/*
 *  Copyright 2001-2006 Stephen Colebourne
 *
 *  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 org.joda.time;

import java.io.Serializable;

import org.joda.time.base.BaseInterval;
import org.joda.time.chrono.ISOChronology;
import org.joda.time.format.ISODateTimeFormat;
import org.joda.time.format.ISOPeriodFormat;

/**
 * Interval is the standard implementation of an immutable time interval.
 * <p>
 * A time interval represents a period of time between two instants.
 * Intervals are inclusive of the start instant and exclusive of the end.
 * The end instant is always greater than or equal to the start instant.
 * <p>
 * Intervals have a fixed millisecond duration.
 * This is the difference between the start and end instants.
 * The duration is represented separately by {@link ReadableDuration}.
 * As a result, intervals are not comparable.
 * To compare the length of two intervals, you should compare their durations.
 * <p>
 * An interval can also be converted to a {@link ReadablePeriod}.
 * This represents the difference between the start and end points in terms of fields
 * such as years and days.
 * <p>
 * Interval is thread-safe and immutable.
 *
 * @author Brian S O'Neill
 * @author Sean Geoghegan
 * @author Stephen Colebourne
 * @author Julen Parra
 * @since 1.0
 */
public final class Interval
        extends BaseInterval
        implements ReadableInterval, Serializable {

    /** Serialization version */
    private static final long serialVersionUID = 4922451897541386752L;

    //-----------------------------------------------------------------------
    /**
     * Constructs an interval from a start and end instant with the ISO
     * default chronology in the default time zone.
     * 
     * @param startInstant  start of this interval, as milliseconds from 1970-01-01T00:00:00Z.
     * @param endInstant  end of this interval, as milliseconds from 1970-01-01T00:00:00Z.
     * @throws IllegalArgumentException if the end is before the start
     */
    public Interval(long startInstant, long endInstant) {
        super(startInstant, endInstant, null);
    }

    /**
     * Constructs an interval from a start and end instant with the ISO
     * default chronology in the specified time zone.
     * 
     * @param startInstant  start of this interval, as milliseconds from 1970-01-01T00:00:00Z.
     * @param endInstant  end of this interval, as milliseconds from 1970-01-01T00:00:00Z.
     * @param zone  the time zone to use, null means default zone
     * @throws IllegalArgumentException if the end is before the start
     * @since 1.5
     */
    public Interval(long startInstant, long endInstant, DateTimeZone zone) {
        super(startInstant, endInstant, ISOChronology.getInstance(zone));
    }

    /**
     * Constructs an interval from a start and end instant with the
     * specified chronology.
     * 
     * @param chronology  the chronology to use, null is ISO default
     * @param startInstant  start of this interval, as milliseconds from 1970-01-01T00:00:00Z.
     * @param endInstant  end of this interval, as milliseconds from 1970-01-01T00:00:00Z.
     * @throws IllegalArgumentException if the end is before the start
     */
    public Interval(long startInstant, long endInstant, Chronology chronology) {
        super(startInstant, endInstant, chronology);
    }

    /**
     * Constructs an interval from a start and end instant.
     * <p>
     * The chronology used is that of the start instant.
     * 
     * @param start  start of this interval, null means now
     * @param end  end of this interval, null means now
     * @throws IllegalArgumentException if the end is before the start
     */
    public Interval(ReadableInstant start, ReadableInstant end) {
        super(start, end);
    }

    /**
     * Constructs an interval from a start instant and a duration.
     * 
     * @param start  start of this interval, null means now
     * @param duration  the duration of this interval, null means zero length
     * @throws IllegalArgumentException if the end is before the start
     * @throws ArithmeticException if the end instant exceeds the capacity of a long
     */
    public Interval(ReadableInstant start, ReadableDuration duration) {
        super(start, duration);
    }

    /**
     * Constructs an interval from a millisecond duration and an end instant.
     * 
     * @param duration  the duration of this interval, null means zero length
     * @param end  end of this interval, null means now
     * @throws IllegalArgumentException if the end is before the start
     * @throws ArithmeticException if the start instant exceeds the capacity of a long
     */
    public Interval(ReadableDuration duration, ReadableInstant end) {
        super(duration, end);
    }

    /**
     * Constructs an interval from a start instant and a time period.
     * <p>
     * When forming the interval, the chronology from the instant is used
     * if present, otherwise the chronology of the period is used.
     * 
     * @param start  start of this interval, null means now
     * @param period  the period of this interval, null means zero length
     * @throws IllegalArgumentException if the end is before the start
     * @throws ArithmeticException if the end instant exceeds the capacity of a long
     */
    public Interval(ReadableInstant start, ReadablePeriod period) {
        super(start, period);
    }

    /**
     * Constructs an interval from a time period and an end instant.
     * <p>
     * When forming the interval, the chronology from the instant is used
     * if present, otherwise the chronology of the period is used.
     * 
     * @param period  the period of this interval, null means zero length
     * @param end  end of this interval, null means now
     * @throws IllegalArgumentException if the end is before the start
     * @throws ArithmeticException if the start instant exceeds the capacity of a long
     */
    public Interval(ReadablePeriod period, ReadableInstant end) {
        super(period, end);
    }

    /**
     * Constructs a time interval by converting or copying from another object.
     * <p>
     * The recognised object types are defined in
     * {@link org.joda.time.convert.ConverterManager ConverterManager} and
     * include ReadableInterval and String.
     * The String formats are described by {@link ISODateTimeFormat#dateTimeParser()}
     * and {@link ISOPeriodFormat#standard()}, and may be 'datetime/datetime',
     * 'datetime/period' or 'period/datetime'.
     * 
     * @param interval  the time interval to copy
     * @throws IllegalArgumentException if the interval is invalid
     */
    public Interval(Object interval) {
        super(interval, null);
    }

    /**
     * Constructs a time interval by converting or copying from another object,
     * overriding the chronology.
     * <p>
     * The recognised object types are defined in
     * {@link org.joda.time.convert.ConverterManager ConverterManager} and
     * include ReadableInterval and String.
     * The String formats are described by {@link ISODateTimeFormat#dateTimeParser()}
     * and {@link ISOPeriodFormat#standard()}, and may be 'datetime/datetime',
     * 'datetime/period' or 'period/datetime'.
     * 
     * @param interval  the time interval to copy
     * @param chronology  the chronology to use, null means ISO default
     * @throws IllegalArgumentException if the interval is invalid
     */
    public Interval(Object interval, Chronology chronology) {
        super(interval, chronology);
    }

    //-----------------------------------------------------------------------
    /**
     * Get this interval as an immutable <code>Interval</code> object
     * by returning <code>this</code>.
     *
     * @return <code>this</code>
     */
    public Interval toInterval() {
        return this;
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the overlap between this interval and another interval.
     * <p>
     * Intervals are inclusive of the start instant and exclusive of the end.
     * An interval overlaps another if it shares some common part of the
     * datetime continuum. This method returns the amount of the overlap,
     * only if the intervals actually do overlap.
     * If the intervals do not overlap, then null is returned.
     * <p>
     * When two intervals are compared the result is one of three states:
     * (a) they abut, (b) there is a gap between them, (c) they overlap.
     * The abuts state takes precedence over the other two, thus a zero duration
     * interval at the start of a larger interval abuts and does not overlap.
     * <p>
     * The chronology of the returned interval is the same as that of
     * this interval (the chronology of the interval parameter is not used).
     * Note that the use of the chronology was only correctly implemented
     * in version 1.3.
     *
     * @param interval  the interval to examine, null means now
     * @return the overlap interval, null if no overlap
     * @since 1.1
     */
    public Interval overlap(ReadableInterval interval) {
        interval = DateTimeUtils.getReadableInterval(interval);
        if (overlaps(interval) == false) {
            return null;
        }
        long start = Math.max(getStartMillis(), interval.getStartMillis());
        long end = Math.min(getEndMillis(), interval.getEndMillis());
        return new Interval(start, end, getChronology());
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the gap between this interval and another interval.
     * The other interval can be either before or after this interval.
     * <p>
     * Intervals are inclusive of the start instant and exclusive of the end.
     * An interval has a gap to another interval if there is a non-zero
     * duration between them. This method returns the amount of the gap only
     * if the intervals do actually have a gap between them.
     * If the intervals overlap or abut, then null is returned.
     * <p>
     * When two intervals are compared the result is one of three states:
     * (a) they abut, (b) there is a gap between them, (c) they overlap.
     * The abuts state takes precedence over the other two, thus a zero duration
     * interval at the start of a larger interval abuts and does not overlap.
     * <p>
     * The chronology of the returned interval is the same as that of
     * this interval (the chronology of the interval parameter is not used).
     * Note that the use of the chronology was only correctly implemented
     * in version 1.3.
     *
     * @param interval  the interval to examine, null means now
     * @return the gap interval, null if no gap
     * @since 1.1
     */
    public Interval gap(ReadableInterval interval) {
        interval = DateTimeUtils.getReadableInterval(interval);
        long otherStart = interval.getStartMillis();
        long otherEnd = interval.getEndMillis();
        long thisStart = getStartMillis();
        long thisEnd = getEndMillis();
        if (thisStart > otherEnd) {
            return new Interval(otherEnd, thisStart, getChronology());
        } else if (otherStart > thisEnd) {
            return new Interval(thisEnd, otherStart, getChronology());
        } else {
            return null;
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Does this interval abut with the interval specified.
     * <p>
     * Intervals are inclusive of the start instant and exclusive of the end.
     * An interval abuts if it starts immediately after, or ends immediately
     * before this interval without overlap.
     * A zero duration interval abuts with itself.
     * <p>
     * When two intervals are compared the result is one of three states:
     * (a) they abut, (b) there is a gap between them, (c) they overlap.
     * The abuts state takes precedence over the other two, thus a zero duration
     * interval at the start of a larger interval abuts and does not overlap.
     * <p>
     * For example:
     * <pre>
     * [09:00 to 10:00) abuts [08:00 to 08:30)  = false (completely before)
     * [09:00 to 10:00) abuts [08:00 to 09:00)  = true
     * [09:00 to 10:00) abuts [08:00 to 09:01)  = false (overlaps)
     * 
     * [09:00 to 10:00) abuts [09:00 to 09:00)  = true
     * [09:00 to 10:00) abuts [09:00 to 09:01)  = false (overlaps)
     * 
     * [09:00 to 10:00) abuts [10:00 to 10:00)  = true
     * [09:00 to 10:00) abuts [10:00 to 10:30)  = true
     * 
     * [09:00 to 10:00) abuts [10:30 to 11:00)  = false (completely after)
     * 
     * [14:00 to 14:00) abuts [14:00 to 14:00)  = true
     * [14:00 to 14:00) abuts [14:00 to 15:00)  = true
     * [14:00 to 14:00) abuts [13:00 to 14:00)  = true
     * </pre>
     *
     * @param interval  the interval to examine, null means now
     * @return true if the interval abuts
     * @since 1.1
     */
    public boolean abuts(ReadableInterval interval) {
        if (interval == null) {
            long now = DateTimeUtils.currentTimeMillis();
            return (getStartMillis() == now || getEndMillis() == now);
        } else {
            return (interval.getEndMillis() == getStartMillis() ||
                    getEndMillis() == interval.getStartMillis());
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Creates a new interval with the same start and end, but a different chronology.
     *
     * @param chronology  the chronology to use, null means ISO default
     * @return an interval with a different chronology
     */
    public Interval withChronology(Chronology chronology) {
        if (getChronology() == chronology) {
            return this;
        }
        return new Interval(getStartMillis(), getEndMillis(), chronology);
    }

    /**
     * Creates a new interval with the specified start millisecond instant.
     *
     * @param startInstant  the start instant for the new interval
     * @return an interval with the end from this interval and the specified start
     * @throws IllegalArgumentException if the resulting interval has end before start
     */
    public Interval withStartMillis(long startInstant) {
        if (startInstant == getStartMillis()) {
            return this;
        }
        return new Interval(startInstant, getEndMillis(), getChronology());
    }

    /**
     * Creates a new interval with the specified start instant.
     *
     * @param start  the start instant for the new interval, null means now
     * @return an interval with the end from this interval and the specified start
     * @throws IllegalArgumentException if the resulting interval has end before start
     */
    public Interval withStart(ReadableInstant start) {
        long startMillis = DateTimeUtils.getInstantMillis(start);
        return withStartMillis(startMillis);
    }

    /**
     * Creates a new interval with the specified start millisecond instant.
     *
     * @param endInstant  the end instant for the new interval
     * @return an interval with the start from this interval and the specified end
     * @throws IllegalArgumentException if the resulting interval has end before start
     */
    public Interval withEndMillis(long endInstant) {
        if (endInstant == getEndMillis()) {
            return this;
        }
        return new Interval(getStartMillis(), endInstant, getChronology());
    }

    /**
     * Creates a new interval with the specified end instant.
     *
     * @param end  the end instant for the new interval, null means now
     * @return an interval with the start from this interval and the specified end
     * @throws IllegalArgumentException if the resulting interval has end before start
     */
    public Interval withEnd(ReadableInstant end) {
        long endMillis = DateTimeUtils.getInstantMillis(end);
        return withEndMillis(endMillis);
    }

    //-----------------------------------------------------------------------
    /**
     * Creates a new interval with the specified duration after the start instant.
     *
     * @param duration  the duration to add to the start to get the new end instant, null means zero
     * @return an interval with the start from this interval and a calculated end
     * @throws IllegalArgumentException if the duration is negative
     */
    public Interval withDurationAfterStart(ReadableDuration duration) {
        long durationMillis = DateTimeUtils.getDurationMillis(duration);
        if (durationMillis == toDurationMillis()) {
            return this;
        }
        Chronology chrono = getChronology();
        long startMillis = getStartMillis();
        long endMillis = chrono.add(startMillis, durationMillis, 1);
        return new Interval(startMillis, endMillis, chrono);
    }

    /**
     * Creates a new interval with the specified duration before the end instant.
     *
     * @param duration  the duration to add to the start to get the new end instant, null means zero
     * @return an interval with the start from this interval and a calculated end
     * @throws IllegalArgumentException if the duration is negative
     */
    public Interval withDurationBeforeEnd(ReadableDuration duration) {
        long durationMillis = DateTimeUtils.getDurationMillis(duration);
        if (durationMillis == toDurationMillis()) {
            return this;
        }
        Chronology chrono = getChronology();
        long endMillis = getEndMillis();
        long startMillis = chrono.add(endMillis, durationMillis, -1);
        return new Interval(startMillis, endMillis, chrono);
    }

    //-----------------------------------------------------------------------
    /**
     * Creates a new interval with the specified period after the start instant.
     *
     * @param period  the period to add to the start to get the new end instant, null means zero
     * @return an interval with the start from this interval and a calculated end
     * @throws IllegalArgumentException if the period is negative
     */
    public Interval withPeriodAfterStart(ReadablePeriod period) {
        if (period == null) {
            return withDurationAfterStart(null);
        }
        Chronology chrono = getChronology();
        long startMillis = getStartMillis();
        long endMillis = chrono.add(period, startMillis, 1);
        return new Interval(startMillis, endMillis, chrono);
    }

    /**
     * Creates a new interval with the specified period before the end instant.
     *
     * @param period  the period to add to the start to get the new end instant, null means zero
     * @return an interval with the start from this interval and a calculated end
     * @throws IllegalArgumentException if the period is negative
     */
    public Interval withPeriodBeforeEnd(ReadablePeriod period) {
        if (period == null) {
            return withDurationBeforeEnd(null);
        }
        Chronology chrono = getChronology();
        long endMillis = getEndMillis();
        long startMillis = chrono.add(period, endMillis, -1);
        return new Interval(startMillis, endMillis, chrono);
    }

}
