import { mkdir, readdir } from 'node:fs/promises';
import path from 'node:path';
import { atomicWriteJson, readJsonFile } from '../coding-projects/atomic-json';
import type { TeacherTopic, TeacherTopicList } from '../../shared/coding-teacher';
import { TeacherError } from './config-client';

export function teacherTopicId(id: string): string {
  if (!/^[0-9a-f]{8}(?:-[0-9a-f]{4}){3}-[0-9a-f]{12}$/i.test(id))
    throw new TeacherError(400, 'teacher_topic_invalid', '老师话题标识无效。');
  return id;
}
export class TeacherTopicStore {
  private readonly cache = new Map<string, Promise<TeacherTopic>>();
  constructor(readonly directory: string) {}
  async list(): Promise<TeacherTopicList> {
    await mkdir(this.directory, { recursive: true });
    const names = await readdir(this.directory);
    const topics = await Promise.all(
      names
        .filter((name) => name.endsWith('.json') && name !== 'index.json')
        .map((name) => this.read(name.slice(0, -5)))
    );
    let last: string | null = null;
    try {
      last = (
        (await readJsonFile(path.join(this.directory, 'index.json'))) as {
          lastSelectedTopicId: string;
        }
      ).lastSelectedTopicId;
    } catch {
      /* index is disposable; topic files own history */
    }
    const items = topics
      .map((topic) => ({
        id: topic.id,
        title: topic.requests[0]?.text.slice(0, 32) || '新话题',
        updatedAt: topic.updatedAt,
        version: topic.version,
      }))
      .sort((a, b) => b.updatedAt.localeCompare(a.updatedAt));
    return {
      items,
      lastSelectedTopicId: items.some((item) => item.id === last) ? last : (items[0]?.id ?? null),
    };
  }
  async read(id: string): Promise<TeacherTopic> {
    teacherTopicId(id);
    let pending = this.cache.get(id);
    if (!pending) {
      pending = (async () => {
        let topic: TeacherTopic;
        try {
          topic = (await readJsonFile(path.join(this.directory, id + '.json'))) as TeacherTopic;
        } catch {
          throw new TeacherError(404, 'teacher_topic_not_found', '老师话题不存在或无法读取。');
        }
        if (topic.id !== id || topic.schemaVersion !== 1 || !Array.isArray(topic.requests))
          throw new TeacherError(409, 'teacher_topic_invalid', '老师历史无法读取。');
        let recovered = false;
        for (const request of topic.requests)
          if (request.status === 'preparing' || request.status === 'running') {
            request.status = 'interrupted';
            request.error = '应用已重启，本次回复中断。';
            recovered = true;
          }
        if (recovered) {
          topic.revision++;
          await this.save(topic);
        }
        return topic;
      })();
      this.cache.set(id, pending);
      pending.catch(() => this.cache.delete(id));
    }
    return await pending;
  }
  async save(topic: TeacherTopic) {
    await mkdir(this.directory, { recursive: true });
    const saved = { ...topic };
    delete saved.unsaved;
    await atomicWriteJson(path.join(this.directory, teacherTopicId(topic.id) + '.json'), saved);
    topic.unsaved = false;
    this.cache.set(topic.id, Promise.resolve(topic));
  }
  async select(id: string) {
    await atomicWriteJson(path.join(this.directory, 'index.json'), {
      lastSelectedTopicId: teacherTopicId(id),
    });
  }
}