/**
 * `materialProgress`: draws `<x-progress>`, M3 Expressive's progress indicator — linear or
 * circular, flat or wavy, determinate or indeterminate — the way androidx Compose Material 3
 * draws it, frame by frame, into the component's SVG.
 *
 * The server renders a first frame (the value, or a still of the indeterminate animation), so
 * the indicator is right before this runs. This then owns the SVG, which is `wire:ignore`: a
 * Livewire morph only changes the root's `data-md-value` (so does `x-bind`, for `bind`), and a
 * MutationObserver turns that into motion.
 *
 * - A new value moves on M3 Expressive's effects-slow spring (damping ratio 1, stiffness 800,
 *   motion.css). Compose recommends a spring that does not bounce either
 *   (ProgressIndicatorDefaults.ProgressAnimationSpec): a progress that overshoots is briefly a lie.
 *   The duration token scales it, so reduced motion makes it instant.
 * - Wavy: full amplitude between 10% and 95%, flat outside (indicatorAmplitude), reached in
 *   500 ms (standard easing growing, emphasized-accelerate flattening); the wave travels a
 *   wavelength a second. The circular wave is a RoundedPolygon star morphing from a circle.
 * - Indeterminate: Compose's keyframes — two lines chasing over 1750 ms; an arc that grows and
 *   shrinks over 6 s while it turns 1080° plus a quarter turn every 1.5 s.
 * - Reduced motion: values jump, the wave stands still, and an indeterminate indicator holds
 *   one frame of its animation.
 *
 * Frames are drawn only while something moves and the indicator is on screen.
 *
 * ---------------------------------------------------------------------------------------
 * Ported from androidx (https://github.com/androidx/androidx), commit
 * 27cf9a7d5788aa0f5f2d8b6699ce279560daf326:
 *
 *   compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/ProgressIndicator.kt
 *   compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/WavyProgressIndicator.kt
 *   compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/internal/LinearWavyProgressModifiers.kt
 *   compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/internal/CircularWavyProgressModifiers.kt
 *   compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/internal/ShapeUtil.kt
 *   compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/tokens/*ProgressIndicatorTokens.kt
 *   compose/animation/animation-core/src/commonMain/kotlin/androidx/compose/animation/core/VectorizedAnimationSpec.kt (keyframes)
 *   graphics/graphics-shapes/src/commonMain/kotlin/androidx/graphics/shapes/*.kt (via shapes.js:
 *   RoundedPolygon, CornerRounding, Cubic, Morph, FeatureMapping, PolygonMeasure)
 *
 * Copyright 2022-2025 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * ---------------------------------------------------------------------------------------
 */

import { asCubics, circlePolygon, match, point, rounding, star as starPolygon } from './shapes.js'
import { ms } from './util.js'

const SVG = 'http://www.w3.org/2000/svg'
const WATCHED = ['data-md-value', 'data-md-max', 'data-md-circular', 'data-md-wavy', 'data-md-thick']

// Tokens: *ProgressIndicatorTokens, WavyProgressIndicatorDefaults, ProgressIndicator.kt ----

const GAP = 4
const STOP_SIZE = 4
const STOP_TRAILING_SPACE = 6
const LINEAR_WAVELENGTH = 40
const LINEAR_INDETERMINATE_WAVELENGTH = 20
const CIRCULAR_WAVELENGTH = 15
const MIN_CIRCULAR_VERTICES = 5
const WAVE_PERIOD = 1000
const AMPLITUDE_DURATION = 500
const LINEAR_CYCLE = 1750
const CIRCULAR_CYCLE = 6000

// effects-slow (motion.css): the spring a new value moves on, and the time it settles in.
const VALUE_STIFFNESS = 800
const VALUE_SETTLE = 330

/** The frames an indeterminate indicator holds under reduced motion; the server draws the same. */
const LINEAR_STILL = 875
const CIRCULAR_STILL = 2000

// Easing and keyframes ------------------------------------------------------------------

const linear = (fraction) => fraction

/** CubicBezierEasing: the curve's y where its x is `fraction`, x found by bisection. */
function cubicBezier(x1, y1, x2, y2) {
    const axis = (t, p1, p2) => 3 * (1 - t) * (1 - t) * t * p1 + 3 * (1 - t) * t * t * p2 + t * t * t

    return (fraction) => {
        if (fraction <= 0 || fraction >= 1) {
            return Math.min(Math.max(fraction, 0), 1)
        }

        let low = 0
        let high = 1

        for (let i = 0; i < 24; i++) {
            const middle = (low + high) / 2

            if (axis(middle, x1, x2) < fraction) {
                low = middle
            } else {
                high = middle
            }
        }

        return axis((low + high) / 2, y1, y2)
    }
}

const STANDARD = cubicBezier(0.2, 0, 0, 1)
const EMPHASIZED_ACCELERATE = cubicBezier(0.3, 0, 0.8, 0.15)
const EMPHASIZED_DECELERATE = cubicBezier(0.05, 0.7, 0.1, 1)

/**
 * An infinitely repeating Compose `keyframes` spec: `[time, value, easing]` entries, where an
 * entry's easing shapes the interval that starts at it. As in VectorizedKeyframesSpec, the
 * implicit start (at 0 ms, from `initial`) and any entry without an easing are linear, and the
 * spec ends on `target` when no entry sits at its end.
 */
function keyframes(duration, initial, target, entries) {
    const frames = [...entries]

    if (frames[0][0] !== 0) {
        frames.unshift([0, initial])
    }

    if (frames.at(-1)[0] !== duration) {
        frames.push([duration, target])
    }

    return (ms) => {
        const time = ms % duration
        let i = 0

        while (i < frames.length - 2 && time >= frames[i + 1][0]) {
            i++
        }

        const [start, from, easing = linear] = frames[i]
        const [end, to] = frames[i + 1]

        return from + (to - from) * easing((time - start) / (end - start))
    }
}

const line = (delay, duration) => keyframes(LINEAR_CYCLE, 0, 1, [[delay, 0, EMPHASIZED_ACCELERATE], [delay + duration, 1]])

/** linearIndeterminate*AnimationSpec, in the order the drawing takes them: [tail, head, tail, head]. */
const LINEAR_LINES = [line(250, 1000), line(0, 1000), line(900, 850), line(650, 850)]

const CIRCULAR_TURN = keyframes(CIRCULAR_CYCLE, 0, 360, [
    [300, 90, EMPHASIZED_DECELERATE],
    [1500, 90],
    [1800, 180],
    [3000, 180],
    [3300, 270],
    [4500, 270],
    [4800, 360],
])

const CIRCULAR_SWEEP = keyframes(CIRCULAR_CYCLE, 0.1, 0.87, [
    [3000, 0.87, STANDARD],
    [6000, 0.1],
])

/** The global rotation (1080° in 6 s, linear) plus the additional quarter turns. */
const circularRotation = (ms) => ((ms % CIRCULAR_CYCLE) / CIRCULAR_CYCLE) * 1080 + CIRCULAR_TURN(ms)

/** WavyProgressIndicatorDefaults.indicatorAmplitude. */
const amplitudeFor = (progress) => (progress <= 0.1 || progress >= 0.95 ? 0 : 1)

const clamp = (value, min, max) => Math.min(Math.max(value, min), max)
const round = (value) => Math.round(value * 1000) / 1000

/** A straight stroke; a zero-length one is nudged so every engine still draws its round caps. */
function straight(x0, y, x1) {
    return `M${round(x0)} ${round(y)}L${round(Math.abs(x1 - x0) < 0.001 ? x0 + 0.001 : x1)} ${round(y)}`
}

/** DrawScope.drawArc: `sweep` degrees clockwise from `start` (0° is 3 o'clock); none for 0. */
function arc(cx, cy, radius, start, sweep) {
    if (sweep === 0) {
        return ''
    }

    if (Math.abs(sweep) >= 360) {
        const [r, left, right] = [round(radius), round(cx - radius), round(cx + radius)]

        return `M${right} ${round(cy)}A${r} ${r} 0 1 1 ${left} ${round(cy)}A${r} ${r} 0 1 1 ${right} ${round(cy)}Z`
    }

    const from = (start * Math.PI) / 180
    const to = ((start + sweep) * Math.PI) / 180
    const [x0, y0] = [cx + radius * Math.cos(from), cy + radius * Math.sin(from)]
    const [x1, y1] = [cx + radius * Math.cos(to), cy + radius * Math.sin(to)]

    if (Math.hypot(x1 - x0, y1 - y0) < 0.01) {
        return `M${round(x0)} ${round(y0)}L${round(x0 + 0.001)} ${round(y0)}`
    }

    return `M${round(x0)} ${round(y0)}A${round(radius)} ${round(radius)} 0 ${Math.abs(sweep) > 180 ? 1 : 0} ${sweep > 0 ? 1 : 0} ${round(x1)} ${round(y1)}`
}

// The linear wave -----------------------------------------------------------------------

const waves = new Map()

/**
 * One half-wavelength of LinearProgressDrawingCache's full path: a quadratic from (0, 0) through
 * the control point (h / 2, ±height) to (h, 0). Every half-wave has the same length, so a table
 * of arc length against the curve parameter locates any distance along the whole path.
 */
function halfWave(halfWavelength, height) {
    const key = `${halfWavelength}:${height}`

    if (!waves.has(key)) {
        const steps = 64
        const lengths = new Float64Array(steps + 1)
        const speed = (t) => Math.hypot(halfWavelength, 2 * height * (1 - 2 * t))

        for (let i = 1; i <= steps; i++) {
            const [a, b] = [(i - 1) / steps, i / steps]
            lengths[i] = lengths[i - 1] + ((b - a) / 6) * (speed(a) + 4 * speed((a + b) / 2) + speed(b))
        }

        const length = lengths[steps]

        const parameterAt = (distance) => {
            const d = clamp(distance, 0, length)
            let low = 0
            let high = steps

            while (high - low > 1) {
                const middle = (low + high) >> 1

                if (lengths[middle] <= d) {
                    low = middle
                } else {
                    high = middle
                }
            }

            const span = lengths[high] - lengths[low]

            return (low + (span > 0 ? (d - lengths[low]) / span : 0)) / steps
        }

        waves.set(key, { length, parameterAt })
    }

    return waves.get(key)
}

/**
 * PathMeasure.getSegment on the full wave from `from` to `to` (distances), then Compose's
 * transform: shifted back by the wave's phase and flattened towards the centre line by
 * `amplitude` — as exact quadratic pieces.
 */
function waveSegment(from, to, halfWavelength, height, shift, middle, amplitude) {
    const wave = halfWave(halfWavelength, height)

    const locate = (distance) => {
        const index = Math.floor(distance / wave.length)

        return [index, wave.parameterAt(distance - index * wave.length)]
    }

    const sign = (index) => (index % 2 === 0 ? 1 : -1)
    const x = (index, t) => round((index + t) * halfWavelength - shift)
    const y = (index, bump) => round(middle + amplitude * sign(index) * height * bump)

    const [first, t0] = locate(from)
    const [last, t1] = locate(to)
    let d = `M${x(first, t0)} ${y(first, 2 * t0 * (1 - t0))}`

    for (let index = first; index <= last; index++) {
        const a = index === first ? t0 : 0
        const b = index === last ? t1 : 1

        if (b <= a) {
            continue
        }

        // The quadratic's blossom at (a, b) is the control point of its piece from a to b.
        d += `Q${x(index, (a + b) / 2)} ${y(index, a + b - 2 * a * b)} ${x(index, b)} ${y(index, 2 * b * (1 - b))}`
    }

    return d
}

// The circular wave ---------------------------------------------------------------------

const circularShapes = new Map()

/** CircularShapes: the track's circle and the active indicator's star, matched in vertex count. */
function shapesFor(vertexCount) {
    if (!circularShapes.has(vertexCount)) {
        const circle = circlePolygon(vertexCount).normalized()
        const star = starPolygon(vertexCount, { innerRadius: 0.75, cornerRounding: rounding(0.35, 0.4), innerCornerRounding: rounding(0.5) }).normalized()
        let pairs = null

        circularShapes.set(vertexCount, {
            circle,
            star,
            morph: () => (pairs ??= match(circle, star)),
        })
    }

    return circularShapes.get(vertexCount)
}

const GAUSS_LEGENDRE = [
    [0.1834346424956498, 0.362683783378362],
    [0.525532409916329, 0.3137066458778873],
    [0.7966664774136267, 0.2223810344533745],
    [0.9602898564975363, 0.1012285362903763],
]

// Pure arithmetic rather than getTotalLength(): WebKit lays the whole page out on that call, even
// for a detached path, and this runs every frame while the amplitude animates.
function cubicLength(c) {
    let sum = 0

    for (const [node, weight] of GAUSS_LEGENDRE) {
        for (const t of [(1 - node) / 2, (1 + node) / 2]) {
            const u = 1 - t
            const dx = 3 * (u * u * (c[2] - c[0]) + 2 * u * t * (c[4] - c[2]) + t * t * (c[6] - c[4]))
            const dy = 3 * (u * u * (c[3] - c[1]) + 2 * u * t * (c[5] - c[3]) + t * t * (c[7] - c[5]))
            sum += weight * Math.hypot(dx, dy)
        }
    }

    return sum / 2
}

/**
 * pathFromCubics (turned so it starts at 12 o'clock, repeated once when the wave travels) and
 * processPath (scaled to the container less the stroke, its control-point bounds centred).
 */
function circularPath(cubics, pivot, repeat, scale, cx, cy) {
    const angle = Math.atan2(cubics[0][1] - pivot.y, cubics[0][0] - pivot.x)
    const turn = -angle + (270 * Math.PI) / 180
    const [sin, cos] = [Math.sin(turn), Math.cos(turn)]
    let [left, top, right, bottom] = [Infinity, Infinity, -Infinity, -Infinity]

    const moved = cubics.map((c) => {
        const out = new Array(8)

        for (let i = 0; i < 8; i += 2) {
            out[i] = (cos * c[i] - sin * c[i + 1]) * scale
            out[i + 1] = (sin * c[i] + cos * c[i + 1]) * scale
            left = Math.min(left, out[i])
            right = Math.max(right, out[i])
            top = Math.min(top, out[i + 1])
            bottom = Math.max(bottom, out[i + 1])
        }

        return out
    })

    const [dx, dy] = [cx - (left + right) / 2, cy - (top + bottom) / 2]
    const loop = moved.map((c) => `C${round(c[2] + dx)} ${round(c[3] + dy)} ${round(c[4] + dx)} ${round(c[5] + dy)} ${round(c[6] + dx)} ${round(c[7] + dy)}`).join('')
    const start = `${round(moved[0][0] + dx)} ${round(moved[0][1] + dy)}`
    const loopLength = moved.reduce((sum, c) => sum + cubicLength(c), 0)

    return {
        d: repeat ? `M${start}${loop}L${start}${loop}Z` : `M${start}${loop}Z`,
        length: repeat ? loopLength * 2 : loopLength,
    }
}

// The component -------------------------------------------------------------------------

function svgElement(name, attributes) {
    const element = document.createElementNS(SVG, name)

    for (const [key, value] of Object.entries(attributes)) {
        element.setAttribute(key, value)
    }

    return element
}

class Indicator {
    constructor(element) {
        this.element = element
        this.svg = element.querySelector(':scope > svg')
        this.frame = null
        this.last = null
        this.visible = true
        this.width = 0
        this.height = 0
        this.written = new Map()
        this.motion = window.matchMedia('(prefers-reduced-motion: reduce)')
        this.onMotionChange = () => this.schedule()
        this.motion.addEventListener('change', this.onMotionChange)

        this.read(true)
        this.measure()

        this.resizes = new ResizeObserver(() => this.measure() && this.schedule())
        this.resizes.observe(element)

        this.intersections = new IntersectionObserver((entries) => {
            this.visible = entries.at(-1).isIntersecting

            if (this.visible) {
                this.schedule()
            }
        })
        this.intersections.observe(element)

        this.mutations = new MutationObserver(() => {
            this.read(false)
            this.schedule()
        })
        this.mutations.observe(element, { attributes: true, attributeFilter: WATCHED })

        this.draw(this.motion.matches)
        this.schedule()
    }

    destroy() {
        cancelAnimationFrame(this.frame)
        this.motion.removeEventListener('change', this.onMotionChange)
        this.resizes.disconnect()
        this.intersections.disconnect()
        this.mutations.disconnect()
    }

    /** Takes the root's attributes: the shape, and the value to show (null: indeterminate). */
    read(initial) {
        const element = this.element
        const shape = WATCHED.slice(2).map((name) => element.hasAttribute(name)).join()
        const maximum = parseFloat(element.getAttribute('data-md-max')) > 0 ? parseFloat(element.getAttribute('data-md-max')) : 100
        const raw = element.getAttribute('data-md-value')
        const number = raw === null || raw.trim() === '' ? NaN : Number(raw)
        const target = Number.isFinite(number) ? clamp(number / maximum, 0, 1) : null

        if (initial || shape !== this.shape) {
            this.shape = shape
            this.circular = element.hasAttribute('data-md-circular')
            this.wavy = element.hasAttribute('data-md-wavy')
            this.stroke = element.hasAttribute('data-md-thick') ? 8 : 4
            this.build()
            this.reset(target)
        } else if ((target === null) !== (this.target === null)) {
            // Compose draws determinate and indeterminate indicators as two different composables.
            this.reset(target)
        } else if (target !== null && target !== this.target) {
            const duration = ms(element, '--md-sys-motion-effects-slow-duration') ?? VALUE_SETTLE
            this.timeScale = duration > 0 && !this.motion.matches ? VALUE_SETTLE / duration : 0
        }

        this.target = target
    }

    reset(target) {
        this.target = target
        this.progress = target
        this.velocity = 0
        this.timeScale = 0
        this.clock = 0
        this.offset = 0
        this.amplitude = target === null ? 1 : amplitudeFor(target)
        this.amplitudeGoal = this.amplitude
        this.amplitudeAnimation = null
        this.morphed = false
        this.vertexCount = MIN_CIRCULAR_VERTICES
        this.paths = {}
    }

    build() {
        const stroke = { fill: 'none', 'stroke-width': this.stroke, 'stroke-linecap': 'round' }

        this.group = svgElement('g', {})
        this.track = svgElement('path', stroke)
        this.active = svgElement('path', { ...stroke, stroke: 'currentColor' })
        this.stop = svgElement('circle', { fill: 'currentColor', stroke: 'none', r: 0 })
        this.written.clear()

        this.group.append(this.track, this.active, this.stop)
        this.svg.removeAttribute('viewBox')
        this.svg.replaceChildren(this.group)
    }

    measure() {
        const [width, height] = [this.element.offsetWidth, this.element.offsetHeight]
        const changed = width !== this.width || height !== this.height

        this.width = width
        this.height = height

        return changed
    }

    schedule() {
        if (this.frame === null) {
            this.frame = requestAnimationFrame((now) => this.tick(now))
        }
    }

    tick(now) {
        this.frame = null

        const reduced = this.motion.matches
        const elapsed = this.last === null ? 0 : Math.min(now - this.last, 64)
        this.last = now

        if (!reduced) {
            this.clock += elapsed
        }

        const moving = this.advance(elapsed, reduced)
        this.draw(reduced)

        if (moving && this.visible && this.element.isConnected) {
            this.schedule()
        } else {
            this.last = null
        }
    }

    /** Steps every animation by `elapsed` ms; true while any of them still moves. */
    advance(elapsed, reduced) {
        let moving = false

        if (this.target === null) {
            moving = !reduced
        } else if (this.progress !== this.target || this.velocity !== 0) {
            if (this.timeScale === 0 || reduced) {
                this.progress = this.target
                this.velocity = 0
            } else {
                // A critically damped spring, solved exactly, so a new target keeps the velocity.
                const omega = Math.sqrt(VALUE_STIFFNESS)
                const t = (elapsed / 1000) * this.timeScale
                const d0 = this.progress - this.target
                const c = this.velocity + omega * d0
                const decay = Math.exp(-omega * t)

                this.progress = this.target + (d0 + c * t) * decay
                this.velocity = (c - omega * (d0 + c * t)) * decay

                if (Math.abs(this.progress - this.target) < 1e-4 && Math.abs(this.velocity) < 1e-3) {
                    this.progress = this.target
                    this.velocity = 0
                } else {
                    moving = true
                }
            }
        }

        if (!this.wavy) {
            return moving
        }

        const animation = this.amplitudeAnimation

        if (animation) {
            animation.elapsed += elapsed
            const fraction = animation.duration > 0 ? Math.min(animation.elapsed / animation.duration, 1) : 1
            this.amplitude = animation.from + (animation.to - animation.from) * animation.easing(fraction)

            if (fraction >= 1) {
                this.amplitudeAnimation = null
            } else {
                moving = true
            }
        }

        // As in Compose, a new amplitude animation starts only once the running one has ended.
        const goal = this.target === null ? 1 : amplitudeFor(clamp(this.progress, 0, 1))

        if (!this.amplitudeAnimation && goal !== this.amplitudeGoal) {
            const duration = reduced ? 0 : (ms(this.element, '--md-sys-motion-duration-long') ?? AMPLITUDE_DURATION)

            this.amplitudeGoal = goal
            this.morphed = true

            if (duration > 0) {
                this.amplitudeAnimation = {
                    from: this.amplitude,
                    to: goal,
                    easing: this.amplitude < goal ? STANDARD : EMPHASIZED_ACCELERATE,
                    duration,
                    elapsed: 0,
                }
                moving = true
            } else {
                this.amplitude = goal
            }
        }

        if (this.amplitude > 0 && !reduced) {
            const period = this.circular ? WAVE_PERIOD * this.vertexCount : WAVE_PERIOD
            this.offset = (this.offset + elapsed / period) % 1
            moving = true
        }

        return moving
    }

    draw(reduced) {
        if (this.width <= 0 || this.height <= 0) {
            return
        }

        const still = this.circular ? CIRCULAR_STILL : LINEAR_STILL
        const time = reduced ? still : this.clock
        const offset = reduced ? 0 : this.offset

        if (this.circular) {
            this.wavy ? this.drawCircularWavy(time, offset) : this.drawCircular(time)
        } else {
            this.wavy ? this.drawLinearWavy(time, offset) : this.drawLinear(time)
        }
    }

    write(element, name, value) {
        const key = element === this.track ? `t${name}` : element === this.active ? `a${name}` : element === this.stop ? `s${name}` : `g${name}`

        if (this.written.get(key) === value) {
            return
        }

        this.written.set(key, value)

        if (value === null) {
            element.removeAttribute(name)
        } else {
            element.setAttribute(name, value)
        }
    }

    stopAt(cx, cy, radius) {
        this.write(this.stop, 'cx', round(cx))
        this.write(this.stop, 'cy', round(cy))
        this.write(this.stop, 'r', round(Math.max(radius, 0)))
    }

    /** LinearProgressIndicator. */
    drawLinear(time) {
        const [width, height, stroke] = [this.width, this.height, this.stroke]
        const cap = height > width ? 0 : stroke / 2
        const gap = (GAP + (height > width ? 0 : stroke)) / width
        const middle = height / 2
        let track = ''
        let active = ''

        // drawLinearIndicator: a line between two fractions, kept inside for its round caps.
        const bar = (start, end) => (Math.abs(end - start) > 0 ? straight(clamp(start * width, cap, width - cap), middle, clamp(end * width, cap, width - cap)) : '')

        if (this.target !== null) {
            const progress = clamp(this.progress, 0, 1)
            const trackStart = progress + Math.min(progress, gap)

            if (trackStart <= 1) {
                track += bar(trackStart, 1)
            }

            active += bar(0, progress)

            const size = Math.min(STOP_SIZE, height)
            this.stopAt(width - size / 2 - Math.min((height - size) / 2, STOP_TRAILING_SPACE), middle, size / 2)
        } else {
            const [firstTail, firstHead, secondTail, secondHead] = LINEAR_LINES.map((spec) => spec(time))

            if (firstHead < 1 - gap) {
                track += bar(firstHead > 0 ? firstHead + gap : 0, 1)
            }

            if (firstHead - firstTail > 0) {
                active += bar(firstHead, firstTail)
            }

            if (firstTail > gap) {
                track += bar(secondHead > 0 ? secondHead + gap : 0, firstTail < 1 ? firstTail - gap : 1)
            }

            if (secondHead - secondTail > 0) {
                active += bar(secondHead, secondTail)
            }

            if (secondTail > gap) {
                track += bar(0, secondTail < 1 ? secondTail - gap : 1)
            }

            this.stopAt(0, 0, 0)
        }

        this.write(this.track, 'd', track)
        this.write(this.active, 'd', active)
    }

    /** LinearWavyProgressIndicator: LinearProgressDrawingCache.updateDrawPaths and drawStopIndicator. */
    drawLinearWavy(time, offset) {
        const [width, height, stroke] = [this.width, this.height, this.stroke]
        const determinate = this.target !== null
        const cap = height > width ? 0 : stroke / 2
        const middle = height / 2
        const wavelength = determinate ? LINEAR_WAVELENGTH : LINEAR_INDETERMINATE_WAVELENGTH
        const halfWavelength = wavelength / 2
        const waveHeight = height - stroke
        const amplitude = this.amplitude
        const fractions = determinate ? [0, clamp(this.progress, 0, 1)] : LINEAR_LINES.map((spec) => spec(time))

        // The full path: a line, or enough half-waves to cover the width plus two wavelengths.
        const halfWaves = Math.floor((width + wavelength * 2) / halfWavelength)
        const fullLength = amplitude !== 0 ? halfWaves * halfWave(halfWavelength, waveHeight).length : width
        const scale = fullLength / ((amplitude !== 0 ? halfWaves * halfWavelength : width) + 0.00000001)

        let trackGap = GAP
        let activeVisible = false
        let nextTrackEnd = width - cap
        let track = `M${round(nextTrackEnd)} ${round(middle)}`
        let active = ''

        for (let i = 0; i < fractions.length / 2; i++) {
            const [start, end] = [fractions[i * 2], fractions[i * 2 + 1]]
            const [tail, head] = [start * width, end * width]

            if (i === 0) {
                trackGap = head < cap ? 0 : Math.min(head - cap, GAP)
                activeVisible = head >= cap
            }

            const adjustedHead = clamp(head, cap, width - cap)
            const adjustedTail = clamp(tail, cap, width - cap)

            if (Math.abs(end - start) > 0) {
                const shift = amplitude !== 0 ? offset * wavelength : 0
                const from = Math.max((adjustedTail + shift) * scale, 0)
                const to = Math.min((adjustedHead + shift) * scale, fullLength)

                // android.graphics.PathMeasure.getSegment draws nothing for an empty segment.
                if (from < to) {
                    active += amplitude !== 0 ? waveSegment(from, to, halfWavelength, waveHeight, shift, middle, amplitude) : straight(from, middle, to)
                }
            }

            const spacing = activeVisible ? trackGap + cap * 2 : trackGap

            if (nextTrackEnd > adjustedHead + spacing) {
                track += `L${round(Math.max(cap, adjustedHead + spacing))} ${round(middle)}`
            }

            if (head > tail) {
                nextTrackEnd = Math.max(cap, adjustedTail - spacing)
                track += `M${round(nextTrackEnd)} ${round(middle)}`
            }
        }

        if (nextTrackEnd > cap) {
            track += `L${round(cap)} ${round(middle)}`
        }

        this.write(this.track, 'd', track)
        this.write(this.active, 'd', active)

        if (!determinate) {
            this.stopAt(0, 0, 0)

            return
        }

        let size = Math.min(stroke, STOP_SIZE)
        let x = width - size - (size === stroke ? 0 : stroke / 4)
        const progressX = width * fractions[1] + cap

        if (x <= progressX) {
            size = Math.max(0, size - (progressX - x))
            x = progressX
        }

        this.stopAt(x + size / 2, middle, size / 2)
    }

    /** CircularProgressIndicator. */
    drawCircular(time) {
        const size = Math.min(this.width, this.height)
        const [cx, cy, stroke] = [this.width / 2, this.height / 2, this.stroke]
        const radius = (size - stroke) / 2
        const gapSweep = ((GAP + stroke) / (Math.PI * size)) * 360

        if (this.target !== null) {
            const sweep = clamp(this.progress, 0, 1) * 360
            const trackGap = Math.min(sweep, gapSweep)

            this.write(this.group, 'transform', null)
            this.write(this.track, 'd', arc(cx, cy, radius, 270 + sweep + trackGap, 360 - sweep - trackGap * 2))
            this.write(this.active, 'd', arc(cx, cy, radius, 270, sweep))
        } else {
            // circularIndeterminateTrackColor is transparent: no track while it spins.
            this.write(this.group, 'transform', `rotate(${round(circularRotation(time))} ${round(cx)} ${round(cy)})`)
            this.write(this.track, 'd', '')
            this.write(this.active, 'd', arc(cx, cy, radius, 0, CIRCULAR_SWEEP(time) * 360))
        }
    }

    /** CircularWavyProgressIndicator: CircularProgressDrawingCache.updateDrawPaths, as dashes. */
    drawCircularWavy(time, offset) {
        const size = Math.min(this.width, this.height)
        const [cx, cy, stroke] = [this.width / 2, this.height / 2, this.stroke]
        const cap = stroke / 2
        const determinate = this.target !== null
        const vertexCount = Math.max(MIN_CIRCULAR_VERTICES, Math.round((2 * Math.PI * (size / 2 - stroke / 2)) / CIRCULAR_WAVELENGTH))
        const amplitude = this.amplitude
        const motion = determinate || amplitude > 0
        const end = determinate ? clamp(this.progress, 0, 1) : CIRCULAR_SWEEP(time)
        const shapes = shapesFor(vertexCount)

        this.vertexCount = vertexCount

        const trackKey = `${vertexCount}|${size}|${stroke}|${cx}|${cy}`

        if (this.paths.trackKey !== trackKey) {
            this.paths.trackKey = trackKey
            this.paths.track = circularPath(shapes.circle.cubics, shapes.circle.center, false, size - stroke, cx, cy)
        }

        // CircularShapes.getProgressPath: the Morph once an amplitude animation has needed one.
        const progressKey = `${trackKey}|${amplitude}|${motion}|${this.morphed}`

        if (this.paths.progressKey !== progressKey) {
            let [cubics, pivot] = [shapes.circle.cubics, shapes.circle.center]

            if (this.morphed) {
                ;[cubics, pivot] = [asCubics(shapes.morph(), amplitude), point(0.5, 0.5)]
            } else if (amplitude === 1) {
                ;[cubics, pivot] = [shapes.star.cubics, shapes.star.center]
            }

            this.paths.progressKey = progressKey
            this.paths.progress = circularPath(cubics, pivot, motion, size - stroke, cx, cy)
        }

        const { track, progress } = this.paths
        const progressLength = motion ? progress.length / 2 : progress.length
        const stop = end * progressLength
        const spacing = Math.min(stop, cap) * 2 + Math.min(stop, GAP)
        const phase = motion ? clamp(offset, 0, 1) : 0
        const shift = phase * progressLength

        this.write(this.group, 'transform', determinate ? null : `rotate(${round(circularRotation(time) + 90)} ${round(cx)} ${round(cy)})`)
        this.dash(this.active, progress, shift, stop + shift)
        this.write(this.active, 'transform', phase * 360 % 360 !== 0 ? `rotate(${round(-(phase * 360) % 360)} ${round(cx)} ${round(cy)})` : null)
        this.dash(this.track, track, end * track.length + spacing, track.length - spacing)
    }

    /** PathMeasure.getSegment as a single dash: nothing when the segment is empty. */
    dash(element, path, from, to) {
        const [start, stop] = [Math.max(from, 0), Math.min(to, path.length)]

        this.write(element, 'd', path.d)
        this.write(element, 'pathLength', round(path.length))

        if (!(start < stop)) {
            this.write(element, 'visibility', 'hidden')

            return
        }

        this.write(element, 'visibility', null)
        this.write(element, 'stroke-dasharray', `${round(stop - start)} ${round(path.length * 2)}`)
        this.write(element, 'stroke-dashoffset', round(-start))
    }
}

document.addEventListener('alpine:init', () => {
    window.Alpine.data('materialProgress', () => {
        // Kept out of the returned object: Alpine makes that reactive, and a proxy on every
        // per-frame read would cost more than the drawing.
        let indicator = null

        return {
            init() {
                // After this element's own x-bind has written a bound value.
                this.$nextTick(() => {
                    if (this.$el.isConnected && indicator === null) {
                        indicator = new Indicator(this.$el)
                    }
                })
            },

            destroy() {
                indicator?.destroy()
                indicator = null
            },
        }
    })
})