/**
 * 系统深色模式监听 — 提供初始值与变更回调
 * 旧设备 wx.onThemeChange 失败时退化为只读一次
 */

const STORAGE_KEY = 'dark_mode_pref'

function _readSystemTheme() {
  try {
    const info = wx.getSystemInfoSync()
    return info.theme === 'dark' ? true : false
  } catch (e) {
    return false
  }
}

function getInitialDarkMode() {
  const pref = wx.getStorageSync(STORAGE_KEY) || 'system'
  if (pref === 'system') return _readSystemTheme()
  return pref === 'dark'
}

function getPref() {
  return wx.getStorageSync(STORAGE_KEY) || 'system'
}

function setPref(value) {
  if (!['system', 'light', 'dark'].includes(value)) return
  wx.setStorageSync(STORAGE_KEY, value)
}

function watchDarkMode(onChange) {
  if (typeof wx.onThemeChange !== 'function') return
  try {
    wx.onThemeChange(({ theme }) => {
      const pref = getPref()
      if (pref === 'system') onChange(theme === 'dark')
    })
  } catch (e) {
    // 旧设备不支持,忽略
  }
}

module.exports = {
  getInitialDarkMode,
  getPref,
  setPref,
  watchDarkMode
}