window.addEventListener('load', init);

let slides;
let currentSlide;
let topicList;

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

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;
	}
}

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;
	}
}

function getTopicListContent() {
	let results = [...document.querySelectorAll('h1, h2, h3, h4, h5, h6')];
	let resultHtml = '<ul>';
	let currentLevel = 1;

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

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

		if (level > currentLevel) {
			resultHtml += `<ul><li><a href="#${parentSlideID}">${element.textContent}</a></li>`;
			currentLevel = level;
		} else if (level < currentLevel) {
			resultHtml += `</ul></li><li><a href="#${parentSlideID}">${element.textContent}</a></li></li>`;
			currentLevel = level;
		} else {
			resultHtml += `<li><a href="#${parentSlideID}">${element.textContent}</a>`;
		}
	})

	return resultHtml + '</ul>';
}

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.boxShadow = '0 5px 15px	rgba(0, 0, 0, 0.3)';
	topicList.style.maxHeight = 'calc(100vh - 8rem)';
	topicList.style.visibility = 'hidden';

	topicList.querySelectorAll('a').forEach(link => {
		link.addEventListener('click', e => topicList.style.visibility = 'hidden');
	})
	return topicList;
}

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') {
				topicList.style.visibility = 'hidden';
			} else {
				topicList.style.visibility = 'visible';
			}
		} else {
			lastCtrlPress = Date.now();
		}
	}
}