decePubClient/tests/e2e/Mobile/fit.js

// The phone tests' measurements (Mobile/Fit.cs), added to every page of a phone session as an init script. Each call
// returns plain data, so no element handle outlives a scroll: Virtualize recycles the feed's cards.
//   settle()   waits for fonts, for the page to stop changing, two frames and the pictures in view
//   primary()  marks the page's main scroller, the one the sweep steps through
//   step(f)    scrolls it by f of its height; false at its end
//   measure(s) what doesn't fit: sideways overflow, boxes beyond the screen, cut popovers, small targets, small text;
//              with a selector, the targets inside what it matches only (an open menu or dialog)
window.__fit = (() => {
	const scrolls = value => value === "auto" || value === "scroll"
	const shown = el => el.checkVisibility({ opacityProperty: true, visibilityProperty: true })
	let styles = new Map()
	const style = el => {
		let found = styles.get(el)
		if (!found)
			styles.set(el, found = getComputedStyle(el))
		return found
	}

	// a short name for an element: its id, else its first data-* attribute, else tags and classes up to three levels
	function name(el, depth = 0) {
		if (el === document.scrollingElement || el === document.documentElement || el === document.body)
			return "document"
		if (el.id)
			return "#" + el.id
		const data = [...el.attributes].find(a => a.name.startsWith("data-") && !a.name.startsWith("data-fit"))
		const own = el.tagName.toLowerCase() + (data ? `[${data.name}]` : [...el.classList].slice(0, 3).map(c => "." + c).join(""))
		const parent = el.parentElement
		return data || depth >= 2 || !parent || parent === document.body ? own : `${name(parent, depth + 1)} > ${own}`
	}

	const text = el => (el.getAttribute("aria-label") || el.getAttribute("title") || el.innerText || el.value || "")
		.trim().replace(/\s+/g, " ").slice(0, 40)

	// the card an element is in (its ActivityPub id), for finding it again
	const card = el => el.closest("[data-uri]")?.getAttribute("data-uri") ?? null

	function describe(el, box) {
		return {
			element: name(el), text: text(el), card: card(el),
			box: [box.left, box.top, box.width, box.height].map(Math.round)
		}
	}

	function scrollers() {
		const found = [document.scrollingElement]
		for (const el of document.body.querySelectorAll("*")) {
			const s = style(el)
			if ((scrolls(s.overflowX) || scrolls(s.overflowY)) && el.clientWidth > 0 && el.clientHeight > 0 && shown(el))
				found.push(el)
		}
		return found
	}

	// the part of an element's box that can be seen: cut by every ancestor that clips, up to the screen for a fixed one
	function visibleRect(el) {
		const own = el.getBoundingClientRect()
		const box = { left: own.left, top: own.top, right: own.right, bottom: own.bottom }
		if (style(el).position !== "fixed")
			for (let a = el.parentElement; a && a !== document.body && a !== document.documentElement; a = a.parentElement) {
				const s = style(a)
				if (s.overflowX !== "visible" || s.overflowY !== "visible") {
					const clip = a.getBoundingClientRect()
					if (s.overflowX !== "visible") {
						box.left = Math.max(box.left, clip.left)
						box.right = Math.min(box.right, clip.right)
					}
					if (s.overflowY !== "visible") {
						box.top = Math.max(box.top, clip.top)
						box.bottom = Math.min(box.bottom, clip.bottom)
					}
				}
				if (s.position === "fixed")
					break
			}
		return box
	}

	// the part of the screen an element's clipping ancestors let through: where a tap can reach it at all
	function clipOf(el) {
		const box = { left: 0, top: 0, right: innerWidth, bottom: innerHeight }
		if (style(el).position === "fixed")
			return box
		for (let a = el.parentElement; a && a !== document.body && a !== document.documentElement; a = a.parentElement) {
			const s = style(a)
			if (s.overflowX !== "visible" || s.overflowY !== "visible") {
				const clip = a.getBoundingClientRect()
				box.left = Math.max(box.left, clip.left)
				box.right = Math.min(box.right, clip.right)
				box.top = Math.max(box.top, clip.top)
				box.bottom = Math.min(box.bottom, clip.bottom)
			}
			if (s.position === "fixed")
				break
		}
		return box
	}

	// an element inside a nested clipping box (a sideways strip, a truncated name) doesn't widen the scroller holding it
	function clippedWithin(el, scroller) {
		for (let a = el.parentElement; a && a !== scroller; a = a.parentElement)
			if (style(a).overflowX !== "visible")
				return true
		return false
	}

	// sideways scroll in the document or in a scroller that isn't meant to scroll sideways (data-scroll-x), with the
	// element reaching furthest right
	function overflow() {
		const found = []
		for (const scroller of scrollers()) {
			if (scroller.hasAttribute?.("data-scroll-x"))
				continue
			const extra = scroller.scrollWidth - scroller.clientWidth
			if (extra <= 1)
				continue
			const limit = scroller === document.scrollingElement ? innerWidth : scroller.getBoundingClientRect().right
			let worst = null, right = limit + 0.5
			for (const el of scroller.querySelectorAll("*")) {
				const r = el.getBoundingClientRect()
				if (r.width > 0 && r.right > right && !el.closest("[data-scroll-x]") && !clippedWithin(el, scroller)) {
					worst = el
					right = r.right
				}
			}
			found.push({
				element: name(scroller), extra: Math.round(extra),
				culprit: worst ? { ...describe(worst, worst.getBoundingClientRect()), past: Math.round(right - limit) } : null
			})
		}
		return found
	}

	// what can be seen of it lies past the screen's sides: the outermost such element only
	function beyond() {
		const found = [], reported = []
		for (const el of document.body.querySelectorAll("*")) {
			if (found.length >= 30)
				break
			if (el.closest("[data-scroll-x]") !== null && !el.hasAttribute("data-scroll-x"))
				continue
			const own = el.getBoundingClientRect()
			if (own.width <= 1 && own.height <= 1 || reported.some(r => r.contains(el)) || !shown(el))
				continue
			const seen = visibleRect(el)
			if (seen.right - seen.left <= 0.5 || seen.bottom - seen.top <= 0.5)
				continue
			if (seen.right > innerWidth + 1 || seen.left < -1) {
				reported.push(el)
				found.push(describe(el, own))
			}
		}
		return found
	}

	// open menus, dialogs, sheets and tips must be whole: inside the screen and not cut by what holds them
	function popovers() {
		const found = []
		for (const el of document.querySelectorAll(".dropdown-content, .modal-open > .modal-box, [data-sheet], [data-nav-panel], .tooltip-content")) {
			if (!shown(el))
				continue
			const own = el.getBoundingClientRect()
			if (own.width < 1 || own.height < 1)
				continue
			const seen = visibleRect(el)
			const outside = own.left < -1 || own.right > innerWidth + 1 || own.top < -1 || own.bottom > innerHeight + 1
			const cut = seen.left > own.left + 1 || seen.right < own.right - 1 || seen.top > own.top + 1 || seen.bottom < own.bottom - 1
			if (outside || cut)
				found.push({ ...describe(el, own), outside, cut })
		}
		return found
	}

	const candidates = "a[href], button, select, textarea, summary, [role=button], [role=tab], [role=link], [tabindex='0'], "
		+ "input:not([type=hidden]), label:has(> input[type=checkbox]), label:has(> input[type=radio]), label:has(> .toggle)"

	function exempt(el) {
		return el.tagName === "A" && el.closest(".post-content") !== null
			|| el.matches("video, audio, :disabled, [aria-disabled=true], .btn-disabled, .modal-backdrop > button")
			|| el.closest("[aria-hidden=true], [data-touch-exempt], [inert]") !== null
			// a checkbox, radio or toggle inside a label is measured as its label
			|| el.matches("input[type=checkbox], input[type=radio]") && el.closest("label") !== null
	}

	// a control floating over the page (the round New post button) covers what scrolls under it, by design: a probe that
	// lands on one says nothing about the target's own room
	function floating(hit, el) {
		for (let a = hit; a && a !== document.body; a = a.parentElement)
			if (style(a).position === "fixed")
				return !a.contains(el)
		return false
	}

	// a tap at this point reaches the element: on it, inside it, on its label's control, or on a label holding it
	function reaches(el, x, y) {
		const hit = document.elementFromPoint(x, y)
		if (!hit)
			return false
		if (hit === el || el.contains(hit))
			return true
		if (el.tagName === "LABEL" && el.control && (hit === el.control || el.control.contains(hit)))
			return true
		const label = hit.closest("label")
		return label !== null && label.contains(el)
	}

	// a target needs a 44x44 CSS px hit area (Apple's guideline, WCAG 2.5.5): the centre and four points 21px away must
	// reach it, so a neighbour reaching into that square fails it as much as a small box does. Only targets a tap can reach
	// now are judged; one under an overlay or out of view is judged at another step
	function targets(scope) {
		const small = [], tiny = []
		const within = scope ? [...document.querySelectorAll(scope)].flatMap(s => [...s.querySelectorAll(candidates)]) : document.querySelectorAll(candidates)
		for (const el of within) {
			if (exempt(el) || !shown(el))
				continue
			const own = el.getBoundingClientRect()
			if (own.width < 1 || own.height < 1)
				continue
			const x = own.left + own.width / 2, y = own.top + own.height / 2
			if (x < 0 || x >= innerWidth || y < 0 || y >= innerHeight)
				continue
			const seen = visibleRect(el)
			if (x < seen.left || x > seen.right || y < seen.top || y > seen.bottom || !reaches(el, x, y))
				continue
			if (el.matches("input[type=range]")) {
				if (own.height < 28 || own.width < 120)
					small.push({ ...describe(el, own), failed: ["range"] })
				continue
			}
			// a probe beyond what the scroller shows (a card half under the feed's top edge) can't be tapped there anyway
			const clip = clipOf(el)
			const failed = [], hit = {}
			for (const [dx, dy, side] of [[-21, 0, "left"], [21, 0, "right"], [0, -21, "up"], [0, 21, "down"]]) {
				const px = Math.min(clip.right - 1, Math.max(clip.left, x + dx)), py = Math.min(clip.bottom - 1, Math.max(clip.top, y + dy))
				if (!reaches(el, px, py)) {
					const other = document.elementFromPoint(px, py)
					if (other && floating(other, el))
						continue
					failed.push(side)
					hit[side] = other ? name(other) : null
				}
			}
			if (failed.length > 0)
				small.push({ ...describe(el, own), failed, hit })
			if (text(el) && el.innerText?.trim() && parseFloat(style(el).fontSize) < 12)
				tiny.push({ ...describe(el, own), fontSize: parseFloat(style(el).fontSize) })
		}
		return { small, tiny }
	}

	function measure(scope) {
		styles = new Map()
		const { small, tiny } = targets(scope)
		const result = { url: location.pathname + location.search, overflow: overflow(), beyond: beyond(), popovers: popovers(), small, tiny }
		styles = new Map()
		return result
	}

	function primary() {
		styles = new Map()
		document.querySelectorAll("[data-fit-primary]").forEach(e => e.removeAttribute("data-fit-primary"))
		let best = null, area = 0
		for (const el of scrollers()) {
			if (el.scrollHeight <= el.clientHeight + 4)
				continue
			const size = el.clientWidth * el.clientHeight
			if (size > area) {
				best = el
				area = size
			}
		}
		best ??= document.scrollingElement
		best.setAttribute("data-fit-primary", "")
		styles = new Map()
		return name(best)
	}

	function step(fraction) {
		const el = document.querySelector("[data-fit-primary]") ?? document.scrollingElement
		const before = el.scrollTop
		el.scrollTo({ top: before + el.clientHeight * fraction, behavior: "instant" })
		return el.scrollTop > before + 1
	}

	async function settle() {
		await document.fonts.ready
		await new Promise(resolve => {
			let timer
			const done = () => {
				observer.disconnect()
				clearTimeout(timer)
				clearTimeout(cap)
				resolve()
			}
			const observer = new MutationObserver(() => {
				clearTimeout(timer)
				timer = setTimeout(done, 400)
			})
			observer.observe(document.body, { subtree: true, childList: true, characterData: true, attributes: true })
			timer = setTimeout(done, 400)
			const cap = setTimeout(done, 8000)
		})
		await new Promise(resolve => requestAnimationFrame(() => requestAnimationFrame(resolve)))
		const until = Date.now() + 3000
		const inView = img => {
			const r = img.getBoundingClientRect()
			return r.bottom > 0 && r.top < innerHeight && r.right > 0 && r.left < innerWidth
		}
		while (Date.now() < until && [...document.images].some(img => inView(img) && !img.complete))
			await new Promise(resolve => setTimeout(resolve, 100))
	}

	return { settle, primary, step, measure }
})()