3: 二维码
    const qrX = CANVAS_WIDTH - QR_SIZE - 60;
    ctx.drawImage(qrcodeLocalPath, qrX, QR_Y, QR_SIZE, QR_SIZE);

    // L4: slogan
    ctx.setFillStyle('#333333');
    ctx.setFontSize(36);
    ctx.setTextAlign('center');
    if (slogan.brandLine) {
      ctx.fillText(slogan.brandLine, CANVAS_WIDTH / 2, SLOGAN_Y + 30);
    }
    ctx.setFontSize(24);
    ctx.setFillStyle('#666666');
    // if (slogan.brandDesc) {
    //   ctx.fillText(slogan.brandDesc, CANVAS_WIDTH / 2, SLOGAN_Y + 70);
    // }

    ctx.draw(false, () => {
      uni.canvasToTempFilePath({
        canvasId: canvasId,
        x: 0, y: 0,
        width: CANVAS_WIDTH, height: CANVAS_HEIGHT,
        destWidth: CANVAS_WIDTH, destHeight: CANVAS_HEIGHT,
        fileType: 'png', quality: 1,
        success: (res) => resolve({ tempFilePath: res.tempFilePath, width: CANVAS_WIDTH, height: CANVAS_HEIGHT }),
        fail: (err) => reject(new Error('canvasToTempFilePath failed: ' + (err && err.errMsg ? err.errMsg : JSON.stringify(err))))
      });
    });
  });
}

/**
 * 计算 composeKey(spec § 5.4)
 * 用于 L1/L2 缓存查询;任一字段变化则重合成
 *
 * 入参用本地临时路径(_doc/uniapp_temp_<timestamp>/download/...)。
 * ⚠️ 当前 trade-off:temp 路径含时间戳,每次 pick 都不同 → L1/L2 cache 实际不会命中,
 *  每次 pick 都会重合成。代码保留 cache 结构以备将来切回 URL-based key 时复用。
 */
export function computeComposeKey(opts) {
  const { coverLocalPath = '', qrcodeLocalPath = '', avatarLocalPath = '', nickname = '', slogan = {} } = opts;
  return [coverLocalPath, qrcodeLocalPath, avatarLocalPath, nickname, slogan.brandLine || '', slogan.brandDesc || ''].join('|');
}