import SwiftUI

struct FuelSavingsAdjustmentView: View {
    @Binding var amount: FuelSavingsFillAmount
    let referencePricePencePerLitre: Double?

    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) {
            Text("How much are you filling up?")
                .font(.subheadline.weight(.semibold))
            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("Changes the estimate for this session only — your Settings default stays unchanged.")
                .font(.caption2)
                .foregroundStyle(.secondary)
        }
    }

    private var unitBinding: Binding<FuelSavingsFillUnit> {
        Binding(
            get: { amount.unit },
            set: { newUnit in
                guard newUnit != amount.unit else { return }
                if let referencePricePencePerLitre,
                   let converted = try? FuelSavingsCalculator.convert(amount: amount, to: newUnit, referencePricePencePerLitre: referencePricePencePerLitre) {
                    amount = converted
                } else {
                    amount = FuelSavingsFillAmount(value: newUnit == .pounds ? 40 : 30, unit: 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) }
        )
    }
}

struct FuelSavingsSummaryView: View {
    let availability: FuelSavingsAvailability?
    let amount: FuelSavingsFillAmount
    var baselineStationName: String? = nil
    var compact: Bool = false
    /// Sizes the "extra return travel" caption in the user's own unit (the
    /// stored figure is miles) — used by both the row banner and the detail sheet.
    var distanceUnit: DistanceUnit = .miles
    var showInfoAction: (() -> Void)? = nil

    private func comparisonLabel(for result: FuelSavingsResult) -> String {
        FuelSavingsFormat.comparisonLabel(status: result.status)
    }

    var body: some View {
        switch availability {
        case .available(let result):
            if compact {
                // FULL-WIDTH banner under the row. Inline inside the middle
                // column the capsule truncated ("Approx. £2.75 better off after
                // tra…") because
                // the column is squeezed by the price block — the verdict is the
                // point of this sort mode, so it gets its own line with room.
                // Colour carries the verdict: green save, red worse off, grey
                // break even, blue baseline. lineLimit + minimumScaleFactor keep
                // it to one line, so rows stay even.
                VStack(alignment: .leading, spacing: 2) {
                    HStack(alignment: .firstTextBaseline, spacing: 6) {
                        capsule(for: result, compact: true)
                            .accessibilityLabel(accessibilityHeadline(for: result))
                        Text(comparisonLabel(for: result))
                            .font(.caption2)
                            .foregroundStyle(.secondary)
                            .lineLimit(1)
                            .layoutPriority(1)
                            .accessibilityLabel("Comparison: \(comparisonLabel(for: result))")
                    }
                    if let extraTravel = FuelSavingsFormat.extraTravelLabel(
                        extraDistanceMiles: result.extraDistanceMiles,
                        unit: distanceUnit,
                        confidence: result.journeyConfidence
                    ) {
                        Text(extraTravel)
                            .font(.caption2)
                            .foregroundStyle(.secondary)
                            .lineLimit(1)
                            .minimumScaleFactor(0.85)
                            .accessibilityLabel(spokenExtraTravel(for: result, fallback: extraTravel))
                    }
                }
                // Aligns the banner with the row's text column (46 pt logo + 12
                // pt spacing) so it reads as part of the row, not the cell.
                .padding(.leading, 58)
            } else {
                // Detail sheet: the SAME verdict capsule and the SAME caption as
                // the listing rows (one implementation, so wording and colour
                // cannot drift), followed by the breakdown only this view has
                // room for. The old shape led with a status word + headline that
                // matched neither the listing nor each other.
                VStack(alignment: .leading, spacing: 10) {
                    HStack(alignment: .firstTextBaseline, spacing: 6) {
                        capsule(for: result, compact: false)
                            .accessibilityLabel(accessibilityHeadline(for: result))
                        Text(comparisonLabel(for: result))
                            .font(.subheadline)
                            .foregroundStyle(.secondary)
                            .lineLimit(1)
                            .layoutPriority(1)
                            .accessibilityLabel("Comparison: \(comparisonLabel(for: result))")
                    }
                    LabeledContent("Your fill-up", value: amountText)
                    LabeledContent("Fuel you'll receive", value: String(format: "%.2f litres", result.fillLitres))
                        .monospacedDigit()
                    if let extraTravel = FuelSavingsFormat.extraTravelLabel(
                        extraDistanceMiles: result.extraDistanceMiles,
                        unit: distanceUnit,
                        confidence: result.journeyConfidence
                    ) {
                        Text(extraTravel)
                            .font(.subheadline)
                            .foregroundStyle(.secondary)
                            .accessibilityLabel(spokenExtraTravel(for: result, fallback: extraTravel))
                    }
                    if result.status == .baseline {
                        Text("Your closest eligible station by journey distance is the baseline — every other saving is measured against it.")
                            .font(.caption)
                            .foregroundStyle(.secondary)
                    } else {
                        Text("Compared with \(baselineStationName ?? "your closest station").")
                            .font(.caption)
                            .foregroundStyle(.secondary)
                        LabeledContent(
                            result.grossSavingGBP >= 0 ? "Fuel-price saving" : "Fuel-price difference",
                            value: result.grossSavingGBP >= 0
                                ? FuelSavingsFormat.money(result.grossSavingGBP)
                                : "Costs \(FuelSavingsFormat.money(abs(result.grossSavingGBP))) more"
                        )
                        LabeledContent("Extra driving cost", value: FuelSavingsFormat.money(result.extraDrivingCostGBP))
                        Divider()
                        LabeledContent {
                            Text(result.headline())
                                .fontWeight(.semibold)
                                .foregroundStyle(capsuleColor(for: result.status))
                                .monospacedDigit()
                        } label: {
                            Text("Total")
                                .fontWeight(.semibold)
                        }
                        if result.journeyConfidence.isEstimated {
                            Text("Estimated from straight-line or incomplete route data — refined once both routes are measured.")
                                .font(.caption2)
                                .foregroundStyle(.secondary)
                        }
                        Text("Estimate covers fuel cost only. It excludes time, parking, tolls and wear.")
                            .font(.caption2)
                            .foregroundStyle(.secondary)
                    }
                    if let showInfoAction {
                        Rectangle()
                            .fill(Color(.separator))
                            .frame(height: 0.5)
                            .padding(.vertical, 4)
                        Button(action: showInfoAction) {
                            HStack(spacing: 8) {
                                Text("How Best Value works")
                                Spacer(minLength: 8)
                                Image(systemName: "chevron.forward")
                                    .font(.footnote.weight(.semibold))
                                    .foregroundStyle(.tertiary)
                            }
                        }
                        .buttonStyle(.plain)
                    }
                }
            }
        case .unavailable(let reason):
            Text(compact ? "Savings unavailable" : "Best Value unavailable: \(reason)")
                .font(compact ? .caption2 : .caption)
                .foregroundStyle(.secondary)
        case nil:
            EmptyView()
        }
    }

    private var amountText: String {
        switch amount.unit {
        case .pounds: return String(format: "£%.0f", amount.value)
        case .litres: return String(format: "%.0f litres", amount.value)
        }
    }

    /// VoiceOver form of the extra-travel caption ("Approximately 6.4 miles extra
    /// return travel"): the abbreviation is spelled out and the unit is a word.
    /// Falls back to the visible string if no spoken form exists.
    private func spokenExtraTravel(for result: FuelSavingsResult, fallback: String) -> String {
        FuelSavingsFormat.extraTravelSpokenLabel(
            extraDistanceMiles: result.extraDistanceMiles,
            unit: distanceUnit,
            confidence: result.journeyConfidence
        ) ?? fallback
    }

    /// VoiceOver form of the verdict. `spokenHeadline()` spells "Approx." out for
    /// estimated comparisons and leaves the plain words ("Break even", "Closest
    /// station") alone — one source, so visible and spoken copy cannot drift.
    private func accessibilityHeadline(for result: FuelSavingsResult) -> String {
        result.spokenHeadline()
    }

    /// The colour-coded verdict capsule — ONE implementation for the listing rows
    /// and the detail sheet, so the verdict reads identically in both; the sheet
    /// just gets the larger font and padding.
    ///
    /// 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.
    private func capsule(for result: FuelSavingsResult, compact: Bool) -> some View {
        HStack(spacing: compact ? 3 : 5) {
            Image(systemName: symbol(for: result.status))
                .accessibilityHidden(true)
            Text(result.capsuleHeadline())
                .lineLimit(1)
        }
        .font(compact ? .caption.weight(.semibold) : .headline)
        .foregroundStyle(capsuleColor(for: result.status))
        .padding(.horizontal, compact ? 8 : 12)
        .padding(.vertical, compact ? 4 : 7)
        .background(Capsule().fill(capsuleColor(for: result.status).opacity(0.15)))
    }

    /// Verdict colour: green save, red worse off, grey break even, blue
    /// baseline — the same green/amber/red family the price dot already uses.
    private func capsuleColor(for status: FuelSavingsStatus) -> Color {
        switch status {
        case .worthTheDrive: return .green
        case .notWorthTheDrive: return .red
        case .breakEven: return .secondary
        case .baseline: return .blue
        }
    }

    private 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"
        }
    }
}