/**
 * WAL / journal（M4）：关键动作先追加 JSONL 落盘再执行；重放幂等。
 * state/wal-<owner>.jsonl：{seq,ts,type,taskId,key,data}
 * 重放重建：lastSeq、幂等键集合、每任务事件流（供崩溃恢复 DAG 进度）。
 */
import { openSync, appendFileSync, readFileSync, existsSync, mkdirSync, closeSync } from "node:fs";
import { resolve } from "node:path";

export class WAL {
  constructor(stateRoot, owner) {
    mkdirSync(stateRoot, { recursive: true });
    this.owner = owner;
    this.file = resolve(stateRoot, `wal-${owner.replace(/[^A-Za-z0-9_-]/g, "_")}.jsonl`);
    this.seq = 0;
    this.keys = new Set();
    this.byTask = new Map();
    this._recover();
  }

  _recover() {
    if (!existsSync(this.file)) return;
    const lines = readFileSync(this.file, "utf8").split(/\r?\n/).filter(Boolean);
    for (const line of lines) {
      let e;
      try {
        e = JSON.parse(line);
      } catch {
        continue; // 尾部截断行跳过
      }
      this.seq = Math.max(this.seq, e.seq || 0);
      if (e.key) this.keys.add(e.key);
      if (e.taskId) {
        if (!this.byTask.has(e.taskId)) this.byTask.set(e.taskId, []);
        this.byTask.get(e.taskId).push(e);
      }
    }
  }

  /** 先写 journal。key 为幂等键：重复 key 返回既有 seq，不重复落盘。 */
  append(type, { taskId = null, key = null, data = {} } = {}) {
    if (key && this.keys.has(key)) {
      return { duplicated: true, seq: this.seq };
    }
    const entry = { seq: ++this.seq, ts: Date.now(), owner: this.owner, type, taskId, key, data };
    const fd = openSync(this.file, "a");
    try {
      appendFileSync(fd, JSON.stringify(entry) + "\n");
    } finally {
      closeSync(fd); // 关闭触发刷盘，保证 kill -9 后可重放
    }
    if (key) this.keys.add(key);
    if (taskId) {
      if (!this.byTask.has(taskId)) this.byTask.set(taskId, []);
      this.byTask.get(taskId).push(entry);
    }
    return { duplicated: false, entry, seq: this.seq };
  }

  has(key) {
    return this.keys.has(key);
  }

  events(taskId) {
    return this.byTask.get(taskId) || [];
  }

  /** 崩溃恢复视角：已 claim 但未 settled 的任务及其进度。 */
  recoverInFlight() {
    const out = [];
    for (const [taskId, events] of this.byTask) {
      const types = new Set(events.map((e) => e.type));
      if (types.has("task.claimed") && !types.has("task.settled")) {
        out.push({ taskId, events: events.map((e) => ({ type: e.type, key: e.key, data: e.data })) });
      }
    }
    return out;
  }
}