background.js

const shadeBlendConvert = function (p, from, to) {
  if(typeof(p)!="number"||p<-1||p>1||typeof(from)!="string"||(from[0]!='r'&&from[0]!='#')||(to&&typeof(to)!="string"))return null; //ErrorCheck
  if(!this.sbcRip)this.sbcRip=(d)=>{
      let l=d.length,RGB={};
      if(l>9){
          d=d.split(",");
          if(d.length<3||d.length>4)return null;//ErrorCheck
          RGB[0]=i(d[0].split("(")[1]),RGB[1]=i(d[1]),RGB[2]=i(d[2]),RGB[3]=d[3]?parseFloat(d[3]):-1;
      }else{
          if(l==8||l==6||l<4)return null; //ErrorCheck
          if(l<6)d="#"+d[1]+d[1]+d[2]+d[2]+d[3]+d[3]+(l>4?d[4]+""+d[4]:""); //3 or 4 digit
          d=i(d.slice(1),16),RGB[0]=d>>16&255,RGB[1]=d>>8&255,RGB[2]=d&255,RGB[3]=-1;
          if(l==9||l==5)RGB[3]=r((RGB[2]/255)*10000)/10000,RGB[2]=RGB[1],RGB[1]=RGB[0],RGB[0]=d>>24&255;
      }
  return RGB;}
  var i=parseInt,r=Math.round,h=from.length>9,h=typeof(to)=="string"?to.length>9?true:to=="c"?!h:false:h,b=p<0,p=b?p*-1:p,to=to&&to!="c"?to:b?"#000000":"#FFFFFF",f=this.sbcRip(from),t=this.sbcRip(to);
  if(!f||!t)return null; //ErrorCheck
  if(h)return "rgb"+(f[3]>-1||t[3]>-1?"a(":"(")+r((t[0]-f[0])*p+f[0])+","+r((t[1]-f[1])*p+f[1])+","+r((t[2]-f[2])*p+f[2])+(f[3]<0&&t[3]<0?")":","+(f[3]>-1&&t[3]>-1?r(((t[3]-f[3])*p+f[3])*10000)/10000:t[3]<0?f[3]:t[3])+")");
  else return "#"+(0x100000000+r((t[0]-f[0])*p+f[0])*0x1000000+r((t[1]-f[1])*p+f[1])*0x10000+r((t[2]-f[2])*p+f[2])*0x100+(f[3]>-1&&t[3]>-1?r(((t[3]-f[3])*p+f[3])*255):t[3]>-1?r(t[3]*255):f[3]>-1?r(f[3]*255):255)).toString(16).slice(1,f[3]>-1||t[3]>-1?undefined:-2);
}

let theme = null;

class containersTheme {
  constructor() {
    browser.tabs.onActivated.addListener((activeInfo) => {
      this.updateTabContainerTheme(activeInfo.tabId, activeInfo.windowId);
    });
  }

  isUnpaintedTheme(currentCookieStore) {
    return (currentCookieStore == "firefox-default" ||
            currentCookieStore == "firefox-private");
  }

  async updateTabContainerTheme(tabId, windowId) {

    if (theme == null) {
      theme = await browser.theme.getCurrent();
    } else {
      var newTheme = await browser.theme.getCurrent();

      if (newTheme.colors.frame != theme.colors.frame){
        theme = JSON.parse(JSON.stringify(newTheme));
      }
    }

    if (theme.colors == null) { return; }

    let extensionSettings = await browser.storage.sync.get();
    var tab = await browser.tabs.get(tabId);

    if (!this.isUnpaintedTheme(tab.cookieStoreId)) {
      var themeInfo = JSON.parse(JSON.stringify(theme));

      var container = await browser.contextualIdentities.get(tab.cookieStoreId);

      var toolbarColor = shadeBlendConvert(-0.6, container.colorCode);

      themeInfo.colors.toolbar = toolbarColor;
      themeInfo.colors.tab_line = toolbarColor;
      if(extensionSettings.urlBox) {
        themeInfo.colors.toolbar_field = toolbarColor;
      }

      browser.theme.update(windowId, themeInfo);

    } else {
      browser.theme.update(windowId, theme);
    }

  }
}

new containersTheme();