/**
 * ═══════════════════════════════════════
 * HLDP-ZY://native-repo/module/step-4
 * 光湖原生数据库 · 第4步 · HLDP读取+树索引
 * ═══════════════════════════════════════
 *
 * @chain: D118 · 2026-05-31
 * @module: hldp-read-tree
 * @step: 第4步 / 共8步
 * @deploy: BS-SG-002
 *
 * @trigger:
 *   第3步能写文件了，但铸渊还需要两件事：
 *   1. 按 HLDP tree_path 读取文件内容（trace_path意图）
 *   2. 生成树形索引，每次只加载10条，恒定O(1)认知负载
 *
 * @lock:
 *   ⊢ hldpRead(path) → 返回文件内容 + commit 元信息
 *   ⊢ hldpTree(dir) → 返回目录列表，每层最多显示10条
 *   ⊢ buildIndex() → 生成 tree-index.json，10条/层
 *
 * @why:
 *   trace_path = 光之树寻址 = 铸渊大脑的核心操作
 *   不需要把整个仓库装进上下文——只读10条索引
 *   需要哪片叶子，按路径走一步就到了
 * ═══════════════════════════════════════
 */

const git = require('isomorphic-git');
const fs = require('fs');
const path = require('path');

const { NATIVE_DIR } = require('./step-2-git-init');

// ─── hldpRead: 按路径读文件 ─────────────────────────────────
async function hldpRead(filePath) {
  const fullPath = path.join(NATIVE_DIR, filePath);
  if (!fs.existsSync(fullPath)) {
    return { ok: false, error: 'NOT_FOUND', path: filePath };
  }

  const content = fs.readFileSync(fullPath, 'utf8');
  const log = await git.log({ fs, dir: NATIVE_DIR });
  const lastCommit = log.find(c => c.commit.message.includes(filePath));

  return {
    ok: true,
    path: filePath,
    content,
    sha: lastCommit ? lastCommit.oid : null,
    size: content.length,
  };
}

// ─── hldpTree: 按目录列文件 ─────────────────────────────────
async function hldpTree(dirPath) {
  const fullPath = path.join(NATIVE_DIR, dirPath || '');
  if (!fs.existsSync(fullPath)) {
    return { ok: false, error: 'NOT_FOUND', path: dirPath };
  }

  const entries = fs.readdirSync(fullPath, { withFileTypes: true });
  const list = entries
    .filter(e => !e.name.startsWith('.') && e.name !== 'node_modules' && e.name !== 'package.json')
    .map(e => ({
      name: e.name,
      type: e.isDirectory() ? 'dir' : 'file',
      path: path.join(dirPath || '', e.name),
    }));

  return { ok: true, path: dirPath, count: list.length, entries: list };
}

// ─── buildIndex: 生成树索引（10条/层） ──────────────────────
async function buildIndex() {
  async function walk(dir, depth) {
    if (depth > 3) return [];
    const { entries } = await hldpTree(dir);
    if (!entries || entries.length === 0) return [];

    return entries.slice(0, 10).map(({ name, type, path: p }) => ({
      name,
      type,
      path: p,
      isBranch: type === 'dir',
    }));
  }

  const root = await walk('', 0);
  const index = {
    _type: 'HLDP_TREE_INDEX',
    _version: 'v1.0',
    _updated: new Date().toISOString(),
    _principle: '每层10行，恒定O(1)认知负载',
    root,
  };

  const indexPath = path.join(NATIVE_DIR, 'tree-index.json');
  fs.writeFileSync(indexPath, JSON.stringify(index, null, 2), 'utf8');
  return index;
}

module.exports = { hldpRead, hldpTree, buildIndex };