background.js

let mode

// hook request headers
chrome.webRequest.onBeforeSendHeaders.addListener(function (details) {
  const header = {
    name: 'X-Real-IP',
    value: '118.88.88.88'
  }
  if (mode > 0) details.requestHeaders.push(header)
  return { requestHeaders: details.requestHeaders }
}, { urls: ['*://music.163.com/*'] }, ['blocking', 'requestHeaders'])

// redirect cdn access
chrome.webRequest.onBeforeRequest.addListener(function (details) {
  const redirectUrl = details.url.replace(
    /(m\d+?)(?!c)\.music\.126\.net/, '$1c.music.126.net'
  )
  if (redirectUrl != details.url && mode > 1) return { redirectUrl: redirectUrl }
}, { urls: ['*://*.music.126.net/*'] }, ['blocking'])

// mode switch
chrome.browserAction.onClicked.addListener(function (tab) {
  mode = (mode + 1) % 3
  setMode()
})

// initialize
chrome.storage.local.get('mode', function (data) {
  mode = (typeof(data.mode) === "undefined") ? 2 : data.mode
  setMode()
})

// sync ui & storage
function setMode(){
  chrome.storage.local.set({ mode: mode })
  const titles = ['closed','normal','enhanced']
  const icons = ['images/grey.svg','images/red.svg','images/blue.svg']
  chrome.browserAction.setIcon({ path: icons[mode] })
  chrome.browserAction.setTitle({ title: chrome.i18n.getMessage("name") + ' ' + '[' + chrome.i18n.getMessage(titles[mode]) + ']' })
}