const TEMPLATE = document.createElement("template");
TEMPLATE.innerHTML = `
<style>
:host {
	display: block;
	scroll-behavior: smooth;
}

#navigation {
	position: sticky;
	bottom: 0;
	left: 0;
	width: 100%;

	background: inherit;
	color: inherit;
	font-weight: bold;

	display: flex;
	flex-direction: row;
	justify-content: center;
	align-items: stretch;

	padding: 0.5ex;
	box-sizing: border-box;
}

:host(.single-panel) #navigation {
	display: none;
}

#navigation .progress-container {
	flex: 1;
	flex-shrink: 100;
}

#navigation button {
	flex-shrink: 0;
	width: 3em;
	height: 3em;
	background: none;
	border: none;
	display: flex;
	justify-content: center;
	align-items: center;
	padding: 0;
	cursor: pointer;
}

#navigation button img {
	height: 1.5em;
}

.progress-container {
	position: relative;
}

.progress-container progress {
	width: 100%;
	box-sizing: border-box;
	position: absolute;
	top: 0;
	left: 0;
	width: 100%;
	opacity: 0;
	z-index: -1;
}

#progress-dots {
	display: flex;
	flex-direction: row;
	justify-content: center;
	align-items: center;
	overflow-x: auto;
	gap: 0.5ex;
	height: 100%;
}

#progress-dots .dot {
	width: 0.75ex;
	height: 0.75ex;
	border-radius: 100%;
	background: currentColor;
}

#progress-dots .dot.active {
	transform: scale(1.5);
}

#content {
	display: flex;
	flex-direction: row;
	justify-content: flex-start;
	align-items: flex-start;
	overflow-x: auto;
	scroll-snap-type: x mandatory;
	scroll-behavior: inherit;
}

#content ::slotted(*) {
	width: 100%;
	flex-shrink: 0;
	scroll-snap-align: start;
	box-sizing: border-box;
}
</style>

<section id="content"><slot></slot></section>

<nav id="navigation" part="navigation-panel">
	<button id="nav-left-panel" title="Aller au panneau de gauche" part="nav-button-left">
		<img alt="Fleche vers la gauche" src="${new URL("../../icons/arrow-left.svg", import.meta.url)}"/>
	</button>
	<div class="progress-container">
		<progress id="panel-progress-bar" value="0"></progress>
		<div id="progress-dots" aria-hidden="true"></div>
	</div>
	<button id="nav-right-panel" title="Aller au panneau de droite" part="nav-button-right" >
		<img alt="Fleche vers la droite" src="${new URL("../../icons/arrow-right.svg", import.meta.url)}"/>
	</button>
</nav>
`

export class BidiPanelElement extends HTMLElement {
	
	shadow

	mutationObserver

	#lastActive
	#currentIndex

	get contentContainer(){
		return this.shadow.getElementById("content")
	}

	get progressBar(){
		return this.shadow.getElementById("panel-progress-bar")
	}

	get progressDotsContainer(){
		return this.shadow.getElementById("progress-dots")
	}

	get activeChildrenIndex(){
		let thisGeometry = this.getBoundingClientRect()
		let progress = this.contentContainer.scrollLeft / (this.contentContainer.scrollWidth - thisGeometry.width)
		let focusedElementIndex = Math.floor(progress * this.children.length)
		if(Number.isFinite(focusedElementIndex)){
			return focusedElementIndex
		} else {
			return null
		}
	}

	set activeChildrenIndex(newIndex){
		this.setActiveChildrenIndex(newIndex, {behavior: "auto"})
	}

	setActiveChildrenIndex(newIndex, options){
		let newPanel = this.children[newIndex]
		let newPanelRect = newPanel.getBoundingClientRect()
		let selfRect = this.getBoundingClientRect()
		this.contentContainer.scrollTo({
			left: this.contentContainer.scrollLeft + ( newPanelRect.left - selfRect.left ),
			behavior: options?.behavior || "auto"
		})
		this.#currentIndex = newIndex
	}

	get activeChildren(){
		return this.children[this.activeChildrenIndex]
	}

	connectedCallback(){
		if(!this.shadow){
			this.shadow = this.attachShadow({ mode: "open" })
			this.shadow.append(TEMPLATE.content.cloneNode(true))
		}
		this.contentContainer.addEventListener("scroll", this.handleContentScroll.bind(this))
		this.shadow.getElementById("nav-left-panel").addEventListener("click", () => this.previous());
		this.shadow.getElementById("nav-right-panel").addEventListener("click", () => this.next());
		
		this.mutationObserver = (new MutationObserver(this.handleMutations.bind(this)))
		this.mutationObserver.observe(this, {childList:true})

		this.updateProgress()
	}

	handleMutations(mutation){
		let newIndex = this.#currentIndex
		this.updateProgress()
		if(Number.isFinite(newIndex)){
			this.setActiveChildrenIndex(newIndex, {behavior: "instant"})
		}
	}

	handleContentScroll(e){
		this.updateProgress()
		this.#currentIndex = this.activeChildrenIndex
		if(this.#currentIndex != this.#lastActive){
			this.dispatchEvent(new ActivePanelChangeEvent("activePanelChange", this.#currentIndex))
			this.#lastActive = this.#currentIndex
		}
	}

	updateProgress(){
		let focusedElementIndex = this.activeChildrenIndex;

		let progressBar = this.progressBar;
		progressBar.value = focusedElementIndex;
		progressBar.min = 0;
		progressBar.max = this.children.length-1;

		this.classList.toggle("single-panel", this.children.length == 1)
		this.classList.toggle("empty", this.children.length == 0)

		let dotsContainer = this.progressDotsContainer;
		if(dotsContainer.children.length != parseInt(progressBar.max)+1){
			let dots = (new Array(this.children.length))
				.fill(0)
				.map(() => {
					let el = document.createElement("div")
					el.classList.add("dot")
					el.part = "dot"
					return el
				});
			dotsContainer.replaceChildren(...dots)
		}
		for(let inactiveDot of dotsContainer.querySelectorAll(".active")){
			inactiveDot.part = "dot"
			inactiveDot.classList.remove("active")
		}

		let activeDot = dotsContainer.children[parseInt(progressBar.value)]
		if(activeDot){
			activeDot.part = "dot-active"
			activeDot.classList.add("active")
		}
	}

	next(){
		let nextItem = this.activeChildrenIndex + 1;
		if(nextItem < this.children.length){
			this.activeChildrenIndex = nextItem
		}
	}

	previous(){
		let nextItem = this.activeChildrenIndex - 1;
		if(nextItem >= 0){
			this.activeChildrenIndex = nextItem
		}
	}
}

export class ActivePanelChangeEvent extends Event {
	constructor(name, activePanelIndex){
		super(name)
		this.activePanelIndex = activePanelIndex
	}
}

customElements.define("camp-bidi-panel", BidiPanelElement);