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+/**
+ * Copyright (C) 2011 Hakim El Hattab, http://hakim.se
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+/**
+ * Handles the very minimal navigation logic involved in the 
+ * slideshow. Including keyboard navigation, touch interaction 
+ * and URL history behavior.
+ * 
+ * Slides are given unique hash based URL's so that they can be 
+ * opened directly. I didn't use the HTML5 History API for this 
+ * as it would have required the addition of server side rewrite 
+ * rules and hence require more effort for anyone to set up.
+ * 
+ * This component can be called from other scripts via a tiny API:
+ * - Slideshow.navigateTo( indexh, indexv );
+ * - Slideshow.navigateLeft();
+ * - Slideshow.navigateRight();
+ * - Slideshow.navigateUp();
+ * - Slideshow.navigateDown();
+ * 
+ * 
+ * version 0.1:
+ * - First release
+ * 
+ * version 0.2:		
+ * - Refactored code and added inline documentation
+ * - Slides now have unique URL's
+ * - A basic API to invoke navigation was added
+ * 
+ * version 0.3:		
+ * - Added licensing terms
+ * 
+ * 	
+ * @author Hakim El Hattab
+ * @version 0.3
+ */
+var Slideshow = (function(){
+	
+	var indexh = 0,
+		indexv = 0;
+	
+	/**
+	 * Activates the main program logic.
+	 */
+	function initialize() {
+		document.addEventListener('keydown', onDocumentKeyDown, false);
+		document.addEventListener('touchstart', onDocumentTouchStart, false);
+		window.addEventListener('hashchange', onWindowHashChange, false);
+		
+		// Read the initial state of the URL (hash)
+		readURL();
+	}
+	
+	/**
+	 * Handler for the document level 'keydown' event.
+	 * 
+	 * @param {Object} event
+	 */
+	function onDocumentKeyDown( event ) {
+		
+		if( event.keyCode >= 37 && event.keyCode <= 40 ) {
+			
+			switch( event.keyCode ) {
+				case 37: navigateLeft(); break; // left
+				case 39: navigateRight(); break; // right
+				case 38: navigateUp(); break; // up
+				case 40: navigateDown(); break; // down
+			}
+			
+			slide();
+			
+			event.preventDefault();
+			
+		}
+	}
+	
+	/**
+	 * Handler for the document level 'touchstart' event.
+	 * 
+	 * This enables very basic tap interaction for touch
+	 * devices. Added mainly for performance testing of 3D
+	 * transforms on iOS but was so happily surprised with
+	 * how smoothly it runs so I left it in here. Apple +1
+	 * 
+	 * @param {Object} event
+	 */
+	function onDocumentTouchStart( event ) {
+		
+		// We're only interested in one point taps
+		if (event.touches.length == 1) {
+			event.preventDefault();
+			
+			var point = {
+				x: event.touches[0].clientX,
+				y: event.touches[0].clientY
+			};
+			
+			// Define the extent of the areas that may be tapped
+			// to navigate
+			var wt = window.innerWidth * 0.3;
+			var ht = window.innerHeight * 0.3;
+			
+			if( point.x < wt ) {
+				navigateLeft();
+			}
+			else if( point.x > window.innerWidth - wt ) {
+				navigateRight();
+			}
+			else if( point.y < ht ) {
+				navigateUp();
+			}
+			else if( point.y > window.innerHeight - ht ) {
+				navigateDown();
+			}
+			
+			slide();
+			
+		}
+	}
+	
+	
+	/**
+	 * Handler for the window level 'hashchange' event.
+	 * 
+	 * @param {Object} event
+	 */
+	function onWindowHashChange( event ) {
+		readURL();
+	}
+	
+	/**
+	 * Updates one dimension of slides by showing the slide
+	 * with the specified index.
+	 * 
+	 * @param {String} selector A CSS selector that will fetch
+	 * the group of slides we are working with
+	 * @param {Number} index The index of the slide that should be
+	 * shown
+	 * 
+	 * @return {Number} The index of the slide that is now shown,
+	 * might differ from the passed in index if it was out of 
+	 * bounds.
+	 */
+	function updateSlides( selector, index ) {
+		
+		// Select all slides and convert the NodeList result to
+		// an array
+		var slides = Array.prototype.slice.call( document.querySelectorAll( selector ) );
+		
+		if( slides.length ) {
+			// Enforce max and minimum index bounds
+			index = Math.max(Math.min(index, slides.length - 1), 0);
+			
+			slides[index].setAttribute('class', 'present');
+			
+			// Any element previous to index is given the 'past' class
+			slides.slice(0, index).map(function(element){
+				element.setAttribute('class', 'past');
+			});
+			
+			// Any element subsequent to index is given the 'future' class
+			slides.slice(index + 1).map(function(element){
+				element.setAttribute('class', 'future');
+			});
+		}
+		else {
+			// Since there are no slides we can't be anywhere beyond the 
+			// zeroth index
+			index = 0;
+		}
+		
+		return index;
+		
+	}
+	
+	/**
+	 * Updates the visual slides to represent the currently
+	 * set indices. 
+	 */
+	function slide() {
+		indexh = updateSlides( '#main>section', indexh );
+		indexv = updateSlides( 'section.present>section', indexv );
+		
+		writeURL();
+	}
+	
+	/**
+	 * Reads the current URL (hash) and navigates accordingly.
+	 */
+	function readURL() {
+		// Break the hash down to separate components
+		var bits = window.location.hash.slice(2).split('/');
+		
+		// Read the index components of the hash
+		indexh = bits[0] ? parseInt( bits[0] ) : 0;
+		indexv = bits[1] ? parseInt( bits[1] ) : 0;
+		
+		navigateTo( indexh, indexv );
+	}
+	
+	/**
+	 * Updates the page URL (hash) to reflect the current
+	 * navigational state. 
+	 */
+	function writeURL() {
+		var url = '/';
+		
+		// Only include the minimum possible number of components in
+		// the URL
+		if( indexh > 0 || indexv > 0 ) url += indexh
+		if( indexv > 0 ) url += '/' + indexv
+		
+		window.location.hash = url;
+	}
+	
+	/**
+	 * Triggers a navigation to the specified indices.
+	 * 
+	 * @param {Number} h The horizontal index of the slide to show
+	 * @param {Number} v The vertical index of the slide to show
+	 */
+	function navigateTo( h, v ) {
+		indexh = h === undefined ? indexh : h;
+		indexv = v === undefined ? indexv : v;
+		
+		slide();
+	}
+	
+	function navigateLeft() {
+		indexh --;
+		indexv = 0;
+		slide();
+	}
+	function navigateRight() {
+		indexh ++;
+		indexv = 0;
+		slide();
+	}
+	function navigateUp() {
+		indexv --;
+		slide();
+	}
+	function navigateDown() {
+		indexv ++;
+		slide();
+	}
+	
+	// Initialize the program. Done right before returning to ensure
+	// that any inline variable definitions are available to all
+	// functions 
+	initialize();
+	
+	// Expose some methods publicly
+	return {
+		navigateTo: navigateTo,
+		navigateLeft: navigateLeft,
+		navigateRight: navigateRight,
+		navigateUp: navigateUp,
+		navigateDown: navigateDown
+	};
+	
+})();
+