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package uk.ac.rdg.resc.edal.util.chronologies;

import org.joda.time.DateTimeField;
import org.joda.time.DateTimeFieldType;
import org.joda.time.DurationField;
import org.joda.time.IllegalFieldValueException;
import org.joda.time.field.ImpreciseDateTimeField;

/**
 * A {@link DateTimeField} representing a month within a year of fixed duration.
 * 
 * @author Jon
 */
final class MonthOfFixedYearDateTimeField extends ImpreciseDateTimeField {
    private final FixedYearVariableMonthChronology chron;
    private final int[] daysInMonth;
    private final int numMonthsInYear;

    public MonthOfFixedYearDateTimeField(FixedYearVariableMonthChronology chron) {
        super(DateTimeFieldType.monthOfYear(), chron.getAverageMillisInMonth());
        this.chron = chron;
        this.daysInMonth = chron.getMonthLengths();
        this.numMonthsInYear = chron.getMonthLengths().length;
    }

    @Override
    public int get(long instant) {
        int dayOfYear = this.chron.dayOfYear().get(instant);
        /* Now search through the months of the year */
        int totalDays = 0;
        for (int i = 0; i < daysInMonth.length; i++) {
            totalDays += daysInMonth[i];
            if (dayOfYear <= totalDays) {
                /* Month numbers are one-based */
                return i + 1;
            }
        }
        throw new AssertionError("Shouldn't get here");
    }

    @Override
    public long set(long instant, int value) {
        /* Check for illegal values: this is not a lenient field */
        if (value < 1 || value > this.numMonthsInYear) {
            throw new IllegalFieldValueException(this.getType(), value, 1, this.numMonthsInYear);
        }
        /* What is the current month? */
        int monthOfYear = this.get(instant);
        /* How many months do we have to add to arrive at the new value */
        int monthsToAdd = value - monthOfYear;
        /* Now add the required number of months */
        return this.add(instant, monthsToAdd);
    }

    @Override
    public long add(final long instant, final int numMonths) {
        if (numMonths == 0)
            return instant;

        /* Calculate the number of years we have to add */
        int numYearsToAdd = numMonths / this.numMonthsInYear;
        /* Add the required number of years to the millisecond instant */
        long newInstant = instant + numYearsToAdd * this.chron.years().getUnitMillis();

        /* What is the current month? */
        int monthOfYear = this.get(instant);
        /* Calculate the number of months we have to add */
        int numMonthsToAdd = numMonths % this.numMonthsInYear;
        /* Add the required number of months TODO!!! */
        if (numMonthsToAdd > 0) {
            /* Add the months, starting with the current month */
            for (int i = 0; i < numMonthsToAdd; i++) {
                /* monthOfYear is 1-based */
                int monthToAdd = monthOfYear - 1 + i;
                /* we might wrap around the array */
                monthToAdd %= this.numMonthsInYear;
                long millisToAdd = this.daysInMonth[monthToAdd] * this.chron.days().getUnitMillis();
                newInstant += millisToAdd;
            }
        } else if (numMonthsToAdd < 0) {
            /* Subtract the month lengths, starting with the previous month */
            for (int i = 0; i < Math.abs(numMonthsToAdd); i++) {
                /*
                 * The previous month is monthOfYear - 2 because monthOfYear is
                 * 1-based
                 */
                int monthToSubtract = monthOfYear - 2 - i;
                /* we might wrap around the array */
                if (monthToSubtract < 0)
                    monthToSubtract += this.numMonthsInYear;
                long millisToSubtract = this.daysInMonth[monthToSubtract]
                        * this.chron.days().getUnitMillis();
                newInstant -= millisToSubtract;
            }
        }

        return newInstant;
    }

    @Override
    public long add(long instant, long numMonths) {
        if (numMonths > Integer.MAX_VALUE) {
            throw new IllegalArgumentException("Value too large");
        }
        return this.add(instant, (int) numMonths);
    }

    @Override
    public long roundFloor(long instant) {
        int year = this.chron.year().get(instant);
        int monthOfYear = this.get(instant);
        int numCompleteMonths = monthOfYear - 1;

        long millis = (year - 1970) * this.chron.years().getUnitMillis();
        for (int i = 0; i < numCompleteMonths; i++) {
            millis += this.daysInMonth[i] * this.chron.days().getUnitMillis();
        }

        return millis;
    }

    @Override
    public int getMinimumValue() {
        return 1;
    }

    @Override
    public int getMaximumValue() {
        return this.numMonthsInYear;
    }

    @Override
    public DurationField getRangeDurationField() {
        return this.chron.years();
    }

    /** Always returns false: does not accept impossible months like Floopuary */
    @Override
    public boolean isLenient() {
        return false;
    }

}
