/*!
 * zoom.js 0.2
 * http://lab.hakim.se/zoom-js
 * MIT licensed
 * 
 * Copyright (C) 2011-2012 Hakim El Hattab, http://hakim.se
 */
var zoom = (function(){

    // The current zoom level (scale)
    var level = 1;
    
    // The current mouse position, used for panning
    var mouseX = 0,
        mouseY = 0;
    
    // Timeout before pan is activated
    var panEngageTimeout = -1,
        panUpdateInterval = -1;

    // Check for transform support so that we can fallback otherwise
    var supportsTransforms =    'WebkitTransform' in document.body.style ||
                                'MozTransform' in document.body.style ||
                                'msTransform' in document.body.style ||
                                'OTransform' in document.body.style ||
                                'transform' in document.body.style;
    
    if( supportsTransforms ) {
        // The easing that will be applied when we zoom in/out
        document.body.style.transition = 'transform 0.8s ease';
        document.body.style.OTransition = '-o-transform 0.8s ease';
        document.body.style.msTransition = '-ms-transform 0.8s ease';
        document.body.style.MozTransition = '-moz-transform 0.8s ease';
        document.body.style.WebkitTransition = '-webkit-transform 0.8s ease';
    }
    
    // Zoom out if the user hits escape
    document.addEventListener( 'keyup', function( event ) {
        if( level !== 1 && event.keyCode === 27 ) {
            zoom.out();
        }
    } );

    // Monitor mouse movement for panning
    document.addEventListener( 'mousemove', function( event ) {
        if( level !== 1 ) {
            mouseX = event.clientX;
            mouseY = event.clientY;
        }
    } );

    /**
     * Applies the CSS required to zoom in, prioritizes use of CSS3 
     * transforms but falls back on zoom for IE.
     * 
     * @param {Number} pageOffsetX 
     * @param {Number} pageOffsetY 
     * @param {Number} elementOffsetX 
     * @param {Number} elementOffsetY 
     * @param {Number} scale 
     */
    function magnify( pageOffsetX, pageOffsetY, elementOffsetX, elementOffsetY, scale ) {

        if( supportsTransforms ) {
            var origin = pageOffsetX +'px '+ pageOffsetY +'px',
                transform = 'translate('+ -elementOffsetX +'px,'+ -elementOffsetY +'px) scale('+ scale +')';
            
            document.body.style.transformOrigin = origin;
            document.body.style.OTransformOrigin = origin;
            document.body.style.msTransformOrigin = origin;
            document.body.style.MozTransformOrigin = origin;
            document.body.style.WebkitTransformOrigin = origin;

            document.body.style.transform = transform;
            document.body.style.OTransform = transform;
            document.body.style.msTransform = transform;
            document.body.style.MozTransform = transform;
            document.body.style.WebkitTransform = transform;
        }
        else {
            // Reset all values
            if( scale === 1 ) {
                document.body.style.position = '';
                document.body.style.left = '';
                document.body.style.top = '';
                document.body.style.width = '';
                document.body.style.height = '';
                document.body.style.zoom = '';
            }
            // Apply scale
            else {
                document.body.style.position = 'relative';
                document.body.style.left = ( - ( pageOffsetX + elementOffsetX ) / scale ) + 'px';
                document.body.style.top = ( - ( pageOffsetY + elementOffsetY ) / scale ) + 'px';
                document.body.style.width = ( scale * 100 ) + '%';
                document.body.style.height = ( scale * 100 ) + '%';
                document.body.style.zoom = scale;
            }
        }

        level = scale;
    }

    /**
     * Pan the document when the mosue cursor approaches the edges 
     * of the window.
     */
    function pan() {
        var range = 0.12,
            rangeX = window.innerWidth * range,
            rangeY = window.innerHeight * range,
            scrollOffset = getScrollOffset();
        
        // Up
        if( mouseY < rangeY ) {
            window.scroll( scrollOffset.x, scrollOffset.y - ( 1 - ( mouseY / rangeY ) ) * ( 14 / level ) );
        }
        // Down
        else if( mouseY > window.innerHeight - rangeY ) {
            window.scroll( scrollOffset.x, scrollOffset.y + ( 1 - ( window.innerHeight - mouseY ) / rangeY ) * ( 14 / level ) );
        }

        // Left
        if( mouseX < rangeX ) {
            window.scroll( scrollOffset.x - ( 1 - ( mouseX / rangeX ) ) * ( 14 / level ), scrollOffset.y );
        }
        // Right
        else if( mouseX > window.innerWidth - rangeX ) {
            window.scroll( scrollOffset.x + ( 1 - ( window.innerWidth - mouseX ) / rangeX ) * ( 14 / level ), scrollOffset.y );
        }
    }

    function getScrollOffset() {
        return {
            x: window.scrollX !== undefined ? window.scrollX : window.pageXOffset,
            y: window.scrollY !== undefined ? window.scrollY : window.pageXYffset
        }
    }

    return {
        /**
         * Zooms in on either a rectangle or HTML element.
         * 
         * @param {Object} options
         *   - element: HTML element to zoom in on
         *   OR
         *   - x/y: coordinates in non-transformed space to zoom in on
         *   - width/height: the portion of the screen to zoom in on
         *   - scale: can be used instead of width/height to explicitly set scale
         */
        to: function( options ) {
            // Due to an implementation limitation we can't zoom in
            // to another element without zooming out first
            if( level !== 1 ) {
                zoom.out();
            }
            else {
                options.x = options.x || 0;
                options.y = options.y || 0;

                // If an element is set, that takes precedence
                if( !!options.element ) {
                    // Space around the zoomed in element to leave on screen
                    var padding = 20;

                    options.width = options.element.getBoundingClientRect().width + ( padding * 2 );
                    options.height = options.element.getBoundingClientRect().height + ( padding * 2 );
                    options.x = options.element.getBoundingClientRect().left - padding;
                    options.y = options.element.getBoundingClientRect().top - padding;
                }

                // If width/height values are set, calculate scale from those values
                if( options.width !== undefined && options.height !== undefined ) {
                    options.scale = Math.max( Math.min( window.innerWidth / options.width, window.innerHeight / options.height ), 1 );
                }

                if( options.scale > 1 ) {
                    options.x *= options.scale;
                    options.y *= options.scale;

                    var scrollOffset = getScrollOffset();

                    magnify( scrollOffset.x, scrollOffset.y, options.x, options.y, options.scale );

                    if( options.pan !== false ) {

                        // Wait with engaging panning as it may conflict with the
                        // zoom transition
                        panEngageTimeout = setTimeout( function() {
                            panUpdateInterval = setInterval( pan, 1000 / 60 );
                        }, 800 );

                    }
                }
            }
        },

        /**
         * Resets the document zoom state to its default.
         */
        out: function() {
            clearTimeout( panEngageTimeout );
            clearInterval( panUpdateInterval );

            var scrollOffset = getScrollOffset();
            
            magnify( scrollOffset.x, scrollOffset.y, 0, 0, 1 );

            level = 1;
        },

        // Alias
        magnify: function( options ) { this.to( options ) },
        reset: function() { this.out() },
        
        zoomLevel: function() {
            return level;
        }
    }
    
})();

