/* ========================================================================
 * PlantUML : a free UML diagram generator
 * ========================================================================
 *
 * (C) Copyright 2009-2025, Arnaud Roques
 *
 * Project Info:  https://plantuml.com
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 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
 * License for more details.
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 * You should have received a copy of the GNU General Public
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 * Original Author:  Arnaud Roques, Mario Kušek
 * 
 *
 */
package net.sourceforge.plantuml.project.ngm.math;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * Immutable implementation of {@link PiecewiseConstant} that models a workload
 * pattern defined by specific dates.
 *
 * <p>
 * Each specific {@link LocalDate} value is associated with a constant
 * {@link Fraction} representing the workload for that day (for example 3/10 for
 * 30%). A zero value is meaningful and represents no allocation on that day.
 * </p>
 *
 * <p>
 * For any date not explicitly mapped, a default value is returned.
 * </p>
 */
public final class PiecewiseConstantSpecificDays extends AbstractPiecewiseConstant {

	/**
	 * Mapping of specific dates to their corresponding workload fractions.
	 */
	private final Map<LocalDate, Fraction> dayToFraction;

	/**
	 * Default workload fraction for dates not explicitly mapped.
	 */
	private final Fraction defaultValue;

	/**
	 * Constructs a PiecewiseConstantSpecificDays with the given default value.
	 * 
	 * @param value The default workload fraction.
	 */
	private PiecewiseConstantSpecificDays(Fraction value) {
		this(value, Collections.emptyMap());
	}

	/**
	 * Constructs a PiecewiseConstantSpecificDays with the given default value and
	 * specific day-to-fraction mapping.
	 * 
	 * @param value         The default workload fraction.
	 * @param dayToFraction Mapping of specific dates to their workload fractions.
	 */
	private PiecewiseConstantSpecificDays(Fraction value, Map<LocalDate, Fraction> dayToFraction) {
		defaultValue = value;
		this.dayToFraction = dayToFraction;
	}

	private Fraction getValue(LocalDate localDate) {
		if (dayToFraction.containsKey(localDate))
			return dayToFraction.get(localDate);

		return defaultValue;
	}

	/**
	 * Creates a PiecewiseConstantSpecificDays with the given default value.
	 * 
	 * @param value The default workload fraction.
	 * @return A new PiecewiseConstantSpecificDays instance.
	 */
	public static PiecewiseConstantSpecificDays of(Fraction value) {
		return new PiecewiseConstantSpecificDays(value);
	}

	/**
	 * Returns a new PiecewiseConstantSpecificDays with the specified day associated
	 * with the given fraction.
	 * 
	 * @param day   The specific date to associate.
	 * @param value The workload fraction for the specified date.
	 * @return A new PiecewiseConstantSpecificDays instance with the updated
	 *         mapping.
	 */
	public PiecewiseConstantSpecificDays withDay(LocalDate day, Fraction value) {
		final Map<LocalDate, Fraction> newDayToFraction = new HashMap<>(dayToFraction);
		newDayToFraction.put(day, value);
		return new PiecewiseConstantSpecificDays(defaultValue, newDayToFraction);
	}

	@Override
	public Segment segmentAt(LocalDateTime instant, TimeDirection direction) {
		if (direction == TimeDirection.FORWARD) {
			final LocalDate day = instant.toLocalDate();
			final LocalDateTime start = day.atStartOfDay();
			final Fraction value = getValue(day);
			return Segment.forward(start, start.plusDays(1), value);
		}

		// BACKWARD: determine which day contains the instant
		final LocalDate day;
		if (instant.toLocalTime().equals(LocalTime.MIDNIGHT))
			day = instant.toLocalDate().minusDays(1);
		else
			day = instant.toLocalDate();

		final LocalDateTime end = day.atStartOfDay();
		final Fraction value = getValue(day);

		return Segment.backward(end.plusDays(1), end, value);

	}

}
