import XCTest
#if SWIFT_PACKAGE
@testable import FuelBoardShared
#endif

final class FuelSavingsCalculatorTests: XCTestCase {
    func testUKMPGConversionUsesImperialGallons() {
        XCTAssertEqual(FuelSavingsCalculator.fuelUsedLitres(distanceMiles: 10, mpg: 45), 1.0102, accuracy: 0.0001)
    }

    func testPoundsBudgetConvertsToLitresUsingBaselinePrice() throws {
        let amount = FuelSavingsFillAmount(value: 40, unit: .pounds)
        let litres = try FuelSavingsCalculator.fillLitres(amount: amount, baselinePricePencePerLitre: 160)
        XCTAssertEqual(litres, 25.0, accuracy: 0.0001)
    }

    func testLitresAmountPassesThrough() throws {
        let amount = FuelSavingsFillAmount(value: 35, unit: .litres)
        let litres = try FuelSavingsCalculator.fillLitres(amount: amount, baselinePricePencePerLitre: 160)
        XCTAssertEqual(litres, 35, accuracy: 0.0001)
    }

    func testNetSavingSubtractsAdditionalDrivingFuelCost() throws {
        let result = try FuelSavingsCalculator.calculate(
            mpg: 45,
            amount: FuelSavingsFillAmount(value: 40, unit: .pounds),
            baselinePricePencePerLitre: 160,
            candidatePricePencePerLitre: 150,
            baselineJourneyMiles: 2,
            candidateJourneyMiles: 8
        )
        XCTAssertEqual(result.fillLitres, 25, accuracy: 0.0001)
        XCTAssertEqual(result.grossSavingGBP, 2.50, accuracy: 0.0001)
        XCTAssertEqual(result.extraDistanceMiles, 6, accuracy: 0.0001)
        XCTAssertEqual(result.extraDrivingCostGBP, 0.9092, accuracy: 0.0001)
        XCTAssertEqual(result.netSavingGBP, 1.5908, accuracy: 0.0001)
        XCTAssertEqual(result.status, .worthTheDrive)
    }

    func testNegativeAndBreakEvenOutcomes() throws {
        let negative = try FuelSavingsCalculator.calculate(
            mpg: 45,
            amount: FuelSavingsFillAmount(value: 10, unit: .litres),
            baselinePricePencePerLitre: 150,
            candidatePricePencePerLitre: 149,
            baselineJourneyMiles: 1,
            candidateJourneyMiles: 20
        )
        XCTAssertEqual(negative.status, .notWorthTheDrive)
        XCTAssertLessThan(negative.netSavingGBP, 0)

        let even = try FuelSavingsCalculator.calculate(
            mpg: 45,
            amount: FuelSavingsFillAmount(value: 10, unit: .litres),
            baselinePricePencePerLitre: 150,
            candidatePricePencePerLitre: 150,
            baselineJourneyMiles: 2,
            candidateJourneyMiles: 2
        )
        XCTAssertEqual(even.status, .breakEven)
    }

    func testInvalidInputsRejected() {
        XCTAssertThrowsError(try FuelSavingsCalculator.fillLitres(amount: FuelSavingsFillAmount(value: 40, unit: .pounds), baselinePricePencePerLitre: 0))
        XCTAssertThrowsError(try FuelSavingsCalculator.calculate(mpg: 0, amount: FuelSavingsFillAmount(value: 40, unit: .pounds), baselinePricePencePerLitre: 160, candidatePricePencePerLitre: 150, baselineJourneyMiles: 1, candidateJourneyMiles: 2))
        XCTAssertThrowsError(try FuelSavingsCalculator.calculate(mpg: 500, amount: FuelSavingsFillAmount(value: 40, unit: .pounds), baselinePricePencePerLitre: 160, candidatePricePencePerLitre: 150, baselineJourneyMiles: 1, candidateJourneyMiles: 2))
    }

    func testSwitchingPoundsToLitresPreservesPhysicalQuantity() throws {
        let pounds = FuelSavingsFillAmount(value: 40, unit: .pounds)
        let litres = try FuelSavingsCalculator.convert(amount: pounds, to: .litres, referencePricePencePerLitre: 160)
        XCTAssertEqual(litres.unit, .litres)
        XCTAssertEqual(litres.value, 25, accuracy: 0.0001)
        let back = try FuelSavingsCalculator.convert(amount: litres, to: .pounds, referencePricePencePerLitre: 160)
        XCTAssertEqual(back.value, 40, accuracy: 0.0001)
    }

    func testSortingPlacesUnavailableAfterSavingsAndBreaksTies() {
        let a = FuelSavingsRankedStation(stationID: "a", result: .available(.init(fillLitres: 25, grossSavingGBP: 2, extraDrivingCostGBP: 1, extraDistanceMiles: 3, netSavingGBP: 1, status: .worthTheDrive)), distanceMiles: 5, pricePencePerLitre: 150)
        let b = FuelSavingsRankedStation(stationID: "b", result: .available(.init(fillLitres: 25, grossSavingGBP: 3, extraDrivingCostGBP: 1, extraDistanceMiles: 2, netSavingGBP: 2, status: .worthTheDrive)), distanceMiles: 8, pricePencePerLitre: 149)
        let c = FuelSavingsRankedStation(stationID: "c", result: .unavailable("No route"), distanceMiles: 1, pricePencePerLitre: 140)
        XCTAssertEqual(FuelSavingsCalculator.sortedForWorthTheDrive([a, c, b]).map(\.stationID), ["b", "a", "c"])
    }
}

final class FuelSavingsSettingsTests: XCTestCase {
    func testSettingsValidationRequiresEnabledMPGAndFillAmount() {
        XCTAssertFalse(FuelSavingsSettings(enabled: false, mpg: 45, preferredAmount: .init(value: 40, unit: .pounds)).isConfigured)
        XCTAssertFalse(FuelSavingsSettings(enabled: true, mpg: 0, preferredAmount: .init(value: 40, unit: .pounds)).isConfigured)
        XCTAssertFalse(FuelSavingsSettings(enabled: true, mpg: 45, preferredAmount: .init(value: 0, unit: .pounds)).isConfigured)
        XCTAssertTrue(FuelSavingsSettings(enabled: true, mpg: 45, preferredAmount: .init(value: 40, unit: .pounds)).isConfigured)
    }
}