import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'

/**
 * Unit tests for useExchangeStream memory management (max 1000 cached messages).
 * Validates: Requirement 7.1 - client-side message cap enforcement
 *
 * We test the appendMessage logic directly by extracting it into a testable pattern
 * since the composable relies on Vue reactivity and EventSource which require mocking.
 */

const MAX_CACHED_MESSAGES = 1000

interface CwmpExchange {
  deviceId: string
  direction: 'CPE→ACS' | 'ACS→CPE'
  timestamp: string
  sessionId: string
  cwmpMethod: string
  rawXml: string
  sequenceNumber: number
  createdAt?: string
}

/**
 * Simulates the appendMessage logic from useExchangeStream.ts
 * This is the exact same logic used in the composable.
 */
function appendMessage(messages: CwmpExchange[], exchange: CwmpExchange): CwmpExchange[] {
  let result = [...messages, exchange]
  if (result.length > MAX_CACHED_MESSAGES) {
    result = result.slice(-MAX_CACHED_MESSAGES)
  }
  return result
}

function createExchange(sequenceNumber: number): CwmpExchange {
  return {
    deviceId: 'test-device',
    direction: 'CPE→ACS',
    timestamp: new Date(Date.now() + sequenceNumber * 1000).toISOString(),
    sessionId: 'session-1',
    cwmpMethod: 'Inform',
    rawXml: `<soap:Envelope><soap:Body><cwmp:Inform/></soap:Body></soap:Envelope>`,
    sequenceNumber,
  }
}

describe('useExchangeStream memory management', () => {
  describe('appendMessage cap enforcement', () => {
    it('should allow messages up to MAX_CACHED_MESSAGES without discarding', () => {
      let messages: CwmpExchange[] = []

      for (let i = 1; i <= MAX_CACHED_MESSAGES; i++) {
        messages = appendMessage(messages, createExchange(i))
      }

      expect(messages.length).toBe(MAX_CACHED_MESSAGES)
      expect(messages[0].sequenceNumber).toBe(1)
      expect(messages[messages.length - 1].sequenceNumber).toBe(MAX_CACHED_MESSAGES)
    })

    it('should discard oldest message when exceeding the cap', () => {
      let messages: CwmpExchange[] = []

      // Fill to cap
      for (let i = 1; i <= MAX_CACHED_MESSAGES; i++) {
        messages = appendMessage(messages, createExchange(i))
      }

      // Add one more (1001)
      messages = appendMessage(messages, createExchange(MAX_CACHED_MESSAGES + 1))

      expect(messages.length).toBe(MAX_CACHED_MESSAGES)
      // Oldest (seq 1) should be discarded, newest starts at seq 2
      expect(messages[0].sequenceNumber).toBe(2)
      expect(messages[messages.length - 1].sequenceNumber).toBe(MAX_CACHED_MESSAGES + 1)
    })

    it('should always keep the most recent messages when adding many past the cap', () => {
      let messages: CwmpExchange[] = []

      // Add 1500 messages (500 over the cap)
      const totalMessages = 1500
      for (let i = 1; i <= totalMessages; i++) {
        messages = appendMessage(messages, createExchange(i))
      }

      expect(messages.length).toBe(MAX_CACHED_MESSAGES)
      // Should keep messages 501 through 1500
      expect(messages[0].sequenceNumber).toBe(totalMessages - MAX_CACHED_MESSAGES + 1)
      expect(messages[messages.length - 1].sequenceNumber).toBe(totalMessages)
    })

    it('should handle empty initial state', () => {
      let messages: CwmpExchange[] = []
      messages = appendMessage(messages, createExchange(1))

      expect(messages.length).toBe(1)
      expect(messages[0].sequenceNumber).toBe(1)
    })

    it('should never exceed MAX_CACHED_MESSAGES regardless of input pattern', () => {
      let messages: CwmpExchange[] = []

      // Rapid burst of 2000 messages
      for (let i = 1; i <= 2000; i++) {
        messages = appendMessage(messages, createExchange(i))
        expect(messages.length).toBeLessThanOrEqual(MAX_CACHED_MESSAGES)
      }

      expect(messages.length).toBe(MAX_CACHED_MESSAGES)
    })

    it('should preserve chronological order after cap enforcement', () => {
      let messages: CwmpExchange[] = []

      for (let i = 1; i <= 1200; i++) {
        messages = appendMessage(messages, createExchange(i))
      }

      // Verify all remaining messages are in ascending order
      for (let i = 1; i < messages.length; i++) {
        expect(messages[i].sequenceNumber).toBeGreaterThan(messages[i - 1].sequenceNumber)
        expect(messages[i].timestamp > messages[i - 1].timestamp).toBe(true)
      }
    })

    it('should correctly handle cap at exactly MAX_CACHED_MESSAGES boundary', () => {
      let messages: CwmpExchange[] = []

      // Add exactly MAX_CACHED_MESSAGES messages
      for (let i = 1; i <= MAX_CACHED_MESSAGES; i++) {
        messages = appendMessage(messages, createExchange(i))
      }

      expect(messages.length).toBe(MAX_CACHED_MESSAGES)
      expect(messages[0].sequenceNumber).toBe(1)

      // Add one more to go over by 1
      messages = appendMessage(messages, createExchange(MAX_CACHED_MESSAGES + 1))
      expect(messages.length).toBe(MAX_CACHED_MESSAGES)
      expect(messages[0].sequenceNumber).toBe(2)
    })
  })
})