import SwiftUI

/// The More info sheet's facts row: the selected fuel's price on the left, the
/// distance on the right, separated by a hairline down the middle.
///
/// Every figure comes from the sheet's existing sources — the price through
/// `FuelStore.priceText` and the distance through
/// `FuelStore.stationDistanceDisplay(...)` — so this row can never disagree with
/// the listing row, the widget or the Live Activity, and both columns keep the
/// shared "Approx." confidence marking.
struct StationFactsRow: View {
    let station: FuelStation
    let selectedFuel: FuelType
    let priceAge: FuelPriceFreshness.Assessment
    let distance: StationDistanceDisplay?
    let distanceUnit: DistanceUnit

    var body: some View {
        HStack(alignment: .top, spacing: 12) {
            fuelColumn
            StationFactsDivider()
            distanceColumn
        }
        .padding(.vertical, 2)
    }

    private var fuelColumn: some View {
        VStack(alignment: .leading, spacing: 3) {
            Text(selectedFuel.displayName)
                .font(.caption)
                .foregroundStyle(.secondary)
            Text(priceText)
                .font(.title2.weight(.bold))
                .monospacedDigit()
            StationPriceAgeView(assessment: priceAge, compact: true)
        }
        .frame(maxWidth: .infinity, alignment: .leading)
        .accessibilityElement(children: .combine)
    }

    private var distanceColumn: some View {
        VStack(alignment: .leading, spacing: 3) {
            Text("Distance")
                .font(.caption)
                .foregroundStyle(.secondary)
            Text(distanceText)
                .font(.title2.weight(.bold))
                .monospacedDigit()
            Text(returnText)
                .font(.caption2)
                .foregroundStyle(.secondary)
                .monospacedDigit()
        }
        .frame(maxWidth: .infinity, alignment: .leading)
        .accessibilityElement(children: .combine)
    }

    /// The selected grade's price, exactly as the listing row prints it. A
    /// missing grade shows an em dash rather than hiding the column, so the row
    /// keeps its two-column shape.
    private var priceText: String {
        guard let price = station.prices[selectedFuel] else { return "—" }
        return FuelStore.priceText(price, style: .stationSign)
    }

    /// One-way distance, with its confidence marker, from the shared display.
    private var distanceText: String {
        distance?.label(unit: distanceUnit) ?? "—"
    }

    /// Out-and-back distance, same source and same marker rule.
    private var returnText: String {
        distance?.returnLabel(unit: distanceUnit) ?? ""
    }
}

/// A one-pixel vertical hairline between the facts row's two columns, drawn in
/// the List's own separator colour so it matches every other line on the sheet.
/// Decorative: VoiceOver reads each column as one phrase instead.
private struct StationFactsDivider: View {
    var body: some View {
        Rectangle()
            .fill(Color(.separator))
            .frame(width: 0.5)
            .frame(maxHeight: .infinity)
            .accessibilityHidden(true)
    }
}

/// The More info sheet's Best Value card: the verdict, then the figures it is
/// built from.
///
/// Nothing is recomputed here — every number comes from the shared
/// `FuelSavingsResult`, the verdict capsule is the same `FuelSavingsCapsule` the
/// listing rows use, and the total is the shared `headline()`. Wording and
/// colour therefore cannot drift between the sheet and the list.
struct BestValueDetailCard: View {
    let availability: FuelSavingsAvailability
    let amount: FuelSavingsFillAmount
    let baselineStationName: String?
    let distanceUnit: DistanceUnit

    var body: some View {
        switch availability {
        case .available(let result):
            availableBody(result)
        case .unavailable(let reason):
            Text("Best Value unavailable: \(reason)")
                .font(.caption)
                .foregroundStyle(.secondary)
        }
    }

    private func availableBody(_ result: FuelSavingsResult) -> some View {
        VStack(alignment: .leading, spacing: 14) {
            header(result)
            verdict(result)
            panels(result)
            workings(result)
        }
    }

    /// Card title on the left, the verdict badge on the right — the same capsule
    /// the listing rows carry, so the badge and the large capsule below it can
    /// never disagree.
    private func header(_ result: FuelSavingsResult) -> some View {
        HStack(alignment: .firstTextBaseline, spacing: 10) {
            Text("Best Value")
                .font(.headline)
            Spacer(minLength: 8)
            FuelSavingsCapsule(result: result)
        }
    }

    /// The verdict capsule keeps its own line above the working, as before.
    private func verdict(_ result: FuelSavingsResult) -> some View {
        VStack(alignment: .leading, spacing: 4) {
            FuelSavingsCapsule(result: result, compact: false)
                .accessibilityLabel(result.spokenHeadline())
            Text(FuelSavingsFormat.comparisonLabel(status: result.status))
                .font(.subheadline)
                .foregroundStyle(.secondary)
        }
    }

    /// The two figures the estimate is made OF, side by side: what the user
    /// spends, and how much fuel that buys at this station.
    private func panels(_ result: FuelSavingsResult) -> some View {
        HStack(spacing: 10) {
            panel(symbol: "fuelpump.fill",
                  title: "Your fill-up",
                  value: Self.amountText(amount))
            panel(symbol: "drop.fill",
                  title: "Fuel you'll receive",
                  value: String(format: "%.2f litres", result.fillLitres))
        }
    }

    private func panel(symbol: String, title: String, value: String) -> some View {
        VStack(alignment: .leading, spacing: 6) {
            HStack(spacing: 5) {
                Image(systemName: symbol)
                    .font(.caption)
                    .foregroundStyle(.secondary)
                    .accessibilityHidden(true)
                Text(title)
                    .font(.caption)
                    .foregroundStyle(.secondary)
                    .lineLimit(1)
                    .minimumScaleFactor(0.8)
            }
            Text(value)
                .font(.title3.weight(.semibold))
                .monospacedDigit()
                .lineLimit(1)
                .minimumScaleFactor(0.8)
        }
        .frame(maxWidth: .infinity, alignment: .leading)
        .padding(.horizontal, 12)
        .padding(.vertical, 10)
        .background(RoundedRectangle(cornerRadius: 10).fill(Color.primary.opacity(0.06)))
        .accessibilityElement(children: .combine)
    }

    /// The working: what the extra travel adds, what the pump saves, and the
    /// total. A baseline station has nothing to save against itself, so it stops
    /// after the panels — the capsule above already says "Closest station".
    @ViewBuilder
    private func workings(_ result: FuelSavingsResult) -> some View {
        if result.status != .baseline {
            Divider()
            extraTravelRow(result)
            savingRows(result)
            Divider()
            totalRow(result)
            if let baselineStationName {
                Text("Compared with \(baselineStationName).")
                    .font(.caption)
                    .foregroundStyle(.secondary)
            }
        }
        if result.journeyConfidence.isEstimated {
            Text("Estimated from straight-line or incomplete route data — refined once both routes are measured.")
                .font(.caption2)
                .foregroundStyle(.secondary)
        }
    }

    /// The extra driving a saving has to beat, named in the row label and
    /// measured in the value — same figure and same "Approx." rule as the shared
    /// caption, from the shared formatter.
    @ViewBuilder
    private func extraTravelRow(_ result: FuelSavingsResult) -> some View {
        if let extraTravel = FuelSavingsFormat.extraTravelDistanceLabel(
            extraDistanceMiles: result.extraDistanceMiles,
            unit: distanceUnit,
            confidence: result.journeyConfidence
        ) {
            LabeledContent("Extra return travel", value: extraTravel)
                .monospacedDigit()
        }
    }

    @ViewBuilder
    private func savingRows(_ result: FuelSavingsResult) -> some View {
        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"
        )
        .monospacedDigit()
        LabeledContent("Extra driving cost", value: FuelSavingsFormat.money(result.extraDrivingCostGBP))
            .monospacedDigit()
    }

    /// The Total row is the WORKINGS; the capsule above is the quick verdict.
    /// Both take their wording and colour from the shared result.
    private func totalRow(_ result: FuelSavingsResult) -> some View {
        LabeledContent {
            Text(result.headline())
                .fontWeight(.semibold)
                .foregroundStyle(FuelSavingsCapsule.color(for: result.status))
                .monospacedDigit()
        } label: {
            Text("Total")
                .fontWeight(.semibold)
        }
    }

    /// "£60" or "60 litres" — the same strings the sheet printed before the
    /// redesign, so the fill-up reads identically in both units.
    static func amountText(_ amount: FuelSavingsFillAmount) -> String {
        switch amount.unit {
        case .pounds: return String(format: "£%.0f", amount.value)
        case .litres: return String(format: "%.0f litres", amount.value)
        }
    }
}

/// "How Best Value works" lives in the shared `HowBestValueRow`
/// (HowBestValueSheet.swift) — the same row the Key sheet uses, so the sheet and
/// the Key cannot drift.