import { describe, test, expect, beforeEach, mock } from 'bun:test'
import { mockConfigModule } from './helpers/mock-config'

// Mock config
mock.module('../config', () => mockConfigModule())

import { Hono } from 'hono'
import { storeReset } from '../store'
import {
  removeEventBus,
  getAllEventBuses,
  getEventBus,
} from '../transport/event-bus'
import { createSSEWriter, createSSEStream } from '../transport/sse-writer'

/** Read up to N bytes from a Response stream, then cancel */
async function readPartialStream(
  res: Response,
  maxBytes = 4096,
): Promise<string> {
  const reader = res.body?.getReader()
  if (!reader) return ''
  const chunks: Uint8Array[] = []
  let totalBytes = 0
  try {
    while (totalBytes < maxBytes) {
      const { done, value } = await reader.read()
      if (done) break
      chunks.push(value)
      totalBytes += value.length
      // Cancel after we have some data (first keepalive + any initial events)
      if (totalBytes > 0) break
    }
  } finally {
    reader.cancel()
  }
  const combined = new Uint8Array(totalBytes)
  let offset = 0
  for (const chunk of chunks) {
    combined.set(chunk, offset)
    offset += chunk.length
  }
  return new TextDecoder().decode(combined)
}

describe('SSE Writer', () => {
  describe('createSSEWriter', () => {
    test('creates SSEWriter with send and close methods', () => {
      const app = new Hono()
      let capturedWriter: ReturnType<typeof createSSEWriter> | null = null

      app.get('/test', c => {
        capturedWriter = createSSEWriter(c)
        return c.text('ok')
      })

      app.request('/test')
      expect(capturedWriter).not.toBeNull()
      expect(typeof capturedWriter!.send).toBe('function')
      expect(typeof capturedWriter!.close).toBe('function')
    })
  })

  describe('createSSEStream', () => {
    beforeEach(() => {
      storeReset()
      for (const [key] of getAllEventBuses()) {
        removeEventBus(key)
      }
    })

    test('returns Response with correct SSE headers', async () => {
      const app = new Hono()

      app.get('/stream/:sessionId', c => {
        const sessionId = c.req.param('sessionId')
        return createSSEStream(c, sessionId, 0)
      })

      const res = await app.request('/stream/s1')
      expect(res.status).toBe(200)
      expect(res.headers.get('Content-Type')).toBe('text/event-stream')
      expect(res.headers.get('Cache-Control')).toBe('no-cache')
      expect(res.headers.get('Connection')).toBe('keep-alive')
      expect(res.headers.get('X-Accel-Buffering')).toBe('no')

      // Cancel the stream
      res.body?.cancel()
    })

    test('sends initial keepalive', async () => {
      const app = new Hono()

      app.get('/stream/:sessionId', c => {
        const sessionId = c.req.param('sessionId')
        return createSSEStream(c, sessionId, 0)
      })

      const res = await app.request('/stream/s2')
      const text = await readPartialStream(res)
      expect(text).toContain(': keepalive')
    })

    test('sends historical events when fromSeqNum > 0', async () => {
      // Pre-populate event bus with events
      const bus = getEventBus('s3')
      bus.publish({
        id: 'e1',
        sessionId: 's3',
        type: 'user',
        payload: { content: 'hello' },
        direction: 'outbound',
      })
      bus.publish({
        id: 'e2',
        sessionId: 's3',
        type: 'assistant',
        payload: { content: 'hi' },
        direction: 'inbound',
      })

      const app = new Hono()

      app.get('/stream/:sessionId', c => {
        const sessionId = c.req.param('sessionId')
        const fromSeq = parseInt(c.req.query('fromSeq') || '0', 10)
        return createSSEStream(c, sessionId, fromSeq)
      })

      const res = await app.request('/stream/s3?fromSeq=1')
      const text = await readPartialStream(res)
      // Should replay events since seq 1 (i.e., event 2)
      expect(text).toContain('"seqNum":2')
      expect(text).toContain('assistant')
    })

    test('no historical events when fromSeqNum is 0', async () => {
      const bus = getEventBus('s5')
      bus.publish({
        id: 'e1',
        sessionId: 's5',
        type: 'user',
        payload: {},
        direction: 'outbound',
      })

      const app = new Hono()

      app.get('/stream/:sessionId', c => {
        const sessionId = c.req.param('sessionId')
        return createSSEStream(c, sessionId, 0)
      })

      const res = await app.request('/stream/s5')
      const text = await readPartialStream(res)
      // With fromSeqNum=0, no historical replay, just keepalive
      expect(text).toContain(': keepalive')
      // Should NOT contain event data (only keepalive)
      expect(text).not.toContain('event: message')
    })

    test('subscribes to new events and delivers them', async () => {
      const app = new Hono()

      app.get('/stream/:sessionId', c => {
        const sessionId = c.req.param('sessionId')
        return createSSEStream(c, sessionId, 0)
      })

      const res = await app.request('/stream/s6')

      // Read initial keepalive first
      const reader = res.body!.getReader()
      const { value: firstChunk } = await reader.read()
      const initialText = new TextDecoder().decode(firstChunk!)
      expect(initialText).toContain(': keepalive')

      // Now publish an event
      const bus = getEventBus('s6')
      bus.publish({
        id: 'e1',
        sessionId: 's6',
        type: 'user',
        payload: { content: 'real-time' },
        direction: 'outbound',
      })

      // Read the event
      const { value: secondChunk } = await reader.read()
      const eventText = new TextDecoder().decode(secondChunk!)
      expect(eventText).toContain('event: message')
      expect(eventText).toContain('real-time')

      reader.cancel()
    })
  })
})