// ========================================================================
// SproutCore -- JavaScript Application Framework
// Copyright ©2006-2008, Sprout Systems, Inc. and contributors.
// Portions copyright ©2008 Apple, Inc.  All rights reserved.
// ========================================================================

/**
  @namespace

  Any views you implement that are scrollable should include this mixin to
  provide basic support for scrolling actions.  You can also override any 
  of these methods as needed for your own specific behaviors.
  
  Often times instead of adding SC.Scrollable to your view, you should
  place your view inside of an SC.ScrollView.  See that class for more 
  info.
  
  Note that isScrollable must always be true.

*/
SC.Scrollable = {
  
  /** Informs the view system that the receiver is scrollable.
  
    Must always be true.
  */
  isScrollable: true,
  
  /** 
    Amount to scroll one vertical line.
  
    Used by the default implementation of scrollDownLine() and scrollUpLine().  Defaults
    to 20px.
  */
  verticalLineScroll: 20,
  
  /**
    Amount to scroll one horizontal line.
  
    Used by the default implementation of scrollLeftLine() and scrollRightLine(). Defaults
    to 20px.
  */
  horizontalLineScroll: 20,
  
  /**
    Amount to scroll one vertical page.
    
    Used by the default implementation of scrollUpPage() and scrollDownPage(). Defaults to
    current innerFrame height.
  */
  verticalPageScroll: function() {
    return this.get('innerFrame').height ;
  }.property('innerFrame'),
  
  /**
    Amount to scroll one horizontal page.
    
    Used by the default implementation of scrollLeftPage() and scrollRightPage().  Defaults
    to current innerFrame width.
  */
  horizontalPageScroll: function() {
    return this.get('innerFrame').width ;  
  }.property('innerFrame'),
  
  /**
    Returns true if the receiver has enough vertical content to require 
    scrolling.
    
    If you do not want to allow vertical scrolling, override this to be false 
    and set the appropriate CSS.
    
  */
  hasVerticalScroller: function() {
    return this.get('scrollFrame').height > this.get('innerFrame').height ;
  }.property('scrollFrame'),
  
  /**
    Returns true if the receiver has enough horizontal content to require 
    scrolling.
    
    If you do not want to allow horizontal scrolling, override this to be 
    false and set the appropriate CSS.
    
  */
  hasHorizontalScroller: function() {
    return this.get('scrollFrame').width > this.get('innerFrame').width ;
  }.property('scrollFrame'),

  /**
    Scrolls the receiver in the horizontal and vertical directions by the 
    amount specified, if allowed.
    
    @param {Point} amount the amount to scroll.  Must include x, y or both
    @returns {Point} the actual amount scrolled.
  */
  scrollBy: function(amount) {
    var sf = this.get('scrollFrame') ;
    var f = this.get('innerFrame') ;

    if (!this.get('hasVerticalScroller')) amount.y = 0 ;
    if (sf.height <= f.height) amount.y = 0 ;
    
    if (!this.get('hasHorizontalScroller')) amount.x = 0 ; 
    if (sf.width <= f.width) amount.x = 0 ;

    // compute new sf
    var newSf = { x: sf.x - (amount.x || 0), y: sf.y - (amount.y || 0) } ;
    this.set('scrollFrame', newSf) ;
    newSf = this.get('scrollFrame') ;
    
    return { x: newSf.x - sf.x, y: newSf.y - sf.y }; 
  },

  /**
    Scrolls the receiver to the specified x,y coordinate
  */
  scrollTo: function(x,y) {
    this.set('scrollFrame', { x: 0-x, y: 0-y }) ;  
  },
  
  /**
    Scroll the view to make the passed frame visible.
    
    Frame must be relative to the receiver's offsetParent.
    
    @param {SC.ClassicView} view the view you want to make visible
  */
  scrollToVisible: function(view) {

    // get frames and convert them to proper offsets
    var f = this.get('innerFrame') ;
    var sf = this.get('scrollFrame') ;
    
    // frame of the view, relative to the top of the scroll frame
    var vf = this.convertFrameFromView(view.get('frame'), view) ;
    vf.x -= (f.x + sf.x); vf.y -= (f.y + sf.y);
    
    // first visible origin
    var vo = { 
      x: 0-sf.x, 
      y: 0-sf.y, 
      width: f.width, 
      height: f.height 
    };

    // if top edge is not visible, shift origin
    vo.y -= Math.max(0, SC.minY(vo) - SC.minY(vf)) ;
    vo.x -= Math.max(0, SC.minX(vo) - SC.minX(vf)) ;

    // if bottom edge is not visible, shift origin
    vo.y += Math.max(0, SC.maxY(vf) - SC.maxY(vo)) ;
    vo.x += Math.max(0, SC.maxX(vf) - SC.maxX(vo)) ;

    // scroll to that origin.
    this.scrollTo(vo.x, vo.y) ;
  },
  
  /**
    Scrolls the receiver down one line if allowed.
    
    @param {Number} lines number of lines to scroll
    @returns {Number} the amount actually scrolled.
  */
  scrollDownLine: function(lines) {
    if (lines === undefined) lines = 1 ;
    return this.scrollBy({ y: this.get('verticalLineScroll')*lines }).y ;
  },

  /**
    Scrolls the receiver down up line if allowed.
    
    @param {Number} lines number of lines to scroll
    @returns {Number} the amount actually scrolled.
  */
  scrollUpLine: function(lines) {
    if (lines === undefined) lines = 1 ;
    return 0-this.scrollBy({ y: 0-this.get('verticalLineScroll')*lines }).y ;
  },

  /**
    Scrolls the receiver right one line if allowed.
    
    @param {Number} lines number of lines to scroll
    @returns {Number} the amount actually scrolled.
  */
  scrollRightLine: function(lines) {
    if (lines === undefined) lines = 1 ;
    return this.scrollTo({ y: this.get('horizontalLineScroll')*lines }).x ;
  },

  /**
    Scrolls the receiver left one line if allowed.
    
    @param {Number} lines number of lines to scroll
    @returns {Number} the amount actually scrolled.
  */
  scrollLeftLine: function(lines) {
    if (lines === undefined) lines = 1 ;
    return 0-this.scrollTo({ y: 0-this.get('horizontalLineScroll')*lines }).x ;
  },

  /**
    Scrolls the receiver down one page if allowed.
    
    @param {Number} pages number of pages to scroll
    @returns {Number} the amount actually scrolled.
  */
  scrollDownPage: function(pages) {
    if (pages === undefined) pages = 1 ;
    return this.scrollBy({ y: this.get('verticalPageScroll')*pages }).y ;
  },

  /**
    Scrolls the receiver down up page if allowed.
    
    @param {Number} pages number of pages to scroll
    @returns {Number} the amount actually scrolled.
  */
  scrollUpPage: function(pages) {
    if (pages === undefined) pages = 1 ;
    return 0-this.scrollBy({ y: 0-this.get('verticalPageScroll')*pages }).y ;
  },

  /**
    Scrolls the receiver right one page if allowed.
    
    @param {Number} pages number of pages to scroll
    @returns {Number} the amount actually scrolled.
  */
  scrollRightPage: function(pages) {
    if (pages === undefined) pages = 1 ;
    return this.scrollTo({ y: this.get('horizontalPageScroll')*pages }).x ;
  },

  /**
    Scrolls the receiver left one page if allowed.
    
    @param {Number} pages number of pages to scroll
    @returns {Number} the amount actually scrolled.
  */
  scrollLeftPage: function(pages) {
    if (pages === undefined) pages = 1 ;
    return 0-this.scrollTo({ y: 0-this.get('horizontalPageScroll')*pages }).x ;
  }
  
} ;