import { describe, it, expect } from 'vitest';
import { LaneQueue, LaneQueueRejectedError } from './lane-queue.js';

describe('LaneQueue', () => {
  it('executes a single item immediately', async () => {
    const queue = new LaneQueue();
    const result = await queue.enqueue('lane-a', async () => 42);
    expect(result).toBe(42);
  });

  it('serialises items within the same lane', async () => {
    const queue = new LaneQueue();
    const order: number[] = [];

    // Create a deferred to control timing
    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      order.push(1);
      await firstBlocks;
      order.push(2);
      return 'first';
    });

    const p2 = queue.enqueue('lane-a', async () => {
      order.push(3);
      return 'second';
    });

    const p3 = queue.enqueue('lane-a', async () => {
      order.push(4);
      return 'third';
    });

    // Only item 1 should have started
    expect(order).toEqual([1]);
    expect(queue.queueLength('lane-a')).toBe(2);
    expect(queue.isProcessing('lane-a')).toBe(true);

    // Release the first item
    resolveFirst();
    const results = await Promise.all([p1, p2, p3]);

    expect(results).toEqual(['first', 'second', 'third']);
    expect(order).toEqual([1, 2, 3, 4]);
  });

  it('runs independent lanes in parallel', async () => {
    const queue = new LaneQueue();
    const running: string[] = [];

    let resolveA!: () => void;
    const blocksA = new Promise<void>((r) => { resolveA = r; });
    let resolveB!: () => void;
    const blocksB = new Promise<void>((r) => { resolveB = r; });

    const pA = queue.enqueue('lane-a', async () => {
      running.push('a-start');
      await blocksA;
      running.push('a-end');
      return 'A';
    });

    const pB = queue.enqueue('lane-b', async () => {
      running.push('b-start');
      await blocksB;
      running.push('b-end');
      return 'B';
    });

    // Both should have started concurrently
    // Wait a tick for async execution
    await new Promise<void>((r) => queueMicrotask(r));
    expect(running).toContain('a-start');
    expect(running).toContain('b-start');

    resolveA();
    resolveB();
    const [rA, rB] = await Promise.all([pA, pB]);

    expect(rA).toBe('A');
    expect(rB).toBe('B');
  });

  it('error in one item does not block the next', async () => {
    const queue = new LaneQueue();

    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      await firstBlocks;
      throw new Error('boom');
    });

    const p2 = queue.enqueue('lane-a', async () => 'recovered');

    resolveFirst();

    await expect(p1).rejects.toThrow('boom');
    const result = await p2;
    expect(result).toBe('recovered');
  });

  it('cancel rejects pending items but does not affect active', async () => {
    const queue = new LaneQueue();

    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      await firstBlocks;
      return 'active';
    });

    const p2 = queue.enqueue('lane-a', async () => 'pending-1');
    const p3 = queue.enqueue('lane-a', async () => 'pending-2');

    expect(queue.queueLength('lane-a')).toBe(2);

    // Cancel pending items
    queue.cancel('lane-a');
    expect(queue.queueLength('lane-a')).toBe(0);

    // Active work should still complete
    resolveFirst();
    const result = await p1;
    expect(result).toBe('active');

    // Pending items should have been rejected
    await expect(p2).rejects.toThrow('Lane cancelled');
    await expect(p3).rejects.toThrow('Lane cancelled');
  });

  it('reports queue length correctly', async () => {
    const queue = new LaneQueue();

    expect(queue.queueLength('lane-a')).toBe(0);
    expect(queue.isProcessing('lane-a')).toBe(false);

    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      await firstBlocks;
      return 'done';
    });

    // Active work, no pending
    expect(queue.isProcessing('lane-a')).toBe(true);
    expect(queue.queueLength('lane-a')).toBe(0);

    const p2 = queue.enqueue('lane-a', async () => 'queued-1');
    expect(queue.queueLength('lane-a')).toBe(1);

    const p3 = queue.enqueue('lane-a', async () => 'queued-2');
    expect(queue.queueLength('lane-a')).toBe(2);

    resolveFirst();
    await Promise.all([p1, p2, p3]);

    // After all done, lane should be cleaned up
    expect(queue.isProcessing('lane-a')).toBe(false);
    expect(queue.queueLength('lane-a')).toBe(0);
  });

  it('cleans up empty lanes after completion', async () => {
    const queue = new LaneQueue();

    await queue.enqueue('lane-a', async () => 'done');

    // Lane should be cleaned up (isProcessing returns false, queueLength 0)
    expect(queue.isProcessing('lane-a')).toBe(false);
    expect(queue.queueLength('lane-a')).toBe(0);
  });

  it('cancel on non-existent lane is a no-op', () => {
    const queue = new LaneQueue();
    // Should not throw
    queue.cancel('no-such-lane');
    expect(queue.queueLength('no-such-lane')).toBe(0);
  });

  it('can enqueue new work after a lane completes', async () => {
    const queue = new LaneQueue();

    const r1 = await queue.enqueue('lane-a', async () => 'first');
    expect(r1).toBe('first');

    const r2 = await queue.enqueue('lane-a', async () => 'second');
    expect(r2).toBe('second');
  });

  it('followup mode keeps only the most recent pending request', async () => {
    const queue = new LaneQueue({ mode: 'followup' });
    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      await firstBlocks;
      return 'active';
    });
    const p2 = queue.enqueue('lane-a', async () => 'old-pending');
    const p3 = queue.enqueue('lane-a', async () => 'latest-pending');

    await expect(p2).rejects.toThrow('Superseded by newer follow-up request');
    resolveFirst();

    await expect(p1).resolves.toBe('active');
    await expect(p3).resolves.toBe('latest-pending');
  });

  it('steer_backlog mode replaces existing pending backlog with latest request', async () => {
    const queue = new LaneQueue({ mode: 'steer_backlog' });
    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      await firstBlocks;
      return 'active';
    });
    const p2 = queue.enqueue('lane-a', async () => 'old-pending');
    const p3 = queue.enqueue('lane-a', async () => 'new-pending');

    await expect(p2).rejects.toThrow('Superseded by newer request');
    resolveFirst();

    await expect(p1).resolves.toBe('active');
    await expect(p3).resolves.toBe('new-pending');
  });

  it('drop_new overflow rejects newest request when cap is reached', async () => {
    const queue = new LaneQueue({ cap: 1, overflow: 'drop_new' });
    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      await firstBlocks;
      return 'active';
    });
    const p2 = queue.enqueue('lane-a', async () => 'pending-1');
    const p3 = queue.enqueue('lane-a', async () => 'pending-2');

    await expect(p3).rejects.toThrow('Lane queue full (drop_new): request rejected with 1 pending');
    resolveFirst();

    await expect(p1).resolves.toBe('active');
    await expect(p2).resolves.toBe('pending-1');
  });

  it('drop_old overflow evicts oldest pending request when cap is reached', async () => {
    const queue = new LaneQueue({ cap: 1, overflow: 'drop_old' });
    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      await firstBlocks;
      return 'active';
    });
    const p2 = queue.enqueue('lane-a', async () => 'old-pending');
    const p3 = queue.enqueue('lane-a', async () => 'new-pending');

    await expect(p2).rejects.toThrow('Lane queue overflow (drop_old): oldest pending request dropped');
    resolveFirst();

    await expect(p1).resolves.toBe('active');
    await expect(p3).resolves.toBe('new-pending');
  });

  it('supports per-enqueue policy overrides', async () => {
    const queue = new LaneQueue({ mode: 'collect', cap: 10, overflow: 'drop_old' });
    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      await firstBlocks;
      return 'active';
    });
    const p2 = queue.enqueue('lane-a', async () => 'old-pending', { mode: 'steer' });
    const p3 = queue.enqueue('lane-a', async () => 'latest-pending', { mode: 'steer' });

    await expect(p2).rejects.toThrow('Superseded by newer request');
    resolveFirst();

    await expect(p1).resolves.toBe('active');
    await expect(p3).resolves.toBe('latest-pending');
  });

  it('applies debounce before starting queued work', async () => {
    const queue = new LaneQueue({ debounceMs: 25 });
    const events: string[] = [];
    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      events.push('active:start');
      await firstBlocks;
      events.push('active:end');
      return 'active';
    });

    const p2 = queue.enqueue('lane-a', async () => {
      events.push('next:start');
      return 'next';
    });

    resolveFirst();
    await p1;
    expect(queue.isProcessing('lane-a')).toBe(true);
    expect(events).toEqual(['active:start', 'active:end']);
    await new Promise((r) => setTimeout(r, 40));
    await expect(p2).resolves.toBe('next');
    expect(events).toEqual(['active:start', 'active:end', 'next:start']);
  });

  it('returns structured queue rejection errors', async () => {
    const queue = new LaneQueue({ cap: 1, overflow: 'drop_new' });
    let resolveFirst!: () => void;
    const firstBlocks = new Promise<void>((r) => { resolveFirst = r; });

    const p1 = queue.enqueue('lane-a', async () => {
      await firstBlocks;
      return 'active';
    });
    const p2 = queue.enqueue('lane-a', async () => 'pending');
    const p3 = queue.enqueue('lane-a', async () => 'dropped');

    const err = await p3.catch((e) => e) as LaneQueueRejectedError;
    expect(err).toBeInstanceOf(LaneQueueRejectedError);
    expect(err.details.code).toBe('overflow');
    expect(err.details.overflow).toBe('drop_new');
    expect(err.details.laneId).toBe('lane-a');

    resolveFirst();
    await expect(p1).resolves.toBe('active');
    await expect(p2).resolves.toBe('pending');
  });
});