fuelboard/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsTests.swift

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"])
    }

    func testBestValueAlertCandidateRequiresConfiguredSavingsAndThreshold() {
        let stations = [
            station("near", lat: 0, lng: 0, price: 160),
            station("cheap", lat: 0, lng: 0, price: 150),
        ]
        let journeys = ["near": 2.0, "cheap": 4.0]
        let off = FuelSavingsSettings(enabled: false, mpg: 45, preferredAmount: .init(value: 40, unit: .pounds))
        XCTAssertNil(FuelSavingsCalculator.bestValueAlertCandidate(
            stations: stations,
            fuel: .e10,
            settings: off,
            amount: off.preferredAmount,
            minimumNetSavingGBP: 1.0,
            journeyMiles: { journeys[$0.id].map { FuelSavingsJourney(miles: $0, basis: .roadRoute) } }
        ))

        let on = FuelSavingsSettings(enabled: true, mpg: 45, preferredAmount: .init(value: 40, unit: .pounds))
        XCTAssertNil(FuelSavingsCalculator.bestValueAlertCandidate(
            stations: stations,
            fuel: .e10,
            settings: on,
            amount: on.preferredAmount,
            minimumNetSavingGBP: 5.0,
            journeyMiles: { journeys[$0.id].map { FuelSavingsJourney(miles: $0, basis: .roadRoute) } }
        ))
    }

    func testBestValueAlertCandidatePicksHighestNetSavingAboveThreshold() throws {
        let stations = [
            station("baseline", lat: 0, lng: 0, price: 160),
            station("small", lat: 0, lng: 0, price: 154),
            station("best", lat: 0, lng: 0, price: 148),
        ]
        let journeys = ["baseline": 2.0, "small": 4.0, "best": 6.0]
        let settings = FuelSavingsSettings(enabled: true, mpg: 45, preferredAmount: .init(value: 40, unit: .pounds))
        let candidate = FuelSavingsCalculator.bestValueAlertCandidate(
            stations: stations,
            fuel: .e10,
            settings: settings,
            amount: settings.preferredAmount,
            minimumNetSavingGBP: 1.0,
            journeyMiles: { journeys[$0.id].map { FuelSavingsJourney(miles: $0, basis: .roadRoute) } }
        )
        XCTAssertEqual(candidate?.station.id, "best")
        XCTAssertEqual(candidate?.result.status, .worthTheDrive)
        XCTAssertGreaterThan(candidate?.result.netSavingGBP ?? 0, 1.0)
    }

    func testBestValueAlertCandidateBreaksTiesByDistanceThenPrice() throws {
        let first = FuelSavingsResult(fillLitres: 25, grossSavingGBP: 3, extraDrivingCostGBP: 1, extraDistanceMiles: 2, netSavingGBP: 2, status: .worthTheDrive)
        let nearer = FuelSavingsRankedStation(stationID: "nearer", result: .available(first), distanceMiles: 4, pricePencePerLitre: 149)
        let farther = FuelSavingsRankedStation(stationID: "farther", result: .available(first), distanceMiles: 8, pricePencePerLitre: 145)
        XCTAssertEqual(FuelSavingsCalculator.sortedForWorthTheDrive([farther, nearer]).first?.stationID, "nearer")
    }

    private func station(_ id: String, lat: Double, lng: Double, price: Double) -> FuelStation {
        FuelStation(id: id, name: id, brand: id, address: "", postcode: "", lat: lat, lng: lng, prices: [.e10: price], priceUpdated: nil)
    }
}

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)
    }
}