import { afterEach, describe, expect, it, vi } from 'vitest'
import {
  createBackgroundPreloadScheduler,
  getBackgroundPreloadPolicy
} from '@/services/performance/backgroundPreloadScheduler'

describe('backgroundPreloadScheduler', () => {
  afterEach(() => {
    vi.useRealTimers()
  })

  it('waits for an idle window after the defer delay', () => {
    vi.useFakeTimers()
    let idleCallback: (() => void) | null = null
    const task = vi.fn()
    const scheduler = createBackgroundPreloadScheduler({
      setTimeout,
      clearTimeout,
      requestIdleCallback: (callback) => {
        idleCallback = () => callback({ didTimeout: false })
        return 1
      },
      cancelIdleCallback: vi.fn()
    })

    expect(scheduler.schedule(task, { delayMs: 500 })).toBe(true)
    vi.advanceTimersByTime(499)
    expect(task).not.toHaveBeenCalled()

    vi.advanceTimersByTime(1)
    expect(task).not.toHaveBeenCalled()
    idleCallback?.()
    expect(task).toHaveBeenCalledTimes(1)
  })

  it('cancels work that has not entered the idle window', () => {
    vi.useFakeTimers()
    const task = vi.fn()
    const scheduler = createBackgroundPreloadScheduler({
      setTimeout,
      clearTimeout,
      requestIdleCallback: vi.fn(() => 1),
      cancelIdleCallback: vi.fn()
    })

    scheduler.schedule(task, { delayMs: 500 })
    scheduler.cancel()
    vi.advanceTimersByTime(1000)

    expect(task).not.toHaveBeenCalled()
  })

  it('skips background work for data-saving and slow-network connections', () => {
    expect(getBackgroundPreloadPolicy({ saveData: true })).toEqual({
      allowed: false,
      reason: 'save-data',
      delayMs: 0
    })
    expect(getBackgroundPreloadPolicy({ effectiveType: '2g' })).toEqual({
      allowed: false,
      reason: 'slow-network',
      delayMs: 0
    })
    expect(getBackgroundPreloadPolicy({ effectiveType: 'slow-2g' })).toEqual({
      allowed: false,
      reason: 'slow-network',
      delayMs: 0
    })
    expect(getBackgroundPreloadPolicy({ effectiveType: '4g', downlink: 1.49, rtt: 80 })).toEqual({
      allowed: false,
      reason: 'slow-network',
      delayMs: 0
    })
    expect(getBackgroundPreloadPolicy({ effectiveType: '4g', downlink: 8, rtt: 500 })).toEqual({
      allowed: false,
      reason: 'slow-network',
      delayMs: 0
    })
    expect(getBackgroundPreloadPolicy({ effectiveType: '3g', downlink: 1.2, rtt: 120 })).toEqual({
      allowed: false,
      reason: 'slow-network',
      delayMs: 0
    })
    expect(getBackgroundPreloadPolicy({ effectiveType: '3g' })).toEqual({
      allowed: true,
      reason: 'normal',
      delayMs: 2400
    })
    expect(getBackgroundPreloadPolicy({ effectiveType: '4g', downlink: 1.5, rtt: 499 })).toEqual({
      allowed: true,
      reason: 'normal',
      delayMs: 900
    })
  })
})