/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

const ContentPanning = {
  init: function cp_init() {
    ['mousedown', 'mouseup', 'mousemove'].forEach(function(type) {
      addEventListener(type, ContentPanning, true);
    });

    addMessageListener("Viewport:Change", this._recvViewportChange.bind(this));
  },

  handleEvent: function cp_handleEvent(evt) {
    switch (evt.type) {
      case 'mousedown':
        this.onTouchStart(evt);
        break;
      case 'mousemove':
        this.onTouchMove(evt);
        break;
      case 'mouseup':
        this.onTouchEnd(evt);
        break;
      case 'click':
        evt.stopPropagation();
        evt.preventDefault();
        
        let target = evt.target;
        let view = target.ownerDocument ? target.ownerDocument.defaultView
                                        : target;
        view.removeEventListener('click', this, true, true);
        break;
    }
  },

  position: new Point(0 , 0),

  onTouchStart: function cp_onTouchStart(evt) {
    this.dragging = true;
    this.panning = false;

    let oldTarget = this.target;
    [this.target, this.scrollCallback] = this.getPannable(evt.target);

    // If there is a pan animation running (from a previous pan gesture) and
    // the user touch back the screen, stop this animation immediatly and
    // prevent the possible click action if the touch happens on the same
    // target.
    this.preventNextClick = false;
    if (KineticPanning.active) {
      KineticPanning.stop();

      if (oldTarget && oldTarget == this.target)
        this.preventNextClick = true;
    }


    this.position.set(evt.screenX, evt.screenY);
    KineticPanning.record(new Point(0, 0), evt.timeStamp);
  },

  onTouchEnd: function cp_onTouchEnd(evt) {
    if (!this.dragging)
      return;
    this.dragging = false;

    this.onTouchMove(evt);

    let click = evt.detail;
    if (this.target && click && (this.panning || this.preventNextClick)) {
      let target = this.target;
      let view = target.ownerDocument ? target.ownerDocument.defaultView
                                      : target;
      view.addEventListener('click', this, true, true);
    }

    if (this.panning)
      KineticPanning.start(this);
  },

  onTouchMove: function cp_onTouchMove(evt) {
    if (!this.dragging || !this.scrollCallback)
      return;

    let current = this.position;
    let delta = new Point(evt.screenX - current.x, evt.screenY - current.y);
    current.set(evt.screenX, evt.screenY);

    KineticPanning.record(delta, evt.timeStamp);
    this.scrollCallback(delta.scale(-1));

    // If a pan action happens, cancel the active state of the
    // current target.
    if (!this.panning && KineticPanning.isPan()) {
      this.panning = true;
      this._resetActive();
    }
  },


  onKineticBegin: function cp_onKineticBegin(evt) {
  },

  onKineticPan: function cp_onKineticPan(delta) {
    return !this.scrollCallback(delta);
  },

  onKineticEnd: function cp_onKineticEnd() {
    if (!this.dragging)
      this.scrollCallback = null;
  },

  getPannable: function cp_getPannable(node) {
    if (!(node instanceof Ci.nsIDOMHTMLElement) || node.tagName == 'HTML')
      return [null, null];

    let nodeContent = node.ownerDocument.defaultView;
    while (!(node instanceof Ci.nsIDOMHTMLBodyElement)) {
      let style = nodeContent.getComputedStyle(node, null);

      let overflow = [style.getPropertyValue('overflow'),
                      style.getPropertyValue('overflow-x'),
                      style.getPropertyValue('overflow-y')];

      let rect = node.getBoundingClientRect();
      let isAuto = (overflow.indexOf('auto') != -1 &&
                   (rect.height < node.scrollHeight ||
                    rect.width < node.scrollWidth));

      let isScroll = (overflow.indexOf('scroll') != -1);
      if (isScroll || isAuto)
        return [node, this._generateCallback(node)];

      node = node.parentNode;
    }

    if (ContentPanning._asyncPanZoomForViewportFrame &&
        nodeContent === content)
      // The parent context is asynchronously panning and zooming our
      // root scrollable frame, so don't use our synchronous fallback.
      return [null, null];

    return [nodeContent, this._generateCallback(nodeContent)];
  },

  _generateCallback: function cp_generateCallback(content) {
    function scroll(delta) {
      if (content instanceof Ci.nsIDOMHTMLElement) {
        let oldX = content.scrollLeft, oldY = content.scrollTop;
        content.scrollLeft += delta.x;
        content.scrollTop += delta.y;
        let newX = content.scrollLeft, newY = content.scrollTop;
        return (newX != oldX) || (newY != oldY);
      } else {
        let oldX = content.scrollX, oldY = content.scrollY;
        content.scrollBy(delta.x, delta.y);
        let newX = content.scrollX, newY = content.scrollY;
        return (newX != oldX) || (newY != oldY);
      }
    }
    return scroll;
  },

  get _domUtils() {
    delete this._domUtils;
    return this._domUtils = Cc['@mozilla.org/inspector/dom-utils;1']
                              .getService(Ci.inIDOMUtils);
  },

  _resetActive: function cp_resetActive() {
    let root = this.target.ownerDocument || this.target.document;

    const kStateActive = 0x00000001;
    this._domUtils.setContentState(root.documentElement, kStateActive);
  },

  get _asyncPanZoomForViewportFrame() {
    return docShell.asyncPanZoomEnabled;
  },

  _recvViewportChange: function(data) {
    let viewport = data.json;
    let displayPort = viewport.displayPort;

    let screenWidth = viewport.screenSize.width;
    let screenHeight = viewport.screenSize.height;

    let x = viewport.x;
    let y = viewport.y;

    let cwu = content.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
    cwu.setCSSViewport(screenWidth, screenHeight);

    // Set scroll position
    cwu.setScrollPositionClampingScrollPortSize(
      screenWidth / viewport.zoom, screenHeight / viewport.zoom);
    content.scrollTo(x, y);
    cwu.setResolution(displayPort.resolution, displayPort.resolution);

    let element = null;
    if (content.document && (element = content.document.documentElement)) {
      cwu.setDisplayPortForElement(displayPort.left,
                                   displayPort.top,
                                   displayPort.width,
                                   displayPort.height,
                                   element);
    }
  }
};

ContentPanning.init();

// Min/max velocity of kinetic panning. This is in pixels/millisecond.
const kMinVelocity = 0.4;
const kMaxVelocity = 6;

// Constants that affect the "friction" of the scroll pane.
const kExponentialC = 1000;
const kPolynomialC = 100 / 1000000;

// How often do we change the position of the scroll pane?
// Too often and panning may jerk near the end.
// Too little and panning will be choppy. In milliseconds.
const kUpdateInterval = 16;

// The numbers of momentums to use for calculating the velocity of the pan.
// Those are taken from the end of the action
const kSamples = 5;

const KineticPanning = {
  _position: new Point(0, 0),
  _velocity: new Point(0, 0),
  _acceleration: new Point(0, 0),

  get active() {
    return this.target !== null;
  },

  target: null,
  start: function kp_start(target) {
    this.target = target;

    // Calculate the initial velocity of the movement based on user input
    let momentums = this.momentums.slice(-kSamples);

    let distance = new Point(0, 0);
    momentums.forEach(function(momentum) {
      distance.add(momentum.dx, momentum.dy);
    });

    let elapsed = momentums[momentums.length - 1].time - momentums[0].time;

    function clampFromZero(x, min, max) {
      if (x >= 0)
        return Math.max(min, Math.min(max, x));
      return Math.min(-min, Math.max(-max, x));
    }

    let velocityX = clampFromZero(distance.x / elapsed, 0, kMaxVelocity);
    let velocityY = clampFromZero(distance.y / elapsed, 0, kMaxVelocity);

    let velocity = this._velocity;
    velocity.set(Math.abs(velocityX) < kMinVelocity ? 0 : velocityX,
                 Math.abs(velocityY) < kMinVelocity ? 0 : velocityY);
    this.momentums = [];

    // Set acceleration vector to opposite signs of velocity
    function sign(x) {
      return x ? (x > 0 ? 1 : -1) : 0;
    }

    this._acceleration.set(velocity.clone().map(sign).scale(-kPolynomialC));

    // Reset the position
    this._position.set(0, 0);

    this._startAnimation();

    this.target.onKineticBegin();
  },

  stop: function kp_stop() {
    if (!this.target)
      return;

    this.momentums = [];
    this.distance.set(0, 0);

    this.target.onKineticEnd();
    this.target = null;
  },

  momentums: [],
  record: function kp_record(delta, timestamp) {
    this.momentums.push({ 'time': timestamp, 'dx' : delta.x, 'dy' : delta.y });
    this.distance.add(delta.x, delta.y);
  },

  get threshold() {
    let dpi = content.QueryInterface(Ci.nsIInterfaceRequestor)
                     .getInterface(Ci.nsIDOMWindowUtils)
                     .displayDPI;

    let threshold = Services.prefs.getIntPref('ui.dragThresholdX') / 240 * dpi;

    delete this.threshold;
    return this.threshold = threshold;
  },

  distance: new Point(0, 0),
  isPan: function cp_isPan() {
    return (Math.abs(this.distance.x) > this.threshold ||
            Math.abs(this.distance.y) > this.threshold);
  },

  _startAnimation: function kp_startAnimation() {
    let c = kExponentialC;
    function getNextPosition(position, v, a, t) {
      // Important traits for this function:
      //   p(t=0) is 0
      //   p'(t=0) is v0
      //
      // We use exponential to get a smoother stop, but by itself exponential
      // is too smooth at the end. Adding a polynomial with the appropriate
      // weight helps to balance
      position.set(v.x * Math.exp(-t / c) * -c + a.x * t * t + v.x * c,
                   v.y * Math.exp(-t / c) * -c + a.y * t * t + v.y * c);
    }

    let startTime = content.mozAnimationStartTime;
    let elapsedTime = 0, targetedTime = 0, averageTime = 0;

    let velocity = this._velocity;
    let acceleration = this._acceleration;

    let position = this._position;
    let nextPosition = new Point(0, 0);
    let delta = new Point(0, 0);

    let callback = (function(timestamp) {
      if (!this.target)
        return;

      // To make animation end fast enough but to keep smoothness, average the
      // ideal time frame (smooth animation) with the actual time lapse
      // (end fast enough).
      // Animation will never take longer than 2 times the ideal length of time.
      elapsedTime = timestamp - startTime;
      targetedTime += kUpdateInterval;
      averageTime = (targetedTime + elapsedTime) / 2;

      // Calculate new position.
      getNextPosition(nextPosition, velocity, acceleration, averageTime);
      delta.set(Math.round(nextPosition.x - position.x),
                Math.round(nextPosition.y - position.y));

      // Test to see if movement is finished for each component.
      if (delta.x * acceleration.x > 0)
        delta.x = position.x = velocity.x = acceleration.x = 0;

      if (delta.y * acceleration.y > 0)
        delta.y = position.y = velocity.y = acceleration.y = 0;

      if (velocity.equals(0, 0) || delta.equals(0, 0)) {
        this.stop();
        return;
      }

      position.add(delta);
      if (this.target.onKineticPan(delta.scale(-1))) {
        this.stop();
        return;
      }

      content.mozRequestAnimationFrame(callback);
    }).bind(this);

    content.mozRequestAnimationFrame(callback);
  }
};