// The feed's globe (Components/Feed/GlobePanel.razor), on the vendored globe.gl (wwwroot/vendor/globe, loaded the first
// time a globe is shown). It looks at the average place of the located posts in view: the spherical mean of their
// points, so posts on either side of the antimeridian average correctly, from an altitude that fits their spread.
// Hovering a post pulses a ring where it is and draws an arc to it from PrivaPub's server; leaving it goes back to the
// view. Posts of servers behind a CDN have no place: they are grouped per CDN in labels on a ring above the Arctic,
// which says "CDN" rather than any place; hovering one draws its arc to that group and a ring where the server was
// before the CDN, when PrivaPub saw it there. Day texture with the light theme, night with the dark one; motion follows prefers-reduced-motion. It
// renders only while something moves (a camera flight, a hovered post's pulse, auto-rotation, the reader dragging or
// zooming) and never while the page or the globe is hidden: an idle globe costs no GPU time. No .NET round-trip on scroll or hover: the posts' places come in one
// call per feed change (setPosts), the cards are matched by data-post-id.

const vendor = new URL("../vendor/globe/", import.meta.url).href
const textures = { day: vendor + "earth-blue-marble.jpg", night: vendor + "earth-night.jpg" }
const reducedMotion = matchMedia("(prefers-reduced-motion: reduce)")

let loading = null
let state = null

function loadLibrary() {
	if (window.Globe)
		return Promise.resolve(window.Globe)
	loading ??= new Promise((resolve, reject) => {
		const script = document.createElement("script")
		script.src = vendor + "globe.gl.min.js"
		script.onload = () => resolve(window.Globe)
		script.onerror = () => { loading = null; reject(new Error("globe.gl could not be loaded")) }
		document.head.appendChild(script)
	})
	return loading
}

// Creates the globe in element once it has a size (it may start hidden on a phone), following the cards of the
// scroll container.
export function create(element, scrollContainerId) {
	dispose()
	state = {
		element,
		scroller: document.getElementById(scrollContainerId),
		globe: null,
		points: new Map(),
		self: null,
		visible: new Set(),
		hovered: null,
		view: null,
		spreadKm: 0,
		frames: 0,
		fps: 0,
		renderer: null,
		texture: null,
		paused: false,
		idle: false,
		running: true,
		interacting: false,
		awakeUntil: 0,
		observers: [],
		listeners: [],
		timers: [],
		error: null
	}
	const sizeObserver = new ResizeObserver(() => resize())
	sizeObserver.observe(element)
	state.observers.push(sizeObserver)
	resize()
	watchCards()
	watchTheme()
	watchVisibility()
}

// The located posts of the feed: [{ key, lat, lng, src, label, host, serverLat, serverLng, range, cdn, beforeLat,
// beforeLng, beforeLabel }] (src "cdn" posts have no lat/lng, only their CDN's key), and PrivaPub's own place
// ({ lat, lng, label } or null), where every arc starts.
export function setPosts(posts, self) {
	if (!state)
		return
	state.points = new Map(posts.filter(p => p.src === "cdn" ? !!p.cdn : Number.isFinite(p.lat) && Number.isFinite(p.lng)).map(p => [p.key, p]))
	state.self = self && Number.isFinite(self.lat) && Number.isFinite(self.lng) ? self : null
	drawPoints()
	scheduleView()
	wake()
}

// Live numbers for the nerd stats overlay; null until the globe exists.
export function stats() {
	if (!state?.globe)
		return state?.error ? { error: state.error } : null
	const camera = state.globe.pointOfView()
	const visibleLocated = [...state.visible].filter(key => placed(state.points.get(key))).length
	return {
		latitude: round(camera.lat, 2),
		longitude: round(camera.lng, 2),
		altitude: round(camera.altitude, 2),
		visible: state.visible.size,
		visibleLocated,
		centroidLatitude: state.view ? round(state.view.lat, 2) : null,
		centroidLongitude: state.view ? round(state.view.lng, 2) : null,
		spreadKm: Math.round(state.spreadKm),
		points: aggregate().length,
		posts: state.points.size,
		servers: new Set([...state.points.values()].map(p => p.host)).size,
		cdnGroups: cdnGroups().length,
		fps: state.fps,
		renderer: state.renderer,
		texture: state.texture,
		anisotropy: state.anisotropy,
		autoRotate: !!state.globe.controls().autoRotate,
		paused: state.paused,
		idle: state.idle,
		hovered: state.hovered && state.points.has(state.hovered) ? state.points.get(state.hovered).label ?? state.hovered : null,
		arcs: state.globe.arcsData().length,
		rings: state.globe.ringsData().length
	}
}

export function dispose() {
	if (!state)
		return
	state.observers.forEach(observer => observer.disconnect())
	state.listeners.forEach(([target, type, listener]) => target.removeEventListener(type, listener))
	state.timers.forEach(timer => clearInterval(timer))
	if (state.globe) {
		state.globe.pauseAnimation()
		state.globe._destructor?.()
		state.element.replaceChildren()
	}
	state = null
}

function resize() {
	const { width, height } = state.element.getBoundingClientRect()
	if (width < 10 || height < 10) {
		pause(true)
		return
	}
	if (!state.globe) {
		build(width, height)
		return
	}
	state.globe.width(width).height(height)
	pause(document.visibilityState !== "visible")
	wake()
}

async function build(width, height) {
	if (state.building)
		return
	state.building = true
	const current = state
	try {
		const Globe = await loadLibrary()
		if (state !== current)
			return
		const globe = new Globe(state.element, { rendererConfig: { antialias: true, alpha: true } })
		state.globe = globe
		globe.width(width).height(height)
			.backgroundColor("rgba(0,0,0,0)")
			.showAtmosphere(true)
			.atmosphereAltitude(0.18)
			.pointsMerge(false)
			.pointAltitude(p => 0.01 + Math.min(p.count, 30) * 0.004)
			.pointRadius(p => 0.25 + Math.min(Math.sqrt(p.count), 6) * 0.12)
			.pointColor(p => colour(p.src))
			.pointLabel(p => label(p))
			.pointsTransitionDuration(reducedMotion.matches ? 0 : 600)
			.ringColor(r => t => r.colour.replace(/[\d.]+\)$/, `${(1 - t).toFixed(2)})`))
			.ringMaxRadius(r => r.radius)
			.ringPropagationSpeed(r => r.speed)
			.ringRepeatPeriod(r => r.period)
			.arcColor(() => [colour("self", 0.9), colour("server", 0.9)])
			.arcStroke(0.6)
			.arcAltitudeAutoScale(0.4)
			.arcDashLength(0.45)
			.arcDashGap(0.25)
			.arcDashInitialGap(1)
			.arcDashAnimateTime(reducedMotion.matches ? 0 : 1600)
			.htmlLat(g => g.lat)
			.htmlLng(g => g.lng)
			.htmlAltitude(0.12)
			.htmlElement(cdnLabel)
		sharpen(globe)
		const controls = globe.controls()
		controls.autoRotateSpeed = 0.35
		controls.enableDamping = true
		controls.addEventListener("start", () => {
			state.interacting = true
			wake()
		})
		controls.addEventListener("end", () => {
			state.interacting = false
			wake(1500)
		})
		listen(state.element, "pointermove", () => wake(1000))
		globe.pointOfView({ lat: 30, lng: 10, altitude: 2.6 * narrowness() }, 0)
		applyTheme()
		readRenderer()
		countFrames()
		drawPoints()
		scheduleView()
		pause(document.visibilityState !== "visible")
	} catch (e) {
		state.error = e.message
		console.error(e)
		window.logFromJs?.(e.message, "globe.build")
	} finally {
		if (state === current)
			state.building = false
	}
}

// The globe is a UV sphere: towards the poles its triangles narrow to slivers meeting at one point, and texture
// coordinates interpolated across them pinch the map into a star around the axis. Each pixel computes its own instead,
// from its exact point on the sphere (the inverse of three.js SphereGeometry's mapping), so the map is drawn the same
// everywhere. The mipmap level comes from gradients taken on whichever of two longitude ranges has no jump at that pixel,
// and the map wraps around horizontally (keepSharp), so the 180° meridian shows no seam; anisotropic filtering keeps
// high latitudes sharp at grazing angles, at 8× at most: sharper than that is barely visible and costs on phones.
function sharpen(globe) {
	const material = globe.globeMaterial()
	material.onBeforeCompile = shader => {
		shader.vertexShader = shader.vertexShader
			.replace("#include <common>", "#include <common>\nvarying vec3 vSpherePoint;")
			.replace("#include <begin_vertex>", "#include <begin_vertex>\nvSpherePoint = position;")
		shader.fragmentShader = shader.fragmentShader
			.replace("#include <common>", "#include <common>\nvarying vec3 vSpherePoint;")
			.replace("#include <map_fragment>", `
#ifdef USE_MAP
	vec3 spherePoint = normalize(vSpherePoint);
	float sphereU = atan(spherePoint.z, -spherePoint.x) / (2.0 * PI);
	float sphereV = 1.0 - acos(clamp(spherePoint.y, -1.0, 1.0)) / PI;
	float uWhole = fract(sphereU);
	float uShifted = fract(sphereU + 0.5) - 0.5;
	vec2 gradientX = vec2(dFdx(uWhole), dFdx(sphereV));
	vec2 gradientY = vec2(dFdy(uWhole), dFdy(sphereV));
	float shiftedX = dFdx(uShifted);
	float shiftedY = dFdy(uShifted);
	if (abs(shiftedX) + abs(shiftedY) < abs(gradientX.x) + abs(gradientY.x)) {
		gradientX.x = shiftedX;
		gradientY.x = shiftedY;
	}
	vec4 sampledDiffuseColor = textureGrad(map, vec2(uWhole, sphereV), gradientX, gradientY);
	diffuseColor *= sampledDiffuseColor;
#endif`)
	}
	material.customProgramCacheKey = () => "privapub-per-pixel-sphere"
	material.needsUpdate = true
	state.anisotropy = Math.min(8, globe.renderer().capabilities.getMaxAnisotropy())
}

// Every texture the globe loads (a theme change loads the other one) wraps around horizontally, so filtering at the
// 180° meridian blends the map's two edges instead of clamping each, and gets anisotropic filtering.
const RepeatWrapping = 1000//three.js's RepeatWrapping: the bundle does not expose THREE
function keepSharp() {
	const map = state?.globe?.globeMaterial().map
	if (map && (map.anisotropy !== state.anisotropy || map.wrapS !== RepeatWrapping)) {
		map.anisotropy = state.anisotropy
		map.wrapS = RepeatWrapping
		map.needsUpdate = true
		wake(500)
	}
}

// Which cards are in view: an IntersectionObserver on every [data-post-id] of the scroll container, re-attached as
// the list changes; hover by delegation on the container.
function watchCards() {
	const scroller = state.scroller
	if (!scroller)
		return
	const visibility = new IntersectionObserver(entries => {
		for (const entry of entries) {
			const key = entry.target.dataset.postId
			if (entry.isIntersecting)
				state.visible.add(key)
			else
				state.visible.delete(key)
		}
		scheduleView()
	}, { root: scroller, threshold: 0.35 })
	const observeAll = () => scroller.querySelectorAll("[data-post-id]").forEach(card => visibility.observe(card))
	observeAll()
	const changes = new MutationObserver(mutations => {
		for (const mutation of mutations)
			for (const node of mutation.removedNodes)
				if (node.nodeType === 1 && node.dataset?.postId)
					state.visible.delete(node.dataset.postId)
		observeAll()
		scheduleView()
	})
	changes.observe(scroller, { childList: true, subtree: true })
	state.observers.push(visibility, changes)

	listen(scroller, "mouseover", event => {
		const card = event.target.closest?.("[data-post-id]")
		if (card && card.dataset.postId !== state.hovered)
			hover(card.dataset.postId)
	})
	listen(scroller, "mouseleave", () => hover(null))
	listen(scroller, "mouseout", event => {
		const from = event.target.closest?.("[data-post-id]")
		const to = event.relatedTarget?.closest?.("[data-post-id]")
		if (from && !to)
			hover(null)
	})
}

function watchTheme() {
	const themeObserver = new MutationObserver(() => applyTheme())
	themeObserver.observe(document.documentElement, { attributes: true, attributeFilter: ["data-theme", "style", "class"] })
	state.observers.push(themeObserver)
	const scheme = matchMedia("(prefers-color-scheme: dark)")
	listen(scheme, "change", () => applyTheme())
}

function watchVisibility() {
	listen(document, "visibilitychange", () => pause(document.visibilityState !== "visible" || !hasSize()))
	listen(reducedMotion, "change", () => scheduleView())
}

function listen(target, type, listener) {
	target.addEventListener(type, listener)
	state.listeners.push([target, type, listener])
}

function hasSize() {
	const { width, height } = state.element.getBoundingClientRect()
	return width >= 10 && height >= 10
}

function pause(paused) {
	if (!state?.globe || state.paused === paused)
		return
	state.paused = paused
	render()
}

// globe.gl draws every frame; this keeps its loop running only while the globe is shown and something moves.
function render() {
	const run = !state.paused && !state.idle
	if (run === state.running)
		return
	state.running = run
	if (run)
		state.globe.resumeAnimation()
	else
		state.globe.pauseAnimation()
}

// Something is about to move: draw for at least ms more.
function wake(ms = 1500) {
	if (!state?.globe)
		return
	state.awakeUntil = Math.max(state.awakeUntil, performance.now() + ms)
	if (state.idle) {
		state.idle = false
		render()
	}
}

// Checked every second: nothing hovered, dragged, rotating or flying, so the last frame can stay on screen.
function settle() {
	if (!state?.globe || state.idle)
		return
	if (state.hovered || state.interacting || state.globe.controls().autoRotate || performance.now() < state.awakeUntil)
		return
	state.idle = true
	render()
}

function applyTheme() {
	if (!state?.globe)
		return
	const dark = window.neoTheme?.isDark?.() ?? matchMedia("(prefers-color-scheme: dark)").matches
	const texture = dark ? "night" : "day"
	if (state.texture !== texture) {
		state.texture = texture
		state.globe.globeImageUrl(textures[texture])
	}
	state.colours = null
	state.globe.atmosphereColor(colour("server", 1))
	drawPoints()
	wake(2000)
}

// The theme's colours, resolved to rgb (the tokens are hsl() of CSS variables, which three.js cannot read).
function colour(kind, alpha = 0.95) {
	state.colours ??= (() => {
		const probe = document.createElement("span")
		probe.style.display = "none"
		document.body.appendChild(probe)
		const read = token => {
			probe.style.color = `var(${token})`
			return getComputedStyle(probe).color
		}
		const colours = {
			server: read("--color-primary"),
			place: read("--color-accent"),
			country: read("--color-secondary"),
			nearyou: read("--color-success"),
			self: read("--color-base-content")
		}
		probe.remove()
		return colours
	})()
	const rgb = (state.colours[kind] ?? state.colours.server).match(/[\d.]+/g)?.slice(0, 3) ?? [128, 128, 128]
	return `rgba(${rgb.join(",")},${alpha})`
}

// A post with a place on Earth (not a CDN-fronted server's).
function placed(post) {
	return !!post && post.src !== "cdn"
}

// The CDN groups, each at its own longitude on a ring at 68°N, ordered by key so they keep their places.
function cdnGroups() {
	const byKey = new Map()
	for (const post of state.points.values()) {
		if (post.src !== "cdn")
			continue
		const group = byKey.get(post.cdn) ?? { key: post.cdn, name: post.label, hosts: new Set(), count: 0 }
		group.count++
		if (post.host)
			group.hosts.add(post.host)
		byKey.set(post.cdn, group)
	}
	const groups = [...byKey.values()].sort((a, b) => a.key.localeCompare(b.key))
	groups.forEach((group, i) => {
		group.lat = 68
		group.lng = -180 + (i + 0.5) * 360 / groups.length
	})
	return groups
}

// Posts at the same place are one point; PrivaPub's own server is a point of its own.
function aggregate() {
	const byPlace = new Map()
	for (const post of state.points.values()) {
		if (!placed(post))
			continue
		const kind = post.src === "event" ? "place" : post.src
		const id = `${kind}:${post.lat.toFixed(2)},${post.lng.toFixed(2)}`
		const point = byPlace.get(id) ?? { lat: post.lat, lng: post.lng, src: kind, label: post.label, hosts: new Set(), count: 0 }
		point.count++
		if (post.host)
			point.hosts.add(post.host)
		byPlace.set(id, point)
	}
	const points = [...byPlace.values()]
	if (state.self)
		points.push({ lat: state.self.lat, lng: state.self.lng, src: "self", label: state.self.label, hosts: new Set([state.self.host]), count: 1 })
	return points
}

function drawPoints() {
	if (!state?.globe)
		return
	state.groups = cdnGroups()
	state.globe.pointsData(aggregate())
	state.globe.htmlElementsData(state.groups)
	drawRings()
}

function cdnLabel(group) {
	const element = document.createElement("div")
	element.className = "globe-cdn"
	element.textContent = `☁ ${group.name} · ${group.count}`
	element.title = [...group.hosts].slice(0, 10).join("\n")
	return element
}

function label(point) {
	const escape = text => String(text ?? "").replace(/[&<>"']/g, c => ({ "&": "&amp;", "<": "&lt;", ">": "&gt;", '"': "&quot;", "'": "&#39;" })[c])
	const hosts = [...point.hosts].slice(0, 4).map(escape).join("<br>")
	const more = point.hosts.size > 4 ? `<br>+${point.hosts.size - 4}` : ""
	return `<div class="globe-label"><b>${escape(point.label || "")}</b><br>${hosts}${more}` +
		`<br><span>${point.count} · ${escape(point.src)} · ${point.lat.toFixed(2)}, ${point.lng.toFixed(2)}</span></div>`
}

// The pulse under the hovered post, and the reach of located posts around the reader.
function drawRings() {
	if (!state?.globe)
		return
	const rings = []
	const hovered = state.hovered && state.points.get(state.hovered)
	if (placed(hovered))
		rings.push({ lat: hovered.lat, lng: hovered.lng, radius: 4, speed: 3, period: reducedMotion.matches ? 100000 : 900, colour: colour(hovered.src, 1) })
	else if (hovered && Number.isFinite(hovered.beforeLat))
		rings.push({ lat: hovered.beforeLat, lng: hovered.beforeLng, radius: 3, speed: 1.5, period: reducedMotion.matches ? 100000 : 1400, colour: colour("country", 1) })
	const reach = Math.max(0, ...[...state.points.values()].filter(p => p.src === "nearyou").map(p => p.range ?? 0))
	const reader = [...state.points.values()].find(p => p.src === "nearyou")
	if (reader && reach > 0)
		rings.push({ lat: reader.lat, lng: reader.lng, radius: reach / 111, speed: reach / 111 / 2, period: reducedMotion.matches ? 100000 : 2400, colour: colour("nearyou", 0.8) })
	state.globe.ringsData(rings)
}

function hover(key) {
	if (!state?.globe || state.hovered === key)
		return
	state.hovered = key
	wake(1300)
	const post = key && state.points.get(key)
	drawRings()
	if (!post) {
		state.globe.arcsData([])
		fly(state.view, 900)
		return
	}
	if (!placed(post)) {
		const group = state.groups?.find(g => g.key === post.cdn)
		state.globe.arcsData(group && state.self ? [{ startLat: state.self.lat, startLng: state.self.lng, endLat: group.lat, endLng: group.lng }] : [])
		const target = Number.isFinite(post.beforeLat) ? { lat: post.beforeLat, lng: post.beforeLng } : group
		if (target && distance(state.globe.pointOfView(), target) > 2500)
			fly({ lat: target.lat, lng: target.lng, altitude: state.globe.pointOfView().altitude }, 900)
		return
	}
	const from = post.src === "place" || post.src === "event"
		? (Number.isFinite(post.serverLat) ? { lat: post.serverLat, lng: post.serverLng } : state.self)
		: state.self
	state.globe.arcsData(from && distance(from, post) > 30
		? [{ startLat: from.lat, startLng: from.lng, endLat: post.lat, endLng: post.lng }]
		: [])
	const camera = state.globe.pointOfView()
	if (distance(camera, post) > 2500)
		fly({ lat: post.lat, lng: post.lng, altitude: camera.altitude }, 900)
}

let viewTimer = null
function scheduleView() {
	clearTimeout(viewTimer)
	viewTimer = setTimeout(updateView, 250)
}

// The spherical mean of the located posts in view, and an altitude that fits their spread.
function updateView() {
	if (!state?.globe)
		return
	const located = [...state.visible].map(key => state.points.get(key)).filter(placed)
	const controls = state.globe.controls()
	if (located.length === 0) {
		state.view = null
		state.spreadKm = 0
		controls.autoRotate = !reducedMotion.matches
		wake()
		return
	}
	controls.autoRotate = false
	let x = 0, y = 0, z = 0
	for (const p of located) {
		const lat = p.lat * Math.PI / 180, lng = p.lng * Math.PI / 180
		x += Math.cos(lat) * Math.cos(lng)
		y += Math.cos(lat) * Math.sin(lng)
		z += Math.sin(lat)
	}
	const mean = {
		lat: Math.atan2(z, Math.hypot(x, y)) * 180 / Math.PI,
		lng: Math.atan2(y, x) * 180 / Math.PI
	}
	state.spreadKm = Math.max(0, ...located.map(p => distance(mean, p)))
	mean.altitude = Math.min(3.6, (1.5 + state.spreadKm / 3500) * narrowness())
	state.view = mean
	if (!state.hovered)
		fly(mean, 1200)
}

function fly(view, ms) {
	if (!view || !state?.globe)
		return
	wake((reducedMotion.matches ? 0 : ms) + 400)
	state.globe.pointOfView(view, reducedMotion.matches ? 0 : ms)
}

// A column taller than wide shows less of the globe across: the camera moves back to keep it whole.
function narrowness() {
	const { width, height } = state.element.getBoundingClientRect()
	return width > 0 && height > width ? Math.min(1.8, height / width) : 1
}

// Great-circle distance in kilometres.
function distance(a, b) {
	const toRadians = degrees => degrees * Math.PI / 180
	const dLat = toRadians(b.lat - a.lat), dLng = toRadians(b.lng - a.lng)
	const h = Math.sin(dLat / 2) ** 2 + Math.cos(toRadians(a.lat)) * Math.cos(toRadians(b.lat)) * Math.sin(dLng / 2) ** 2
	return 2 * 6371 * Math.asin(Math.min(1, Math.sqrt(h)))
}

function readRenderer() {
	try {
		const gl = state.globe.renderer().getContext()
		const info = gl.getExtension("WEBGL_debug_renderer_info")
		state.renderer = info ? gl.getParameter(info.UNMASKED_RENDERER_WEBGL) : gl.getParameter(gl.RENDERER)
	} catch {
		state.renderer = null
	}
}

// Frames per second, counted over each second while the globe renders.
function countFrames() {
	const current = state
	const tick = () => {
		if (state !== current)
			return
		if (state.running)
			state.frames++
		keepSharp()
		requestAnimationFrame(tick)
	}
	requestAnimationFrame(tick)
	state.timers.push(setInterval(() => {
		state.fps = state.running ? state.frames : 0
		state.frames = 0
		settle()
	}, 1000))
}

function round(value, digits) {
	return Number.isFinite(value) ? Number(value.toFixed(digits)) : null
}