/**
 * `x-figure`: a figure counts to its value — from zero when it first appears, and from what
 * it said before when the server changes it.
 *
 * The server renders the real value, so without JavaScript, in a test or in a screenshot the
 * figure is simply right. Only a figure with exactly one number in it moves — "39.6",
 * "1,204 km", "CHF 12.50" — and a time, a date or a range is left alone rather than counted
 * as if it were one quantity. The format is the target's: its decimals and its thousands
 * separator, so a column of counting figures keeps its width under `tabular-nums`.
 *
 * The curve decelerates and never overshoots, unlike the spatial springs, because a figure
 * that passes its value is briefly a lie. The duration is the spatial-slow token's, which
 * reduced motion sets to zero — and then the figure is written once, as it is.
 *
 * A re-render that leaves the text the same never reaches the observer, so a Livewire round
 * trip does not replay it; one that changes it counts from the figure on screen, even
 * mid-count. The observer ignores the directive's own writes by comparing against the last
 * thing it wrote.
 */
const FIGURE = /[-−]?\d{1,3}(?:[,'’]\d{3})+(?:\.\d+)?|[-−]?\d+(?:\.\d+)?/g

const readFigure = (text) => {
    const matches = [...text.matchAll(FIGURE)]

    if (matches.length !== 1) {
        return null
    }

    const [raw] = matches[0]

    return {
        value: Number(raw.replace(/[,'’]/g, '').replace('−', '-')),
        decimals: raw.includes('.') ? raw.split('.')[1].length : 0,
        separator: raw.match(/\d([,'’])\d{3}/)?.[1] ?? '',
        minus: raw.startsWith('−') ? '−' : '-',
        before: text.slice(0, matches[0].index),
        after: text.slice(matches[0].index + raw.length),
    }
}

const writeFigure = (figure, value) => {
    let [whole, fraction] = Math.abs(value).toFixed(figure.decimals).split('.')

    if (figure.separator) {
        whole = whole.replace(/\B(?=(\d{3})+(?!\d))/g, figure.separator)
    }

    const sign = value < 0 && Number(Math.abs(value).toFixed(figure.decimals)) !== 0 ? figure.minus : ''

    return figure.before + sign + whole + (fraction ? `.${fraction}` : '') + figure.after
}

document.addEventListener('alpine:init', () => {
    window.Alpine.directive('figure', (el, _, { cleanup }) => {
        const text = () => (el.childNodes.length === 1 && el.firstChild.nodeType === Node.TEXT_NODE ? el.firstChild : null)

        // In milliseconds, whichever unit arrives: a minifier turns `600ms` into `.6s`, and a
        // bare parseFloat would read that as 0.6ms — an instant count.
        const duration = () => {
            const token = getComputedStyle(document.documentElement).getPropertyValue('--md-sys-motion-spatial-slow-duration').trim()
            const value = parseFloat(token) || 0

            return token.endsWith('ms') ? value : value * 1000
        }

        let written = text()?.data ?? null
        let frame = null

        const count = (from, target) => {
            cancelAnimationFrame(frame)

            const node = text()
            const length = duration()

            if (!node || !target || length === 0 || from === target.value) {
                return
            }

            const started = performance.now()

            const step = (now) => {
                const progress = Math.min(1, (now - started) / length)
                const eased = 1 - Math.pow(1 - progress, 4)

                written = progress === 1 ? writeFigure(target, target.value) : writeFigure(target, from + (target.value - from) * eased)
                node.data = written

                if (progress < 1) {
                    frame = requestAnimationFrame(step)
                }
            }

            written = writeFigure(target, from)
            node.data = written
            frame = requestAnimationFrame(step)
        }

        const observer = new MutationObserver(() => {
            const node = text()

            if (!node || node.data === written) {
                return
            }

            const target = readFigure(node.data)
            const shown = written === null ? null : readFigure(written)

            written = node.data
            count(shown?.value ?? 0, target)
        })

        observer.observe(el, { characterData: true, childList: true, subtree: true })

        count(0, written === null ? null : readFigure(written))

        cleanup(() => {
            cancelAnimationFrame(frame)
            observer.disconnect()
        })
    })
})