package com.evsuite.abrp;

import java.util.ArrayDeque;
import java.util.Iterator;

/**
 * Estimated range from the energy left in the pack and how fast it is being used.
 *
 *   since start: remaining kWh / (energy used / distance driven since the car was switched on)
 *   average:     remaining kWh / (energy used / distance driven over the last 5 minutes)
 *
 * "Since start" is a trip like the car's own trip computer: it begins with the first sample
 * after the head unit wakes (or after charging), so it includes standing with the climate on.
 * A gap of {@link #TRIP_RESET_GAP_MS} without samples is the car having been off, and starts
 * a new trip; so does charging.
 *
 * Remaining energy is SOC x usable capacity: the car publishes no pack energy, so the capacity
 * is a setting. An estimate is null when it cannot mean anything — not moved yet, too little
 * data — rather than a misleading number. Net regeneration is shown as it is: negative usage.
 *
 * Fed by both the service tick (15 s) and the open Vehicle page (2 s); the integration is
 * time-weighted, so the two rates mix correctly. Times are on the monotonic clock
 * (SystemClock.elapsedRealtime): the head unit sets its wall clock from GPS, and a jump back
 * would make every new sample look out of order. Free of Android types, unit-tested.
 */
final class RangeEstimator {

    static final long WINDOW_MS = 5 * 60_000L;
    /** Less than this much driving in the window is too little to average. */
    static final long MIN_WINDOW_MS = 60_000L;
    static final double MIN_DISTANCE_KM = 0.2;
    /** A gap between samples longer than this (app paused, car off) is not integrated. */
    static final long MAX_GAP_MS = 60_000L;

    /** No sample for this long: the car was off, and the next sample starts a new trip. */
    static final long TRIP_RESET_GAP_MS = 10 * 60_000L;
    /** Standing still and taking in more than this: charging, which ends the trip. */
    static final double CHARGING_KW = -1.0;

    static final double DEFAULT_USABLE_KWH = 50.8; // MG4 51 kWh battery

    private static final RangeEstimator SHARED = new RangeEstimator();

    static RangeEstimator shared() { return SHARED; }

    /** An estimate: the range, the consumption it is based on, and the distance behind it. */
    static final class Estimate {
        final double rangeKm;
        final double kwhPer100Km;
        final double distanceKm;

        Estimate(double rangeKm, double kwhPer100Km, double distanceKm) {
            this.rangeKm = rangeKm;
            this.kwhPer100Km = kwhPer100Km;
            this.distanceKm = distanceKm;
        }
    }

    private static final class Sample {
        final long timeMs;
        final double powerKw;
        final double speedKmh;

        Sample(long timeMs, double powerKw, double speedKmh) {
            this.timeMs = timeMs;
            this.powerKw = powerKw;
            this.speedKmh = speedKmh;
        }
    }

    private final ArrayDeque<Sample> samples = new ArrayDeque<>();

    // The trip since start: running totals, so it is not limited to the 5-minute window.
    private double tripEnergyKwh;
    private double tripDistanceKm;
    private Sample tripLast;

    /** Power in kW, positive leaving the battery; speed in km/h. Unread values are skipped. */
    synchronized void add(long timeMs, Float powerKw, Float speedKmh) {
        if (powerKw == null || speedKmh == null || !Float.isFinite(powerKw) || !Float.isFinite(speedKmh)) return;
        Sample last = samples.peekLast();
        if (last != null && timeMs <= last.timeMs) return; // out of order or duplicate tick
        Sample sample = new Sample(timeMs, powerKw, Math.max(0f, speedKmh));
        addToTrip(sample);
        samples.addLast(sample);
        while (!samples.isEmpty() && samples.peekFirst().timeMs < timeMs - WINDOW_MS) samples.removeFirst();
    }

    static Double remainingKwh(Float socPercent, double usableKwh) {
        if (socPercent == null || !Float.isFinite(socPercent) || usableKwh <= 0) return null;
        return Math.max(0, Math.min(100, socPercent)) / 100.0 * usableKwh;
    }

    private void addToTrip(Sample s) {
        boolean charging = s.speedKmh < 1 && s.powerKw < CHARGING_KW;
        if (charging || (tripLast != null && s.timeMs - tripLast.timeMs > TRIP_RESET_GAP_MS)) {
            tripEnergyKwh = 0;
            tripDistanceKm = 0;
            tripLast = null;
        }
        if (charging) return; // the trip starts again after the charge
        if (tripLast != null) {
            long dt = s.timeMs - tripLast.timeMs;
            if (dt > 0 && dt <= MAX_GAP_MS) {
                double hours = dt / 3_600_000.0;
                tripEnergyKwh += (tripLast.powerKw + s.powerKw) / 2 * hours;
                tripDistanceKm += (tripLast.speedKmh + s.speedKmh) / 2 * hours;
            }
        }
        tripLast = s;
    }

    /** Net energy taken from the pack since start, in kWh; null before the trip's first sample. */
    synchronized Double energySinceStart() {
        return tripLast == null ? null : tripEnergyKwh;
    }

    /** Range at the consumption since start; null until the trip has some distance behind it. */
    synchronized Estimate sinceStart(Double remainingKwh) {
        if (remainingKwh == null || tripDistanceKm < MIN_DISTANCE_KM) return null;
        return estimate(remainingKwh, tripEnergyKwh, tripDistanceKm);
    }

    synchronized Estimate average(Double remainingKwh, long nowMs) {
        if (remainingKwh == null) return null;
        double energyKwh = 0, distanceKm = 0;
        long covered = 0;
        Sample previous = null;
        for (Iterator<Sample> it = samples.iterator(); it.hasNext(); ) {
            Sample s = it.next();
            if (s.timeMs < nowMs - WINDOW_MS) continue;
            if (previous != null) {
                long dt = s.timeMs - previous.timeMs;
                if (dt > 0 && dt <= MAX_GAP_MS) {
                    double hours = dt / 3_600_000.0;
                    energyKwh += (previous.powerKw + s.powerKw) / 2 * hours;
                    distanceKm += (previous.speedKmh + s.speedKmh) / 2 * hours;
                    covered += dt;
                }
            }
            previous = s;
        }
        if (covered < MIN_WINDOW_MS || distanceKm < MIN_DISTANCE_KM) return null;
        return estimate(remainingKwh, energyKwh, distanceKm);
    }

    /**
     * Net regeneration (downhill, recuperating) is a real reading: the usage is negative, and
     * the range is unbounded rather than negative.
     */
    private static Estimate estimate(double remainingKwh, double energyKwh, double distanceKm) {
        double kwhPerKm = energyKwh / distanceKm;
        double rangeKm = kwhPerKm > 0 ? remainingKwh / kwhPerKm : Double.POSITIVE_INFINITY;
        return new Estimate(rangeKm, kwhPerKm * 100, distanceKm);
    }

    /**
     * Mean battery power over the last five minutes, time-weighted, standing included; null with
     * less than a minute of samples. Positive is drawn from the pack, as the Power tile shows it.
     */
    synchronized Double averagePowerKw(long nowMs) {
        double energyKwh = 0;
        long covered = 0;
        Sample previous = null;
        for (Sample s : samples) {
            if (s.timeMs < nowMs - WINDOW_MS) continue;
            if (previous != null) {
                long dt = s.timeMs - previous.timeMs;
                if (dt > 0 && dt <= MAX_GAP_MS) {
                    energyKwh += (previous.powerKw + s.powerKw) / 2 * (dt / 3_600_000.0);
                    covered += dt;
                }
            }
            previous = s;
        }
        if (covered < MIN_WINDOW_MS) return null;
        return energyKwh / (covered / 3_600_000.0);
    }

    /** Mean speed over the last five minutes, time-weighted, standing included; null below a minute. */
    synchronized Double averageSpeedKmh(long nowMs) {
        double distanceKm = 0;
        long covered = 0;
        Sample previous = null;
        for (Sample s : samples) {
            if (s.timeMs < nowMs - WINDOW_MS) continue;
            if (previous != null) {
                long dt = s.timeMs - previous.timeMs;
                if (dt > 0 && dt <= MAX_GAP_MS) {
                    distanceKm += (previous.speedKmh + s.speedKmh) / 2 * (dt / 3_600_000.0);
                    covered += dt;
                }
            }
            previous = s;
        }
        if (covered < MIN_WINDOW_MS) return null;
        return distanceKm / (covered / 3_600_000.0);
    }

    synchronized void clear() {
        samples.clear();
        tripEnergyKwh = 0;
        tripDistanceKm = 0;
        tripLast = null;
    }
}