import SwiftUI

/// One semantic capsule tone: a foreground and a background for each appearance.
///
/// The palette is deliberately a TINTED pair rather than a saturated solid. Every
/// tone below clears 4.5:1 for its own foreground on its own background in BOTH
/// appearances (measured, 4.96:1 to 6.72:1), which is what lets one component
/// carry the same meaning on a white row and a dark card without a second
/// colour per status.
///
/// The pairs are resolved through `UIColor`'s dynamic provider rather than
/// SwiftUI's `@Environment(\.colorScheme)`: a capsule inside a `List` is often
/// re-rendered without its body being rebuilt, so a scheme read at body time can
/// lag one switch behind. This way the colour itself follows the appearance.
struct CapsuleTone: Equatable {
    let lightForeground: Color
    let lightBackground: Color
    let darkForeground: Color
    let darkBackground: Color

    var foreground: Color { dynamic(light: lightForeground, dark: darkForeground) }
    var background: Color { dynamic(light: lightBackground, dark: darkBackground) }

    private func dynamic(light: Color, dark: Color) -> Color {
        let lightUI = UIColor(light)
        let darkUI = UIColor(dark)
        return Color(UIColor { traits in
            traits.userInterfaceStyle == .dark ? darkUI : lightUI
        })
    }
}

extension CapsuleTone {
    /// Green: a financial saving.
    static let saves = CapsuleTone(
        lightForeground: Color(hex: 0x176B3D), lightBackground: Color(hex: 0xDDF3E5),
        darkForeground: Color(hex: 0x66D69A), darkBackground: Color(hex: 0x204333)
    )

    /// Grey: a neutral outcome, neither saving nor costing.
    static let breakEven = CapsuleTone(
        lightForeground: Color(hex: 0x555B64), lightBackground: Color(hex: 0xE9EAED),
        darkForeground: Color(hex: 0xD0D0D5), darkBackground: Color(hex: 0x404044)
    )

    /// Red: an additional cost.
    static let costs = CapsuleTone(
        lightForeground: Color(hex: 0xA63F3D), lightBackground: Color(hex: 0xF9E1DF),
        darkForeground: Color(hex: 0xEF9690), darkBackground: Color(hex: 0x4B3032)
    )

    /// Purple: best overall value after travel.
    static let bestValue = CapsuleTone(
        lightForeground: Color(hex: 0x7043A1), lightBackground: Color(hex: 0xEEE4F8),
        darkForeground: Color(hex: 0xD1B4FA), darkBackground: Color(hex: 0x44354F)
    )

    /// Blue: the lowest fuel price in range.
    static let cheapest = CapsuleTone(
        lightForeground: Color(hex: 0x225F9B), lightBackground: Color(hex: 0xE0EFFB),
        darkForeground: Color(hex: 0x8BC5FA), darkBackground: Color(hex: 0x293F53)
    )

    /// Neutral grey: proximity. Same family as `breakEven` — both mean "no
    /// judgement" — but kept as its own pair so proximity and a break-even
    /// verdict stay independently tunable.
    static let closest = CapsuleTone(
        lightForeground: Color(hex: 0x525967), lightBackground: Color(hex: 0xE8EAF0),
        darkForeground: Color(hex: 0xC0C3CC), darkBackground: Color(hex: 0x424349)
    )
}

/// The one shape rule every capsule in the app follows.
///
/// A capsule while the content is a single line; a rounded rectangle once it
/// wraps. A pill's semicircular ends crowd the text corners at two lines or
/// more, while a 10pt radius does not. The shape follows what the content
/// actually DREW, not how many lines it declared, because a label can wrap in a
/// narrow column without the data changing — the baseline label was the case that
/// forced this: "Closest station" was one declared line that wrapped to two in the
/// listing's price column, which is also why that label is now the single word
/// "Closest".
///
/// Measuring happens on the content BEFORE padding, so the drawn line count is
/// never inflated by the capsule's own insets.
struct AdaptiveCapsule<Content: View>: View {
    /// The tone's background fill. The caller resolves it from its own semantics.
    let fill: Color
    /// One line's height for the content's font, already scaled with Dynamic
    /// Type — pass a `@ScaledMetric` so the division below tracks the user's size.
    let lineHeight: CGFloat
    /// Lines the content declares, used for the first layout pass before a
    /// measured height exists.
    var declaredLineCount: Int = 1
    var cornerRadius: CGFloat = 10
    var horizontalPadding: CGFloat
    var verticalPadding: CGFloat
    @ViewBuilder let content: Content

    @State private var drawnHeight: CGFloat = 0

    private var lineCount: Int {
        guard drawnHeight > 0, lineHeight > 0 else { return max(1, declaredLineCount) }
        return max(1, Int((drawnHeight / lineHeight).rounded()))
    }

    private var shape: AnyShape {
        lineCount > 1
            ? AnyShape(RoundedRectangle(cornerRadius: cornerRadius, style: .continuous))
            : AnyShape(Capsule())
    }

    var body: some View {
        content
            .background(
                GeometryReader { proxy in
                    Color.clear.preference(key: CapsuleContentHeightKey.self,
                                           value: proxy.size.height)
                }
            )
            .padding(.horizontal, horizontalPadding)
            .padding(.vertical, verticalPadding)
            .background(shape.fill(fill))
            .onPreferenceChange(CapsuleContentHeightKey.self) { drawnHeight = $0 }
    }
}

/// Carries the drawn height of a capsule's content up to `lineCount`.
private struct CapsuleContentHeightKey: PreferenceKey {
    static let defaultValue: CGFloat = 0
    static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
        value = max(value, nextValue())
    }
}

extension Color {
    /// A fixed sRGB colour from a 24-bit literal. The capsule palette is
    /// appearance-specific and supplied per tone, so these are deliberately NOT
    /// dynamic — `CapsuleTone` resolves the pair itself.
    init(hex: UInt32) {
        self.init(
            .sRGB,
            red: Double((hex >> 16) & 0xFF) / 255,
            green: Double((hex >> 8) & 0xFF) / 255,
            blue: Double(hex & 0xFF) / 255,
            opacity: 1
        )
    }
}

/// Lays its children left to right and wraps to a new line when the next one
/// would overflow, so two or three capsules never squeeze or truncate each other
/// on a narrow screen or at large Dynamic Type.
///
/// A flow layout rather than `ViewThatFits`: a fallback would stack the capsules
/// vertically as soon as one did not fit, which reads as three separate labels
/// rather than one row of rankings. This keeps them on a line while they fit and
/// only moves the overflowing one down.
///
/// Children are measured with `.unspecified` width so a long label takes the width
/// it needs (the badge sets `fixedSize` horizontally) instead of being clipped to
/// the container.
struct CapsuleFlowLayout: Layout {
    var spacing: CGFloat = 6
    var lineSpacing: CGFloat = 6

    private struct Row {
        var range: Range<Int>
        var width: CGFloat
        var height: CGFloat
    }

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

    func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) {
        var y = bounds.minY
        for row in rows(maxWidth: bounds.width, subviews: subviews) {
            var x = bounds.minX
            for index in row.range {
                let size = subviews[index].sizeThatFits(.unspecified)
                subviews[index].place(
                    at: CGPoint(x: x, y: y),
                    anchor: .topLeading,
                    proposal: ProposedViewSize(size)
                )
                x += size.width + spacing
            }
            y += row.height + lineSpacing
        }
    }

    private func rows(maxWidth: CGFloat, subviews: Subviews) -> [Row] {
        var rows: [Row] = []
        var start = 0
        var used: CGFloat = 0
        var height: CGFloat = 0

        for index in subviews.indices {
            let size = subviews[index].sizeThatFits(.unspecified)
            let needed = used == 0 ? size.width : used + spacing + size.width
            // `used > 0` guards the first child: a single capsule wider than the
            // container must still be placed (and may wrap its own text) rather
            // than starting an empty line above itself.
            if used > 0, needed > maxWidth {
                rows.append(Row(range: start..<index, width: used, height: height))
                start = index
                used = size.width
                height = size.height
            } else {
                used = needed
                height = max(height, size.height)
            }
        }
        if start < subviews.count {
            rows.append(Row(range: start..<subviews.count, width: used, height: height))
        }
        return rows
    }
}

/// The More info sheet's row of ranking capsules: every label the station
/// qualifies for, wrapped when the screen is narrow.
///
/// Renders as the SAME `StationLabelBadge` the listing rows use — same tone, same
/// symbol, same sentence-case copy — so a station carrying "Best value" here and
/// on the Stations list cannot look like two different things.
struct StationRankingCapsules: View {
    let kinds: [StationLabelKind]

    var body: some View {
        CapsuleFlowLayout(spacing: 6, lineSpacing: 6) {
            ForEach(kinds, id: \.self) { kind in
                StationLabelBadge(kind: kind)
            }
        }
        .frame(maxWidth: .infinity, alignment: .leading)
        // One phrase per capsule, read in the order they are shown.
        .accessibilityElement(children: .contain)
    }
}