package com.evsuite.abrp;

import java.time.LocalDate;
import java.time.temporal.ChronoUnit;

/**
 * The lease's mileage allowance: 40,000 km over four years from 1 May 2023, accruing evenly per
 * day. The Overview's Vehicle info card shows what is allowed by today and how far the odometer
 * is above or below it. Pure Java, so it is unit-tested.
 */
final class LeaseAllowance {

    static final LocalDate START = LocalDate.of(2023, 5, 1);
    static final LocalDate END = START.plusYears(4);
    static final double TOTAL_KM = 40_000d;

    private LeaseAllowance() {}

    /** Kilometres allowed by {@code today}: none before the start, all of them from the end on. */
    static double allowedKm(LocalDate today) {
        long total = ChronoUnit.DAYS.between(START, END);
        long elapsed = Math.max(0L, Math.min(total, ChronoUnit.DAYS.between(START, today)));
        return TOTAL_KM * elapsed / total;
    }

    /** Odometer minus allowance: positive over, negative under; null when the odometer is unread. */
    static Double differenceKm(Float odometerKm, LocalDate today) {
        if (odometerKm == null || !Float.isFinite(odometerKm)) return null;
        return odometerKm - allowedKm(today);
    }
}