VulpesOS/gaia/shared/elements/gaia_grid/js/grid_layout.js

'use strict';
/* global devicePixelRatio */
/* global verticalPreferences */

(function(exports) {

  const maxIconsPerRow = 4;

  // 320 / 5 = 64px | 480 / 5 = 96px | 540 / 5 = 108px | ...
  const iconScaleFactorMaxIconsPerRow = 5;

  const minIconsPerRow = 3;

  // 320 / 3.8 = 84px | 480 / 3.8 = 126px | 540 / 3.8 = 142px | ...
  const iconScaleFactorMinIconsPerRow = 3.8;

  const distanceBetweenIconsWithMinIconsPerRow = 36;

  const distanceBetweenIconsWithMaxIconsPerRow = 38;

  const eachTextRowHeight = 20;

  var constraintSize;

  function GridLayout(gridView) {
    this.gridView = gridView;

    if (window.verticalPreferences) {
      verticalPreferences.get('grid.cols').then(value => {
        this.cols = value;
        this.onReady();
      }, this.onReady);
      verticalPreferences.addEventListener('updated', this);
    } else {
      this.onReady();
    }
  }

  GridLayout.prototype = {

    minIconsPerRow: minIconsPerRow,

    maxIconsPerRow: maxIconsPerRow,

    _cols: minIconsPerRow,

    _offsetY: 0,

    _percent: 1,

    /**
     * The visible height of each divider.
     * Calculated by the divider class and cached here.
     */
    _dividerLineHeight: 0,

    get percent() {
      return this._percent;
    },

    get cols() {
      return this._cols;
    },

    set cols(value) {
      if (!value || value === this._cols) {
        return;
      }

      if (window.verticalPreferences) {
        verticalPreferences.put('grid.cols', value);
      }

      // Reset the y-offset because we will re-render everything anyway.
      this._offsetY = 0;

      this._percent = value == minIconsPerRow ? 1 :
        minIconsPerRow / maxIconsPerRow;
      this._cols = value;
    },

    /**
     * The width of the grid.
     */
    get constraintSize() {
      if (!constraintSize) {
        this.calculateSize();
      }
      return constraintSize;
    },

    /**
     * The height of each grid item.
     */
    get gridItemHeight() {
      var height = this.gridIconSize +
            (this._cols === minIconsPerRow ?
                             distanceBetweenIconsWithMinIconsPerRow :
                             distanceBetweenIconsWithMaxIconsPerRow);

      // Increase height for additional rows of text.
      var defaultTextRows = 2;
      var definedRows = parseInt(
        this.gridView.element.getAttribute('text-rows'), 10);
      if (definedRows > defaultTextRows) {
        height += (definedRows - defaultTextRows) * eachTextRowHeight;
      }

      return height;
    },

    /**
     * The width of each grid item.
     * This number changes based on current zoom level.
     */
    get gridItemWidth() {
      return this.constraintSize / this._cols;
    },

    /**
     * Returns the maximum size in pixels for an icon image. It is the size when
     * the grid is displayed with the minimum number of columns per row.
     */
    get gridMaxIconSize() {
      var baseSize = (this.constraintSize / iconScaleFactorMinIconsPerRow);
      return baseSize * devicePixelRatio;
    },

    /**
     * Returns the icon image size depending on grid configuration and screen
     * characteristics.
     */
    get gridIconSize() {
      var numCols = this._cols;

      var size = this.constraintSize / numCols;
      if (numCols === minIconsPerRow) {
        size = this.constraintSize / iconScaleFactorMinIconsPerRow;
      } else if (numCols === maxIconsPerRow) {
        size = this.constraintSize / iconScaleFactorMaxIconsPerRow;
      }
      return Math.floor(size);
    },

    /**
     * Gets the current offset of the Y-axis for the current zoom level.
     * This value is updated by calling zoom.stepYAxis. For example, each
     * group of three icons, or a divider, should increment this value.
     * The value is reset and recalculated when the zoom level changes.
     */
    get offsetY() {
      return this._offsetY;
    },

    set offsetY(value) {
      this._offsetY = value;
    },

    /**
     * After we render a row we need to store the current position of the y-axis
     */
    stepYAxis: function(value) {
      this._offsetY += value;
    },

    /**
     * General event handler.
     */
    handleEvent: function(e) {
      switch(e.type) {
        case 'updated':
          var prop = e.target;
          if (prop.name === 'grid.cols') {
            this.cols = parseInt(prop.value, 10);
            this.gridView.render();
          }

          break;
      }
    },

    calculateSize: function() {
      constraintSize = Math.min(window.screen.width, window.screen.height);
    },

    onReady: function() {
      window.dispatchEvent(new CustomEvent('gaiagrid-layout-ready'));
    }
  };

  exports.GridLayout = GridLayout;

}(window));