/**
 * KVStore — 自研 KV 引擎单元测试
 *
 * 覆盖：
 * 1. 基本读写（put/get/delete/exists/listKeys）
 * 2. putMany/deleteMany 原子性（多 key 一次落盘）
 * 3. 跨实例持久化（SharedMemory 全局注册表，close 不清数据）
 * 4. 崩溃恢复：日志重放（未 checkpoint 数据恢复）
 * 5. checkpoint 后恢复（快照 + 水位跳过）
 * 6. 快照损坏 → 全量日志重放自愈
 * 7. 日志损坏 → 截断至损坏处（丢弃未确认尾部）
 * 8. 写入失败原子性（日志失败不更新内存索引）
 * 9. clear / repair
 * 10. 并发写与 checkpoint 串行（无交错丢数据）
 */
import { KVStore } from '../../src/engine/kvstore/index';
import { SharedMemoryBackend } from '../../src/engine/kvstore/shared_memory_medium';
import { encodeLogRecord, parseLogRecords, KVLogOp } from '../../src/engine/kvstore/log';
import { encodeSnapshot, decodeSnapshot } from '../../src/engine/kvstore/snapshot';

let dbCounter = 0;
function uniqueDB(): string {
  return `kv-${Date.now()}-${++dbCounter}-${Math.random().toString(36).slice(2, 8)}`;
}

const enc = (s: string) => new TextEncoder().encode(s).buffer as ArrayBuffer;
const dec = (b: ArrayBuffer | null) => (b ? new TextDecoder().decode(b) : null);

beforeEach(() => {
  SharedMemoryBackend.clearRegistry();
});

describe('KVStore — 基本读写', () => {
  it('put/get/delete/exists/listKeys/size', async () => {
    const kv = new KVStore(new SharedMemoryBackend());
    await kv.open(uniqueDB());
    await kv.put('a', enc('AAA'));
    await kv.put('b', enc('BBB'));
    expect(dec(await kv.get('a'))).toBe('AAA');
    expect(await kv.exists('b')).toBe(true);
    expect(await kv.exists('nope')).toBe(false);
    expect((await kv.listKeys()).sort()).toEqual(['a', 'b']);
    expect(kv.size()).toBe(2);

    await kv.delete('a');
    expect(await kv.exists('a')).toBe(false);
    expect(kv.size()).toBe(1);
    await kv.close();
  });

  it('putMany 多 key 原子写入', async () => {
    const kv = new KVStore(new SharedMemoryBackend());
    await kv.open(uniqueDB());
    await kv.putMany({ a: enc('1'), b: enc('2'), c: enc('3') });
    expect(dec(await kv.get('a'))).toBe('1');
    expect(dec(await kv.get('c'))).toBe('3');
    await kv.deleteMany(['a', 'c']);
    expect(await kv.exists('a')).toBe(false);
    expect(await kv.exists('c')).toBe(false);
    expect(await kv.exists('b')).toBe(true);
    await kv.close();
  });
});

describe('KVStore — 持久化与崩溃恢复', () => {
  it('未 checkpoint 的数据：close 后重开经日志重放恢复', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv1 = new KVStore(medium);
    await kv1.open(dbName);
    await kv1.putMany({ a: enc('AAA'), b: enc('BBB') });
    await kv1.put('c', enc('CCC'));
    await kv1.delete('b');
    await kv1.close();

    // 模拟"崩溃后重开"（新实例，共享介质）
    const kv2 = new KVStore(medium);
    await kv2.open(dbName);
    expect(dec(await kv2.get('a'))).toBe('AAA');
    expect(await kv2.exists('b')).toBe(false);
    expect(dec(await kv2.get('c'))).toBe('CCC');
    await kv2.close();
  });

  it('checkpoint 后重开：快照加载 + 日志水位跳过（无重复/无丢失）', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv1 = new KVStore(medium, 0); // 关闭自动 checkpoint
    await kv1.open(dbName);
    await kv1.putMany({ a: enc('A1'), b: enc('B1') });
    await kv1.checkpoint();
    // checkpoint 后新写入（进日志）
    await kv1.put('c', enc('C1'));
    await kv1.put('a', enc('A2'));
    await kv1.close();

    const kv2 = new KVStore(medium, 0);
    await kv2.open(dbName);
    expect(dec(await kv2.get('a'))).toBe('A2'); // 日志重放覆盖快照值
    expect(dec(await kv2.get('b'))).toBe('B1');
    expect(dec(await kv2.get('c'))).toBe('C1');
    await kv2.close();
  });

  it('多次 checkpoint + 截断日志后重开正确', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv1 = new KVStore(medium, 0);
    await kv1.open(dbName);
    for (let i = 0; i < 10; i++) {
      await kv1.put(`k${i}`, enc(`v${i}`));
      await kv1.checkpoint();
    }
    await kv1.put('last', enc('L'));
    await kv1.close();

    const kv2 = new KVStore(medium, 0);
    await kv2.open(dbName);
    expect(kv2.size()).toBe(11);
    expect(dec(await kv2.get('k9'))).toBe('v9');
    expect(dec(await kv2.get('last'))).toBe('L');
    await kv2.close();
  });

  it('快照损坏 → 全量日志重放自愈（数据不丢）', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv1 = new KVStore(medium, 0);
    await kv1.open(dbName);
    await kv1.putMany({ a: enc('AAA'), b: enc('BBB') });
    await kv1.checkpoint();
    await kv1.put('c', enc('CCC'));
    await kv1.close();

    // 篡改快照（模拟损坏）
    const snap = await medium.read('__kv_snapshot');
    const corrupted = new Uint8Array(snap as ArrayBuffer);
    corrupted[20] ^= 0xff;
    await medium.write('__kv_snapshot', corrupted.buffer as ArrayBuffer);

    const kv2 = new KVStore(medium, 0);
    await kv2.open(dbName);
    // 快照损坏 → 全量日志重放
    expect(dec(await kv2.get('a'))).toBe('AAA');
    expect(dec(await kv2.get('b'))).toBe('BBB');
    expect(dec(await kv2.get('c'))).toBe('CCC');
    await kv2.close();
  });

  it('日志损坏尾部 → 截断至损坏处（丢弃未确认尾部，已确认数据保留）', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv1 = new KVStore(medium, 0);
    await kv1.open(dbName);
    await kv1.put('confirmed', enc('KEEP'));
    await kv1.put('confirmed2', enc('KEEP2'));
    await kv1.close();

    // 追加一条损坏记录（模拟写入中断：半写记录）
    const bad = encodeLogRecord(999, { damaged: enc('X') });
    const corrupted = new Uint8Array(bad);
    corrupted[20] ^= 0xff; // 破坏 CRC
    // close 后介质实例不可用，重新打开访问"磁盘"
    const disk = new SharedMemoryBackend();
    await disk.open(dbName);
    const log = await disk.read('__kv_log');
    const combined = new Uint8Array((log as ArrayBuffer).byteLength + corrupted.byteLength);
    combined.set(new Uint8Array(log as ArrayBuffer), 0);
    combined.set(corrupted, (log as ArrayBuffer).byteLength);
    await disk.write('__kv_log', combined.buffer as ArrayBuffer);

    const kv2 = new KVStore(medium, 0);
    await kv2.open(dbName);
    expect(dec(await kv2.get('confirmed'))).toBe('KEEP');
    expect(dec(await kv2.get('confirmed2'))).toBe('KEEP2');
    expect(await kv2.exists('damaged')).toBe(false);
    // 损坏日志已被截断（重开后再写正常）
    await kv2.put('after', enc('OK'));
    await kv2.close();
    const kv3 = new KVStore(medium, 0);
    await kv3.open(dbName);
    expect(dec(await kv3.get('after'))).toBe('OK');
    await kv3.close();
  });

  it('写入失败 → 内存索引不更新（原子性）', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv = new KVStore(medium, 0);
    await kv.open(dbName);

    // 注入日志追加失败
    const origAppend = medium.append!.bind(medium);
    medium.append = async () => { throw new Error('disk full'); };
    await expect(kv.put('x', enc('X'))).rejects.toMatchObject({ code: 'KV_LOG_ERROR' });
    expect(await kv.exists('x')).toBe(false);

    medium.append = origAppend;
    await kv.put('y', enc('Y'));
    expect(dec(await kv.get('y'))).toBe('Y');
    await kv.close();
  });
});

describe('KVStore — 维护与并发', () => {
  it('clear 清空全部（保留库），重开为空', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv1 = new KVStore(medium, 0);
    await kv1.open(dbName);
    await kv1.putMany({ a: enc('1'), b: enc('2') });
    await kv1.checkpoint();
    await kv1.put('c', enc('3'));
    await kv1.clear();
    expect(kv1.size()).toBe(0);
    await kv1.close();

    const kv2 = new KVStore(medium, 0);
    await kv2.open(dbName);
    expect(kv2.size()).toBe(0);
    await kv2.close();
  });

  it('repair 清理损坏快照与日志（损坏快照数据无法恢复，日志数据保留）', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv1 = new KVStore(medium, 0);
    await kv1.open(dbName);
    await kv1.put('a', enc('A'));
    await kv1.checkpoint(); // 快照成为 a 的唯一副本（日志已截断）
    await kv1.put('b', enc('B')); // 日志中（seq=2）
    await kv1.close();

    // 快照损坏 + 日志尾部损坏
    const disk = new SharedMemoryBackend();
    await disk.open(dbName);
    const snap = new Uint8Array(await disk.read('__kv_snapshot') as ArrayBuffer);
    snap[10] ^= 0xff;
    await disk.write('__kv_snapshot', snap.buffer as ArrayBuffer);
    const bad = encodeLogRecord(500, { junk: enc('J') });
    bad[15] ^= 0xff;
    const log = new Uint8Array(await disk.read('__kv_log') as ArrayBuffer);
    const combined = new Uint8Array(log.byteLength + bad.byteLength);
    combined.set(log, 0); combined.set(bad, log.byteLength);
    await disk.write('__kv_log', combined.buffer as ArrayBuffer);

    const kv2 = new KVStore(medium, 0);
    await kv2.open(dbName);
    const discarded = await kv2.repair();
    expect(discarded).toBeGreaterThan(0);
    // 快照损坏（a 的唯一副本丢失）+ 损坏日志尾部被截断 → 日志数据 b 完整
    expect(await kv2.exists('a')).toBe(false);
    expect(dec(await kv2.get('b'))).toBe('B');
    // repair 后介质上的损坏快照已清理
    expect(await medium.exists('__kv_snapshot')).toBe(false);
    await kv2.close();
  });

  it('并发写 + checkpoint 串行（无交错丢数据）', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv = new KVStore(medium, 0);
    await kv.open(dbName);

    // 并发发起大量写入 + 中途 checkpoint
    const writes = [] as Promise<void>[];
    for (let i = 0; i < 200; i++) {
      writes.push(kv.put(`k${i}`, enc(`v${i}`)));
      if (i === 100) writes.push(kv.checkpoint());
    }
    await Promise.all(writes);

    expect(kv.size()).toBe(200);
    await kv.close();

    // 重开验证全部恢复
    const kv2 = new KVStore(medium, 0);
    await kv2.open(dbName);
    expect(kv2.size()).toBe(200);
    expect(dec(await kv2.get('k150'))).toBe('v150');
    await kv2.close();
  });

  it('自动 checkpoint 阈值触发（日志不无限增长）', async () => {
    const dbName = uniqueDB();
    const medium = new SharedMemoryBackend();
    const kv = new KVStore(medium, 256); // 小阈值
    await kv.open(dbName);
    for (let i = 0; i < 50; i++) {
      await kv.put(`k${i}`, enc(`value-${i}-`.repeat(10)));
    }
    // 自动 checkpoint 后日志应被截断
    const log = await medium.read('__kv_log');
    expect((log as ArrayBuffer).byteLength).toBeLessThan(4096);
    await kv.close();

    const kv2 = new KVStore(medium, 256);
    await kv2.open(dbName);
    expect(kv2.size()).toBe(50);
    await kv2.close();
  });
});

describe('KVStore — 编解码单元', () => {
  it('encodeLogRecord / parseLogRecords 往返', () => {
    const rec = encodeLogRecord(1, { a: enc('A'), b: enc('BB') }, ['del']);
    const records: { seq: number; entries: { op: KVLogOp; key: string; value: ArrayBuffer }[] }[] = [];
    parseLogRecords(rec, (r) => records.push(r));
    expect(records).toHaveLength(1);
    expect(records[0].seq).toBe(1);
    expect(records[0].entries).toHaveLength(3);
    expect(dec(records[0].entries[0].value)).toBe('A');
    expect(records[0].entries[2].op).toBe(KVLogOp.DELETE);
  });

  it('多记录日志顺序解析', () => {
    const r1 = encodeLogRecord(1, { a: enc('1') });
    const r2 = encodeLogRecord(2, { b: enc('2') });
    const combined = new Uint8Array(r1.byteLength + r2.byteLength);
    combined.set(r1, 0); combined.set(r2, r1.byteLength);
    const seqs: number[] = [];
    parseLogRecords(combined, (r) => seqs.push(r.seq));
    expect(seqs).toEqual([1, 2]);
  });

  it('encodeSnapshot / decodeSnapshot 往返', () => {
    const entries = new Map<string, ArrayBuffer>([['a', enc('A')], ['b', enc('BB')]]);
    const bytes = encodeSnapshot(42, entries);
    const snap = decodeSnapshot(bytes);
    expect(snap).not.toBeNull();
    expect(snap!.seq).toBe(42);
    expect(dec(snap!.entries.get('a'))).toBe('A');
    expect(dec(snap!.entries.get('b'))).toBe('BB');
  });

  it('损坏快照 decode 返回 null', () => {
    const entries = new Map<string, ArrayBuffer>([['a', enc('A')]]);
    const bytes = encodeSnapshot(1, entries);
    bytes[10] ^= 0xff;
    expect(decodeSnapshot(bytes)).toBeNull();
  });
});