// MigrationService — 旧版数据迁移（FR-D1/D3）
import nodePath from 'node:path';
import { promises as fs } from 'node:fs';
import { MD_EXT } from '@hunter/shared';
import { joinFrontmatter } from '../safe/frontmatter-codec.js';

export interface MigrationResult {
  migrated: boolean;
  count: number;
  errors: { path: string; reason: string }[];
}

export class MigrationService {
  // FR-D1：检测旧版板块三级结构数据（.hunter/boards/），转换为文件库结构
  async detectAndMigrate(root: string): Promise<MigrationResult> {
    const oldDataDir = nodePath.join(root, '.hunter', 'boards');
    const exists = await fs.access(oldDataDir).then(() => true).catch(() => false);
    if (!exists) return { migrated: false, count: 0, errors: [] };

    const errors: { path: string; reason: string }[] = [];
    let count = 0;
    try {
      const boards = await fs.readdir(oldDataDir, { withFileTypes: true });
      for (const board of boards) {
        if (!board.isDirectory()) continue;
        const boardDir = nodePath.join(oldDataDir, board.name);
        try {
          const targetDir = nodePath.join(root, board.name);
          await fs.mkdir(targetDir, { recursive: true });
          await this.convertDir(boardDir, targetDir);
          count++;
        } catch (e) {
          errors.push({ path: board.name, reason: e instanceof Error ? e.message : String(e) });
        }
      }
      if (errors.length === 0) {
        await fs.rename(oldDataDir, nodePath.join(root, '.hunter', 'boards.migrated'));
      }
    } catch (e) {
      errors.push({ path: oldDataDir, reason: e instanceof Error ? e.message : String(e) });
    }
    return { migrated: count > 0, count, errors };
  }

  private async convertDir(srcAbs: string, destAbs: string): Promise<void> {
    const entries = await fs.readdir(srcAbs, { withFileTypes: true });
    for (const e of entries) {
      const srcPath = nodePath.join(srcAbs, e.name);
      if (e.isDirectory()) {
        const destPath = nodePath.join(destAbs, e.name);
        await fs.mkdir(destPath, { recursive: true });
        await this.convertDir(srcPath, destPath);
      } else if (e.isFile() && e.name.endsWith('.json')) {
        const raw = await fs.readFile(srcPath, 'utf8');
        const data = JSON.parse(raw);
        const title = data.title ?? e.name.slice(0, -5);
        const body = data.content ?? '';
        const meta: Record<string, unknown> = { title, createdAt: data.createdAt ?? Date.now() };
        if (data.tags) meta.tags = data.tags;
        if (data.star) meta.star = true;
        const mdName = String(title).replace(/[^\w\u4e00-\u9fa5\-]/g, '_') + MD_EXT;
        await fs.writeFile(nodePath.join(destAbs, mdName), joinFrontmatter(meta as any, body), 'utf8');
      } else if (e.isFile() && e.name.endsWith(MD_EXT)) {
        await fs.copyFile(srcPath, nodePath.join(destAbs, e.name));
      }
    }
  }
}