window.addEventListener('load', slideShow, false);
var whichimage = 0;
function slideShow() {
  
  /* GLOBALS **********************************************************************************************/
  
  var globals = {
    slideDelay: 4000, // The time interval between consecutive slides.
    fadeDelay: 35, // The time interval between individual opacity changes. This should always be much smaller than slideDelay.  
    wrapperID: "slideShowImages", // The ID of the <div> element that contains all of the <img> elements to be shown as a slide show.
    buttonID: "slideShowButton", // The ID of the <button> element that toggles the slide show on and off.
    buttonStartText: "Start Slides", // Text used in the slide show toggle button.
    buttonStopText: "Stop Slides", // Text used in the slide show toggle button.    
    wrapperObject: null, // Will contain a reference to the <div> element that contains all of the <img> elements to be shown as a slide show.
    buttonObject: null, // If present, will contain a reference to the <button> element that toggles the slide show on and off. The initial assumption is that there is no such button element (hence the false value).
    slideImages: [], // Will contain all of the slide image objects.
	slideUrls: [],   // = new Array() // create new array to preload images
	slideHeaders: [],  // Headers for each image
	//slideUrls: [],  // Will contain URLs to match with images.
    slideShowID: null, // A setInterval() ID value used to stop the slide show.
    slideShowRunning: true, // Used to record when the slide show is running and when it's not. The slide show is always initially running. 
	slidewithlink: 0,
    slideIndex: 0 // The index of the current slide image.
  }
  
  /* MAIN *************************************************************************************************/
  
  initializeGlobals();  
  
  if ( insufficientSlideShowMarkup() ) {
    return; // Insufficient slide show markup - exit now.
  }
 
   // Assert: there's at least one slide image.
 
  if (globals.slideImages.length == 1) {
    return; // The solo slide image is already being displayed - exit now.
  }
  
  // Assert: there's at least two slide images.
  
  initializeSlideShowMarkup();
  
  globals.wrapperObject.addEventListener('click', toggleSlideShow, false); // If the user clicks a slide show image, it toggles the slide show on and off.
  
  if (globals.buttonObject) {
    globals.buttonObject.addEventListener('click', toggleSlideShow, false); // This callback is used to toggle the slide show on and off.
  } 
  
  startSlideShow();
  
  /* FUNCTIONS ********************************************************************************************/
  
  function initializeGlobals() {   
    globals.wrapperObject = (document.getElementById(globals.wrapperID) ? document.getElementById(globals.wrapperID) : null);
    globals.buttonObject = (document.getElementById(globals.buttonID) ? document.getElementById(globals.buttonID) : null);   
    
    if (globals.wrapperObject) {
      globals.slideImages = (globals.wrapperObject.querySelectorAll('img') ? globals.wrapperObject.querySelectorAll('img') : []);
      var slideCountr = globals.slideImages.length;
	  for (var i = 0; i < slideCountr; i++) { 
                     globals.slideImages[i].style.opacity = 0;
	     globals.slideImages[i].style.position = "relative";
	  }
	  globals.slideImages[0].style.opacity = 1; // Make the first slide visible.
	  globals.slideUrls[0] = "#!";
	  globals.slideUrls[1] = "#!";
	  globals.slideUrls[2] = "#!";
	  globals.slideUrls[3] = "#!";
	  globals.slideUrls[4] = "#!";
	  globals.slideUrls[5] = "#!";
	  globals.slideUrls[6] = "https://youtu.be/uRCRX5kjYSw";
	  globals.slideHeaders[0] = "Preparation";
	  globals.slideHeaders[1] = "Presentation";
	  globals.slideHeaders[2] = "Delivery";
	  globals.slideHeaders[3] = "Preparation";
	  globals.slideHeaders[4] = "Presentation";
	  globals.slideHeaders[5] = "Delivery";
	  globals.slideHeaders[6] = "Explanation of AcademicRecords.net";
    }
  } // initializeGlobals
  
  // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  function insufficientSlideShowMarkup() {
    if (!globals.wrapperObject) { // There is no wrapper element whose ID is globals.wrapperID - fatal error.
      if (globals.buttonObject) {
        globals.buttonObject.style.display = "none"; // Hide the not needed slide show button element when present.
      }
      return true;
    }
    if (!globals.slideImages.length) { // There needs to be at least one slide <img> element - fatal error.
      if (globals.wrapperObject) {
        globals.wrapperObject.style.display = "none"; // Hide the not needed <div> wrapper element.
      }
    
      if (globals.buttonObject) {
        globals.buttonObject.style.display = "none"; // Hide the not needed slide show button element.
      }
    
      return true;
    }
    
    return false; // The markup expected by this library seems to be present.
  } // insufficientSlideShowMarkup
  
  // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  function initializeSlideShowMarkup() {  
    var slideWidthMax = maxSlideWidth(); // Returns a value that is always in pixel units.
    var slideHeightMax = maxSlideHeight(); // Returns a value that is always in pixel units.
    
    globals.wrapperObject.style.position = "relative";
    globals.wrapperObject.style.overflow = "hidden"; // This is just a safety thing.
    globals.wrapperObject.style.width = slideWidthMax + "px";
    globals.wrapperObject.style.height = slideHeightMax + "px";
    
    var slideCount = globals.slideImages.length;
    for (var i = 0; i < slideCount; i++) { 
      globals.slideImages[i].style.opacity = 0;
      globals.slideImages[i].style.position = "absolute";
      globals.slideImages[i].style.top = (slideHeightMax - globals.slideImages[i].getBoundingClientRect().height) / 2 + "px";   
      globals.slideImages[i].style.left = (slideWidthMax - globals.slideImages[i].getBoundingClientRect().width) / 2 + "px";               
    }
    
    globals.slideImages[0].style.opacity = 1; // Make the first slide visible.
        
    if (globals.buttonObject) {
      globals.buttonObject.textContent = globals.buttonStopText;
    }
  } // initializeSlideShowMarkup
  
  // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    
  function maxSlideWidth() {
    var maxWidth = 0;
    var maxSlideIndex = 0;
    var slideCount = globals.slideImages.length;
    
    for (var i = 0; i < slideCount; i++) {
      if (globals.slideImages[i].width > maxWidth) {
        maxWidth = globals.slideImages[i].width; // The width of the widest slide so far.
        maxSlideIndex = i; // The slide with the widest width so far.
      }
    }
    return globals.slideImages[maxSlideIndex].getBoundingClientRect().width; // Account for the image's border, padding, and margin values. Note that getBoundingClientRect() is always in units of pixels.
  } // maxSlideWidth
  
  // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    
  function maxSlideHeight() {
    var maxHeight = 0;
    var maxSlideIndex = 0;    
    var slideCount = globals.slideImages.length;
    
    for (var i = 0; i < slideCount; i++) {
      if (globals.slideImages[i].height > maxHeight) {
        maxHeight = globals.slideImages[i].height; // The height of the tallest slide so far.
        maxSlideIndex = i; // The slide with the tallest height so far.
      }
    }
    
    return globals.slideImages[maxSlideIndex].getBoundingClientRect().height; // Account for the image's border, padding, and margin values. Note that getBoundingClientRect() is always in units of pixels.
  } // maxSlideHeight
  // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  function startSlideShow() {
    globals.slideShowID = setInterval(transitionSlides, globals.slideDelay);                
  } // startSlideShow
  // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  
  function haltSlideShow() {
    clearInterval(globals.slideShowID);   
  } // haltSlideShow
  // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  
  function toggleSlideShow() {
	  slidelink();
   // if (globals.slideShowRunning) {
   //   haltSlideShow();
   //   if (globals.buttonObject) { 
   //     globals.buttonObject.textContent = globals.buttonStartText; 
   //   }
   // }
   // else {
   //   startSlideShow();
   //   if (globals.buttonObject) { 
   //     globals.buttonObject.textContent = globals.buttonStopText; 
   //   }            
   // }
   // globals.slideShowRunning = !(globals.slideShowRunning);
  } // toggleSlideShow
  
  // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    function slidelink(){
	//alert("Image # = " + whichimage + " is - " + globals.slideUrls[whichimage]);
	if(globals.slideUrls[globals.slideIndex] == "#!")
		;
	else {
		window.open(globals.slideUrls[globals.slideIndex]);
		globals.slidewithlink = globals.slideIndex;
	}
	//window.location = globals.slideUrls[globals.slideIndex];
}
  function transitionSlides() {
    var currentSlide = globals.slideImages[globals.slideIndex];
    
    ++(globals.slideIndex);
	whichimage = globals.slideIndex;
    if (globals.slideIndex >= globals.slideImages.length) {
      globals.slideIndex = 0;
    }
    if(globals.slideUrls[globals.slideIndex] == "#!")
		;
	else {
		globals.slidewithlink = globals.slideIndex;
	}
	//alert("next slide");
    var nextSlide = globals.slideImages[globals.slideIndex];
	var slheader = document.getElementById("slideheader");
	slheader.innerHTML = globals.slideHeaders[globals.slideIndex];
	//slheader.value = globals.slideHeaders[globals.slideIndex];
    
    var currentSlideOpacity = 1; // Fade the current slide out.
    var nextSlideOpacity = 0; // Fade the next slide in.
    var opacityLevelIncrement = 1 / globals.fadeDelay;
    var fadeActiveSlidesID = setInterval(fadeActiveSlides, globals.fadeDelay);
	if(globals.slideUrls[globals.slideIndex] == "#!")  {
		nextSlide.style.cursor='default';
		globals.slideImages[globals.slidewithlink].style.cursor='default';
	}
	else
		nextSlide.style.cursor='hand';
    
    function fadeActiveSlides() {
      currentSlideOpacity -= opacityLevelIncrement;
      nextSlideOpacity += opacityLevelIncrement;
      
      // console.log(currentSlideOpacity + nextSlideOpacity); // This should always be very close to 1.
      
      if (currentSlideOpacity >= 0 && nextSlideOpacity <= 1) {
        currentSlide.style.opacity = currentSlideOpacity;
        nextSlide.style.opacity = nextSlideOpacity; 
      }
      else {
        currentSlide.style.opacity = 0;
        nextSlide.style.opacity = 1; 
        clearInterval(fadeActiveSlidesID);
      }        
    } // fadeActiveSlides
  } // transitionSlides
  
} // slideShow