import { describe, test, expect, vi } from 'vitest'
import {
  createHeartbeat,
  HEARTBEAT_INTERVAL_MS,
  HEARTBEAT_MISS_LIMIT,
  type ScheduleHandle,
} from '../mux/heartbeat.js'

/** A manually-driven fake scheduler: `tick()` fires the scheduled callback; cancel stops it. */
function fakeScheduler() {
  let scheduled: (() => void) | null = null
  const schedule = (fn: () => void): ScheduleHandle => {
    scheduled = fn
    return { cancel: () => (scheduled = null) }
  }
  return { schedule, tick: () => scheduled?.() }
}

describe('heartbeat (T5, §4.1 15s PING/PONG)', () => {
  test('start sends a PING immediately with a fresh 8-byte token', () => {
    const { schedule } = fakeScheduler()
    const pings: Uint8Array[] = []
    const hb = createHeartbeat({ schedule, sendPing: (t) => pings.push(t), onDead: () => {} })
    hb.start()
    expect(pings).toHaveLength(1)
    expect(pings[0]!.length).toBe(8)
  })

  test('a matching onPong resets the miss counter; 3 misses ⇒ onDead exactly once', () => {
    const sched = fakeScheduler()
    const pings: Uint8Array[] = []
    const onDead = vi.fn()
    const hb = createHeartbeat({ schedule: sched.schedule, sendPing: (t) => pings.push(t), onDead })
    hb.start() // ping #1, outstanding set
    hb.onPong(pings[0]!) // matched → miss counter reset
    sched.tick() // outstanding was cleared → no miss, ping #2
    sched.tick() // miss 1, ping #3
    sched.tick() // miss 2, ping #4
    sched.tick() // miss 3 → dead
    expect(onDead).toHaveBeenCalledTimes(1)
    const pingsAfterDead = pings.length
    sched.tick() // no further pings after dead
    expect(pings.length).toBe(pingsAfterDead)
  })

  test('a stale/unknown PONG token does NOT reset the miss counter (anti-replay)', () => {
    const sched = fakeScheduler()
    const onDead = vi.fn()
    const hb = createHeartbeat({ schedule: sched.schedule, sendPing: () => {}, onDead })
    hb.start()
    hb.onPong(new Uint8Array([9, 9, 9, 9, 9, 9, 9, 9])) // wrong token — ignored
    sched.tick() // miss 1
    sched.tick() // miss 2
    sched.tick() // miss 3 → dead despite the spoofed PONG
    expect(onDead).toHaveBeenCalledTimes(1)
  })

  test('stop cancels cleanly (no onDead after stop)', () => {
    const sched = fakeScheduler()
    const onDead = vi.fn()
    const hb = createHeartbeat({ schedule: sched.schedule, sendPing: () => {}, onDead })
    hb.start()
    hb.stop()
    sched.tick() // scheduler cancelled → no-op
    sched.tick()
    sched.tick()
    expect(onDead).not.toHaveBeenCalled()
  })

  test('exposes the §4.1 constants', () => {
    expect(HEARTBEAT_INTERVAL_MS).toBe(15_000)
    expect(HEARTBEAT_MISS_LIMIT).toBe(3)
  })
})
