import SwiftUI

struct FuelSavingsAdjustmentView: View {
    @Binding var amount: FuelSavingsFillAmount

    @State private var showingComparisonHelp = false

    private var range: ClosedRange<Double> {
        FuelSavingsCalculator.fillAmountSliderRange(for: amount.unit)
    }

    private var step: Double {
        FuelSavingsCalculator.fillAmountSliderStep(for: amount.unit)
    }

    /// Read-out of the figure the slider is on. Deliberately NOT a text field:
    /// a typed figure could sit outside the slider's own bounds, leaving the
    /// control and the value it claimed to show disagreeing. Slider-only means
    /// what you see is the figure the estimate actually uses.
    private var valueText: String {
        switch amount.unit {
        case .pounds: return String(format: "£%.0f", amount.value)
        case .litres: return String(format: "%.0f L", amount.value)
        }
    }

    var body: some View {
        VStack(alignment: .leading, spacing: 10) {
            HStack {
                Text("How much fuel?")
                    .font(.subheadline.weight(.semibold))
                Spacer()
                Button {
                    showingComparisonHelp = true
                } label: {
                    Image(systemName: "info.circle")
                }
                .buttonStyle(.plain)
                .foregroundStyle(.secondary)
                .accessibilityLabel("About comparison modes")
                .popover(isPresented: $showingComparisonHelp) {
                    VStack(alignment: .leading, spacing: 12) {
                        Text("Comparison modes")
                            .font(.headline)
                        Text("£: Compare how much fuel your budget buys at each station.")
                            .fixedSize(horizontal: false, vertical: true)
                        Text("Litres: Compare the cost of buying the same amount of fuel.")
                            .fixedSize(horizontal: false, vertical: true)
                    }
                    .font(.footnote)
                    .frame(width: 280, alignment: .leading)
                    .padding()
                    .presentationCompactAdaptation(.popover)
                }
            }
            Picker("Fill-up unit", selection: unitBinding) {
                ForEach(FuelSavingsFillUnit.allCases) { unit in
                    Text(unit.displayName).tag(unit)
                }
            }
            .pickerStyle(.segmented)
            HStack {
                Slider(value: sliderBinding, in: range, step: step)
                    .accessibilityLabel("Fill-up amount")
                    .accessibilityValue(valueText)
                Text(valueText)
                    .monospacedDigit()
                    .frame(width: 72, alignment: .trailing)
            }
            Text("Adjust your fill-up amount for this visit. Your default won’t change.")
                .font(.caption2)
                .foregroundStyle(.secondary)
        }
    }

    private var unitBinding: Binding<FuelSavingsFillUnit> {
        Binding(
            get: { amount.unit },
            set: { newUnit in
                guard newUnit != amount.unit else { return }
                // No one litre figure equals a budget at every candidate price,
                // so switching modes starts from that mode's configured default.
                amount = FuelSavingsCalculator.newComparisonAmount(afterSwitching: amount, to: newUnit)
            }
        )
    }

    private var sliderBinding: Binding<Double> {
        Binding(
            get: { min(max(amount.value, range.lowerBound), range.upperBound) },
            set: { amount.value = min(max($0, range.lowerBound), range.upperBound) }
        )
    }
}

/// The colour-coded monetary verdict capsule used by the detail sheet and other
/// full financial summaries. Listing rows use `ListingFuelSavingsCapsule`.
///
/// An HStack with an explicit spacing, NOT a Label: given the width to spare,
/// a Label lays its icon and title out across the row and leaves a visible gap
/// between them (22pt in the listing row), which read as the text having
/// drifted away from its symbol. The icon is decorative here — the verdict is
/// in the text — so VoiceOver reads the capsule as one phrase.
struct FuelSavingsCapsule: View {
    let result: FuelSavingsResult
    var compact: Bool = true

    /// One line of `.headline` / `.caption`, scaled with Dynamic Type, so the
    /// shared shape rule can tell one drawn line from two.
    @ScaledMetric(relativeTo: .headline) private var headlineLineHeight: CGFloat = 22
    @ScaledMetric(relativeTo: .caption) private var captionLineHeight: CGFloat = 14

    private var tone: CapsuleTone { Self.tone(for: result.status) }

    var body: some View {
        AdaptiveCapsule(
            fill: tone.background,
            lineHeight: compact ? captionLineHeight : headlineLineHeight,
            horizontalPadding: compact ? 8 : 12,
            verticalPadding: compact ? 4 : 7
        ) {
            HStack(spacing: compact ? 3 : 5) {
                Image(systemName: Self.symbol(for: result.status))
                    .accessibilityHidden(true)
                Text(compact ? result.capsuleHeadline() : result.detailCapsuleHeadline())
                    // The detail sheet's capsule sits beside a headline and has the
                    // width for its wording; the listing's is narrow and scales.
                    .lineLimit(compact ? 1 : nil)
                    .minimumScaleFactor(compact ? 0.7 : 1)
            }
            .font(compact ? .caption.weight(.semibold) : .headline)
            .foregroundStyle(tone.foreground)
        }
    }

    /// Verdict tone: green save, red worse off, grey break even, neutral-grey
    /// baseline — the same meanings the price dot's RAG family carries.
    static func tone(for status: FuelSavingsStatus) -> CapsuleTone {
        switch status {
        case .worthTheDrive: return .saves
        case .notWorthTheDrive: return .costs
        case .breakEven: return .breakEven
        case .baseline: return .closestStation
        }
    }

    /// Foreground-only form, for a `Text` that is tinted rather than filled (the
    /// detail sheet's Total row). Keeps one source for the verdict colour.
    static func color(for status: FuelSavingsStatus) -> Color {
        tone(for: status).foreground
    }

    static func symbol(for status: FuelSavingsStatus) -> String {
        switch status {
        case .worthTheDrive: return "checkmark.circle.fill"
        case .breakEven: return "equal.circle.fill"
        case .notWorthTheDrive: return "xmark.circle.fill"
        case .baseline: return "location.circle.fill"
        }
    }
}

/// The station listing's verdict capsule: the words on the first line, the figure
/// on its own line beneath, and "(approx.)" on a third when the journey is an
/// estimate.
///
/// Stations and Favourites share `StationRow`, so both render this. The detail
/// sheet keeps `FuelSavingsCapsule`'s colour-coded monetary verdict on one line;
/// the Key sheet's legend renders this with `showsAmount: false` so it never
/// displays an invented figure.
struct ListingFuelSavingsCapsule: View {
    let result: FuelSavingsResult
    /// Station rows carry the figure; the Key sheet's legend shows the wording only.
    var showsAmount: Bool = true

    /// One caption line's height, scaled with Dynamic Type, for the shared shape
    /// rule. The drawn height is divided by this, so the shape follows the lines
    /// actually on screen rather than the number the verdict declares.
    @ScaledMetric(relativeTo: .caption) private var captionLineHeight: CGFloat = 14

    private var verdict: FuelSavingsResult.ListingVerdict {
        result.listingVerdict(showsAmount: showsAmount)
    }

    private var tone: CapsuleTone { FuelSavingsCapsule.tone(for: result.status) }

    var body: some View {
        AdaptiveCapsule(
            fill: tone.background,
            lineHeight: captionLineHeight,
            declaredLineCount: verdict.lines.count,
            horizontalPadding: 8,
            verticalPadding: 4
        ) {
            HStack(alignment: .firstTextBaseline, spacing: 3) {
                Image(systemName: symbol)
                    .accessibilityHidden(true)
                // One Text per line, not a "\n" inside one string: each line keeps its
                // own localisation key and the amount can be monospaced on its own.
                // Left-aligned: the word and its figure share a left edge, so the
                // block reads as a column rather than a ragged centre.
                VStack(alignment: .leading, spacing: 0) {
                    Text(verdict.headline)
                    if let amount = verdict.amount {
                        Text(amount)
                            .monospacedDigit()
                    }
                    if let qualifier = verdict.qualifier {
                        Text(qualifier)
                    }
                }
                .multilineTextAlignment(.leading)
                // Never compress or truncate: the capsule wraps and the row grows taller.
                .fixedSize(horizontal: false, vertical: true)
            }
            // Tinted foreground on a tinted fill. These capsules carry a figure the
            // eye is asked to read at a glance, so they are filled rather than
            // tinted-text-only; every badge above them stays the quieter tinted form.
            .font(.caption.weight(.semibold))
            .foregroundStyle(tone.foreground)
        }
        // Saves and Costs share one minimum width, so their trailing edges line
        // up down the list whatever the figure's length. Break even and Closest
        // station carry no figure and keep their natural width.
        .frame(minWidth: minimumWidth, alignment: .leading)
        .accessibilityElement(children: .combine)
        .accessibilityLabel(verdict.spokenText)
    }

    /// Saves and Costs only — the two verdicts that carry a figure. 84pt is the
    /// width the widest common amount needs ("£123.45 more"), so shorter figures
    /// pad rather than shrink the pill.
    private var minimumWidth: CGFloat {
        switch result.status {
        case .worthTheDrive, .notWorthTheDrive: return 84
        case .breakEven, .baseline: return 0
        }
    }

    private var symbol: String {
        switch result.status {
        case .worthTheDrive: return "checkmark.circle"
        case .notWorthTheDrive: return "arrow.up.circle"
        case .breakEven: return "equal.circle"
        case .baseline: return "location.circle"
        }
    }
}