import {DEBUG as debug} from '../src/common.js';

const DEBUG = debug || false;

export function getInjection({sessionId}) {
  // Notes:
    // say() function
      // why aliased? Resistant to page overwriting
      // just a precaution as we are already in an isolated world here, but this makes
      // this script more portable if it were introduced globally as well as robust 
      // against API or behaviour changes of the browser or its remote debugging protocol
      // in future
  return `
    {
      const X = 1;
      const DEBUG = ${JSON.stringify(DEBUG, null, 2)};
      const MIN_CHECK_TEXT = 3000;  // min time between checking documentElement.innerText
      const MIN_NOTIFY = 5000;      // min time between telling controller text maybe changed
      const MAX_NOTIFICATIONS = 13; // max times we will tell controller text maybe changed
      const OBSERVER_OPTS = {
        subtree: true,
        childList: true,
        characterData: true
      };
      const Top = globalThis.top;
      let lastInnerText;

      if ( Top === globalThis ) {
        const ConsoleInfo = console.info.bind(console);
        const JSONStringify = JSON.stringify.bind(JSON);
        const TITLE_CHANGES = 10;
        const INITIAL_CHECK_TIME = 500;
        const TIME_MULTIPLIER = Math.E;
        const sessionId = "${sessionId}";
        const sleep = ms => new Promise(res => setTimeout(res, ms));
        const handler = throttle(handleFrameMessage, MIN_NOTIFY);
        let count = 0;

        installTop();

        async function installTop() {
          console.log("Installing in top frame...");
          self.startUrl = location.href;
          say({install: { sessionId, startUrl }});
          await sleep(500);
          beginTitleChecks();
          beginTextNotifications();
          console.log("Installed.");
        }

        function beginTitleChecks() {
          let lastTitle = null;
          let checker;
          let timeToNextCheck = INITIAL_CHECK_TIME;
          let changesLogged = 0;

          check();
          console.log('Begun logging title changes.');

          function check() {
            clearTimeout(checker);
            const currentTitle = document.title; 
            if ( lastTitle !== currentTitle ) {
              say({titleChange: {lastTitle, currentTitle, url: location.href, sessionId}});
              lastTitle = currentTitle;
              changesLogged++;
            } else {
              // increase check time if there's no change
              timeToNextCheck *= TIME_MULTIPLIER;
            }
            if ( changesLogged < TITLE_CHANGES ) {
              checker = setTimeout(check, timeToNextCheck);
            } else {
              console.log('Finished logging title changes.'); 
            }
          }
        }

        function say(thing) {
          ConsoleInfo(JSONStringify(thing));
        }

        function beginTextNotifications() {
          // listen for {textChange:true} messages
          // throttle them
          // on leading throttle edge send message to controller with 
          // console.info(JSON.stringify({textChange:...}));
          self.addEventListener('message', messageParser);

          console.log('Begun notifying of text changes.');

          function messageParser({data, origin}) {
            let source;
            try {
              ({source} = data.frameTextChangeNotification);
              if ( count > MAX_NOTIFICATIONS ) {
                self.removeEventListener('message', messageParser);
                return;
              }
              count++;
              handler({textChange:{source}});
            } catch(e) {
              DEBUG.verboseSlow && console.warn('could not parse message', data, e);
            }
          }
        }

        function handleFrameMessage({textChange}) {
          const {source} = textChange;
          console.log('Telling controller that text changed');
          say({textChange:{source, sessionId, count}});
        }
      } 

      beginTextMutationChecks();

      function beginTextMutationChecks() {
        // create mutation observer for text
        // throttle output

        const observer = new MutationObserver(throttle(check, MIN_CHECK_TEXT));
        observer.observe(document.documentElement || document, OBSERVER_OPTS);

        console.log('Begun observing text changes.');
        
        function check() {
          console.log('check');
          const textMutated = document.documentElement.innerText !== lastInnerText;
          if ( textMutated ) {
            DEBUG.verboseSlow && console.log('Text changed');
            lastInnerText = document.documentElement.innerText;
            Top.postMessage({frameTextChangeNotification:{source:location.href}}, '*');
          }
        }
      }

      // javascript throttle function
        // source: https://stackoverflow.com/a/59378445 
        /*
        function throttle(func, timeFrame) {
          var lastTime = 0;
          return function (...args) {
            var now = new Date();
            if (now - lastTime >= timeFrame) {
              func.apply(this, args);
              lastTime = now;
            }
          };
        }
        */

      // alternate throttle function with trailing edge call
        // source: https://stackoverflow.com/a/27078401
        ///*
        // Notes
          // Returns a function, that, when invoked, will only be triggered at most once
          // during a given window of time. Normally, the throttled function will run
          // as much as it can, without ever going more than once per \`wait\` duration;
          // but if you'd like to disable the execution on the leading edge, pass
          // \`{leading: false}\`. To disable execution on the trailing edge, ditto.
				function throttle(func, wait, options) {
					var context, args, result;
					var timeout = null;
					var previous = 0;
					if (!options) options = {};
					var later = function() {
						previous = options.leading === false ? 0 : Date.now();
						timeout = null;
						result = func.apply(context, args);
						if (!timeout) context = args = null;
					};
					return function() {
						var now = Date.now();
						if (!previous && options.leading === false) previous = now;
						var remaining = wait - (now - previous);
						context = this;
						args = arguments;
						if (remaining <= 0 || remaining > wait) {
							if (timeout) {
								clearTimeout(timeout);
								timeout = null;
							}
							previous = now;
							result = func.apply(context, args);
							if (!timeout) context = args = null;
						} else if (!timeout && options.trailing !== false) {
							timeout = setTimeout(later, remaining);
						}
						return result;
					};
				}
        //*/
    }
  `;
}