import SwiftUI

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

    @State private var textValue: String = ""

    private var range: ClosedRange<Double> {
        amount.unit == .pounds ? 10...100 : 10...80
    }

    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: amount.unit == .pounds ? 5 : 1)
                TextField(amount.unit == .pounds ? "£" : "Litres", text: valueBinding)
                    .keyboardType(.decimalPad)
                    .multilineTextAlignment(.trailing)
                    .frame(width: 72)
                    .textFieldStyle(.roundedBorder)
            }
            Text("Changes the estimate for this session only — your Settings default stays unchanged.")
                .font(.caption2)
                .foregroundStyle(.secondary)
        }
        .onAppear { syncText() }
        .onChange(of: amount.value) { _, _ in syncText() }
        .onChange(of: amount.unit) { _, _ in syncText() }
    }

    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)
                }
                syncText()
            }
        )
    }

    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) }
        )
    }

    private var valueBinding: Binding<String> {
        Binding(
            get: { textValue },
            set: { raw in
                textValue = raw
                if let value = Double(raw), value > 0 {
                    amount.value = min(value, FuelSavingsCalculator.maximumFillAmount(for: amount.unit))
                }
            }
        )
    }

    private func syncText() {
        let value = amount.value
        textValue = value.rounded() == value ? String(format: "%.0f", value) : String(format: "%.1f", value)
    }
}

struct FuelSavingsSummaryView: View {
    let availability: FuelSavingsAvailability?
    let amount: FuelSavingsFillAmount
    let baselineStationName: String?
    var compact: Bool = false

    var body: some View {
        switch availability {
        case .available(let result):
            VStack(alignment: .leading, spacing: compact ? 2 : 8) {
                Label(result.status.displayName, systemImage: symbol(for: result.status))
                    .font(compact ? .caption.weight(.semibold) : .headline)
                Text(result.headline(compact: compact))
                    .font(compact ? .caption2.bold().monospacedDigit() : .subheadline.bold().monospacedDigit())
                if !compact {
                    if result.status == .baseline {
                        Text("Your closest station with a price for this fuel — every other saving is measured against it.")
                            .font(.caption)
                            .foregroundStyle(.secondary)
                    } else {
                        Text("Compared with \(baselineStationName ?? "your nearest station") for \(amountText).").font(.caption).foregroundStyle(.secondary)
                        LabeledContent("Fuel-price saving", value: FuelSavingsFormat.money(result.grossSavingGBP))
                        LabeledContent("Extra driving cost", value: FuelSavingsFormat.money(result.extraDrivingCostGBP))
                        LabeledContent("Extra distance", value: String(format: "%.1f miles", result.extraDistanceMiles))
                        if result.distanceBasis.isEstimate {
                            Text("Estimated from straight-line distance — refined once the route is measured.")
                                .font(.caption2)
                                .foregroundStyle(.secondary)
                        }
                        Text("Estimate covers fuel cost only. It excludes time, parking, tolls and wear.")
                            .font(.caption2)
                            .foregroundStyle(.secondary)
                    }
                }
            }
        case .unavailable(let reason):
            Text(compact ? "Savings unavailable" : "Worth the Drive 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)
        }
    }

    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"
        }
    }
}