/*! Overthrow v.0.1.0. An overflow:auto polyfill for responsive design. (c) 2012: Scott Jehl, Filament Group, Inc. http://filamentgroup.github.com/Overthrow/license.txt */
(function( w, undefined ){

    var doc = w.document,
        docElem = doc.documentElement,
        classtext = "overthrow-enabled",

        // Touch events are used in the polyfill, and thus are a prerequisite
        canBeFilledWithPoly = "ontouchmove" in doc,

        // The following attempts to determine whether the browser has native overflow support
        // so we can enable it but not polyfill
        overflowProbablyAlreadyWorks =
            // Features-first. iOS5 overflow scrolling property check - no UA needed here. thanks Apple :)
            "WebkitOverflowScrolling" in docElem.style ||
            // Touch events aren't supported and screen width is greater than X
            // ...basically, this is a loose "desktop browser" check.
            // It may wrongly opt-in very large tablets with no touch support.
            ( !canBeFilledWithPoly && w.screen.width > 1200 ) ||
            // Hang on to your hats.
            // Whitelist some popular, overflow-supporting mobile browsers for now and the future
            // These browsers are known to get overlow support right, but give us no way of detecting it.
            (function(){
                var ua = w.navigator.userAgent,
                    // Webkit crosses platforms, and the browsers on our list run at least version 534
                    webkit = ua.match( /AppleWebKit\/([0-9]+)/ ),
                    wkversion = webkit && webkit[1],
                    wkLte534 = webkit && wkversion >= 534;

                return (
                    /* Android 3+ with webkit gte 534
                    ~: Mozilla/5.0 (Linux; U; Android 3.0; en-us; Xoom Build/HRI39) AppleWebKit/534.13 (KHTML, like Gecko) Version/4.0 Safari/534.13 */
                    ua.match( /Android ([0-9]+)/ ) && RegExp.$1 >= 3 && wkLte534 ||
                    /* Blackberry 7+ with webkit gte 534
                    ~: Mozilla/5.0 (BlackBerry; U; BlackBerry 9900; en-US) AppleWebKit/534.11+ (KHTML, like Gecko) Version/7.0.0 Mobile Safari/534.11+ */
                    ua.match( / Version\/([0-9]+)/ ) && RegExp.$1 >= 0 && w.blackberry && wkLte534 ||
                    /* Blackberry Playbook with webkit gte 534
                    ~: Mozilla/5.0 (PlayBook; U; RIM Tablet OS 1.0.0; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/0.0.1 Safari/534.8+ */
                    ua.indexOf( /PlayBook/ ) > -1 && RegExp.$1 >= 0 && wkLte534 ||
                    /* Firefox Mobile (Fennec) 4 and up
                    ~: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:2.1.1) Gecko/ Firefox/4.0.2pre Fennec/4.0. */
                    ua.match( /Fennec\/([0-9]+)/ ) && RegExp.$1 >= 4 ||
                    /* WebOS 3 and up (TouchPad too)
                    ~: Mozilla/5.0 (hp-tablet; Linux; hpwOS/3.0.0; U; en-US) AppleWebKit/534.6 (KHTML, like Gecko) wOSBrowser/233.48 Safari/534.6 TouchPad/1.0 */
                    ua.match( /wOSBrowser\/([0-9]+)/ ) && RegExp.$1 >= 233 && wkLte534 ||
                    /* Nokia Browser N8
                    ~: Mozilla/5.0 (Symbian/3; Series60/5.2 NokiaN8-00/012.002; Profile/MIDP-2.1 Configuration/CLDC-1.1 ) AppleWebKit/533.4 (KHTML, like Gecko) NokiaBrowser/7.3.0 Mobile Safari/533.4 3gpp-gba
                    ~: Note: the N9 doesn't have native overflow with one-finger touch. wtf */
                    ua.match( /NokiaBrowser\/([0-9\.]+)/ ) && parseFloat(RegExp.$1) === 7.3 && webkit && wkversion >= 533
                );
            })(),

        // Easing can use any of Robert Penner's equations (http://www.robertpenner.com/easing_terms_of_use.html). By default, overthrow includes ease-out-cubic
        // arguments: t = current iteration, b = initial value, c = end value, d = total iterations
        // use w.overthrow.easing to provide a custom function externally, or pass an easing function as a callback to the toss method
        defaultEasing = function (t, b, c, d) {
            return c*((t=t/d-1)*t*t + 1) + b;
        },

        enabled = false,

        // Keeper of intervals
        timeKeeper,

        /* toss scrolls and element with easing

        // elem is the element to scroll
        // options hash:
            * left is the desired horizontal scroll. Default is "+0". For relative distances, pass a string with "+" or "-" in front.
            * top is the desired vertical scroll. Default is "+0". For relative distances, pass a string with "+" or "-" in front.
            * duration is the number of milliseconds the throw will take. Default is 100.
            * easing is an optional custom easing function. Default is w.overthrow.easing. Must follow the easing function signature
        */
        toss = function( elem, options ){
            var i = 0,
                sLeft = elem.scrollLeft,
                sTop = elem.scrollTop,
                // Toss defaults
                o = {
                    top: "+0",
                    left: "+0",
                    duration: 100,
                    easing: w.overthrow.easing
                },
                endLeft, endTop;

            // Mixin based on predefined defaults
            if( options ){
                for( var j in o ){
                    if( options[ j ] !== undefined ){
                        o[ j ] = options[ j ];
                    }
                }
            }

            // Convert relative values to ints
            // First the left val
            if( typeof o.left === "string" ){
                o.left = parseFloat( o.left );
                endLeft = o.left + sLeft;
            }
            else {
                endLeft = o.left;
                o.left = o.left - sLeft;
            }
            // Then the top val
            if( typeof o.top === "string" ){
                o.top = parseFloat( o.top );
                endTop = o.top + sTop;
            }
            else {
                endTop = o.top;
                o.top = o.top - sTop;
            }

            timeKeeper = setInterval(function(){
                if( i++ < o.duration ){
                    elem.scrollLeft = o.easing( i, sLeft, o.left, o.duration );
                    elem.scrollTop = o.easing( i, sTop, o.top, o.duration );
                }
                else{
                    if( endLeft !== elem.scrollLeft ){
                        elem.scrollLeft = endLeft;
                    }
                    if( endTop !== elem.scrollTop ){
                        elem.scrollTop = endTop;
                    }
                    intercept();
                }
            }, 1 );

            // Return the values, post-mixin, with end values specified
            return { top: endTop, left: endLeft, duration: o.duration, easing: o.easing };
        },

        // find closest overthrow (elem or a parent)
        closest = function( target, ascend ){
            return !ascend && target.className && target.className.indexOf( "overthrow" ) > -1 && target || closest( target.parentNode );
        },

        // Intercept any throw in progress
        intercept = function(){
            clearInterval( timeKeeper );
        },

        // Enable and potentially polyfill overflow
        enable = function(){

            // If it's on,
            if( enabled ){
                return;
            }
            // It's on.
            enabled = true;

            // If overflowProbablyAlreadyWorks or at least the element canBeFilledWithPoly, add a class to cue CSS that assumes overflow scrolling will work (setting height on elements and such)
            if( overflowProbablyAlreadyWorks || canBeFilledWithPoly ){
                docElem.className += " " + classtext;
            }

            // Destroy everything later. If you want to.
            w.overthrow.forget = function(){
                // Strip the class name from docElem
                docElem.className = docElem.className.replace( classtext, "" );
                // Remove touch binding (check for method support since this part isn't qualified by touch support like the rest)
                if( doc.removeEventListener ){
                    doc.removeEventListener( "touchstart", start, false );
                }
                // reset easing to default
                w.overthrow.easing = defaultEasing;

                // Let 'em know
                enabled = false;
            };

            // If overflowProbablyAlreadyWorks or it doesn't look like the browser canBeFilledWithPoly, our job is done here. Exit viewport left.
            if( overflowProbablyAlreadyWorks || !canBeFilledWithPoly ){
                return;
            }

            // Fill 'er up!
            // From here down, all logic is associated with touch scroll handling
                // elem references the overthrow element in use
            var elem,

                // The last several Y values are kept here
                lastTops = [],

                // The last several X values are kept here
                lastLefts = [],

                // lastDown will be true if the last scroll direction was down, false if it was up
                lastDown,

                // lastRight will be true if the last scroll direction was right, false if it was left
                lastRight,

                // For a new gesture, or change in direction, reset the values from last scroll
                resetVertTracking = function(){
                    lastTops = [];
                    lastDown = null;
                },

                resetHorTracking = function(){
                    lastLefts = [];
                    lastRight = null;
                },

                // After releasing touchend, throw the overthrow element, depending on momentum
                finishScroll = function(){
                    // Come up with a distance and duration based on how
                    // Multipliers are tweaked to a comfortable balance across platforms
                    var top = ( lastTops[ 0 ] - lastTops[ lastTops.length -1 ] ) * 8,
                        left = ( lastLefts[ 0 ] - lastLefts[ lastLefts.length -1 ] ) * 8,
                        duration = Math.max( Math.abs( left ), Math.abs( top ) ) / 8;

                    // Make top and left relative-style strings (positive vals need "+" prefix)
                    top = ( top > 0 ? "+" : "" ) + top;
                    left = ( left > 0 ? "+" : "" ) + left;

                    // Make sure there's a significant amount of throw involved, otherwise, just stay still
                    if( !isNaN( duration ) && duration > 0 && ( Math.abs( left ) > 80 || Math.abs( top ) > 80 ) ){
                        toss( elem, { left: left, top: top, duration: duration } );
                    }
                },

                // On webkit, touch events hardly trickle through textareas and inputs
                // Disabling CSS pointer events makes sure they do, but it also makes the controls innaccessible
                // Toggling pointer events at the right moments seems to do the trick
                // Thanks Thomas Bachem http://stackoverflow.com/a/5798681 for the following
                inputs,
                setPointers = function( val ){
                    inputs = elem.querySelectorAll( "textarea, input" );
                    for( var i = 0, il = inputs.length; i < il; i++ ) {
                        inputs[ i ].style.pointerEvents = val;
                    }
                },

                // For nested overthrows, changeScrollTarget restarts a touch event cycle on a parent or child overthrow
                changeScrollTarget = function( startEvent, ascend ){
                    if( doc.createEvent ){
                        var newTarget = ( !ascend || ascend === undefined ) && elem.parentNode || elem.touchchild || elem,
                            tEnd;

                        if( newTarget !== elem ){
                            tEnd = doc.createEvent( "HTMLEvents" );
                            tEnd.initEvent( "touchend", true, true );
                            elem.dispatchEvent( tEnd );
                            newTarget.touchchild = elem;
                            elem = newTarget;
                            newTarget.dispatchEvent( startEvent );
                        }
                    }
                },

                // Touchstart handler
                // On touchstart, touchmove and touchend are freshly bound, and all three share a bunch of vars set by touchstart
                // Touchend unbinds them again, until next time
                start = function( e ){

                    // Stop any throw in progress
                    intercept();

                    // Reset the distance and direction tracking
                    resetVertTracking();
                    resetHorTracking();

                    elem = closest( e.target );

                    if( !elem || elem === docElem || e.touches.length > 1 ){
                        return;
                    }

                    setPointers( "none" );
                    var touchStartE = e,
                        scrollT = elem.scrollTop,
                        scrollL = elem.scrollLeft,
                        height = elem.offsetHeight,
                        width = elem.offsetWidth,
                        startY = e.touches[ 0 ].pageY,
                        startX = e.touches[ 0 ].pageX,
                        scrollHeight = elem.scrollHeight,
                        scrollWidth = elem.scrollWidth,

                        // Touchmove handler
                        move = function( e ){

                            var ty = scrollT + startY - e.touches[ 0 ].pageY,
                                tx = scrollL + startX - e.touches[ 0 ].pageX,
                                down = ty >= ( lastTops.length ? lastTops[ 0 ] : 0 ),
                                right = tx >= ( lastLefts.length ? lastLefts[ 0 ] : 0 );

                            // If there's room to scroll the current container, prevent the default window scroll
                            if( ( ty > 0 && ty < scrollHeight - height ) || ( tx > 0 && tx < scrollWidth - width ) ){
                                e.preventDefault();
                            }
                            // This bubbling is dumb. Needs a rethink.
                            else {
                                changeScrollTarget( touchStartE );
                            }

                            // If down and lastDown are inequal, the y scroll has changed direction. Reset tracking.
                            if( lastDown && down !== lastDown ){
                                resetVertTracking();
                            }

                            // If right and lastRight are inequal, the x scroll has changed direction. Reset tracking.
                            if( lastRight && right !== lastRight ){
                                resetHorTracking();
                            }

                            // remember the last direction in which we were headed
                            lastDown = down;
                            lastRight = right;

                            // set the container's scroll
                            elem.scrollTop = ty;
                            elem.scrollLeft = tx;

                            lastTops.unshift( ty );
                            lastLefts.unshift( tx );

                            if( lastTops.length > 3 ){
                                lastTops.pop();
                            }
                            if( lastLefts.length > 3 ){
                                lastLefts.pop();
                            }
                        },

                        // Touchend handler
                        end = function( e ){
                            // Apply momentum based easing for a graceful finish
                            finishScroll();
                            // Bring the pointers back
                            setPointers( "auto" );
                            setTimeout( function(){
                                setPointers( "none" );
                            }, 450 );
                            elem.removeEventListener( "touchmove", move, false );
                            elem.removeEventListener( "touchend", end, false );
                        };

                    elem.addEventListener( "touchmove", move, false );
                    elem.addEventListener( "touchend", end, false );
                };

            // Bind to touch, handle move and end within
            doc.addEventListener( "touchstart", start, false );
        };

    // Expose overthrow API
    w.overthrow = {
        set: enable,
        forget: function(){},
        easing: defaultEasing,
        toss: toss,
        intercept: intercept,
        closest: closest,
        support: overflowProbablyAlreadyWorks ? "native" : canBeFilledWithPoly && "polyfilled" || "none"
    };

    // Auto-init
    enable();

})( this );
