import { describe, expect, it, vi } from 'vitest'
import { createLogger } from '../src/log/logger.js'
import { createBackoff } from '../src/transport/backoff.js'
import {
  STABLE_RUN_MS,
  superviseFrpc,
  type FrpcChild,
  type SpawnFrpc,
} from '../src/transport/frpSupervise.js'

const silentLogger = createLogger('error', () => {})

/**
 * A fake frpc child whose exit is driven from the test. `kill()` models a real process: it dies,
 * firing the exit handler (so the supervisor's `stop()` — which kills the live child — can unblock).
 * exit/kill fire the handler at most once.
 */
function makeChild(): { child: FrpcChild; exit: (code: number | null) => void; killed: boolean } {
  let onExit: ((code: number | null) => void) | null = null
  let alive = true
  const state = { killed: false }
  const fire = (code: number | null): void => {
    if (!alive) return
    alive = false
    onExit?.(code)
  }
  return {
    child: {
      onExit: (cb) => {
        onExit = cb
      },
      isAlive: () => alive,
      kill: () => {
        state.killed = true
        fire(null)
      },
    },
    exit: (code) => fire(code),
    get killed() {
      return state.killed
    },
  }
}

describe('superviseFrpc (B4/H4 — restart-on-exit backoff)', () => {
  it('spawns the frpc binary with -c <toml> via the child seam', async () => {
    const spawn: SpawnFrpc = vi.fn(() => makeChild().child)
    superviseFrpc('/opt/agent/bin/frpc', '/state/frpc.toml', {
      spawn,
      sleep: async () => {},
      logger: silentLogger,
    })
    await Promise.resolve()
    expect(spawn).toHaveBeenCalledWith('/opt/agent/bin/frpc', '/state/frpc.toml')
  })

  it('restarts the child on exit, backing off 1s → 2s → 4s', async () => {
    const children = [makeChild(), makeChild(), makeChild(), makeChild()]
    let n = 0
    const spawn: SpawnFrpc = () => children[n++]!.child
    const sleeps: number[] = []
    // now() fixed so no run counts as "stable" ⇒ backoff monotonically increases.
    const handle = superviseFrpc('/frpc', '/toml', {
      spawn,
      backoff: createBackoff(),
      sleep: async (ms) => {
        sleeps.push(ms)
      },
      logger: silentLogger,
      now: () => 1000,
    })

    // Crash three times; each crash schedules the next spawn after the growing backoff.
    for (let i = 0; i < 3; i += 1) {
      children[i]!.exit(1)
      await Promise.resolve()
      await Promise.resolve()
    }
    expect(sleeps).toEqual([1000, 2000, 4000])

    await handle.stop()
  })

  it('resets the backoff after a run that stayed up past the stability window', async () => {
    const children = [makeChild(), makeChild(), makeChild()]
    let n = 0
    const spawn: SpawnFrpc = () => children[n++]!.child
    const sleeps: number[] = []
    let clock = 0
    const handle = superviseFrpc('/frpc', '/toml', {
      spawn,
      backoff: createBackoff(),
      sleep: async (ms) => {
        sleeps.push(ms)
      },
      logger: silentLogger,
      now: () => clock,
    })

    // First run crashes instantly ⇒ backoff 1s.
    children[0]!.exit(1)
    await Promise.resolve()
    await Promise.resolve()
    // Second run stays up past STABLE_RUN_MS before dying ⇒ backoff resets to 1s (not 2s).
    clock += STABLE_RUN_MS + 1
    children[1]!.exit(1)
    await Promise.resolve()
    await Promise.resolve()

    expect(sleeps).toEqual([1000, 1000])
    await handle.stop()
  })

  it('stop() halts the loop and kills the live child; done resolves 0', async () => {
    const c = makeChild()
    const spawn: SpawnFrpc = () => c.child
    const handle = superviseFrpc('/frpc', '/toml', {
      spawn,
      sleep: async () => {},
      logger: silentLogger,
    })
    await Promise.resolve()
    expect(handle.isChildAlive()).toBe(true)

    // stop() kills the child; that fires the exit handler and the loop observes `stopped` → breaks.
    const stopping = handle.stop()
    c.exit(null)
    await expect(stopping).resolves.toBeUndefined()
    await expect(handle.done).resolves.toBe(0)
    expect(c.killed).toBe(true)
  })

  it('does not restart after stop (no spawn past shutdown)', async () => {
    const first = makeChild()
    let n = 0
    const spawn: SpawnFrpc = vi.fn(() => (n++ === 0 ? first.child : makeChild().child))
    const handle = superviseFrpc('/frpc', '/toml', {
      spawn,
      sleep: async () => {},
      logger: silentLogger,
    })
    await Promise.resolve()
    const stopping = handle.stop()
    first.exit(0)
    await stopping
    expect(spawn).toHaveBeenCalledTimes(1)
  })
})