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
	}
}