/*
 * Copyright 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.internal.telephony;

import static com.android.internal.annotations.VisibleForTesting.Visibility.PACKAGE;

import com.android.internal.annotations.VisibleForTesting;
import com.android.telephony.Rlog;

import java.time.DateTimeException;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import java.util.Objects;
import java.util.TimeZone;
import java.util.regex.Pattern;

/**
 * Represents NITZ data. Various static methods are provided to help with parsing and interpretation
 * of NITZ data.
 *
 * {@hide}
 */
@VisibleForTesting(visibility = PACKAGE)
public final class NitzData {
    private static final String LOG_TAG = ServiceStateTracker.LOG_TAG;
    private static final int MS_PER_QUARTER_HOUR = 15 * 60 * 1000;
    private static final int MS_PER_HOUR = 60 * 60 * 1000;

    private static final Pattern NITZ_SPLIT_PATTERN = Pattern.compile("[/:,+-]");

    // Stored For logging / debugging only.
    private final String mOriginalString;

    private final int mZoneOffset;

    private final Integer mDstOffset;

    private final long mCurrentTimeMillis;

    private final TimeZone mEmulatorHostTimeZone;

    private NitzData(String originalString, int zoneOffsetMillis, Integer dstOffsetMillis,
            long unixEpochTimeMillis, TimeZone emulatorHostTimeZone) {
        if (originalString == null) {
            throw new NullPointerException("originalString==null");
        }
        this.mOriginalString = originalString;
        this.mZoneOffset = zoneOffsetMillis;
        this.mDstOffset = dstOffsetMillis;
        this.mCurrentTimeMillis = unixEpochTimeMillis;
        this.mEmulatorHostTimeZone = emulatorHostTimeZone;
    }

    /**
     * Parses the supplied NITZ string, returning the encoded data.
     */
    public static NitzData parse(String nitz) {
        // "yy/mm/dd,hh:mm:ss(+/-)tz[,dt[,tzid]]"
        // tz, dt are in number of quarter-hours

        try {
            String[] nitzSubs = NITZ_SPLIT_PATTERN.split(nitz);

            int year = Integer.parseInt(nitzSubs[0]);
            if (year < 1 || year > 99) {
                // 0 > year > 99 imply an invalid string.
                //
                // At the time of this comment (year 2023), a zero year is considered invalid and
                // assumed to be the result of invalid data being converted to zero in the code that
                // turns the binary NITZ into a string. For the next few decades at least, Android
                // devices should not need to interpret zero. Hopefully, NITZ will be replaced by
                // the time that's not true, or folks dealing the Y2K1 issue can handle it.
                //
                // DateTimeException is also thrown by LocalDateTime below if the values are out of
                // range and will be handled in the catch block.
                throw new DateTimeException("Invalid NITZ year == 0");
            }

            // Values < {current year} could be considered invalid but are used in test code, so no
            // window is applied to adjust low values < {current year} with "+ 2100" (and would also
            // need to consider zero as valid). Code that processes the NitzData is in a better
            // position to log and discard obviously invalid NITZ signals from past years.
            year += 2000;

            int month = Integer.parseInt(nitzSubs[1]);
            int date = Integer.parseInt(nitzSubs[2]);
            int hour = Integer.parseInt(nitzSubs[3]);
            int minute = Integer.parseInt(nitzSubs[4]);
            int second = Integer.parseInt(nitzSubs[5]);

            // NITZ time (hour:min:sec) will be in UTC but it supplies the timezone
            // offset as well (which we won't worry about until later).
            // The LocalDateTime.of() will throw DateTimeException for values outside the allowed
            // range for the Gregorian calendar.
            long epochMillis = LocalDateTime.of(year, month, date, hour, minute, second)
                    .toInstant(ZoneOffset.UTC)
                    .toEpochMilli();

            // The offset received from NITZ is the offset to add to get current local time.
            boolean sign = (nitz.indexOf('-') == -1);
            int totalUtcOffsetQuarterHours = Integer.parseInt(nitzSubs[6]);
            int totalUtcOffsetMillis =
                    (sign ? 1 : -1) * totalUtcOffsetQuarterHours * MS_PER_QUARTER_HOUR;

            // DST correction is already applied to the UTC offset. We could subtract it if we
            // wanted the raw offset.
            Integer dstAdjustmentHours =
                    (nitzSubs.length >= 8) ? Integer.parseInt(nitzSubs[7]) : null;
            Integer dstAdjustmentMillis = null;
            if (dstAdjustmentHours != null) {
                dstAdjustmentMillis = dstAdjustmentHours * MS_PER_HOUR;
            }

            // As a special extension, the Android emulator appends the name of
            // the host computer's timezone to the nitz string. This is zoneinfo
            // timezone name of the form Area!Location or Area!Location!SubLocation
            // so we need to convert the ! into /
            TimeZone zone = null;
            if (nitzSubs.length >= 9) {
                String tzname = nitzSubs[8].replace('!', '/');
                zone = TimeZone.getTimeZone(tzname);
            }
            return new NitzData(nitz, totalUtcOffsetMillis, dstAdjustmentMillis, epochMillis, zone);
        } catch (RuntimeException ex) {
            Rlog.e(LOG_TAG, "NITZ: Parsing NITZ time " + nitz + " ex=" + ex);
            return null;
        }
    }

    /** A method for use in tests to create NitzData instances. */
    public static NitzData createForTests(int zoneOffsetMillis, Integer dstOffsetMillis,
            long unixEpochTimeMillis, TimeZone emulatorHostTimeZone) {
        return new NitzData("Test data", zoneOffsetMillis, dstOffsetMillis, unixEpochTimeMillis,
                emulatorHostTimeZone);
    }

    /**
     * Returns the current time as the number of milliseconds since the beginning of the Unix epoch
     * (1/1/1970 00:00:00 UTC).
     */
    public long getCurrentTimeInMillis() {
        return mCurrentTimeMillis;
    }

    /**
     * Returns the total offset to apply to the {@link #getCurrentTimeInMillis()} to arrive at a
     * local time. NITZ is limited in only being able to express total offsets in multiples of 15
     * minutes.
     *
     * <p>Note that some time zones change offset during the year for reasons other than "daylight
     * savings", e.g. for Ramadan. This is not well handled by most date / time APIs.
     */
    public int getLocalOffsetMillis() {
        return mZoneOffset;
    }

    /**
     * Returns the offset (already included in {@link #getLocalOffsetMillis()}) associated with
     * Daylight Savings Time (DST). This field is optional: {@code null} means the DST offset is
     * unknown. NITZ is limited in only being able to express DST offsets in positive multiples of
     * one or two hours.
     *
     * <p>Callers should remember that standard time / DST is a matter of convention: it has
     * historically been assumed by NITZ and many date/time APIs that DST happens in the summer and
     * the "raw" offset will increase during this time, usually by one hour. However, the tzdb
     * maintainers have moved to different conventions on a country-by-country basis so that some
     * summer times are considered the "standard" time (i.e. in this model winter time is the "DST"
     * and a negative adjustment, usually of (negative) one hour.
     *
     * <p>There is nothing that says NITZ and tzdb need to treat DST conventions the same.
     *
     * <p>At the time of writing Android date/time APIs are sticking with the historic tzdb
     * convention that DST is used in summer time and is <em>always</em> a positive offset but this
     * could change in future. If Android or carriers change the conventions used then it might make
     * NITZ comparisons with tzdb information more error-prone.
     *
     * <p>See also {@link #getLocalOffsetMillis()} for other reasons besides DST that a local offset
     * may change.
     */
    public Integer getDstAdjustmentMillis() {
        return mDstOffset;
    }

    /**
     * Returns {@link true} if the time is in Daylight Savings Time (DST), {@link false} if it is
     * unknown or not in DST. See {@link #getDstAdjustmentMillis()}.
     */
    public boolean isDst() {
        return mDstOffset != null && mDstOffset != 0;
    }


    /**
     * Returns the time zone of the host computer when Android is running in an emulator. It is
     * {@code null} for real devices. This information is communicated via a non-standard Android
     * extension to NITZ.
     */
    public TimeZone getEmulatorHostTimeZone() {
        return mEmulatorHostTimeZone;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        NitzData nitzData = (NitzData) o;

        if (mZoneOffset != nitzData.mZoneOffset) {
            return false;
        }
        if (mCurrentTimeMillis != nitzData.mCurrentTimeMillis) {
            return false;
        }
        if (!mOriginalString.equals(nitzData.mOriginalString)) {
            return false;
        }
        if (!Objects.equals(mDstOffset, nitzData.mDstOffset)) {
            return false;
        }
        return Objects.equals(mEmulatorHostTimeZone, nitzData.mEmulatorHostTimeZone);
    }

    @Override
    public int hashCode() {
        int result = mOriginalString.hashCode();
        result = 31 * result + mZoneOffset;
        result = 31 * result + (mDstOffset != null ? mDstOffset.hashCode() : 0);
        result = 31 * result + Long.hashCode(mCurrentTimeMillis);
        result = 31 * result + (mEmulatorHostTimeZone != null ? mEmulatorHostTimeZone.hashCode()
                : 0);
        return result;
    }

    @Override
    public String toString() {
        return "NitzData{"
                + "mOriginalString=" + mOriginalString
                + ", mZoneOffset=" + mZoneOffset
                + ", mDstOffset=" + mDstOffset
                + ", mCurrentTimeMillis=" + mCurrentTimeMillis
                + ", mEmulatorHostTimeZone=" + mEmulatorHostTimeZone
                + '}';
    }
}