/*! Picturefill - Responsive Images that work today.
*  Author: Scott Jehl, Filament Group, 2012 ( new proposal implemented by Shawn Jansepar )
*  License: MIT/GPLv2
*  Spec: http://picture.responsiveimages.org/
*/
(function( w, doc ) {
	// Enable strict mode
	"use strict";

	// If picture is supported, well, that's awesome. Let's get outta here...
	if ( w.HTMLPictureElement ) {
		return;
	}

	// HTML shim|v it for old IE (IE9 will still need the HTML video tag workaround)
	doc.createElement( "picture" );

	// local object for method references and testing exposure
	var pf = {};

	// namespace
	pf.ns = "picturefill";

	// srcset support test
	pf.srcsetSupported = new w.Image().srcset !== undefined;

	// just a string trim workaround
	pf.trim = function( str ) {
		return str.trim ? str.trim() : str.replace( /^\s+|\s+$/g, "" );
	};

	// just a string endsWith workaround
	pf.endsWith = function( str, suffix ) {
		return str.endsWith ? str.endsWith( suffix ) : str.indexOf( suffix, str.length - suffix.length ) !== -1;
	};

	/**
	 * Shortcut method for matchMedia ( for easy overriding in tests )
	 */
	pf.matchesMedia = function( media ) {
		return w.matchMedia && w.matchMedia( media ).matches;
	};

	/**
	 * Shortcut method for `devicePixelRatio` ( for easy overriding in tests )
	 */
	pf.getDpr = function() {
		return ( w.devicePixelRatio || 1 );
	};

	/**
	 * Get width in css pixel value from a "length" value
	 * http://dev.w3.org/csswg/css-values-3/#length-value
	 */
	pf.getWidthFromLength = function( length ) {
		// If no length was specified, or it is 0, default to `100vw` (per the spec).
		length = length && parseFloat( length ) > 0 ? length : "100vw";

		/**
		* If length is specified in  `vw` units, use `%` instead since the div we’re measuring
		* is injected at the top of the document.
		*
		* TODO: maybe we should put this behind a feature test for `vw`?
		*/
		length = length.replace( "vw", "%" );

		// Create a cached element for getting length value widths
		if ( !pf.lengthEl ) {
			pf.lengthEl = doc.createElement( "div" );
			doc.documentElement.insertBefore( pf.lengthEl, doc.documentElement.firstChild );
		}

		// Positioning styles help prevent padding/margin/width on `html` from throwing calculations off.
		pf.lengthEl.style.cssText = "position: absolute; left: 0; width: " + length + ";";
		// Using offsetWidth to get width from CSS
		return pf.lengthEl.offsetWidth;
	};

	// container of supported mime types that one might need to qualify before using
	pf.types =  {};

	// Add support for standard mime types.
	pf.types["image/jpeg"] = true;
	pf.types["image/gif"] = true;
	pf.types["image/png"] = true;

	// test svg support
	pf.types[ "image/svg+xml" ] = doc.implementation.hasFeature("http://www.w3.org/TR/SVG11/feature#Image", "1.1");

	// test webp support, only when the markup calls for it
	pf.types[ "image/webp" ] = function() {
		// based on Modernizr's lossless img-webp test
		// note: asynchronous
		var img = new w.Image(),
			type = "image/webp";

		img.onerror = function() {
			pf.types[ type ] = false;
			picturefill();
		};
		img.onload = function() {
			pf.types[ type ] = img.width === 1;
			picturefill();
		};
		img.src = "data:image/webp;base64,UklGRh4AAABXRUJQVlA4TBEAAAAvAAAAAAfQ//73v/+BiOh/AAA=";
	};

	/**
	 * Takes a source element and checks if its type attribute is present and if so, supported
	 * Note: for type tests that require a async logic,
	 * you can define them as a function that'll run only if that type needs to be tested. Just make the test function call picturefill again when it is complete.
	 * see the async webp test above for example
	 */
	pf.verifyTypeSupport = function( source ) {
		var type = source.getAttribute( "type" );
		// if type attribute exists, return test result, otherwise return true
		if ( type === null || type === "" ) {
			return true;
		} else {
			// if the type test is a function, run it and return "pending" status. The function will rerun picturefill on pending elements once finished.
			if ( typeof( pf.types[ type ] ) === "function" ) {
				pf.types[ type ]();
				return "pending";
			} else {
				return pf.types[ type ];
			}
		}
	};

	/**
	* Parses an individual `size` and returns the length, and optional media query
	*/
	pf.parseSize = function( sourceSizeStr ) {
		var match = /(\([^)]+\))?\s*(.+)/g.exec( sourceSizeStr );
		return {
			media: match && match[1],
			length: match && match[2]
		};
	};

	/**
	 * Takes a string of sizes and returns the width in pixels as a number
	 */
	pf.findWidthFromSourceSize = function( sourceSizeListStr ) {
		// Split up source size list, ie ( max-width: 30em ) 100%, ( max-width: 50em ) 50%, 33%
		//                            or (min-width:30em) calc(30% - 15px)
		var sourceSizeList = pf.trim( sourceSizeListStr ).split( /\s*,\s*/ ),
			winningLength;

		for ( var i = 0, len = sourceSizeList.length; i < len; i++ ) {
			// Match <media-condition>? length, ie ( min-width: 50em ) 100%
			var sourceSize = sourceSizeList[ i ],
				// Split "( min-width: 50em ) 100%" into separate strings
				parsedSize = pf.parseSize( sourceSize ),
				length = parsedSize.length,
				media = parsedSize.media;

			if ( !length ) {
					continue;
			}
			if ( !media || pf.matchesMedia( media ) ) {
				// if there is no media query or it matches, choose this as our winning length
				// and end algorithm
				winningLength = length;
				break;
			}
		}

		// pass the length to a method that can properly determine length
		// in pixels based on these formats: http://dev.w3.org/csswg/css-values-3/#length-value
		return pf.getWidthFromLength( winningLength );
	};

	pf.parseSrcset = function( srcset ) {
		/**
		* A lot of this was pulled from Boris Smus’ parser for the now-defunct WHATWG `srcset`
		* https://github.com/borismus/srcset-polyfill/blob/master/js/srcset-info.js
		*
		* 1. Let input (`srcset`) be the value passed to this algorithm.
		* 2. Let position be a pointer into input, initially pointing at the start of the string.
		* 3. Let raw candidates be an initially empty ordered list of URLs with associated 
		*    unparsed descriptors. The order of entries in the list is the order in which entries 
		*    are added to the list.
		*/
		var candidates = [];

		while ( srcset !== "" ) {
			srcset = srcset.replace(/^\s+/g,"");

			// 5. Collect a sequence of characters that are not space characters, and let that be url.
			var pos = srcset.search(/\s/g),
				url, descriptor = null;

			if ( pos !== -1 ) {
				url = srcset.slice( 0, pos );

				var last = url[ url.length - 1 ];

				// 6. If url ends with a U+002C COMMA character (,), remove that character from url
				// and let descriptors be the empty string. Otherwise, follow these substeps
				// 6.1. If url is empty, then jump to the step labeled descriptor parser.

				if ( last === "," || url === "" ) {
					url = url.replace(/,+$/, "");
					descriptor = "";
				}
				srcset = srcset.slice( pos + 1 );

				// 6.2. Collect a sequence of characters that are not U+002C COMMA characters (,), and 
				// let that be descriptors.
				if ( descriptor === null ) {
					var descpos = srcset.indexOf(",");
					if ( descpos !== -1 ) {
						descriptor = srcset.slice( 0, descpos );
						srcset = srcset.slice( descpos + 1 );
					} else {
						descriptor = srcset;
						srcset = "";
					}
				}
			} else {
				url = srcset;
				srcset = "";
			}

			// 7. Add url to raw candidates, associated with descriptors.
			if ( url || descriptor ) {
				candidates.push({
					url: url,
					descriptor: descriptor
				});
			}
		}
		return candidates;
	};

	pf.parseDescriptor = function( descriptor, sizes ) {
		// 11. Descriptor parser: Let candidates be an initially empty source set. The order of entries in the list 
		// is the order in which entries are added to the list.
		var sizeDescriptor = descriptor && descriptor.replace(/(^\s+|\s+$)/g, ""),
			widthInCssPixels = sizes ? pf.findWidthFromSourceSize( sizes ) : "100%",
			resCandidate;

			if ( sizeDescriptor ) {
				var splitDescriptor = sizeDescriptor.split(" ");

				for (var i = splitDescriptor.length + 1; i >= 0; i--) {

					var curr = splitDescriptor[ i ],
						lastchar = curr && curr.slice( curr.length - 1 );

					if ( lastchar === "w" || lastchar === "x" ) {
						resCandidate = curr;
					}
					if ( sizes && resCandidate ) {
						// get the dpr by taking the length / width in css pixels
						resCandidate = parseFloat( ( parseInt( curr, 10 ) / widthInCssPixels ) );
					} else {
						// get the dpr by grabbing the value of Nx
						var res = curr && parseFloat( curr, 10 );

						resCandidate = res && !isNaN( res ) && lastchar === "x" || lastchar === "w" ? res : 1;
					}
				}
			} else {
				resCandidate = 1;
			}
		return resCandidate;
	};

	/**
	 * Takes a srcset in the form of url/
	 * ex. "images/pic-medium.png 1x, images/pic-medium-2x.png 2x" or
	 *     "images/pic-medium.png 400w, images/pic-medium-2x.png 800w" or
	 *     "images/pic-small.png"
	 * Get an array of image candidates in the form of
	 *      {url: "/foo/bar.png", resolution: 1}
	 * where resolution is http://dev.w3.org/csswg/css-values-3/#resolution-value
	 * If sizes is specified, resolution is calculated
	 */
	pf.getCandidatesFromSourceSet = function( srcset, sizes ) {
		var candidates = pf.parseSrcset( srcset ),
			formattedCandidates = [];

		for ( var i = 0, len = candidates.length; i < len; i++ ) {
			var candidate = candidates[ i ];

			formattedCandidates.push({
				url: candidate.url,
				resolution: pf.parseDescriptor( candidate.descriptor, sizes )
			});
		}
		return formattedCandidates;
	};

	/*
	 * if it's an img element and it has a srcset property,
	 * we need to remove the attribute so we can manipulate src
	 * (the property's existence infers native srcset support, and a srcset-supporting browser will prioritize srcset's value over our winning picture candidate)
	 * this moves srcset's value to memory for later use and removes the attr
	 */
	pf.dodgeSrcset = function( img ) {
		if ( img.srcset ) {
			img[ pf.ns ].srcset = img.srcset;
			img.removeAttribute( "srcset" );
		}
	};

	/*
	 * Accept a source or img element and process its srcset and sizes attrs
	 */
	pf.processSourceSet = function( el ) {
		var srcset = el.getAttribute( "srcset" ),
			sizes = el.getAttribute( "sizes" ),
			candidates = [];

		// if it's an img element, use the cached srcset property (defined or not)
		if ( el.nodeName.toUpperCase() === "IMG" && el[ pf.ns ] && el[ pf.ns ].srcset ) {
			srcset = el[ pf.ns ].srcset;
		}

		if ( srcset ) {
			candidates = pf.getCandidatesFromSourceSet( srcset, sizes );
		}
		return candidates;
	};

	pf.applyBestCandidate = function( candidates, picImg ) {
		var candidate,
			length,
			bestCandidate;

		candidates.sort( pf.ascendingSort );

		length = candidates.length;
		bestCandidate = candidates[ length - 1 ];

		for ( var i = 0; i < length; i++ ) {
			candidate = candidates[ i ];
			if ( candidate.resolution >= pf.getDpr() ) {
				bestCandidate = candidate;
				break;
			}
		}

		if ( !pf.endsWith( picImg.src, bestCandidate.url ) ) {
			picImg.src = bestCandidate.url;
			// currentSrc attribute and property to match
			// http://picture.responsiveimages.org/#the-img-element
			picImg.currentSrc = picImg.src;
		}
	};

	pf.ascendingSort = function( a, b ) {
		return a.resolution - b.resolution;
	};

	/*
	 * In IE9, <source> elements get removed if they aren't children of
	 * video elements. Thus, we conditionally wrap source elements
	 * using <!--[if IE 9]><video style="display: none;"><![endif]-->
	 * and must account for that here by moving those source elements
	 * back into the picture element.
	 */
	pf.removeVideoShim = function( picture ) {
		var videos = picture.getElementsByTagName( "video" );
		if ( videos.length ) {
			var video = videos[ 0 ],
				vsources = video.getElementsByTagName( "source" );
			while ( vsources.length ) {
				picture.insertBefore( vsources[ 0 ], video );
			}
			// Remove the video element once we're finished removing its children
			video.parentNode.removeChild( video );
		}
	};

	/*
	 * Find all picture elements and,
	 * in browsers that don't natively support srcset, find all img elements
	 * with srcset attrs that don't have picture parents
	 */
	pf.getAllElements = function() {
		var pictures = doc.getElementsByTagName( "picture" ),
			elems = [],
			imgs = doc.getElementsByTagName( "img" );

		for ( var h = 0, len = pictures.length + imgs.length; h < len; h++ ) {
			if ( h < pictures.length ) {
				elems[ h ] = pictures[ h ];
			} else {
				var currImg = imgs[ h - pictures.length ];

				if ( currImg.parentNode.nodeName.toUpperCase() !== "PICTURE" &&
					( ( pf.srcsetSupported && currImg.getAttribute( "sizes" ) ) ||
					currImg.getAttribute( "srcset" ) !== null ) ) {
						elems.push( currImg );
				}
			}
		}
		return elems;
	};

	pf.getMatch = function( picture ) {
		var sources = picture.childNodes,
			match;

		// Go through each child, and if they have media queries, evaluate them
		for ( var j = 0, slen = sources.length; j < slen; j++ ) {
			var source = sources[ j ];

			// ignore non-element nodes
			if ( source.nodeType !== 1 ) {
				continue;
			}

			// Hitting an `img` element stops the search for `sources`.
			// If no previous `source` matches, the `img` itself is evaluated later.
			if ( source.nodeName.toUpperCase() === "IMG" ) {
				return match;
			}

			// ignore non-`source` nodes
			if ( source.nodeName.toUpperCase() !== "SOURCE" ) {
				continue;
			}

			var media = source.getAttribute( "media" );

			// if source does not have a srcset attribute, skip
			if ( !source.getAttribute( "srcset" ) ) {
				continue;
			}

			// if there's no media specified, OR w.matchMedia is supported
			if ( ( !media || pf.matchesMedia( media ) ) ) {
				var typeSupported = pf.verifyTypeSupport( source );

				if ( typeSupported === true ) {
					match = source;
					break;
				} else if ( typeSupported === "pending" ) {
					return false;
				}
			}
		}

		return match;
	};

	function picturefill( options ) {
		var elements,
			element,
			elemType,
			firstMatch,
			candidates,
			picImg;

		options = options || {};
		elements = options.elements || pf.getAllElements();

		// Loop through all elements
		for ( var i = 0, plen = elements.length; i < plen; i++ ) {
			element = elements[ i ];
			elemType = element.nodeName.toUpperCase();
			firstMatch = undefined;
			candidates = undefined;
			picImg = undefined;

			// expando for caching data on the img
			if ( !element[ pf.ns ] ) {
				element[ pf.ns ] = {};
			}

			// if the element has already been evaluated, skip it
			// unless `options.force` is set to true ( this, for example,
			// is set to true when running `picturefill` on `resize` ).
			if ( !options.reevaluate && element[ pf.ns ].evaluated ) {
				continue;
			}

			// if element is a picture element
			if ( elemType === "PICTURE" ) {

				// IE9 video workaround
				pf.removeVideoShim( element );

				// return the first match which might undefined
				// returns false if there is a pending source
				// TODO the return type here is brutal, cleanup
				firstMatch = pf.getMatch( element );

				// if any sources are pending in this picture due to async type test(s)
				// remove the evaluated attr and skip for now ( the pending test will
				// rerun picturefill on this element when complete)
				if ( firstMatch === false ) {
					continue;
				}

				// Find any existing img element in the picture element
				picImg = element.getElementsByTagName( "img" )[ 0 ];
			} else {
				// if it's an img element
				firstMatch = undefined;
				picImg = element;
			}

			if ( picImg ) {

				// expando for caching data on the img
				if ( !picImg[ pf.ns ] ) {
					picImg[ pf.ns ] = {};
				}

				// Cache and remove `srcset` if present and we’re going to be doing `sizes`/`picture` polyfilling to it.
				if ( picImg.srcset && ( elemType === "PICTURE" || picImg.getAttribute( "sizes" ) ) ) {
					pf.dodgeSrcset( picImg );
				}

				if ( firstMatch ) {
					candidates = pf.processSourceSet( firstMatch );
					pf.applyBestCandidate( candidates, picImg );
				} else {
					// No sources matched, so we’re down to processing the inner `img` as a source.
					candidates = pf.processSourceSet( picImg );

					if ( picImg.srcset === undefined || picImg[ pf.ns ].srcset ) {
						// Either `srcset` is completely unsupported, or we need to polyfill `sizes` functionality.
						pf.applyBestCandidate( candidates, picImg );
					} // Else, resolution-only `srcset` is supported natively.
				}

				// set evaluated to true to avoid unnecessary reparsing
				element[ pf.ns ].evaluated = true;
			}
		}
	}

	/**
	 * Sets up picture polyfill by polling the document and running
	 * the polyfill every 250ms until the document is ready.
	 * Also attaches picturefill on resize
	 */
	function runPicturefill() {
		picturefill();
		var intervalId = setInterval( function() {
			// When the document has finished loading, stop checking for new images
			// https://github.com/ded/domready/blob/master/ready.js#L15
			picturefill();
			if ( /^loaded|^i|^c/.test( doc.readyState ) ) {
				clearInterval( intervalId );
				return;
			}
		}, 250 );
		if ( w.addEventListener ) {
			var resizeThrottle;
			w.addEventListener( "resize", function() {
				if (!w._picturefillWorking) {
					w._picturefillWorking = true;
					w.clearTimeout( resizeThrottle );
					resizeThrottle = w.setTimeout( function() {
						picturefill({ reevaluate: true });
						w._picturefillWorking = false;
					}, 60 );
				}
			}, false );
		}
	}

	runPicturefill();

	/* expose methods for testing */
	picturefill._ = pf;

	/* expose picturefill */
	if ( typeof module === "object" && typeof module.exports === "object" ) {
		// CommonJS, just export
		module.exports = picturefill;
	} else if ( typeof define === "function" && define.amd ){
		// AMD support
		define( function() { return picturefill; } );
	} else if ( typeof w === "object" ) {
		// If no AMD and we are in the browser, attach to window
		w.picturefill = picturefill;
	}

} )( this, this.document );
