brunchboy/overlay.html

## overlay.html
<html>
  <head>
    <title>OBS Overlay</title>
    <link rel="stylesheet" type="text/css" href="styles.css">
    <script>
      /** How often to check for changes when no player is playing. */
      const idleInterval = 500;

      /** Keeps track of the previous player state, so we can look for changes. */
      var lastState;

      /**
       * Check whether there is any player currently playing a track.
       *
       * @param state the player parameters object returned by params.json.
       * @return true if at least one player is playing something.
       */
      function isAnyPlayerPlaying(state) {
        return state && Object.values(state.players).find(player => player["is-playing"]) !== undefined;
      }

      /**
       * Calculate how long to wait before next performing an action, depending on player state.
       * If no player is active, return whichever is larger of idleInterval and activeInterval.
       * Otherwise return interval.
       *
       * @param activeInterval how many milliseconds to wait if at least one player is playing.
       * @return the number of milliseconds after which an activity should reschedule itself.
       */
      function nextInterval(activeInterval) {
        if (isAnyPlayerPlaying(lastState)) {
          return activeInterval;
        }
        return (idleInterval > activeInterval)? idleInterval : activeInterval;
      }

      /**
       * Reloads the master playuer artwork at the speciried interval. If no player is playing, then
       * idleInterval will be used instead, unless the specified interval is already longer.
       *
       * @param interval the number of milliseconds that should elapse between reloads.
       */
      function refreshArt(interval) {
        const element = document.getElementById('art');
        const refresher = function() {
          fetch('params.json')
            .then(response => {
              if (response.status == 200) {
                response.json()
                  .then(state => {
                    if (state.master && state.master.number) {
                      element.src = '/artwork/' + state.master.number + '?icons=true';
                    }
                    setTimeout(refresher, nextInterval(interval));
                  })
              } else {
                console.error('Problem updating OBS overlay parameters', response);
                setTimeout(refresher, 5000);
              }
            })
            .catch(error => {
              // TODO: Show something on the page itself.
              console.error('Problem communicating with OBS overlay server', error);
              setTimeout(refresher, 30000);
            });
        }
        setTimeout(refresher, nextInterval(interval));
      }

      /**
       * Given an old and new value for a text element on the page,
       * if they differ, updates the corresponding DOM element to contain
       * the new text.
       *
       * @param id the DOM id of the element to be updated.
       * @param current what the new value for this element should be.
       * @param last the previous value of the element.
       */
      function updateIfChanged(id, current, last) {
        if (current !== last) {
          document.getElementById(id).textContent = current;
        }
      }

      /**
       * Compares the most recently received server state with the previous one, and updates
       * any page text elements whose values need to be be changed.
       *
       * @param state the new server state object.
       */
      function applyChanges(state) {
        const lastPlayer = lastState && lastState.master
        const track = state.master.track;
        const lastTrack = lastPlayer && lastPlayer.track;
          updateIfChanged('artist', track && track.artist, lastTrack && lastTrack.artist);
          updateIfChanged('title', track && track.title, lastTrack && lastTrack.title);
      }

      /**
       * Periodically determines the current player state, and updates the page appropriately.
       *
       * @param interval how often the should be updated, in milliseconds, when a player is active.
       */
      function updateState(interval) {
        const updater = function() {
          fetch('params.json')
            .then(response => {
              if (response.status == 200) {
                response.json()
                  .then(state => {
                    applyChanges(state);
                    lastState = state;
                    setTimeout(updater, nextInterval(interval));
                  })
              } else {
                console.error('Problem updating OBS overlay parameters', response);
                setTimeout(updater, 5000);
              }})
            .catch(error => {
              // TODO: Show something on the page itself.
              console.error('Problem communicating with OBS overlay server', error);
              setTimeout(updater, 30000);
            });
        }
        updater();
      }

      updateState(66);

    </script>
  </head>
  <body>
    <p>
      <img id="art" src="artwork/{{master.number}}?icons=true" width="80" height="80" align="left">
      <script>refreshArt(1000);</script>
      <span id="title" style="font-size:30px" style="font-family:Titillium Web">{{master.track.title}}</span>
      <br>
      <span id="artist" style="font-size:20px" style="font-family:Titillium Web">{{master.track.artist}}.</span>
      </p>
  </body>
</html>
	<html>
	<head>
	<title>OBS Overlay</title>
	<link rel="stylesheet" type="text/css" href="styles.css">
	<script>
	/** How often to check for changes when no player is playing. */
	const idleInterval = 500;

	/** Keeps track of the previous player state, so we can look for changes. */
	var lastState;

	/**
	* Check whether there is any player currently playing a track.
	*
	* @param state the player parameters object returned by params.json.
	* @return true if at least one player is playing something.
	*/
	function isAnyPlayerPlaying(state) {
	return state && Object.values(state.players).find(player => player["is-playing"]) !== undefined;
	}

	/**
	* Calculate how long to wait before next performing an action, depending on player state.
	* If no player is active, return whichever is larger of idleInterval and activeInterval.
	* Otherwise return interval.
	*
	* @param activeInterval how many milliseconds to wait if at least one player is playing.
	* @return the number of milliseconds after which an activity should reschedule itself.
	*/
	function nextInterval(activeInterval) {
	if (isAnyPlayerPlaying(lastState)) {
	return activeInterval;
	}
	return (idleInterval > activeInterval)? idleInterval : activeInterval;
	}

	/**
	* Reloads the master playuer artwork at the speciried interval. If no player is playing, then
	* idleInterval will be used instead, unless the specified interval is already longer.
	*
	* @param interval the number of milliseconds that should elapse between reloads.
	*/
	function refreshArt(interval) {
	const element = document.getElementById('art');
	const refresher = function() {
	fetch('params.json')
	.then(response => {
	if (response.status == 200) {
	response.json()
	.then(state => {
	if (state.master && state.master.number) {
	element.src = '/artwork/' + state.master.number + '?icons=true';
	}
	setTimeout(refresher, nextInterval(interval));
	})
	} else {
	console.error('Problem updating OBS overlay parameters', response);
	setTimeout(refresher, 5000);
	}
	})
	.catch(error => {
	// TODO: Show something on the page itself.
	console.error('Problem communicating with OBS overlay server', error);
	setTimeout(refresher, 30000);
	});
	}
	setTimeout(refresher, nextInterval(interval));
	}

	/**
	* Given an old and new value for a text element on the page,
	* if they differ, updates the corresponding DOM element to contain
	* the new text.
	*
	* @param id the DOM id of the element to be updated.
	* @param current what the new value for this element should be.
	* @param last the previous value of the element.
	*/
	function updateIfChanged(id, current, last) {
	if (current !== last) {
	document.getElementById(id).textContent = current;
	}
	}

	/**
	* Compares the most recently received server state with the previous one, and updates
	* any page text elements whose values need to be be changed.
	*
	* @param state the new server state object.
	*/
	function applyChanges(state) {
	const lastPlayer = lastState && lastState.master
	const track = state.master.track;
	const lastTrack = lastPlayer && lastPlayer.track;
	updateIfChanged('artist', track && track.artist, lastTrack && lastTrack.artist);
	updateIfChanged('title', track && track.title, lastTrack && lastTrack.title);
	}

	/**
	* Periodically determines the current player state, and updates the page appropriately.
	*
	* @param interval how often the should be updated, in milliseconds, when a player is active.
	*/
	function updateState(interval) {
	const updater = function() {
	fetch('params.json')
	.then(response => {
	if (response.status == 200) {
	response.json()
	.then(state => {
	applyChanges(state);
	lastState = state;
	setTimeout(updater, nextInterval(interval));
	})
	} else {
	console.error('Problem updating OBS overlay parameters', response);
	setTimeout(updater, 5000);
	}})
	.catch(error => {
	// TODO: Show something on the page itself.
	console.error('Problem communicating with OBS overlay server', error);
	setTimeout(updater, 30000);
	});
	}
	updater();
	}

	updateState(66);

	</script>
	</head>
	<body>
	<p>
	<img id="art" src="artwork/{{master.number}}?icons=true" width="80" height="80" align="left">
	<script>refreshArt(1000);</script>
	<span id="title" style="font-size:30px" style="font-family:Titillium Web">{{master.track.title}}</span>
	<br>
	<span id="artist" style="font-size:20px" style="font-family:Titillium Web">{{master.track.artist}}.</span>
	</p>
	</body>
	</html>
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