'use strict';

/* global EmojiKeyView, KeyView, SwipingDetector */

(function(exports) {

/**
 * SwipeablePanelView is used to render a panel that is swipeable to go through
 * several sections.
 */

function SwipeablePanelView(layout, options, viewManager) {
  this.layout = layout;
  this.options = options;
  this.viewManager = viewManager;

  this.sections = [];
  this.currentSectionIndex = 0;

  this.indicators = [];

  this.startX = 0;

  this.swipingDetector = null;
}

SwipeablePanelView.prototype.COLUMN_COUNT = 6;

SwipeablePanelView.prototype.KEY_COUNT_PER_PANEL = 18;

SwipeablePanelView.prototype.SWIPE_THRESHOLD = 20;

SwipeablePanelView.prototype.SWIPE_FRACTION = 0.25;

SwipeablePanelView.prototype.SWIPE_SPEED = 0.5;

SwipeablePanelView.prototype.render = function() {
  var panel = document.createElement('div');
  panel.classList.add('swipe-panel');

  var i = 0;
  while (true) {
    var section = this._renderSection(i);
    if (!section) {
      break;
    }
    this.sections.push(section);

    section.classList.add('swipe-section');
    panel.appendChild(section);
    i++;
  }

  // SwipingDetector and SectionIndicator should be initialized
  // only when there are more than one sections in panel.
  if (this.sections.length > 1) {
    this._createSwipingDetector(panel);
    this._renderSectionIndicator(panel);
  }

  this.element = panel;
};

SwipeablePanelView.prototype.gotoSection = function(index) {
  // Stay on the current section.
  if (index === this.currentSectionIndex) {
    var currentPos = this.sections[this.currentSectionIndex].
      getBoundingClientRect();
    if (currentPos.left !== 0) {
      // Move the previous section backwards
      if (index > 0) {
        this._moveSection(index - 1, -this.options.totalWidth);
      }

      this._moveSection(index, 0);

      // Move the next section forwards
      if (index < this.sections.length - 1) {
        this._moveSection(index + 1, this.options.totalWidth);
      }
    }

    return;
  }

  this._moveSection(index, 0);

  var forward = (index >= this.currentSectionIndex) ? 1 : -1;
  // Move the original section
  this._moveSection(this.currentSectionIndex,
                    -forward * this.options.totalWidth);

  this.currentSectionIndex = index;
  this._updateIndicator();
};

SwipeablePanelView.prototype.resize = function resize(totalWidth) {
  this.options.totalWidth = totalWidth;
  this.swipeDetectingPaused = true;

  // Reposition sections when resize;
  this.sections.forEach(function(section, index) {
    var translateX;
    
    if (index === this.currentSectionIndex) {
      translateX = 0; 
    } else if (this.currentSectionIndex > index) {
      translateX = -totalWidth;
    } else {
      translateX = totalWidth; 
    }

    section.style.transform = 'translateX(' + translateX + 'px)';
  }, this);

};

SwipeablePanelView.prototype._moveSection = function(index, distance) {
  var style = this.sections[index].style;
  style.transform = 'translateX(' + distance + 'px)';
  style.transition = 'transform ' + 300 + 'ms ease';
};

SwipeablePanelView.prototype._updateIndicator = function() {
  // Change the section indicator.
  this.indicators.forEach(function(indicator, index) {
      indicator.classList.toggle('active',
        (index == this.currentSectionIndex));
  }, this);
};

SwipeablePanelView.prototype._handleTouchStart = function(evt) {
  this.startX = evt.position.clientX;
  this.deltaX = 0;
  this.swipeDetectingPaused = false;
};

SwipeablePanelView.prototype._handlePan = function(evt) {
  if (this.swipeDetectingPaused) {
    return;
  }

  var totalWidth = this.options.totalWidth;

  // Clear all transition styles
  this.sections.forEach(function(section) {
    section.style.transition = '';
  });

  var currentX = evt.position.clientX;
  this.deltaX = currentX - this.startX;

  var previous;
  var next;
  var current;
  var forward = this.deltaX < 0;

  if (this.currentSectionIndex === 0) {
    if (forward) {
      this.sections[1].style.transform =
        'translateX(' + (totalWidth + this.deltaX) + 'px)';
      this.sections[0].style.transform =
        'translateX(' + this.deltaX + 'px)';
    } else {
      this.startX = currentX;
    }
  } else if (this.currentSectionIndex === this.sections.length - 1) {
    previous =
      this.sections[this.currentSectionIndex - 1].style;

    if (this.deltaX >= 0) {
      previous.transform =
        'translateX(' + (-totalWidth + this.deltaX) + 'px)';
      this.sections[this.currentSectionIndex].style.transform =
        'translateX(' + this.deltaX + 'px)';
    } else {
      this.startX = currentX;
    }
  } else {
    previous = this.sections[this.currentSectionIndex - 1].style;
    next = this.sections[this.currentSectionIndex + 1].style;
    if (this.deltaX >= 0) {
      previous.transform =
        'translateX(' + (-totalWidth + this.deltaX) + 'px)';
      // If we change direction make sure there isn't any part
      // of the page on the other side that stays visible.
      next.transform = 'translateX(' + totalWidth + 'px)';
    } else {
      next.transform = 'translateX(' + (totalWidth + this.deltaX) + 'px)';
      // If we change direction make sure there isn't any part
      // of the page on the other side that stays visible.
      previous.transform =
        'translateX(-' + totalWidth + 'px)';
    }

    current = this.sections[this.currentSectionIndex].style;
    current.transform = 'translateX(' + this.deltaX + 'px)';
  }
};

SwipeablePanelView.prototype._handleSwipe = function(evt) {
  if (this.swipeDetectingPaused) {
    return;
  }

  var totalWidth = this.options.totalWidth;
  var targetIndex = this.currentSectionIndex;
  var forward = evt.direction === 'left';

  var isFarEnough = Math.abs(this.deltaX) > totalWidth * this.SWIPE_FRACTION;
  var velocity = evt.vx;
  var isFastEnough = Math.abs(velocity) > this.SWIPE_SPEED;
  var isSameDirection = velocity === 0 || this.deltaX / velocity >= 0;

  if ((isFarEnough || isFastEnough) && isSameDirection) {
    if (forward && this.currentSectionIndex < this.sections.length - 1) {
      targetIndex = this.currentSectionIndex + 1;
    } else if (!forward && this.currentSectionIndex > 0) {
      targetIndex = this.currentSectionIndex - 1;
    }
  }

  this.gotoSection(targetIndex);
};

SwipeablePanelView.prototype._renderSection = function(index) {
  var panelKeys = this.layout.panelKeys;

  var startIndex = this.KEY_COUNT_PER_PANEL * index;
  if (startIndex >= panelKeys.length) {
    return null;
  }

  var endIndex = Math.min(startIndex + this.KEY_COUNT_PER_PANEL,
                          panelKeys.length);

  var section = document.createElement('div');
  for (var i = startIndex; i < endIndex; i++) {
    var keyView = this._createKeyView(panelKeys[i]);
    keyView.render();
    section.appendChild(keyView.element);
  }

  // Create a dummy element to make the UI look like a grid.
  var itemCount =  i - startIndex;
  if (itemCount % this.COLUMN_COUNT !== 0) {
    var dummyEl = document.createElement('span');
    dummyEl.style.flex = this.COLUMN_COUNT - (itemCount % this.COLUMN_COUNT);
    section.appendChild(dummyEl);
  }

  this.element = section;
  return section;
};

SwipeablePanelView.prototype._renderSectionIndicator = function(panel) {
  var indicatorContainer = document.createElement('div');
  indicatorContainer.classList.add('section-indicator-container');
  for (var j = 0; j < this.sections.length; j++) {
    var dot = document.createElement('span');
    dot.classList.add('section-indicator');
    this.indicators.push(dot);
    indicatorContainer.appendChild(dot);
  }
  this._updateIndicator();

  panel.appendChild(indicatorContainer);
};

SwipeablePanelView.prototype._createSwipingDetector = function(panel) {
  this.swipingDetector = new SwipingDetector(panel);
  this.swipingDetector.start();
  this.swipingDetector.ontouchstart = this._handleTouchStart.bind(this);
  this.swipingDetector.onpan = this._handlePan.bind(this);
  this.swipingDetector.onswipe = this._handleSwipe.bind(this);
};

SwipeablePanelView.prototype._createKeyView = function(keyObject) {
  var target = Object.create(keyObject);
  // Set selection property as true, so it won't trigger send key when
  // swiping.
  target.selection = true;

  var keyView;

  switch (target.type) {
    case 'emoji':
      keyView = new EmojiKeyView(target, {}, this.viewManager);
      break;
    default:
      keyView = new KeyView(target, {}, this.viewManager);
      break;
  }

  return keyView;
};

exports.SwipeablePanelView = SwipeablePanelView;
})(window);