Interest ChipsNew

// Copyright (c) 2026 Saivion Hayes
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, and distribute the Software as part of
// an application, website, or product, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// Commons Clause Restriction
//
// You may use this Software, including for any commercial purpose, so long as
// you do not sell, sublicense, or redistribute the components themselves, whether
// alone, in a bundle, or as a ported version.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

import SwiftUI

/// Colors and metrics for `InterestChips`. `.standard` is the house palette: the brand red on neutral glass.
public struct InterestChipsStyle: Sendable {
    /// A picked chip.
    public var accent: Color
    /// The label and check on a picked chip.
    public var onAccent: Color
    /// Labels on unpicked chips.
    public var label: Color
    /// The title and counter.
    public var secondary: Color
    /// Unpicked labels once the limit is reached.
    public var dimmed: Color
    /// The height of a chip. Grows with Dynamic Type.
    public var chipHeight: CGFloat
    /// The gap between chips, across and down.
    public var spacing: CGFloat

    public init(
        accent: Color = InterestChipsStyle.adaptive(light: 0xFF0000, dark: 0xFF0000),
        onAccent: Color = InterestChipsStyle.adaptive(light: 0x141414, dark: 0x141414),
        label: Color = InterestChipsStyle.adaptive(light: 0x141414, dark: 0xF4F3EF),
        secondary: Color = InterestChipsStyle.adaptive(light: 0x6F6D69, dark: 0x9C9A95),
        dimmed: Color = InterestChipsStyle.adaptive(light: 0xB8B6B0, dark: 0x4F4D4A),
        chipHeight: CGFloat = 40,
        spacing: CGFloat = 8
    ) {
        self.accent = accent
        self.onAccent = onAccent
        self.label = label
        self.secondary = secondary
        self.dimmed = dimmed
        self.chipHeight = max(chipHeight, 32)
        self.spacing = spacing
    }

    public static let standard = InterestChipsStyle()

    /// A color that follows the appearance, from two 0xRRGGBB values.
    public static func adaptive(light: UInt32, dark: UInt32) -> Color {
        Color(UIColor { @Sendable traits in
            let hex = traits.userInterfaceStyle == .dark ? dark : light
            return UIColor(red: CGFloat(hex >> 16 & 0xFF) / 255, green: CGFloat(hex >> 8 & 0xFF) / 255, blue: CGFloat(hex & 0xFF) / 255, alpha: 1)
        })
    }
}

/// Wrapping chips for a multiple choice, each flooding red when picked, with an optional limit.
///
/// - Parameters:
///   - title: An optional heading above the chips, such as `"Pick up to 4"`. VoiceOver reads it as the group's label.
///   - options: The chips, in order.
///   - selection: The picked options.
///   - limit: The most that can be picked. At the limit the rest dim and refuse a tap with a shake. `nil` (the default) is no limit.
///   - style: Colors and metrics. Defaults to the SwiftPieces house palette, adapting to light and dark.
///   - label: Each chip's text.
public struct InterestChips<Option: Hashable>: View {
    public typealias Style = InterestChipsStyle

    @Environment(\.isEnabled) private var isEnabled
    @Binding private var selection: Set<Option>
    @State private var picks = 0
    @State private var refusals = 0
    @State private var shakes: [Option: Int] = [:]

    private let title: String?
    private let options: [Option]
    private let limit: Int?
    private let style: Style
    private let label: (Option) -> String

    public init(_ title: String? = nil, options: [Option], selection: Binding<Set<Option>>, limit: Int? = nil, style: Style = .standard, label: @escaping (Option) -> String) {
        self.title = title
        self.options = options
        self._selection = selection
        self.limit = limit.map { max($0, 1) }
        self.style = style
        self.label = label
    }

    public var body: some View {
        VStack(alignment: .leading, spacing: 14) {
            if title != nil || limit != nil { header }
            InterestChipsFlow(spacing: style.spacing) {
                ForEach(options, id: \.self) { option in
                    InterestChipsChip(text: label(option), isOn: selection.contains(option), isDimmed: isFull && !selection.contains(option), style: style) {
                        toggle(option)
                    }
                    .pieceShake(trigger: shakes[option, default: 0], distance: 6)
                }
            }
        }
        .fontWeight(.semibold)
        .opacity(isEnabled ? 1 : 0.45)
        .sensoryFeedback(.selection, trigger: picks)
        .sensoryFeedback(.impact(flexibility: .rigid), trigger: refusals)
        .accessibilityElement(children: .contain)
        .accessibilityLabel(title ?? "")
    }

    private var header: some View {
        HStack(alignment: .firstTextBaseline) {
            if let title { Text(title).foregroundStyle(style.label) }
            Spacer()
            if let limit {
                Text("\(selection.count) of \(limit)")
                    .monospacedDigit()
                    .foregroundStyle(style.secondary)
                    .contentTransition(.numericText())
                    .animation(.snappy, value: selection.count)
            }
        }
        .accessibilityHidden(true)
    }

    private var isFull: Bool { limit.map { selection.count >= $0 } ?? false }

    private func toggle(_ option: Option) {
        if selection.contains(option) {
            selection.remove(option)
        } else if isFull {
            refusals += 1
            shakes[option, default: 0] += 1
            return
        } else {
            selection.insert(option)
        }
        picks += 1
    }
}

extension InterestChips where Option == String {
    /// Chips labelled by the strings themselves.
    public init(_ title: String? = nil, options: [String], selection: Binding<Set<String>>, limit: Int? = nil, style: Style = .standard) {
        self.init(title, options: options, selection: selection, limit: limit, style: style) { $0 }
    }
}

/// One chip: glass at rest, flooding red from its leading edge when picked.
private struct InterestChipsChip: View {
    let text: String
    let isOn: Bool
    let isDimmed: Bool
    let style: InterestChipsStyle
    let action: () -> Void

    @Environment(\.accessibilityReduceMotion) private var reduceMotion
    @ScaledMetric(relativeTo: .body) private var typeScale: CGFloat = 1
    @State private var width: CGFloat = 0

    var body: some View {
        let height = style.chipHeight * min(typeScale, 1.6)
        let check = 14 * min(typeScale, 1.6)
        Button(action: action) {
            HStack(spacing: 0) {
                Image(systemName: "checkmark")
                    .font(.system(size: check * 0.85, weight: .semibold))
                    .frame(width: isOn ? check : 0)
                    .padding(.trailing, isOn ? 6 : 0)
                    .scaleEffect(isOn ? 1 : 0.3, anchor: .leading)
                    .opacity(isOn ? 1 : 0)
                Text(text)
                    .lineLimit(1)
            }
            .foregroundStyle(isOn ? style.onAccent : isDimmed ? style.dimmed : style.label)
            .padding(.leading, isOn ? 12 : 16)
            .padding(.trailing, 16)
            .frame(height: height)
            .background(alignment: .leading) {
                // The flood: a dot of red at the leading end that widens to the whole chip.
                Capsule()
                    .fill(style.accent)
                    .frame(width: isOn ? max(width, height) : height)
                    .opacity(isOn ? 1 : 0)
            }
            .background { PieceLiquidGroup { Color.clear.pieceLiquid(.capsule, interactive: false) } }
            .onGeometryChange(for: CGFloat.self) { $0.size.width } action: { width = $0 }
            // Half the gap on every side counts as the chip, so taps between chips still land.
            .contentShape(Capsule().inset(by: -style.spacing / 2))
            .animation(PieceMotion(reduceMotion: reduceMotion).morph, value: isOn)
            .animation(.easeOut(duration: 0.2), value: isDimmed)
        }
        .buttonStyle(PiecePressStyle(depth: 2))
        .accessibilityValue(isDimmed ? "Limit reached" : "")
        .accessibilityAddTraits(isOn ? .isSelected : [])
    }
}

/// Lays chips out in rows, wrapping to the width. A chip wider than the width is offered the width and truncates.
private struct InterestChipsFlow: Layout {
    var spacing: CGFloat

    func sizeThatFits(proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) -> CGSize {
        let width = proposal.width ?? .infinity
        let rows = rows(subviews, width: width)
        let height = rows.reduce(0) { $0 + $1.height } + CGFloat(max(rows.count - 1, 0)) * spacing
        let widest = rows.map(\.width).max() ?? 0
        return CGSize(width: width.isFinite ? width : widest, height: height)
    }

    func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) {
        var y = bounds.minY
        for row in rows(subviews, width: bounds.width) {
            var x = bounds.minX
            for item in row.items {
                subviews[item.index].place(at: CGPoint(x: x, y: y), proposal: ProposedViewSize(item.size))
                x += item.size.width + spacing
            }
            y += row.height + spacing
        }
    }

    private func rows(_ subviews: Subviews, width: CGFloat) -> [InterestChipsRow] {
        var rows: [InterestChipsRow] = []
        var current = InterestChipsRow()
        for index in subviews.indices {
            let ideal = subviews[index].sizeThatFits(.unspecified)
            let size = ideal.width > width ? subviews[index].sizeThatFits(ProposedViewSize(width: width, height: nil)) : ideal
            if !current.items.isEmpty, current.width + spacing + size.width > width {
                rows.append(current)
                current = InterestChipsRow()
            }
            current.width += (current.items.isEmpty ? 0 : spacing) + size.width
            current.height = max(current.height, size.height)
            current.items.append((index, size))
        }
        if !current.items.isEmpty { rows.append(current) }
        return rows
    }
}

private struct InterestChipsRow {
    var items: [(index: Int, size: CGSize)] = []
    var width: CGFloat = 0
    var height: CGFloat = 0
}

// MARK: - Example

/// An onboarding step: pick up to four topics, then continue.
private struct InterestChipsExample: View {
    @State private var topics: Set<String> = ["Design", "Travel"]
    private let options = ["Design", "Running", "Cooking", "Travel", "Film", "Gardening", "Music", "Photography", "Coffee", "Books", "Climbing"]

    var body: some View {
        VStack(alignment: .leading, spacing: 24) {
            InterestChips("Pick up to 4", options: options, selection: $topics, limit: 4)
            Text(topics.isEmpty ? "Pick a few to tune your feed." : "We'll start with \(topics.sorted().formatted()).")
                .fontWeight(.semibold)
                .foregroundStyle(.secondary)
        }
        .padding(24)
        .frame(maxWidth: 440)
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .background(InterestChipsStyle.adaptive(light: 0xF3F2EE, dark: 0x121212))
    }
}

#Preview("Light") {
    InterestChipsExample()
}

#Preview("Dark") {
    InterestChipsExample()
        .preferredColorScheme(.dark)
}

// MARK: - Piece motion
//
// The SwiftPieces motion language: shared spring tokens and gesture physics, with the same values in every
// piece. Each piece carries a copy of only the parts it uses, so this file stands alone. Generated from
// registry/foundation/PieceMotion.swift in the SwiftPieces repo; edit it there, not here.
// swiftpieces-motion: 1.1.0 (core, pressMath, press, pressStyle, shake)

/// The SwiftPieces motion language: five spring tiers, and a named role for every moment a piece moves,
/// each with its Reduce Motion substitute.
///
/// Build one from the environment, `PieceMotion(reduceMotion: reduceMotion)`, and pick the role that names
/// what just happened. Never animate the tracking of a finger: set gesture state directly in `onChanged`, so the
/// surface stays under the finger, and spring only the release.
private struct PieceMotion {
    var reduceMotion = false

    // Tiers. Overshoot and settle times are measured from rest with SwiftUI's Spring.
    /// No overshoot, 90% in about 90ms. A press arriving under the finger.
    static var tight: Spring { Spring(duration: 0.14, bounce: 0) }
    /// About 2.8% overshoot, 90% in about 140ms. Snapping to a detent, page or segment.
    static var responsive: Spring { Spring(duration: 0.32, bounce: 0.25) }
    /// About 8.4% overshoot. Visible give: a release, a return from past an edge, a drag settling home.
    static var elastic: Spring { Spring(duration: 0.42, bounce: 0.38) }
    /// About 15% overshoot. A resolved action landing. At most once per interaction.
    static var expressive: Spring { Spring(duration: 0.48, bounce: 0.48) }
    /// About 1.5% overshoot, unhurried. Opening large surfaces and ambient change.
    static var calm: Spring { Spring(duration: 0.5, bounce: 0.2) }

    /// Reduce Motion: settles become this short spring with no overshoot.
    private static var still: Animation { .spring(duration: 0.25, bounce: 0) }

    // Roles.
    /// Touch-down. Starts on the same frame and never bounces under the finger.
    var press: Animation { .spring(Self.tight) }
    /// The finger lifts off a pressed surface, which springs back through rest.
    var release: Animation { reduceMotion ? Self.still : .spring(Self.elastic) }
    /// A dragged thing comes to rest. With a gesture's velocity, use `settle(velocity:from:to:)` instead.
    var settle: Animation { reduceMotion ? Self.still : .spring(Self.elastic) }
    /// Lands on a detent, page or segment.
    var snap: Animation { reduceMotion ? Self.still : .spring(Self.responsive) }
    /// A number, a chart value or anything else people read moves to its new value. Never overshoots, so it
    /// never shows a value that isn't true.
    var value: Animation { reduceMotion ? Self.still : .spring(duration: 0.35, bounce: 0) }
    /// Comes back from past a limit: a pull beyond the edge, a value pushed against its bound.
    var rebound: Animation { reduceMotion ? Self.still : .spring(Self.elastic) }
    /// A shape or container changes size, corner radius or form, with a little give at the end.
    var morph: Animation { reduceMotion ? Self.still : .spring(duration: 0.4, bounce: 0.2) }
    /// Something appears, opens or expands. Opening is a little slower than closing.
    var reveal: Animation { reduceMotion ? .easeOut(duration: 0.2) : .spring(Self.calm) }
    /// Something leaves, closes or collapses. Quick and firm, out of the way.
    var dismiss: Animation { reduceMotion ? .easeIn(duration: 0.18) : .spring(duration: 0.3, bounce: 0.08) }
    /// A resolved action lands: a check, a sent state, a reaction.
    var success: Animation { reduceMotion ? .easeOut(duration: 0.24) : .spring(Self.expressive) }
    /// A refused action. Firm, no wobble; `pieceShake` adds the movement.
    var error: Animation { reduceMotion ? .easeOut(duration: 0.2) : .spring(Self.responsive) }
    /// Slow ambient change. Loops themselves stop under Reduce Motion: check `allowsAmbient`.
    var ambient: Animation { reduceMotion ? .easeInOut(duration: 0.3) : .spring(Self.calm) }

    /// Loops, drifts, idle breathing and parallax run only when this is true.
    var allowsAmbient: Bool { !reduceMotion }

    /// A moving transition, or a plain fade under Reduce Motion.
    func transition(_ transition: AnyTransition) -> AnyTransition {
        reduceMotion ? .opacity : transition
    }

    /// For content replaced inside a container that stays put (a label, a glyph, a count): the old content
    /// blurs out as the new one sharpens in. A fade under Reduce Motion.
    @MainActor var swap: AnyTransition {
        reduceMotion ? .opacity : AnyTransition(.blurReplace)
    }
}

extension PieceMotion {
    /// About `depth` points per edge, not a fixed percentage: an icon sinks to 0.92, a pill 0.95, a card 0.985.
    nonisolated static func pressScale(for size: CGSize, depth: CGFloat = 2.5) -> CGFloat {
        let side = (max(size.width, 1) * max(size.height, 1)).squareRoot()
        return min(max(1 - depth * 2 / side, 0.92), 0.985)
    }

    /// An anchor partway from the center toward the touch, so the press leans into the finger without tipping.
    nonisolated static func pressAnchor(touch: CGPoint?, in size: CGSize, lean: CGFloat = 0.6) -> UnitPoint {
        guard let touch, size.width > 0, size.height > 0 else { return .center }
        let x = min(max(touch.x / size.width, 0), 1)
        let y = min(max(touch.y / size.height, 0), 1)
        return UnitPoint(x: 0.5 + (x - 0.5) * lean, y: 0.5 + (y - 0.5) * lean)
    }
}

/// Sinks on touch-down, leaning toward the touch if given, and springs back from the same lean. Under Reduce
/// Motion it shades instead of moving (darker in light mode, lighter in dark), without turning transparent.
private struct PiecePress: ViewModifier {
    let pressed: Bool
    var touch: CGPoint?
    var depth: CGFloat = 2.5
    @Environment(\.accessibilityReduceMotion) private var reduceMotion
    @Environment(\.colorScheme) private var colorScheme
    @State private var size: CGSize = .zero
    @State private var anchor: UnitPoint = .center

    func body(content: Content) -> some View {
        let motion = PieceMotion(reduceMotion: reduceMotion)
        let scale = pressed && !reduceMotion ? PieceMotion.pressScale(for: size, depth: depth) : 1
        content
            .onGeometryChange(for: CGSize.self) { $0.size } action: { size = $0 }
            .brightness(pressed && reduceMotion ? (colorScheme == .dark ? 0.1 : -0.08) : 0)
            .scaleEffect(scale, anchor: anchor)
            .animation(pressed ? motion.press : motion.release, value: pressed)
            .onChange(of: pressed) { _, isPressed in
                if isPressed { anchor = PieceMotion.pressAnchor(touch: touch, in: size) }
            }
            .onChange(of: touch) { _, touch in
                if pressed, let touch { anchor = PieceMotion.pressAnchor(touch: touch, in: size) }
            }
    }
}

private extension View {
    /// Sinks this view while `pressed`, leaning toward `touch` (in this view's coordinates) when given.
    func piecePress(_ pressed: Bool, touch: CGPoint? = nil, depth: CGFloat = 2.5) -> some View {
        modifier(PiecePress(pressed: pressed, touch: touch, depth: depth))
    }
}

/// Only the press, centered: for chips, rows and tiles, and anything in scrolling content.
private struct PiecePressStyle: ButtonStyle {
    var depth: CGFloat = 2.5

    func makeBody(configuration: Configuration) -> some View {
        configuration.label.piecePress(configuration.isPressed, depth: depth)
    }
}

/// A short decaying side-to-side shake for refused input, each time `trigger` changes. Under Reduce Motion it stays
/// still (same view, no identity change): pair it with a color or message change and the error haptic.
private struct PieceShake: ViewModifier {
    let trigger: AnyHashable
    var distance: CGFloat = 8
    @Environment(\.accessibilityReduceMotion) private var reduceMotion

    func body(content: Content) -> some View {
        let distance = reduceMotion ? 0 : distance
        content.keyframeAnimator(initialValue: CGFloat(0), trigger: trigger) { view, x in
            view.offset(x: x)
        } keyframes: { _ in
            KeyframeTrack {
                CubicKeyframe(-distance, duration: 0.06)
                CubicKeyframe(distance * 0.75, duration: 0.07)
                CubicKeyframe(-distance * 0.5, duration: 0.07)
                CubicKeyframe(distance * 0.25, duration: 0.06)
                SpringKeyframe(0, duration: 0.12, spring: Spring(duration: 0.18, bounce: 0))
            }
        }
    }
}

private extension View {
    /// Shakes this view side to side once each time `trigger` changes, for input that was refused.
    func pieceShake(trigger: some Hashable & Sendable, distance: CGFloat = 8) -> some View {
        modifier(PieceShake(trigger: AnyHashable(trigger), distance: distance))
    }
}

// swiftpieces-motion: end

// MARK: - Piece liquid
//
// The SwiftPieces liquid glass language: glass shapes that merge through a neck, bubbles that bud out of
// and melt back into each other, and the frosted fallback before iOS 26. Each piece carries a copy of only
// the parts it uses, so this file stands alone. Generated from registry/foundation/PieceLiquid.swift in the
// SwiftPieces repo; edit it there, not here. The rules are in LIQUID_GLASS.md.
// swiftpieces-liquid: 1.8.0 (liquid)

/// The liquid glass language: one merge distance, two rest gaps, and the springs a bubble leaves and comes home on.
///
/// Glass shapes inside one `PieceLiquidGroup` melt into each other through a neck when they come within `merge`
/// points. Parts of one control rest `joined`, inside that distance, so the neck holds; separate actions rest
/// `apart`, outside it, so they only goo while one buds out of, or melts back into, another.
private enum PieceLiquid {
    /// Glass shapes closer than this share a neck.
    static let merge: CGFloat = 20
    /// The gap between parts of one control (a stepper's buttons, a progress pill and its stop): the neck holds,
    /// short and smooth, about two thirds of the shapes' height at its waist. Joined parts read best at one height.
    static let joined: CGFloat = 4
    /// The gap between separate actions (menu items, confirm and cancel, chips): they rest as their own bubbles.
    static let apart: CGFloat = 26
    /// How far a bubble shrinks while it is home inside its parent.
    static let homeScale: CGFloat = 0.72

    /// A bubble leaving its parent: slow enough that the neck's stretch and snap read.
    static func split(reduceMotion: Bool) -> Animation {
        reduceMotion ? .easeOut(duration: 0.2) : .spring(duration: 0.62, bounce: 0.22)
    }

    /// A bubble going home. No bounce: a bounce would carry it out through the far side of its parent.
    static func home(reduceMotion: Bool) -> Animation {
        reduceMotion ? .easeIn(duration: 0.18) : .spring(duration: 0.5, bounce: 0)
    }
}

/// A group of glass shapes that merge into one liquid surface. On iOS 26 it is a `GlassEffectContainer`; before
/// that, and under Reduce Transparency, the shapes draw on their own and simply don't merge. `lift` adds the soft
/// shadow liquid glass floats on in light mode.
private struct PieceLiquidGroup<Content: View>: View {
    var spacing: CGFloat = PieceLiquid.merge
    var lift = true
    @ViewBuilder var content: Content
    @Environment(\.accessibilityReduceTransparency) private var reduceTransparency
    @Environment(\.colorScheme) private var colorScheme

    var body: some View {
        container
            .shadow(color: .black.opacity(lift && colorScheme == .light ? 0.07 : 0), radius: 18, y: 8)
    }

    @ViewBuilder private var container: some View {
        #if compiler(>=6.2)
        if #available(iOS 26, *), !reduceTransparency {
            GlassEffectContainer(spacing: spacing) { content }
        } else {
            content
        }
        #else
        content
        #endif
    }
}

/// One liquid glass shape: Liquid Glass on iOS 26, carrying `tint` as a solid colour and swelling under a press when
/// `interactive`; a frosted Material with a light rim and a soft shadow before that; a solid fill under Reduce
/// Transparency.
///
/// The tint is painted inside clear glass rather than tinting the glass. Tinted glass in a group bleeds its colour
/// through every neck as a smear, so a red button would glow into the white pill it is joined to; painted inside,
/// the colour stays crisp to the shape's edge, the necks between shapes are clear glass, and a tint change animates
/// like any colour (tinted glass snaps).
private struct PieceLiquidSurface<S: Shape>: ViewModifier {
    var shape: S
    var tint: Color?
    var interactive: Bool
    @Environment(\.accessibilityReduceTransparency) private var reduceTransparency
    @Environment(\.colorScheme) private var colorScheme
    @Environment(\.pieceLiquidScale) private var scale

    func body(content: Content) -> some View {
        #if compiler(>=6.2)
        if #available(iOS 26, *), !reduceTransparency {
            // Scaled as two parts, content and outline, about the same centre. A scaleEffect on a glass view inside a
            // GlassEffectContainer shrinks the glass but leaves what it carries full size, pinned to its corner.
            content
                .background { shape.fill(tint ?? .clear) }
                .scaleEffect(scale)
                .glassEffect(glass, in: shape.scale(scale))
        } else {
            fallback(content).scaleEffect(scale)
        }
        #else
        fallback(content).scaleEffect(scale)
        #endif
    }

    #if compiler(>=6.2)
    @available(iOS 26, *)
    private var glass: Glass {
        interactive ? Glass.regular.interactive() : .regular
    }
    #endif

    private func fallback(_ content: Content) -> some View {
        let dark = colorScheme == .dark
        return content
            .background {
                if reduceTransparency {
                    shape.fill(tint ?? (dark ? Color(white: 0.17) : Color(white: 0.97)))
                } else {
                    ZStack {
                        shape.fill(.regularMaterial)
                        if let tint { shape.fill(tint.opacity(0.88)) }
                    }
                }
            }
            .overlay { shape.stroke(Color.white.opacity(dark ? 0.14 : 0.7), lineWidth: 0.5) }
            .shadow(color: .black.opacity(dark ? 0.32 : 0.08), radius: 10, y: 5)
    }
}

private struct PieceLiquidScaleKey: EnvironmentKey {
    static let defaultValue: CGFloat = 1
}

private extension EnvironmentValues {
    /// How much the liquid shapes below are scaled, about their own centres. Nested scales multiply.
    var pieceLiquidScale: CGFloat {
        get { self[PieceLiquidScaleKey.self] }
        set { self[PieceLiquidScaleKey.self] = newValue }
    }
}

private extension View {
    /// Draws this view on a liquid glass `shape`. Put it inside a `PieceLiquidGroup` so it can merge with its neighbours.
    func pieceLiquid<S: Shape>(_ shape: S, tint: Color? = nil, interactive: Bool = true) -> some View {
        modifier(PieceLiquidSurface(shape: shape, tint: tint, interactive: interactive))
    }

    /// Scales the liquid glass shapes in this view, content and outline together, about their own centres. Use it
    /// instead of `scaleEffect` on a glass view (a press, a lift, a swell): inside a group a plain `scaleEffect` shrinks
    /// the glass but leaves its content full size and off centre. Animates like any other value.
    func pieceLiquidScale(_ scale: CGFloat) -> some View {
        transformEnvironment(\.pieceLiquidScale) { $0 *= scale }
    }
}

// swiftpieces-liquid: end