window.addEventListener('load', init);
window.addEventListener('resize', reactToResizing);
window.addEventListener('hashchange', resumeOrGoToStart);

let slides;
let currentSlide;

let topicList;
let topicLinks;
let topicListSearch;

const activeTopicLinkClass = 'active-topic-link';
const notMatchingSearchTermsClass = 'not-matching-search-terms';
const topicListSearchClass = 'topic-list-search';

function init() {
	slides = Array.from(document.querySelectorAll('article'));
	for (let i = 0; i < slides.length; i++) {
		slides[i].id = `slide${i}`;
	}
	topicList = createTopicList();
	resumeOrGoToStart();
	document.addEventListener('keydown', onKeyPressed);
}

function resumeOrGoToStart() {
	let urlParts = window.location.href.split('#');
	if (urlParts.length > 1) {
		goToSlide(parseInt(urlParts[1].replace('slide', '')))
	} else {
		goToSlide(0)
	}
}

function goToSlide(index) {
	if (index >= 0 && index < slides.length) {
		currentSlide = index;
		window.location.href = window.location.href.split('#')[0] + `#slide${index}`;

		let oldActiveTopicLinks = topicList.querySelectorAll(`.${activeTopicLinkClass}`);
		[...oldActiveTopicLinks].forEach(link => {
			link.classList.remove(activeTopicLinkClass);
		});

		let newActiveTopicLinks = topicList.querySelectorAll(`[data-slide*=";slide${index};"]`);
		[...newActiveTopicLinks].forEach(link => {
			link.classList.add(activeTopicLinkClass);
		})
	}
}

function goToPreviousSlide() {
	if (!showPreviousFragment()) {
		goToSlide(currentSlide - 1);
	}
}

function goToNextSlide() {
	if (!showNextFragment()) {
		goToSlide(currentSlide + 1);
	}
}

function goToFirstSlide() {
	goToSlide(0);
}

function goToLastSlide() {
	goToSlide(slides.length - 1);
}

function onKeyPressed(event) {
	switch (event.keyCode) {
		case 34: // page down
		case 40: // arrow down
		case 39: // arrow right
			goToNextSlide();
			break;
		case 33: // page up
		case 38: // arrow up
		case 37: // arrow left
			goToPreviousSlide();
			break;
		case 36: // pos1
			goToFirstSlide();
			break;
		case 35: // end
			goToLastSlide();
			break;
		case 17: // ctrl
			toggleTopicList();
			break;
		case 27: // esc
			hideTopicList();
			break;
	}
}

function showNextFragment() {
	let fragments = [...slides[currentSlide].querySelectorAll('.fragment')]
	let visible = [...slides[currentSlide].querySelectorAll('.fragment.visible')]

	if (fragments.length == visible.length) {
		return false;
	} else {
		fragments[visible.length].classList.add('visible')
		return true;
	}
}

function showPreviousFragment() {
	let visible = [...slides[currentSlide].querySelectorAll('.fragment.visible')]

	if (visible.length == 0) {
		return false;
	} else {
		visible[visible.length - 1].classList.remove('visible')
		return true;
	}
}

/**
 * Store for the headline nodes of each chapter.
 */
class HeadlineStore {
	constructor() {
		this.topLevelChildren = [];
	}

	/**
	 * Add a new root node, i.e. the headline of a new chapter.
	 * @param {Node} node the level-1 headline node
	 */
	add(node) {
		this.topLevelChildren.push(node);
	}

	/**
	 * Generate a HTML list of all headline nodes stored in this structure.
	 */
	getHTML() {
		let resultHTML = '<ul>'

		resultHTML += this.topLevelChildren
			.map(root => root.getHTML())
			.join('');

		return resultHTML + '</ul>'
	}
}

/**
 * Data structure storing all headlines for the topic list.
 * Each node knows its parents and children.
 */
class Node {
	constructor(title, level, father, slide) {
		this.children = [];
		this.slidesWithSameTitle = [];
		this.title = title;
		this.level = level;
		this.father = father;
		this.slide = slide;
	}

	/**
	 * Return the child that was added last among all childen.
	 */
	getLastChild() {
		return this.children[this.children.length - 1];
	}

	/**
	 * Add a child node to this headline if the title of the new child node is
	 * different from the title of the node that was added last.
	 * This way, headlines are not added twice if they appear consecutively.
	 * @param {Node} node a subtitle node
	 * @return true, if the node was added, false otherwise
	 */
	addChildNode(node) {
		if (!this.lastChildHasTitle(node.title)) {
			this.children.push(node);
			return true;
		} else {
			return false;
		}
	}

	/**
	 * Each headline can have more than one slide related to it.
	 * Consecutive headlines appear only ones in a dictionary, but they are still
	 * related to all slides. If there are three slides with title »Example« in a
	 * row, the node will have slide1 as its child and slide2 and slide3 as
	 * entries to the slidesWithSameTitle array.
	 * The goal of this is to ultimately highlight the node in the topic list not
	 * only when slide1 is active, but also for slide2 and slide3.
	 * @param {Integer} slide the ID of a related slide
	 */
	addSlideWithSameTitle(slide) {
		this.slidesWithSameTitle.push(slide);
	}

	/**
	 * Whether or not this node's last child has the given title.
	 * @param {String} title the slide's title
	 */
	lastChildHasTitle(title) {
		let len = this.children.length;
		return len > 0 && this.children[len - 1].title == title;
	}

	/**
	 * Generate the HTML anchor content for this node (without any children).
	 */
	getLinkHTML() {
		return `<a data-slide=";slide${this.slide};${
			// Slide IDs have to be surrounded by »;«, otherwise slide10 and slide100
			// would both be highlighted when slide10 is active.
			this.slidesWithSameTitle.map(slide => `slide${slide}`).join(';')
			};" href="javascript:goToSlide(${this.slide})" class="topic-link">${this.title}</a>`
	}

	/**
	 * Generate a list item for the topic list with a sublist of all child nodes.
	 */
	getHTML() {
		let resultHTML = `<li>${this.getLinkHTML()}`;

		if (this.children.length > 0) {
			resultHTML +=
				`<ul>${this.children.map(child => child.getHTML()).join('')}</ul>`
		}

		return resultHTML + '</li>';
	}
}

function getTopicListContent() {
	let results = [...document.querySelectorAll('h1, h2, h3, h4, h5, h6')];
	let resultHTML = `<input type="text" class="${topicListSearchClass}"/>`;
	let currentLevel = 1;

	headlineStore = new HeadlineStore();
	currentNode = null;

	results.forEach(element => {
		let node = element.nodeName;
		let level = parseInt(node[node.length - 1]);
		let title = element.textContent;

		let parentElement = element.parentElement
		while (parentElement.nodeName.toLowerCase() != 'article') {
			parentElement = parentElement.parentElement;
		}

		let slide = parseInt(parentElement.id.replace('slide', ''));

		if (level == 1) {
			// first chapter
			let rootNode = new Node(title, level, null, slide);
			headlineStore.add(rootNode)
			currentNode = rootNode;
		} else if (level > currentLevel) {
			// one or more levels down
			let childNode = new Node(title, level, currentNode, slide);
			if (currentNode.addChildNode(childNode)) {
				currentNode = childNode;
			} else {
				currentNode = currentNode.getLastChild();
				currentNode.addSlideWithSameTitle(slide)
			}
		} else if (level == currentLevel) {
			// same level
			let parentNode = currentNode.father;
			let siblingNode = new Node(title, level, parentNode, slide);
			if (parentNode.addChildNode(siblingNode)) {
				currentNode = siblingNode;
			} else {
				currentNode = parentNode.getLastChild();
				currentNode.addSlideWithSameTitle(slide)
			}
		} else if (level < currentLevel) {
			// one or more levels up
			let parentNode = currentNode
			while (parentNode.level >= level) {
				parentNode = parentNode.father;
			}
			let siblingNode = new Node(title, level, parentNode, slide);
			if (parentNode.addChildNode(siblingNode)) {
				currentNode = siblingNode;
			} else {
				currentNode = parentNode.getLastChild();
			}
		}

		currentLevel = level;
	});

	return resultHTML + headlineStore.getHTML();
}

function createTopicList() {
	let topicList = document.createElement(`div`);
	topicList.innerHTML = getTopicListContent();
	topicList.classList.add('topic-list')
	document.body.appendChild(topicList);
	topicList.style.position = 'fixed';
	topicList.style.top = '4rem';
	topicList.style.left = '50%';
	topicList.style.transform = 'translateX(-50%)';
	topicList.style.backgroundColor = 'white';
	topicList.style.padding = '2rem';
	topicList.style.width = '800px';
	topicList.style.maxHeight = 'calc(100vh - 8rem)';
	topicList.style.boxSizing = 'border-box';
	topicList.style.visibility = 'hidden';
	topicList.style.overflowY = 'scroll';

	topicLinks = [...topicList.querySelectorAll('a')]
	topicLinks.forEach(link => {
		link.addEventListener('click', hideTopicList);
	});

	topicListSearch = topicList.querySelector(`.${topicListSearchClass}`);
	topicListSearch.addEventListener('input', onTopicListSearchInput);

	return topicList;
}

function onTopicListSearchInput(e) {
	let searchTerms = topicListSearch.value.toLowerCase();
	topicLinks.forEach(link => {
		if (link.textContent.toLowerCase().includes(searchTerms) || searchTerms.length == 0) {
			link.classList.remove(notMatchingSearchTermsClass);
			link.removeAttribute('tabindex');
		} else {
			link.tabIndex = -1;
			link.classList.add(notMatchingSearchTermsClass);
		}
	})
}

let lastCtrlPress = null;

function toggleTopicList() {
	if (lastCtrlPress == null) {
		lastCtrlPress = Date.now();
	} else {
		let now = Date.now();
		if (now - lastCtrlPress < 400) {
			lastCtrlPress = null;
			if (topicList.style.visibility === 'visible') {
				hideTopicList();
			} else {
				topicListSearch.value = '';
				onTopicListSearchInput();
				topicList.style.visibility = 'visible';
				topicListSearch.focus();
			}
		} else {
			lastCtrlPress = Date.now();
		}
	}
}

function hideTopicList() {
	if (topicList.style.visibility === 'visible') {
		topicList.style.visibility = 'hidden';
	}
}

function reactToResizing() {
	goToSlide(currentSlide);
}