import { describe, expect, it } from 'vitest';

import {
  RedisTaskRepository,
  TaskAlreadyExistsError,
  TaskOwnershipError,
  TaskTransitionError,
  type RedisTaskClient,
  type RedisTaskTransaction,
} from '../src/task-repository.js';

type QueuedOperation =
  | {
      readonly type: 'set';
      readonly key: string;
      readonly value: string;
      readonly mode?: 'NX' | 'XX';
    }
  | {
      readonly type: 'sadd';
      readonly key: string;
      readonly member: string;
    };

class InMemoryRedisBackend {
  public readonly kv = new Map<string, string>();
  public readonly sets = new Map<string, Set<string>>();
  public readonly revisions = new Map<string, number>();

  public getRevision(key: string): number {
    return this.revisions.get(key) ?? 0;
  }

  public bumpRevision(key: string): void {
    this.revisions.set(key, this.getRevision(key) + 1);
  }
}

class InMemoryRedisTransaction implements RedisTaskTransaction {
  private readonly operations: QueuedOperation[] = [];

  public constructor(
    private readonly backend: InMemoryRedisBackend,
    private readonly watchedRevisions: ReadonlyMap<string, number>,
  ) {}

  public set(key: string, value: string, mode?: 'NX' | 'XX'): RedisTaskTransaction {
    this.operations.push({
      type: 'set',
      key,
      value,
      mode,
    });
    return this;
  }

  public sadd(key: string, member: string): RedisTaskTransaction {
    this.operations.push({
      type: 'sadd',
      key,
      member,
    });
    return this;
  }

  public exec(): Promise<readonly (readonly [Error | null, unknown])[] | null> {
    for (const [key, revision] of this.watchedRevisions.entries()) {
      if (this.backend.getRevision(key) !== revision) {
        return Promise.resolve(null);
      }
    }

    const results: (readonly [Error | null, unknown])[] = [];

    for (const operation of this.operations) {
      if (operation.type === 'set') {
        const exists = this.backend.kv.has(operation.key);
        if (operation.mode === 'NX' && exists) {
          results.push([null, null]);
          continue;
        }

        if (operation.mode === 'XX' && !exists) {
          results.push([null, null]);
          continue;
        }

        this.backend.kv.set(operation.key, operation.value);
        this.backend.bumpRevision(operation.key);
        results.push([null, 'OK']);
        continue;
      }

      const set = this.backend.sets.get(operation.key) ?? new Set<string>();
      const before = set.size;

      set.add(operation.member);
      this.backend.sets.set(operation.key, set);
      this.backend.bumpRevision(operation.key);
      results.push([null, set.size === before ? 0 : 1]);
    }

    return Promise.resolve(results);
  }
}

class InMemoryAtomicRedisClient implements RedisTaskClient {
  private watchedRevisions = new Map<string, number>();

  public constructor(private readonly backend: InMemoryRedisBackend) {}

  public get(key: string): Promise<string | null> {
    return Promise.resolve(this.backend.kv.get(key) ?? null);
  }

  public mget(...keys: string[]): Promise<(string | null)[]> {
    return Promise.resolve(keys.map((key) => this.backend.kv.get(key) ?? null));
  }

  public set(
    key: string,
    value: string,
    mode?: 'NX' | 'XX',
  ): Promise<'OK' | null> {
    const exists = this.backend.kv.has(key);

    if (mode === 'NX' && exists) {
      return Promise.resolve(null);
    }

    if (mode === 'XX' && !exists) {
      return Promise.resolve(null);
    }

    this.backend.kv.set(key, value);
    this.backend.bumpRevision(key);

    return Promise.resolve('OK');
  }

  public smembers(key: string): Promise<string[]> {
    return Promise.resolve([...(this.backend.sets.get(key) ?? new Set<string>())]);
  }

  public sadd(key: string, member: string): Promise<number> {
    const values = this.backend.sets.get(key) ?? new Set<string>();
    const before = values.size;

    values.add(member);
    this.backend.sets.set(key, values);
    this.backend.bumpRevision(key);

    return Promise.resolve(values.size === before ? 0 : 1);
  }

  public watch(...keys: string[]): Promise<'OK'> {
    this.watchedRevisions = new Map(
      keys.map((key) => [key, this.backend.getRevision(key)]),
    );
    return Promise.resolve('OK');
  }

  public unwatch(): Promise<'OK'> {
    this.watchedRevisions.clear();
    return Promise.resolve('OK');
  }

  public multi(): RedisTaskTransaction {
    const watchedSnapshot = new Map(this.watchedRevisions);
    this.watchedRevisions.clear();
    return new InMemoryRedisTransaction(this.backend, watchedSnapshot);
  }
}

class StrictAtomicRedisClient extends InMemoryAtomicRedisClient {
  public override set(
    key: string,
    value: string,
    mode?: 'NX' | 'XX',
  ): Promise<'OK' | null> {
    void key;
    void value;
    void mode;
    throw new Error('Direct set() is not allowed in strict atomic tests.');
  }

  public override sadd(key: string, member: string): Promise<number> {
    void key;
    void member;
    throw new Error('Direct sadd() is not allowed in strict atomic tests.');
  }
}

function createRepositoryPair(now: () => number): [RedisTaskRepository, RedisTaskRepository] {
  const backend = new InMemoryRedisBackend();

  return [
    new RedisTaskRepository({
      client: new InMemoryAtomicRedisClient(backend),
      now,
    }),
    new RedisTaskRepository({
      client: new InMemoryAtomicRedisClient(backend),
      now,
    }),
  ];
}

function createStrictRepositoryPair(
  now: () => number,
): [RedisTaskRepository, RedisTaskRepository] {
  const backend = new InMemoryRedisBackend();

  return [
    new RedisTaskRepository({
      client: new StrictAtomicRedisClient(backend),
      now,
    }),
    new RedisTaskRepository({
      client: new StrictAtomicRedisClient(backend),
      now,
    }),
  ];
}

describe('RedisTaskRepository atomic transitions', () => {
  it('creates atomically under concurrent create race', async () => {
    const [repositoryA, repositoryB] = createStrictRepositoryPair(
      () => 1_700_000_000_000,
    );

    const [createA, createB] = await Promise.allSettled([
      repositoryA.create({
        project: 'queue',
        mission: 'phase1',
        taskId: 'MQ-004-CREATE',
        title: 'create race',
      }),
      repositoryB.create({
        project: 'queue',
        mission: 'phase1',
        taskId: 'MQ-004-CREATE',
        title: 'create race duplicate',
      }),
    ]);

    const fulfilled = [createA, createB].filter(
      (result) => result.status === 'fulfilled',
    );
    const rejected = [createA, createB].filter(
      (result) => result.status === 'rejected',
    );

    expect(fulfilled).toHaveLength(1);
    expect(rejected).toHaveLength(1);
    expect(rejected[0]?.reason).toBeInstanceOf(TaskAlreadyExistsError);
  });

  it('claims a pending task once and blocks concurrent double-claim', async () => {
    let timestamp = 1_700_000_000_000;
    const now = (): number => timestamp;
    const [repositoryA, repositoryB] = createRepositoryPair(now);

    await repositoryA.create({
      project: 'queue',
      mission: 'phase1',
      taskId: 'MQ-004',
      title: 'Atomic claim',
    });

    const [claimA, claimB] = await Promise.allSettled([
      repositoryA.claim('MQ-004', { agentId: 'agent-a', ttlSeconds: 60 }),
      repositoryB.claim('MQ-004', { agentId: 'agent-b', ttlSeconds: 60 }),
    ]);

    const fulfilled = [claimA, claimB].filter((result) => result.status === 'fulfilled');
    const rejected = [claimA, claimB].filter((result) => result.status === 'rejected');

    expect(fulfilled).toHaveLength(1);
    expect(rejected).toHaveLength(1);
  });

  it('allows claim takeover after TTL expiry', async () => {
    let timestamp = 1_700_000_000_000;
    const now = (): number => timestamp;
    const [repositoryA, repositoryB] = createRepositoryPair(now);

    await repositoryA.create({
      project: 'queue',
      mission: 'phase1',
      taskId: 'MQ-004-EXP',
      title: 'TTL expiry',
    });

    await repositoryA.claim('MQ-004-EXP', {
      agentId: 'agent-a',
      ttlSeconds: 1,
    });

    timestamp += 2_000;

    const takeover = await repositoryB.claim('MQ-004-EXP', {
      agentId: 'agent-b',
      ttlSeconds: 60,
    });

    expect(takeover.claimedBy).toBe('agent-b');
  });

  it('releases a claimed task back to pending', async () => {
    const [repository] = createRepositoryPair(() => 1_700_000_000_000);

    await repository.create({
      project: 'queue',
      mission: 'phase1',
      taskId: 'MQ-004-REL',
      title: 'Release test',
    });

    await repository.claim('MQ-004-REL', {
      agentId: 'agent-a',
      ttlSeconds: 60,
    });

    const released = await repository.release('MQ-004-REL', {
      agentId: 'agent-a',
    });

    expect(released.status).toBe('pending');
    expect(released.claimedBy).toBeUndefined();
    expect(released.claimedAt).toBeUndefined();
  });

  it('heartbeats, completes, and fails with valid transitions', async () => {
    let timestamp = 1_700_000_000_000;
    const now = (): number => timestamp;
    const [repository] = createRepositoryPair(now);

    await repository.create({
      project: 'queue',
      mission: 'phase1',
      taskId: 'MQ-004-HCF',
      title: 'Transition test',
    });

    await repository.claim('MQ-004-HCF', {
      agentId: 'agent-a',
      ttlSeconds: 60,
    });

    timestamp += 1_000;
    const heartbeat = await repository.heartbeat('MQ-004-HCF', {
      agentId: 'agent-a',
      ttlSeconds: 120,
    });
    expect(heartbeat.claimTTL).toBe(120);
    expect(heartbeat.claimedAt).toBe(1_700_000_001_000);

    const completed = await repository.complete('MQ-004-HCF', {
      agentId: 'agent-a',
      summary: 'done',
    });
    expect(completed.status).toBe('completed');
    expect(completed.completionSummary).toBe('done');

    await repository.create({
      project: 'queue',
      mission: 'phase1',
      taskId: 'MQ-004-FAIL',
      title: 'Failure test',
    });

    await repository.claim('MQ-004-FAIL', {
      agentId: 'agent-a',
      ttlSeconds: 60,
    });

    const failed = await repository.fail('MQ-004-FAIL', {
      agentId: 'agent-a',
      reason: 'boom',
    });

    expect(failed.status).toBe('failed');
    expect(failed.failureReason).toBe('boom');
    expect(failed.retryCount).toBe(1);
  });

  it('rejects invalid transitions', async () => {
    const [repository] = createRepositoryPair(() => 1_700_000_000_000);

    await repository.create({
      project: 'queue',
      mission: 'phase1',
      taskId: 'MQ-004-INV',
      title: 'Invalid transitions',
    });

    await expect(
      repository.complete('MQ-004-INV', {
        agentId: 'agent-a',
      }),
    ).rejects.toBeInstanceOf(TaskTransitionError);
  });

  it('enforces claim ownership for release and complete', async () => {
    const [repository] = createRepositoryPair(() => 1_700_000_000_000);

    await repository.create({
      project: 'queue',
      mission: 'phase1',
      taskId: 'MQ-004-OWN',
      title: 'Ownership checks',
    });

    await repository.claim('MQ-004-OWN', {
      agentId: 'agent-a',
      ttlSeconds: 60,
    });

    await expect(
      repository.release('MQ-004-OWN', {
        agentId: 'agent-b',
      }),
    ).rejects.toBeInstanceOf(TaskOwnershipError);

    await expect(
      repository.complete('MQ-004-OWN', {
        agentId: 'agent-b',
      }),
    ).rejects.toBeInstanceOf(TaskOwnershipError);
  });

  it('merges concurrent non-conflicting update patches atomically', async () => {
    const [repositoryA, repositoryB] = createRepositoryPair(() => 1_700_000_000_000);

    await repositoryA.create({
      project: 'queue',
      mission: 'phase1',
      taskId: 'MQ-004-UPD',
      title: 'Original title',
      description: 'Original description',
    });

    await Promise.all([
      repositoryA.update('MQ-004-UPD', {
        title: 'Updated title',
      }),
      repositoryB.update('MQ-004-UPD', {
        description: 'Updated description',
      }),
    ]);

    const latest = await repositoryA.get('MQ-004-UPD');

    expect(latest).not.toBeNull();
    expect(latest?.title).toBe('Updated title');
    expect(latest?.description).toBe('Updated description');
  });
});