/**
 * Unit Tests: FIFO Request Queue
 * 
 * Tests T038-T039: Test FIFO queue implementation
 * Tests the queue.js module in isolation
 * 
 * @module tests/unit/queue
 */

import { describe, it } from 'node:test';
import assert from 'node:assert/strict';

// =============================================================================
// T038: Unit test for FIFO queue enqueue/dequeue
// =============================================================================

describe('T038: FIFO Queue Enqueue/Dequeue', () => {
  it('should enqueue and dequeue requests in FIFO order', async () => {
    // TODO: Import RequestQueue from src/queue.js
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    const results = [];

    // Enqueue 3 tasks
    const task1 = async () => {
      await delay(10);
      results.push('task1');
      return 'result1';
    };

    const task2 = async () => {
      await delay(10);
      results.push('task2');
      return 'result2';
    };

    const task3 = async () => {
      await delay(10);
      results.push('task3');
      return 'result3';
    };

    // Enqueue all tasks
    // const promise1 = queue.enqueue(task1);
    // const promise2 = queue.enqueue(task2);
    // const promise3 = queue.enqueue(task3);

    // Wait for all to complete
    // await Promise.all([promise1, promise2, promise3]);

    // Verify FIFO order
    // assert.deepEqual(results, ['task1', 'task2', 'task3'], 'Tasks should complete in FIFO order');
  });

  it('should process tasks sequentially (one at a time)', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    let activeTaskCount = 0;
    let maxActiveTaskCount = 0;

    const createTask = (id) => async () => {
      activeTaskCount++;
      maxActiveTaskCount = Math.max(maxActiveTaskCount, activeTaskCount);
      
      await delay(50);
      
      activeTaskCount--;
      return `task${id}`;
    };

    // Enqueue multiple tasks
    const promises = [];
    for (let i = 1; i <= 5; i++) {
      // promises.push(queue.enqueue(createTask(i)));
    }

    // await Promise.all(promises);

    // Verify only one task was active at a time
    // assert.equal(maxActiveTaskCount, 1, 'Only one task should be active at a time');
  });

  it('should maintain queue order when tasks are added during processing', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    const results = [];

    // Add initial task
    // queue.enqueue(async () => {
    //   await delay(20);
    //   results.push('task1');
    // });

    // Add second task after slight delay
    // await delay(5);
    // queue.enqueue(async () => {
    //   await delay(10);
    //   results.push('task2');
    // });

    // Add third task after slight delay
    // await delay(5);
    // queue.enqueue(async () => {
    //   await delay(10);
    //   results.push('task3');
    // });

    // Wait for all tasks to complete
    // await delay(100);

    // Verify order preserved
    // assert.deepEqual(results, ['task1', 'task2', 'task3'], 'Should maintain FIFO order even when tasks added during processing');
  });

  it('should return task result through promise', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    const task = async () => {
      return 'test-result';
    };

    // const result = await queue.enqueue(task);

    // assert.equal(result, 'test-result', 'Should return task result through promise');
  });

  it('should propagate task errors through promise', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    const task = async () => {
      throw new Error('Task failed');
    };

    // await assert.rejects(
    //   async () => await queue.enqueue(task),
    //   { message: 'Task failed' },
    //   'Should propagate task error'
    // );
  });
});

// =============================================================================
// T039: Unit test for FIFO queue concurrent request handling
// =============================================================================

describe('T039: FIFO Queue Concurrent Request Handling', () => {
  it('should use processing flag to prevent simultaneous execution', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    let processingCheckpoints = [];

    const createTask = (id) => async () => {
      // Log when task starts
      processingCheckpoints.push({ id, event: 'start', time: Date.now() });
      
      await delay(30);
      
      // Log when task ends
      processingCheckpoints.push({ id, event: 'end', time: Date.now() });
      
      return id;
    };

    // Enqueue 3 tasks simultaneously
    const promises = [
      // queue.enqueue(createTask(1)),
      // queue.enqueue(createTask(2)),
      // queue.enqueue(createTask(3))
    ];

    // await Promise.all(promises);

    // Verify processing flag prevented overlap
    // Check that task N ends before task N+1 starts
    // const task1End = processingCheckpoints.find(cp => cp.id === 1 && cp.event === 'end');
    // const task2Start = processingCheckpoints.find(cp => cp.id === 2 && cp.event === 'start');
    // const task2End = processingCheckpoints.find(cp => cp.id === 2 && cp.event === 'end');
    // const task3Start = processingCheckpoints.find(cp => cp.id === 3 && cp.event === 'start');

    // assert.ok(task1End.time <= task2Start.time, 'Task 2 should start after Task 1 ends');
    // assert.ok(task2End.time <= task3Start.time, 'Task 3 should start after Task 2 ends');
  });

  it('should clear processing flag after task completes', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    // Add task
    // await queue.enqueue(async () => {
    //   await delay(10);
    //   return 'done';
    // });

    // Verify processing flag is cleared (queue can accept new tasks)
    // assert.equal(queue.isProcessing(), false, 'Processing flag should be cleared after task completes');
  });

  it('should clear processing flag even if task throws error', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    // Add task that throws error
    try {
      // await queue.enqueue(async () => {
      //   await delay(10);
      //   throw new Error('Task failed');
      // });
    } catch (e) {
      // Expected error
    }

    // Verify processing flag is cleared (queue can accept new tasks)
    // assert.equal(queue.isProcessing(), false, 'Processing flag should be cleared even after task error');

    // Verify next task can be processed
    // const result = await queue.enqueue(async () => 'next-task');
    // assert.equal(result, 'next-task', 'Next task should process successfully after error');
  });

  it('should handle empty queue correctly (no processing when queue empty)', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    // Verify processing flag is false for empty queue
    // assert.equal(queue.isProcessing(), false, 'Processing flag should be false for empty queue');
    // assert.equal(queue.getQueueLength(), 0, 'Queue should be empty');
  });

  it('should use EventEmitter for queue management', async () => {
    // Per task spec: "Implement FIFO request queue class in src/queue.js using Node.js EventEmitter"
    
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    // Verify queue extends or uses EventEmitter
    // assert.ok(queue.on, 'Queue should have EventEmitter methods');
    // assert.ok(queue.emit, 'Queue should have emit method');
  });

  it('should maintain queue array for pending tasks', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    // Add tasks without waiting
    // queue.enqueue(async () => {
    //   await delay(50);
    //   return 'task1';
    // });
    // queue.enqueue(async () => 'task2');
    // queue.enqueue(async () => 'task3');

    // Check queue length while first task is processing
    // await delay(10); // Let first task start processing
    
    // Queue should have 2 pending tasks (task2 and task3)
    // Note: task1 is being processed, not in queue
    // assert.ok(queue.getQueueLength() >= 2, 'Queue should contain pending tasks');
  });

  it('should process queue in correct order after processing flag is cleared', async () => {
    // TODO: Import RequestQueue
    // const { RequestQueue } = await import('../../src/queue.js');
    // const queue = new RequestQueue();

    const results = [];

    // Add first task (starts processing immediately)
    // queue.enqueue(async () => {
    //   await delay(30);
    //   results.push('task1');
    // });

    // Add more tasks while first is processing
    // await delay(5);
    // queue.enqueue(async () => {
    //   results.push('task2');
    // });
    // queue.enqueue(async () => {
    //   results.push('task3');
    // });

    // Wait for all to complete
    // await delay(100);

    // Verify FIFO order maintained
    // assert.deepEqual(results, ['task1', 'task2', 'task3'], 'Should process in FIFO order after processing flag cleared');
  });
});

// =============================================================================
// Helper Functions
// =============================================================================

/**
 * Delay helper for async tests
 * @param {number} ms - Milliseconds to delay
 * @returns {Promise<void>}
 */
function delay(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}