// Mock the MongoDB module completely
const mockDb = {
  collection: jest.fn().mockReturnValue({
    findOne: jest.fn(),
    insertOne: jest.fn(),
    updateOne: jest.fn(),
    deleteOne: jest.fn()
  }),
  admin: jest.fn().mockReturnValue({
    ping: jest.fn().mockResolvedValue(true)
  })
}

const mockClient = {
  connect: jest.fn(),
  close: jest.fn().mockResolvedValue(undefined),
  db: jest.fn().mockReturnValue(mockDb)
}

// The connect method should resolve to the client itself
mockClient.connect.mockResolvedValue(mockClient)

const MockedMongoClient = jest.fn().mockImplementation(() => mockClient)

// Mock the mongodb module
jest.mock('mongodb', () => ({
  MongoClient: MockedMongoClient
}))

// Restore environment before tests
const originalEnv = process.env

describe('MongoDB Connection (Unit Tests)', () => {
  beforeEach(() => {
    jest.resetModules()
    process.env = {
      ...originalEnv,
      MONGODB_URI: 'mongodb://localhost:27017/test',
      MONGODB_DB: 'test'
    }
    jest.clearAllMocks()
    
    // Reset the mock implementation
    MockedMongoClient.mockImplementation(() => mockClient as any)
    mockClient.db.mockReturnValue(mockDb)
  })

  afterEach(() => {
    process.env = originalEnv
  })

  describe('MongoDB URI validation', () => {
    it('should throw error when MONGODB_URI is not set', () => {
      // This test is tricky because the module is cached
      // We'll test this by clearing the module cache and mocking process.env
      const originalMongodbUri = process.env.MONGODB_URI
      delete process.env.MONGODB_URI
      
      // Clear module cache to force re-import
      jest.resetModules()
      
      const { getClientPromise } = require('./mongodb')
      expect(() => getClientPromise()).toThrow('Please add MONGODB_URI to your environment variables')
      
      // Restore environment
      process.env.MONGODB_URI = originalMongodbUri
    })
  })

  describe('Database connection', () => {
    it('should create MongoClient with correct URI and options', async () => {
      // Import after setting up the mock
      const { getClientPromise } = await import('./mongodb')

      await getClientPromise()

      expect(MockedMongoClient).toHaveBeenCalledWith(
        process.env.MONGODB_URI,
        expect.objectContaining({
          maxPoolSize: 10,
          serverSelectionTimeoutMS: 5000,
          socketTimeoutMS: 45000
        })
      )
    })

    it('should return database instance', async () => {
      const { getDb } = await import('./mongodb')
      
      const result = await getDb()
      
      expect(result).toBe(mockDb)
      expect(typeof result.collection).toBe('function')
    })

    it('should return collection from database', async () => {
      const { getCollection } = await import('./mongodb')
      
      const collection = await getCollection('test_collection')

      expect(collection).toBeDefined()
      expect(mockDb.collection).toHaveBeenCalledWith('test_collection')
      expect(typeof collection.findOne).toBe('function')
    })

    it('should check MongoDB connection successfully', async () => {
      const { checkMongoConnection } = await import('./mongodb')
      
      const result = await checkMongoConnection()
      expect(result).toBe(true)
    })

    it('should return false on MongoDB connection failure', async () => {
      // Create a failing client
      const failingClient = {
        connect: jest.fn().mockRejectedValue(new Error('Connection failed')),
        db: jest.fn().mockRejectedValue(new Error('Connection failed')),
        close: jest.fn()
      }
      
      MockedMongoClient.mockImplementation(() => failingClient as any)
      
      // Clear the module cache and re-import
      jest.resetModules()
      const { checkMongoConnection } = await import('./mongodb')
      
      const result = await checkMongoConnection()
      expect(result).toBe(false)
    })
  })

  describe('Connection reuse and caching', () => {
    it('should reuse the same MongoClient instance for multiple calls', async () => {
      const { getClientPromise } = await import('./mongodb')

      const client1 = await getClientPromise()
      const client2 = await getClientPromise()

      // Should be the same client instance
      expect(client1).toBe(client2)
    })
  })
})