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   1  YUI.add('moodle-core-lockscroll', function (Y, NAME) {
   2  
   3  /**
   4   * Provides the ability to lock the scroll for a page, allowing nested
   5   * locking.
   6   *
   7   * @module moodle-core-lockscroll
   8   */
   9  
  10  /**
  11   * Provides the ability to lock the scroll for a page.
  12   *
  13   * This is achieved by applying the class 'lockscroll' to the body Node.
  14   *
  15   * Nested widgets are also supported and the scroll lock is only removed
  16   * when the final plugin instance is disabled.
  17   *
  18   * @class M.core.LockScroll
  19   * @extends Plugin.Base
  20   */
  21  Y.namespace('M.core').LockScroll = Y.Base.create('lockScroll', Y.Plugin.Base, [], {
  22  
  23      /**
  24       * Whether the LockScroll has been activated.
  25       *
  26       * @property _enabled
  27       * @type Boolean
  28       * @protected
  29       */
  30      _enabled: false,
  31  
  32      /**
  33       * Handle destruction of the lockScroll instance, including disabling
  34       * of the current instance.
  35       *
  36       * @method destructor
  37       */
  38      destructor: function() {
  39          this.disableScrollLock();
  40      },
  41  
  42      /**
  43       * Start locking the page scroll.
  44       *
  45       * This is achieved by applying the lockscroll class to the body Node.
  46       *
  47       * A count of the total number of active, and enabled, lockscroll instances is also kept on
  48       * the body to ensure that premature disabling does not occur.
  49       *
  50       * @method enableScrollLock
  51       * @param {Boolean} forceOnSmallWindow Whether to enable the scroll lock, even for small window sizes.
  52       * @chainable
  53       */
  54      enableScrollLock: function(forceOnSmallWindow) {
  55          if (this.isActive()) {
  56              return;
  57          }
  58  
  59          var dialogueHeight = this.get('host').get('boundingBox').get('region').height,
  60              // Most modern browsers use win.innerHeight, but some older versions of IE use documentElement.clientHeight.
  61              // We fall back to 0 if neither can be found which has the effect of disabling scroll locking.
  62              windowHeight = Y.config.win.innerHeight || Y.config.doc.documentElement.clientHeight || 0;
  63  
  64          if (!forceOnSmallWindow && dialogueHeight > (windowHeight - 10)) {
  65              return;
  66          }
  67  
  68          this._enabled = true;
  69          var body = Y.one(Y.config.doc.body);
  70  
  71          // We use a CSS class on the body to handle the actual locking.
  72          body.addClass('lockscroll');
  73  
  74          // Increase the count of active instances - this is used to ensure that we do not
  75          // remove the locking when parent windows are still open.
  76          // Note: We cannot use getData here because data attributes are sandboxed to the instance that created them.
  77          var currentCount = parseInt(body.getAttribute('data-activeScrollLocks'), 10) || 0,
  78              newCount = currentCount + 1;
  79          body.setAttribute('data-activeScrollLocks', newCount);
  80  
  81          return this;
  82      },
  83  
  84      /**
  85       * Stop locking the page scroll.
  86       *
  87       * The instance may be disabled but the scroll lock not removed if other instances of the
  88       * plugin are also active.
  89       *
  90       * @method disableScrollLock
  91       * @chainable
  92       */
  93      disableScrollLock: function() {
  94          if (this.isActive()) {
  95              this._enabled = false;
  96  
  97              var body = Y.one(Y.config.doc.body);
  98  
  99              // Decrease the count of active instances.
 100              // Note: We cannot use getData here because data attributes are sandboxed to the instance that created them.
 101              var currentCount = parseInt(body.getAttribute('data-activeScrollLocks'), 10) || 1,
 102                  newCount = currentCount - 1;
 103  
 104              if (currentCount === 1) {
 105                  body.removeClass('lockscroll');
 106              }
 107  
 108              body.setAttribute('data-activeScrollLocks', currentCount - 1);
 109          }
 110  
 111          return this;
 112      },
 113  
 114      /**
 115       * Return whether scroll locking is active.
 116       *
 117       * @method isActive
 118       * @return Boolean
 119       */
 120      isActive: function() {
 121          return this._enabled;
 122      }
 123  
 124  }, {
 125      NS: 'lockScroll',
 126      ATTRS: {
 127      }
 128  });
 129  
 130  
 131  }, '@VERSION@', {"requires": ["plugin", "base-build"]});