import { readdirSync, statSync, readFileSync, existsSync } from 'node:fs';
import { join, posix, sep, extname, relative } from 'node:path';

const IMAGE_EXTS = new Set(['.png', '.jpg', '.jpeg', '.webp']);
const SPINE_ROOT = 'spine';          // framework/ui/spine/<资源名>/ 为一套 Spine
const SKIPPED = new Set(['.gitkeep']);

/**
 * 可被子游戏覆盖的框架资源目录（spec §2 规则 3 枚举的 8 个目录）。
 * `theme/` 不在其中——那是 §4.2 规定的框架 TS 代码位置，不是资源，不可覆盖。
 */
const COVERABLE_DIRS = new Set([
  'atlas-common', 'atlas-login', 'atlas-hall', 'atlas-room',
  'standalone', 'spine', 'audio', 'font',
]);

/** 列出目录下所有资源的相对路径（正斜杠），排除 .meta 与 .gitkeep。 */
export function listAssets(dir) {
  if (!existsSync(dir)) return [];
  const out = [];
  (function walk(cur) {
    for (const name of readdirSync(cur)) {
      const p = join(cur, name);
      if (statSync(p).isDirectory()) { walk(p); continue; }
      if (name.endsWith('.meta') || SKIPPED.has(name)) continue;
      out.push(relative(dir, p).split(sep).join(posix.sep));
    }
  })(dir);
  return out;
}

/**
 * 列出框架 UI 目录下**可被覆盖**的资源（白名单目录，见 COVERABLE_DIRS）。
 * `frameworkUiDir` 下还有 `theme/`、`README.md` 等非资源内容，
 * 不属于可覆盖范围，也不计入"框架可覆盖资源共 N 个"的统计。
 */
export function listCoverableAssets(frameworkUiDir) {
  return listAssets(frameworkUiDir).filter((rel) => COVERABLE_DIRS.has(rel.split(posix.sep)[0]));
}

/** 读 PNG 宽高；非 PNG 或读取失败返回 null。 */
export function readPngSize(file) {
  try {
    const b = readFileSync(file);
    if (b.length < 24 || b.toString('ascii', 1, 4) !== 'PNG') return null;
    return { width: b.readUInt32BE(16), height: b.readUInt32BE(20) };
  } catch { return null; }
}

const isImage = (rel) => IMAGE_EXTS.has(extname(rel).toLowerCase());
const isSpine = (rel) => rel.split(posix.sep)[0] === SPINE_ROOT;
/** Spine 资源的分组键：spine/<资源名> */
const spineGroup = (rel) => rel.split(posix.sep).slice(0, 2).join(posix.sep);

/**
 * 校验 override 是否合法。规则见 spec §3.2。
 * 返回 { matched: 相对路径[], errors: {path, code, message}[] }。
 */
export function validateOverrides(frameworkUiDir, overrideDir) {
  const fwList = listCoverableAssets(frameworkUiDir);
  const fwSet = new Set(fwList);
  const ovList = listAssets(overrideDir);
  const ovSet = new Set(ovList);

  const matched = [];
  const errors = [];

  // 1) 逐个 override 校验：孤儿 / 尺寸
  for (const rel of ovList) {
    if (!fwSet.has(rel)) {
      const base = rel.slice(0, rel.length - extname(rel).length);
      const alt = fwList.find((f) => f.slice(0, f.length - extname(f).length) === base);
      errors.push({
        path: rel,
        code: 'orphan',
        message: alt
          ? `框架里没有 ${rel}，但存在同名的 ${alt}——扩展名对不上`
          : `框架里没有对应资源：${rel}`,
      });
      continue;
    }

    // Spine 贴图豁免尺寸校验（区域坐标在 .atlas 内，整套替换时自洽）
    const metaPath = join(overrideDir, ...`${rel}.meta`.split(posix.sep));
    const needSizeCheck =
      isImage(rel) && !isSpine(rel) && !existsSync(metaPath);
    if (needSizeCheck) {
      const a = readPngSize(join(frameworkUiDir, ...rel.split(posix.sep)));
      const b = readPngSize(join(overrideDir, ...rel.split(posix.sep)));
      if (!a || !b) {
        const side = !a ? '框架' : 'override';
        errors.push({
          path: rel,
          code: 'size-unreadable',
          message:
            `框架 UI 图片必须是 PNG（无法读取尺寸：${side}）。` +
            `请改用 PNG，或连 .meta 一起提供（例外通道）`,
        });
        continue;
      }
      if (a.width !== b.width || a.height !== b.height) {
        errors.push({
          path: rel,
          code: 'size-mismatch',
          message:
            `尺寸不一致：框架 ${a.width}x${a.height}，override ${b.width}x${b.height}。` +
            `请改为同尺寸，或连 .meta 一起提供（例外通道）`,
        });
        continue;
      }
    }
    matched.push(rel);
  }

  // 2) Spine 整套完整性：override 动了某套，就必须整套都在
  const touchedGroups = new Set(ovList.filter(isSpine).map(spineGroup));
  for (const g of touchedGroups) {
    const required = fwList.filter((f) => isSpine(f) && spineGroup(f) === g);
    const missing = required.filter((f) => !ovSet.has(f));
    if (missing.length) {
      errors.push({
        path: g,
        code: 'spine-incomplete',
        message: `Spine 必须整套覆盖，缺少：${missing.join('、')}`,
      });
    }
  }

  return { matched, errors };
}