window.addEventListener('load', init);

let slides;
let currentSlide;

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

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

function goToPreviousSlide() {
	goToSlide(currentSlide - 1);
}

function goToNextSlide() {
	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;
	}
}