/*
 *  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 org.joda.time.base.BaseSingleFieldPeriod;
import org.joda.time.field.FieldUtils;
import org.joda.time.format.ISOPeriodFormat;
import org.joda.time.format.PeriodFormatter;

/**
 * An immutable time period representing a number of days.
 * <p>
 * <code>Days</code> is an immutable period that can only store days.
 * It does not store years, months or hours for example. As such it is a
 * type-safe way of representing a number of days in an application.
 * <p>
 * The number of days is set in the constructor, and may be queried using
 * <code>getDays()</code>. Basic mathematical operations are provided -
 * <code>plus()</code>, <code>minus()</code>, <code>multipliedBy()</code> and
 * <code>dividedBy()</code>.
 * <p>
 * <code>Days</code> is thread-safe and immutable.
 *
 * @author Stephen Colebourne
 * @since 1.4
 */
public final class Days extends BaseSingleFieldPeriod {

    /** Constant representing zero days. */
    public static final Days ZERO = new Days(0);
    /** Constant representing one day. */
    public static final Days ONE = new Days(1);
    /** Constant representing two days. */
    public static final Days TWO = new Days(2);
    /** Constant representing three days. */
    public static final Days THREE = new Days(3);
    /** Constant representing four days. */
    public static final Days FOUR = new Days(4);
    /** Constant representing five days. */
    public static final Days FIVE = new Days(5);
    /** Constant representing six days. */
    public static final Days SIX = new Days(6);
    /** Constant representing seven days. */
    public static final Days SEVEN = new Days(7);
    /** Constant representing the maximum number of days that can be stored in this object. */
    public static final Days MAX_VALUE = new Days(Integer.MAX_VALUE);
    /** Constant representing the minimum number of days that can be stored in this object. */
    public static final Days MIN_VALUE = new Days(Integer.MIN_VALUE);

    /** The paser to use for this class. */
    private static final PeriodFormatter PARSER = ISOPeriodFormat.standard().withParseType(PeriodType.days());
    /** Serialization version. */
    private static final long serialVersionUID = 87525275727380865L;

    //-----------------------------------------------------------------------
    /**
     * Obtains an instance of <code>Days</code> that may be cached.
     * <code>Days</code> is immutable, so instances can be cached and shared.
     * This factory method provides access to shared instances.
     *
     * @param days  the number of days to obtain an instance for
     * @return the instance of Days
     */
    public static Days days(int days) {
        switch (days) {
            case 0:
                return ZERO;
            case 1:
                return ONE;
            case 2:
                return TWO;
            case 3:
                return THREE;
            case 4:
                return FOUR;
            case 5:
                return FIVE;
            case 6:
                return SIX;
            case 7:
                return SEVEN;
            case Integer.MAX_VALUE:
                return MAX_VALUE;
            case Integer.MIN_VALUE:
                return MIN_VALUE;
            default:
                return new Days(days);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Creates a <code>Days</code> representing the number of whole days
     * between the two specified datetimes. This method corectly handles
     * any daylight savings time changes that may occur during the interval.
     *
     * @param start  the start instant, must not be null
     * @param end  the end instant, must not be null
     * @return the period in days
     * @throws IllegalArgumentException if the instants are null or invalid
     */
    public static Days daysBetween(ReadableInstant start, ReadableInstant end) {
        int amount = BaseSingleFieldPeriod.between(start, end, DurationFieldType.days());
        return Days.days(amount);
    }

    /**
     * Creates a <code>Days</code> representing the number of whole days
     * between the two specified partial datetimes.
     * <p>
     * The two partials must contain the same fields, for example you can specify
     * two <code>LocalDate</code> objects.
     *
     * @param start  the start partial date, must not be null
     * @param end  the end partial date, must not be null
     * @return the period in days
     * @throws IllegalArgumentException if the partials are null or invalid
     */
    public static Days daysBetween(ReadablePartial start, ReadablePartial end) {
        if (start instanceof LocalDate && end instanceof LocalDate)   {
            Chronology chrono = DateTimeUtils.getChronology(start.getChronology());
            int days = chrono.days().getDifference(
                    ((LocalDate) end).getLocalMillis(), ((LocalDate) start).getLocalMillis());
            return Days.days(days);
        }
        int amount = BaseSingleFieldPeriod.between(start, end, ZERO);
        return Days.days(amount);
    }

    /**
     * Creates a <code>Days</code> representing the number of whole days
     * in the specified interval. This method corectly handles any daylight
     * savings time changes that may occur during the interval.
     *
     * @param interval  the interval to extract days from, null returns zero
     * @return the period in days
     * @throws IllegalArgumentException if the partials are null or invalid
     */
    public static Days daysIn(ReadableInterval interval) {
        if (interval == null)   {
            return Days.ZERO;
        }
        int amount = BaseSingleFieldPeriod.between(interval.getStart(), interval.getEnd(), DurationFieldType.days());
        return Days.days(amount);
    }

    /**
     * Creates a new <code>Days</code> representing the number of complete
     * standard length days in the specified period.
     * <p>
     * This factory method converts all fields from the period to hours using standardised
     * durations for each field. Only those fields which have a precise duration in
     * the ISO UTC chronology can be converted.
     * <ul>
     * <li>One week consists of 7 days.
     * <li>One day consists of 24 hours.
     * <li>One hour consists of 60 minutes.
     * <li>One minute consists of 60 seconds.
     * <li>One second consists of 1000 milliseconds.
     * </ul>
     * Months and Years are imprecise and periods containing these values cannot be converted.
     *
     * @param period  the period to get the number of hours from, null returns zero
     * @return the period in days
     * @throws IllegalArgumentException if the period contains imprecise duration values
     */
    public static Days standardDaysIn(ReadablePeriod period) {
        int amount = BaseSingleFieldPeriod.standardPeriodIn(period, DateTimeConstants.MILLIS_PER_DAY);
        return Days.days(amount);
    }

    /**
     * Creates a new <code>Days</code> by parsing a string in the ISO8601 format 'PnD'.
     * <p>
     * The parse will accept the full ISO syntax of PnYnMnWnDTnHnMnS however only the
     * days component may be non-zero. If any other component is non-zero, an exception
     * will be thrown.
     *
     * @param periodStr  the period string, null returns zero
     * @return the period in days
     * @throws IllegalArgumentException if the string format is invalid
     */
    public static Days parseDays(String periodStr) {
        if (periodStr == null) {
            return Days.ZERO;
        }
        Period p = PARSER.parsePeriod(periodStr);
        return Days.days(p.getDays());
    }

    //-----------------------------------------------------------------------
    /**
     * Creates a new instance representing a number of days.
     * You should consider using the factory method {@link #days(int)}
     * instead of the constructor.
     *
     * @param days  the number of days to represent
     */
    private Days(int days) {
        super(days);
    }

    /**
     * Resolves singletons.
     * 
     * @return the singleton instance
     */
    private Object readResolve() {
        return Days.days(getValue());
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the duration field type, which is <code>days</code>.
     *
     * @return the period type
     */
    public DurationFieldType getFieldType() {
        return DurationFieldType.days();
    }

    /**
     * Gets the period type, which is <code>days</code>.
     *
     * @return the period type
     */
    public PeriodType getPeriodType() {
        return PeriodType.days();
    }

    //-----------------------------------------------------------------------
    /**
     * Converts this period in days to a period in weeks assuming a
     * 7 day week.
     * <p>
     * This method allows you to convert between different types of period.
     * However to achieve this it makes the assumption that all weeks are
     * 7 days long.
     * This may not be true for some unusual chronologies. However, it is included
     * as it is a useful operation for many applications and business rules.
     * 
     * @return a period representing the number of weeks for this number of days
     */
    public Weeks toStandardWeeks() {
        return Weeks.weeks(getValue() / DateTimeConstants.DAYS_PER_WEEK);
    }

    /**
     * Converts this period in days to a period in hours assuming a
     * 24 hour day.
     * <p>
     * This method allows you to convert between different types of period.
     * However to achieve this it makes the assumption that all days are 24 hours long.
     * This is not true when daylight savings is considered and may also not
     * be true for some unusual chronologies. However, it is included
     * as it is a useful operation for many applications and business rules.
     * 
     * @return a period representing the number of hours for this number of days
     * @throws ArithmeticException if the number of hours is too large to be represented
     */
    public Hours toStandardHours() {
        return Hours.hours(FieldUtils.safeMultiply(getValue(), DateTimeConstants.HOURS_PER_DAY));
    }

    /**
     * Converts this period in days to a period in minutes assuming a
     * 24 hour day and 60 minute hour.
     * <p>
     * This method allows you to convert between different types of period.
     * However to achieve this it makes the assumption that all days are 24 hours
     * long and all hours are 60 minutes long.
     * This is not true when daylight savings is considered and may also not
     * be true for some unusual chronologies. However, it is included
     * as it is a useful operation for many applications and business rules.
     * 
     * @return a period representing the number of minutes for this number of days
     * @throws ArithmeticException if the number of minutes is too large to be represented
     */
    public Minutes toStandardMinutes() {
        return Minutes.minutes(FieldUtils.safeMultiply(getValue(), DateTimeConstants.MINUTES_PER_DAY));
    }

    /**
     * Converts this period in days to a period in seconds assuming a
     * 24 hour day, 60 minute hour and 60 second minute.
     * <p>
     * This method allows you to convert between different types of period.
     * However to achieve this it makes the assumption that all days are 24 hours
     * long, all hours are 60 minutes long and all minutes are 60 seconds long.
     * This is not true when daylight savings is considered and may also not
     * be true for some unusual chronologies. However, it is included
     * as it is a useful operation for many applications and business rules.
     * 
     * @return a period representing the number of seconds for this number of days
     * @throws ArithmeticException if the number of seconds is too large to be represented
     */
    public Seconds toStandardSeconds() {
        return Seconds.seconds(FieldUtils.safeMultiply(getValue(), DateTimeConstants.SECONDS_PER_DAY));
    }

    //-----------------------------------------------------------------------
    /**
     * Converts this period in days to a duration in milliseconds assuming a
     * 24 hour day, 60 minute hour and 60 second minute.
     * <p>
     * This method allows you to convert from a period to a duration.
     * However to achieve this it makes the assumption that all days are 24 hours
     * long, all hours are 60 minutes and all minutes are 60 seconds.
     * This is not true when daylight savings time is considered, and may also
     * not be true for some unusual chronologies. However, it is included as it
     * is a useful operation for many applications and business rules.
     * 
     * @return a duration equivalent to this number of days
     */
    public Duration toStandardDuration() {
        long days = getValue();  // assign to a long
        return new Duration(days * DateTimeConstants.MILLIS_PER_DAY);
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the number of days that this period represents.
     *
     * @return the number of days in the period
     */
    public int getDays() {
        return getValue();
    }

    //-----------------------------------------------------------------------
    /**
     * Returns a new instance with the specified number of days added.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param days  the amount of days to add, may be negative
     * @return the new period plus the specified number of days
     * @throws ArithmeticException if the result overflows an int
     */
    public Days plus(int days) {
        if (days == 0) {
            return this;
        }
        return Days.days(FieldUtils.safeAdd(getValue(), days));
    }

    /**
     * Returns a new instance with the specified number of days added.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param days  the amount of days to add, may be negative, null means zero
     * @return the new period plus the specified number of days
     * @throws ArithmeticException if the result overflows an int
     */
    public Days plus(Days days) {
        if (days == null) {
            return this;
        }
        return plus(days.getValue());
    }

    //-----------------------------------------------------------------------
    /**
     * Returns a new instance with the specified number of days taken away.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param days  the amount of days to take away, may be negative
     * @return the new period minus the specified number of days
     * @throws ArithmeticException if the result overflows an int
     */
    public Days minus(int days) {
        return plus(FieldUtils.safeNegate(days));
    }

    /**
     * Returns a new instance with the specified number of days taken away.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param days  the amount of days to take away, may be negative, null means zero
     * @return the new period minus the specified number of days
     * @throws ArithmeticException if the result overflows an int
     */
    public Days minus(Days days) {
        if (days == null) {
            return this;
        }
        return minus(days.getValue());
    }

    //-----------------------------------------------------------------------
    /**
     * Returns a new instance with the days multiplied by the specified scalar.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param scalar  the amount to multiply by, may be negative
     * @return the new period multiplied by the specified scalar
     * @throws ArithmeticException if the result overflows an int
     */
    public Days multipliedBy(int scalar) {
        return Days.days(FieldUtils.safeMultiply(getValue(), scalar));
    }

    /**
     * Returns a new instance with the days divided by the specified divisor.
     * The calculation uses integer division, thus 3 divided by 2 is 1.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param divisor  the amount to divide by, may be negative
     * @return the new period divided by the specified divisor
     * @throws ArithmeticException if the divisor is zero
     */
    public Days dividedBy(int divisor) {
        if (divisor == 1) {
            return this;
        }
        return Days.days(getValue() / divisor);
    }

    //-----------------------------------------------------------------------
    /**
     * Returns a new instance with the days value negated.
     *
     * @return the new period with a negated value
     * @throws ArithmeticException if the result overflows an int
     */
    public Days negated() {
        return Days.days(FieldUtils.safeNegate(getValue()));
    }

    //-----------------------------------------------------------------------
    /**
     * Is this days instance greater than the specified number of days.
     *
     * @param other  the other period, null means zero
     * @return true if this days instance is greater than the specified one
     */
    public boolean isGreaterThan(Days other) {
        if (other == null) {
            return getValue() > 0;
        }
        return getValue() > other.getValue();
    }

    /**
     * Is this days instance less than the specified number of days.
     *
     * @param other  the other period, null means zero
     * @return true if this days instance is less than the specified one
     */
    public boolean isLessThan(Days other) {
        if (other == null) {
            return getValue() < 0;
        }
        return getValue() < other.getValue();
    }

    //-----------------------------------------------------------------------
    /**
     * Gets this instance as a String in the ISO8601 duration format.
     * <p>
     * For example, "P4D" represents 4 days.
     *
     * @return the value as an ISO8601 string
     */
    public String toString() {
        return "P" + String.valueOf(getValue()) + "D";
    }

}
