/**
Copyright 2016-2018 Timo Tijhof

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
/**
 * The below code and its rendering in a browser is also
 * available under the terms of the CC BY 4.0 License.
 *
 * Attribution: Timo Tijhof
 * License text at https://creativecommons.org/licenses/by/4.0/
 */

function init() {
  var eventsource;
  var msgsNode = document.getElementById("rc-messages");
  var boxesNode = document.getElementById("rc-boxes");
  var errorNode = DOM.element("div", {
    className: "alert alert-danger"
  });
  var infoNode = DOM.element("div", {
    className: "alert alert-info"
  });
  var boxes = Object.create(null);
  var boxList = [];
  var timerSecNode = document.querySelector(".rc-timer--sec").nextSibling;
  var timerMinNode = document.querySelector(".rc-timer--min").nextSibling;
  var timerHrNode = document.querySelector(".rc-timer--hr").nextSibling;
  var infoTimeout, errorTimeout;

  function printMessage(event) {
    if (event.type === "error") {
      errorNode.textContent = "ERROR: " + JSON.stringify(event.data);
      if (!errorNode.parentNode) {
        msgsNode.append(errorNode);
      }
      // Cancel any plan to hide the error node
      clearTimeout(errorTimeout);
    }
    if (event.type === "info") {
      infoNode.textContent = event.message;
      if (!infoNode.parentNode) {
        msgsNode.append(infoNode);
      }
      hideInfoNode();
    }
  }

  function hideErrorNode() {
    if (!errorTimeout) {
      errorTimeout = setTimeout(function() {
        errorNode.remove();
        errorTimeout = null;
      });
    }
  }

  function hideInfoNode() {
    // Cancel any previous timeout for hiding the info node,
    // and start a new timeout instead.
    clearTimeout(infoTimeout);
    infoTimeout = setTimeout(function() {
      infoNode.remove();
      infoTimeout = null;
    }, 3000);
  }

  function pad(num) {
    return num < 10 ? "0" + num : String(num);
  }

  /**
   * Compare function for Array#sort.
   *
   * @param {Box} a
   * @param {Box} b
   * @return {number}
   */
  function boxesCompare(a, b) {
    // Sort in descending order by highest total
    return b.freq.total - a.freq.total;
  }

  /**
   * Sort the box nodes on the page.
   *
   * This is called from main().
   */
  function resortBoxes() {
    var before, after;
    before = boxList
      .map(function(box) {
        return box.group;
      })
      .join(" ");
    // Sort the list
    boxList.sort(boxesCompare);
    after = boxList
      .map(function(box) {
        return box.group;
      })
      .join(" ");
    if (before === after) {
      // Avoid expensive reflow
      return;
    }
    fastdom.mutate(function() {
      // Create a fragment containing the boxes in order,
      // this implicitly temporarily removes them from the page.
      var frag = document.createDocumentFragment();
      var i;
      for (i = 0; i < boxList.length; i++) {
        frag.append(boxList[i].node);
      }
      // Add the boxes back to the page, in sorted order
      boxesNode.append(frag);
    });
  }

  /**
   * This is called from main().
   */
  function updateTimerTooltip() {
    var timer, elSec, elMin, elHr;
    elSec = Math.floor((DOM.now() - Frequency.start) / 1000);
    elHr = Math.floor(elSec / 3600);
    elSec -= elHr * 3600;
    elMin = Math.floor(elSec / 60);
    elSec -= elMin * 60;
    fastdom.mutate(function() {
      timerSecNode.dataset.value = pad(elSec);
      timerMinNode.dataset.value = pad(elMin);
      timerHrNode.dataset.value = pad(elHr);
    });
  }

  function Box(group) {
    // Start column
    var col = document.createElement("div");
    col.className = "col-md-4";

    // Start .card
    var card = document.createElement("div");
    card.className = "card rc-box";

    // Start .card > .card-body
    var body = document.createElement("div");
    body.className = "card-body";

    // Start .card > .card-body > .card-title
    var title = document.createElement("h5");
    title.className = "card-title rc-box-title";
    title.textContent = group;
    // End .card > .card-body > .card-title
    body.append(title);

    // Start .card > .card-body > .card-text
    var text = document.createElement("p");
    text.className = "card-text";
    text.textContent = "Total: ";

    var totalStat = document.createTextNode("0");
    text.append(totalStat);

    // End .card > .card-body > .card-text
    body.append(text);

    // End .card > .card-body
    card.append(body);
    // End .card
    col.append(card);

    // End column - add column to the page
    fastdom.mutate(function() {
      boxesNode.append(col);
    });

    // Keep reference to the outer-most node and group name
    // for sorting purposes. @see #resortBoxes
    this.node = col;
    this.group = group;

    this.statTextNodes = {
      Total: { count: totalStat, avg: null },
      "Past second": this.addStatNodes(text, "Past second"),
      "Past minute": this.addStatNodes(text, "Past minute"),
      "Past hour": this.addStatNodes(text, "Past hour")
    };
    this.freq = new Frequency(
      {
        "Past second": 1000,
        "Past minute": 60 * 1000,
        "Past hour": 3600 * 1000
      },
      this.set.bind(this)
    );
  }
  /**
   * @private
   */
  Box.prototype.addStatNodes = function(parent, span) {
    var nodes = {
      count: document.createTextNode(".."),
      avg: document.createTextNode("..")
    };

    var statline = document.createElement("div");
    statline.className = "text-muted rc-box-statline";
    statline.append(document.createTextNode(span + ": "));
    statline.append(nodes.count);
    statline.append(document.createTextNode(" (avg: "));
    statline.append(nodes.avg);
    statline.append(document.createTextNode(")"));

    parent.append(statline);

    return nodes;
  };

  /**
   * NOTE: Writes to DOM. Call only in fastdom.mutate().
   *
   * This method is invoked as callback from Frequency#check.
   *
   * @param {string} span Label for time span
   * @param {number|null} count Current count in this time span
   * @param {number|null} avg Running average for this time span
   */
  Box.prototype.set = function(span, count, avg) {
    var textNodes = this.statTextNodes[span];
    if (!textNodes) {
      // Unknown span
      return;
    }
    if (count !== null) {
      // The count is only updated when a time span has been
      // completed. In intermediate updates, only the average
      // is updated.
      textNodes.count.nodeValue = count.toLocaleString();
    }
    if (avg !== null) {
      // Total doesn't need an average
      textNodes.avg.nodeValue = Math.round(avg).toLocaleString();
    }
  };

  /**
   * @param {Object<string, number>} spans Label for a millisecond count (e.g. "last hour": 3600*1000)
   * @param {Function} callback Publish statistics
   * @param {string} callback.span Label
   * @param {number|null} callback.count Current count
   * @param {number|null} callback.avg Running average
   */
  function Frequency(spans, callback) {
    if (!Frequency.start) {
      Frequency.start = DOM.now();
    }

    this.total = 0;
    this.start = Frequency.start;

    this.callback = callback;

    this.intervals = {};
    var label;
    for (label in spans) {
      this.intervals[label] = {
        span: spans[label],
        count: 0,
        since: Frequency.start
      };
    }

    Frequency.register(this);
  }
  /**
   * Shared starting point for all Frequency objects.
   * Our event stream creates Box and Frequency objects
   * on-demand for each wiki it encounters. By giving all
   * Frequency objects the same starting point it solves two
   * problems:
   *
   * - Naturally, the average gets more accurate as time goes on.
   *   However, because Frequency objects are created on-demand,
   *   there would be a bias if they have their own start time.
   *   For example, if after a wiki only has its first event
   *   after listening for 10 minutes, it should reflect right-away
   *   that it received 1 message in a total of 10 minutes, not
   *   1 message in a total of the last second when the Frequency
   *   object was created.
   * - By giving all objects the same 'start' point, the render
   *   of per-second and per-minute values is nicely in sync
   *   for all boxes on the page.
   */
  Frequency.start = null;

  Frequency.registry = [];
  Frequency.register = function(freq) {
    Frequency.registry.push(freq);
  };
  Frequency.checker = function() {
    for (var key in Frequency.registry) {
      Frequency.registry[key].check();
    }
  };
  Frequency.ensureChecker = (function() {
    var pending = false;
    function callback() {
      pending = false;
      Frequency.checker();
    }
    return function ensureChecker() {
      if (!pending) {
        pending = true;
        fastdom.mutate(callback);
      }
    };
  })();
  /**
   * @param {number} increment
   */
  Frequency.prototype.add = function(increment) {
    var key;
    this.total += increment;
    for (key in this.intervals) {
      this.intervals[key].count += increment;
    }
    Frequency.ensureChecker();
  };

  /**
   * NOTE: Writes to DOM. Call only from fastdom.mutate().
   *
   * This method is called from Frequency.ensureChecker().
   */
  Frequency.prototype.check = function() {
    var now, key, interval, ellapsed, count, avg, ellapsedTotal;
    now = DOM.now();
    ellapsedTotal = now - this.start;
    for (key in this.intervals) {
      interval = this.intervals[key];
      avg = this.total * (interval.span / ellapsedTotal);
      ellapsed = now - interval.since;
      if (ellapsed >= interval.span) {
        count = interval.count;
        // Reset
        interval.count = 0;
        interval.since = now;
        // Publish count and average
        this.callback(key, count, avg);
      } else {
        // Publish average only
        this.callback(key, null, avg);
      }
    }
    // Publish total
    this.callback("Total", this.total, null);
  };

  function main() {
    // Set Frequency origin timestamp and start timer animations
    Frequency.start = DOM.now();
    fastdom.mutate(function() {
      document.documentElement.className = "rc-timers--start";
    });

    // The EventSource#onmessage handler will ensure a checker round
    // in the next paint frame (via fastdom) whenever a message is received.
    // Here, we also start an idle loop that ensures averages are updated
    // and boxes are sorted, even when no messages are received for a while.
    DOM.rIC(function idleUpdater() {
      Frequency.ensureChecker();
      resortBoxes();
      setTimeout(function() {
        DOM.rIC(idleUpdater);
      }, 3000);
    });
    DOM.rIC(function idleClockWriter() {
      updateTimerTooltip();
      setTimeout(function() {
        DOM.rIC(idleClockWriter);
      }, 100);
    });

    // Start RecentChange stream
    printMessage({ type: "info", message: "Connecting..." });

    eventsource = new EventSource(
      "https://stream.wikimedia.org/v2/stream/recentchange"
    );
    eventsource.onopen = function() {
      printMessage({ type: "info", message: "Connected!" });
    };
    eventsource.onerror = function(msg) {
      printMessage({ type: "error", data: msg });
    };
    eventsource.onmessage = function(msg) {
      if (!boxes.global) {
        // If the global box doesn't exist yet, this must be
        // the first message. Create the global box.
        boxes.global = new Box("All wikis");
      }

      // Increment box for "All wikis"
      boxes.global.freq.add(1);

      try {
        // Parse message to determine which wiki it is from
        var wiki = JSON.parse(msg.data).server_name;
        var box = boxes[wiki];
        if (!box) {
          // If we haven't seen a message from this wiki before,
          // create a box for it.
          box = boxes[wiki] = new Box(wiki);
          boxList.push(box);
        }
        // Increment box for this wiki
        box.freq.add(1);
      } catch (e) {
        // Ignore JSON parse error
      }

      // If there was an error in the past, remove it, because
      // if we're receiving a message now, the error must have
      // resolved itself.
      if (errorNode.parentNode) {
        hideErrorNode();
      }
    };
  }

  main();
}

/**
 * @var DOM
 */
var DOM = {
  /**
   * @param {string} tagName
   * @param {Object} [props]
   * @return {Element}
   */
  element: function element(tagName, props) {
    var key;
    var node = document.createElement(tagName);
    if (props) {
      for (key in props) {
        node[key] = props[key];
      }
    }
    return node;
  },

  rIC: window.requestIdleCallback
    ? window.requestIdleCallback.bind(window)
    : setTimeout,

  /**
   * @return {number} Timestamp in milliseconds
   */
  now: (function() {
    var perf = window.performance;
    return perf.now
      ? function now() {
          // Use the new HR Time API where available
          return perf.now();
        }
      : Date.now;
  })()
};

// Polyfills
(function() {
  // For https://developer.mozilla.org/en-US/docs/Web/API/ChildNode/remove
  // From: https://github.com/jserz/js_piece/blob/master/DOM/ChildNode/remove()/remove().md
  if (!Element.prototype.hasOwnProperty("remove")) {
    Object.defineProperty(Element.prototype, "remove", {
      configurable: true,
      enumerable: true,
      writable: true,
      value: function remove() {
        if (this.parentNode) this.parentNode.removeChild(this);
      }
    });
  }

  // For https://developer.mozilla.org/en-US/docs/Web/API/ParentNode/append
  // Source: https://github.com/jserz/js_piece/blob/master/DOM/ParentNode/append()/append().md
  [
    Element.prototype,
    Document.prototype,
    DocumentFragment.prototype
  ].forEach(function(proto) {
    if (proto.hasOwnProperty("append")) {
      return;
    }
    Object.defineProperty(proto, "append", {
      configurable: true,
      enumerable: true,
      writable: true,
      value: function append() {
        var argArr = Array.prototype.slice.call(arguments),
          docFrag = document.createDocumentFragment();

        argArr.forEach(function(argItem) {
          var isNode = argItem instanceof Node;
          docFrag.appendChild(
            isNode ? argItem : document.createTextNode(String(argItem))
          );
        });

        this.appendChild(docFrag);
      }
    });
  });
})();

init();