/*
 * Copyright (c) 2007-2013, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 *  * Neither the name of JSR-310 nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.threeten.bp.zone;

import java.io.Serializable;
import java.util.Collections;
import java.util.List;
import java.util.Objects;

import org.threeten.bp.Duration;
import org.threeten.bp.Instant;
import org.threeten.bp.LocalDateTime;
import org.threeten.bp.ZoneId;
import org.threeten.bp.ZoneOffset;

/**
 * The rules defining how the zone offset varies for a single time-zone.
 * <p>
 * The rules model all the historic and future transitions for a time-zone.
 * {@link ZoneOffsetTransition} is used for known transitions, typically historic.
 * {@link ZoneOffsetTransitionRule} is used for future transitions that are based
 * on the result of an algorithm.
 * <p>
 * The rules are loaded via {@link ZoneRulesProvider} using a {@link ZoneId}.
 * The same rules may be shared internally between multiple zone IDs.
 * <p>
 * Serializing an instance of {@code ZoneRules} will store the entire set of rules.
 * It does not store the zone ID as it is not part of the state of this object.
 * <p>
 * A rule implementation may or may not store full information about historic
 * and future transitions, and the information stored is only as accurate as
 * that supplied to the implementation by the rules provider.
 * Applications should treat the data provided as representing the best information
 * available to the implementation of this rule.
 *
 * <h3>Specification for implementors</h3>
 * The supplied implementations of this class are immutable and thread-safe.
 */
public abstract class ZoneRules {

    /**
     * Obtains an instance of {@code ZoneRules} with full transition rules.
     *
     * @param baseStandardOffset  the standard offset to use before legal rules were set, not null
     * @param baseWallOffset  the wall offset to use before legal rules were set, not null
     * @param standardOffsetTransitionList  the list of changes to the standard offset, not null
     * @param transitionList  the list of transitions, not null
     * @param lastRules  the recurring last rules, size 16 or less, not null
     * @return the zone rules, not null
     */
    public static ZoneRules of(ZoneOffset baseStandardOffset,
                               ZoneOffset baseWallOffset,
                               List<ZoneOffsetTransition> standardOffsetTransitionList,
                               List<ZoneOffsetTransition> transitionList,
                               List<ZoneOffsetTransitionRule> lastRules) {
        Objects.requireNonNull(baseStandardOffset, "baseStandardOffset");
        Objects.requireNonNull(baseWallOffset, "baseWallOffset");
        Objects.requireNonNull(standardOffsetTransitionList, "standardOffsetTransitionList");
        Objects.requireNonNull(transitionList, "transitionList");
        Objects.requireNonNull(lastRules, "lastRules");
        return new StandardZoneRules(baseStandardOffset, baseWallOffset,
                             standardOffsetTransitionList, transitionList, lastRules);
    }

    /**
     * Obtains an instance of {@code ZoneRules} that always uses the same offset.
     * <p>
     * The returned rules always have the same offset.
     *
     * @param offset  the offset, not null
     * @return the zone rules, not null
     */
    public static ZoneRules of(ZoneOffset offset) {
        Objects.requireNonNull(offset, "offset");
        return new Fixed(offset);
    }

    /**
     * Restricted constructor.
     */
    ZoneRules() {
    }

    //-----------------------------------------------------------------------
    /**
     * Checks of the zone rules are fixed, such that the offset never varies.
     *
     * @return true if the time-zone is fixed and the offset never changes
     */
    public abstract boolean isFixedOffset();

    //-----------------------------------------------------------------------
    /**
     * Gets the offset applicable at the specified instant in these rules.
     * <p>
     * The mapping from an instant to an offset is simple, there is only
     * one valid offset for each instant.
     * This method returns that offset.
     *
     * @param instant  the instant to find the offset for, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @return the offset, not null
     */
    public abstract ZoneOffset getOffset(Instant instant);

    /**
     * Gets a suitable offset for the specified local date-time in these rules.
     * <p>
     * The mapping from a local date-time to an offset is not straightforward.
     * There are three cases:
     * <p><ul>
     * <li>Normal, with one valid offset. For the vast majority of the year, the normal
     *  case applies, where there is a single valid offset for the local date-time.</li>
     * <li>Gap, with zero valid offsets. This is when clocks jump forward typically
     *  due to the spring daylight savings change from "winter" to "summer".
     *  In a gap there are local date-time values with no valid offset.</li>
     * <li>Overlap, with two valid offsets. This is when clocks are set back typically
     *  due to the autumn daylight savings change from "summer" to "winter".
     *  In an overlap there are local date-time values with two valid offsets.</li>
     * </ul><p>
     * Thus, for any given local date-time there can be zero, one or two valid offsets.
     * This method returns the single offset in the Normal case, and in the Gap or Overlap
     * case it returns the offset before the transition.
     * <p>
     * Since, in the case of Gap and Overlap, the offset returned is a "best" value, rather
     * than the "correct" value, it should be treated with care. Applications that care
     * about the correct offset should use a combination of this method,
     * {@link #getValidOffsets(LocalDateTime)} and {@link #getTransition(LocalDateTime)}.
     *
     * @param localDateTime  the local date-time to query, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @return the best available offset for the local date-time, not null
     */
    public abstract ZoneOffset getOffset(LocalDateTime localDateTime);

    /**
     * Gets the offset applicable at the specified local date-time in these rules.
     * <p>
     * The mapping from a local date-time to an offset is not straightforward.
     * There are three cases:
     * <p><ul>
     * <li>Normal, with one valid offset. For the vast majority of the year, the normal
     *  case applies, where there is a single valid offset for the local date-time.</li>
     * <li>Gap, with zero valid offsets. This is when clocks jump forward typically
     *  due to the spring daylight savings change from "winter" to "summer".
     *  In a gap there are local date-time values with no valid offset.</li>
     * <li>Overlap, with two valid offsets. This is when clocks are set back typically
     *  due to the autumn daylight savings change from "summer" to "winter".
     *  In an overlap there are local date-time values with two valid offsets.</li>
     * </ul><p>
     * Thus, for any given local date-time there can be zero, one or two valid offsets.
     * This method returns that list of valid offsets, which is a list of size 0, 1 or 2.
     * In the case where there are two offsets, the earlier offset is returned at index 0
     * and the later offset at index 1.
     * <p>
     * There are various ways to handle the conversion from a {@code LocalDateTime}.
     * One technique, using this method, would be:
     * <pre>
     *  List<ZoneOffset> validOffsets = rules.getOffset(localDT);
     *  if (validOffsets.size() == 1) {
     *    // Normal case: only one valid offset
     *    zoneOffset = validOffsets.get(0);
     *  } else {
     *    // Gap or Overlap: determine what to do from transition (which will be non-null)
     *    ZoneOffsetTransition trans = rules.getTransition(localDT);
     *  }
     * </pre>
     * <p>
     * In theory, it is possible for there to be more than two valid offsets.
     * This would happen if clocks to be put back more than once in quick succession.
     * This has never happened in the history of time-zones and thus has no special handling.
     * However, if it were to happen, then the list would return more than 2 entries.
     *
     * @param localDateTime  the local date-time to query for valid offsets, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @return the list of valid offsets, may be immutable, not null
     */
    public abstract List<ZoneOffset> getValidOffsets(LocalDateTime localDateTime);

    /**
     * Gets the offset transition applicable at the specified local date-time in these rules.
     * <p>
     * The mapping from a local date-time to an offset is not straightforward.
     * There are three cases:
     * <p><ul>
     * <li>Normal, with one valid offset. For the vast majority of the year, the normal
     *  case applies, where there is a single valid offset for the local date-time.</li>
     * <li>Gap, with zero valid offsets. This is when clocks jump forward typically
     *  due to the spring daylight savings change from "winter" to "summer".
     *  In a gap there are local date-time values with no valid offset.</li>
     * <li>Overlap, with two valid offsets. This is when clocks are set back typically
     *  due to the autumn daylight savings change from "summer" to "winter".
     *  In an overlap there are local date-time values with two valid offsets.</li>
     * </ul><p>
     * A transition is used to model the cases of a Gap or Overlap.
     * The Normal case will return null.
     * <p>
     * There are various ways to handle the conversion from a {@code LocalDateTime}.
     * One technique, using this method, would be:
     * <pre>
     *  ZoneOffsetTransition trans = rules.getTransition(localDT);
     *  if (trans == null) {
     *    // Gap or Overlap: determine what to do from transition
     *  } else {
     *    // Normal case: only one valid offset
     *    zoneOffset = rule.getOffset(localDT);
     *  }
     * </pre>
     *
     * @param localDateTime  the local date-time to query for offset transition, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @return the offset transition, null if the local date-time is not in transition
     */
    public abstract ZoneOffsetTransition getTransition(LocalDateTime localDateTime);

    //-----------------------------------------------------------------------
    /**
     * Gets the standard offset for the specified instant in this zone.
     * <p>
     * This provides access to historic information on how the standard offset
     * has changed over time.
     * The standard offset is the offset before any daylight saving time is applied.
     * This is typically the offset applicable during winter.
     *
     * @param instant  the instant to find the offset information for, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @return the standard offset, not null
     */
    public abstract ZoneOffset getStandardOffset(Instant instant);

    /**
     * Gets the amount of daylight savings in use for the specified instant in this zone.
     * <p>
     * This provides access to historic information on how the amount of daylight
     * savings has changed over time.
     * This is the difference between the standard offset and the actual offset.
     * Typically the amount is zero during winter and one hour during summer.
     * Time-zones are second-based, so the nanosecond part of the duration will be zero.
     *
     * @param instant  the instant to find the daylight savings for, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @return the difference between the standard and actual offset, not null
     */
    public abstract Duration getDaylightSavings(Instant instant);
    //    default {
    //        ZoneOffset standardOffset = getStandardOffset(instant);
    //        ZoneOffset actualOffset = getOffset(instant);
    //        return actualOffset.toDuration().minus(standardOffset.toDuration()).normalized();
    //    }

    /**
     * Checks if the specified instant is in daylight savings.
     * <p>
     * This checks if the standard and actual offsets are the same at the specified instant.
     *
     * @param instant  the instant to find the offset information for, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @return the standard offset, not null
     */
    public abstract boolean isDaylightSavings(Instant instant);
    //    default {
    //        return (getStandardOffset(instant).equals(getOffset(instant)) == false);
    //    }

    /**
     * Checks if the offset date-time is valid for these rules.
     * <p>
     * To be valid, the local date-time must not be in a gap and the offset
     * must match the valid offsets.
     *
     * @param localDateTime  the date-time to check, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @param offset  the offset to check, null returns false
     * @return true if the offset date-time is valid for these rules
     */
    public abstract boolean isValidOffset(LocalDateTime localDateTime, ZoneOffset offset);
    //    default {
    //        return getValidOffsets(dateTime).contains(offset);
    //    }

    //-----------------------------------------------------------------------
    /**
     * Gets the next transition after the specified instant.
     * <p>
     * This returns details of the next transition after the specified instant.
     * For example, if the instant represents a point where "Summer" daylight savings time
     * applies, then the method will return the transition to the next "Winter" time.
     *
     * @param instant  the instant to get the next transition after, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @return the next transition after the specified instant, null if this is after the last transition
     */
    public abstract ZoneOffsetTransition nextTransition(Instant instant);

    /**
     * Gets the previous transition before the specified instant.
     * <p>
     * This returns details of the previous transition after the specified instant.
     * For example, if the instant represents a point where "summer" daylight saving time
     * applies, then the method will return the transition from the previous "winter" time.
     *
     * @param instant  the instant to get the previous transition after, not null, but null
     *  may be ignored if the rules have a single offset for all instants
     * @return the previous transition after the specified instant, null if this is before the first transition
     */
    public abstract ZoneOffsetTransition previousTransition(Instant instant);

    /**
     * Gets the complete list of fully defined transitions.
     * <p>
     * The complete set of transitions for this rules instance is defined by this method
     * and {@link #getTransitionRules()}. This method returns those transitions that have
     * been fully defined. These are typically historical, but may be in the future.
     * <p>
     * The list will be empty for fixed offset rules and for any time-zone where there has
     * only ever been a single offset. The list will also be empty if the transition rules are unknown.
     *
     * @return an immutable list of fully defined transitions, not null
     */
    public abstract List<ZoneOffsetTransition> getTransitions();

    /**
     * Gets the list of transition rules for years beyond those defined in the transition list.
     * <p>
     * The complete set of transitions for this rules instance is defined by this method
     * and {@link #getTransitions()}. This method returns instances of {@link ZoneOffsetTransitionRule}
     * that define an algorithm for when transitions will occur.
     * <p>
     * For any given {@code ZoneRules}, this list contains the transition rules for years
     * beyond those years that have been fully defined. These rules typically refer to future
     * daylight saving time rule changes.
     * <p>
     * If the zone defines daylight savings into the future, then the list will normally
     * be of size two and hold information about entering and exiting daylight savings.
     * If the zone does not have daylight savings, or information about future changes
     * is uncertain, then the list will be empty.
     * <p>
     * The list will be empty for fixed offset rules and for any time-zone where there is no
     * daylight saving time. The list will also be empty if the transition rules are unknown.
     *
     * @return an immutable list of transition rules, not null
     */
    public abstract List<ZoneOffsetTransitionRule> getTransitionRules();

    //-----------------------------------------------------------------------
    /**
     * Checks if this set of rules equals another.
     * <p>
     * Two rule sets are equal if they will always result in the same output
     * for any given input instant or local date-time.
     * Rules from two different groups may return false even if they are in fact the same.
     * <p>
     * This definition should result in implementations comparing their entire state.
     *
     * @param otherRules  the other rules, null returns false
     * @return true if this rules is the same as that specified
     */
    @Override
    public abstract boolean equals(Object otherRules);

    /**
     * Returns a suitable hash code given the definition of {@code #equals}.
     *
     * @return the hash code
     */
    @Override
    public abstract int hashCode();

    //-----------------------------------------------------------------------
    /**
     * Fixed time-zone.
     */
    static final class Fixed extends ZoneRules implements Serializable {
        /** A serialization identifier for this class. */
        private static final long serialVersionUID = -8733721350312276297L;
        /** The offset. */
        private final ZoneOffset offset;

        /**
         * Constructor.
         *
         * @param offset  the offset, not null
         */
        Fixed(ZoneOffset offset) {
            this.offset = offset;
        }

        //-------------------------------------------------------------------------
        @Override
        public boolean isFixedOffset() {
            return true;
        }

        @Override
        public ZoneOffset getOffset(Instant instant) {
            return offset;
        }

        @Override
        public ZoneOffset getOffset(LocalDateTime localDateTime) {
            return offset;
        }

        @Override
        public List<ZoneOffset> getValidOffsets(LocalDateTime localDateTime) {
            return Collections.singletonList(offset);
        }

        @Override
        public ZoneOffsetTransition getTransition(LocalDateTime localDateTime) {
            return null;
        }

        @Override
        public boolean isValidOffset(LocalDateTime dateTime, ZoneOffset offset) {
            return this.offset.equals(offset);
        }

        //-------------------------------------------------------------------------
        @Override
        public ZoneOffset getStandardOffset(Instant instant) {
            return offset;
        }

        @Override
        public Duration getDaylightSavings(Instant instant) {
            return Duration.ZERO;
        }

        @Override
        public boolean isDaylightSavings(Instant instant) {
            return false;
        }

        //-------------------------------------------------------------------------
        @Override
        public ZoneOffsetTransition nextTransition(Instant instant) {
            return null;
        }

        @Override
        public ZoneOffsetTransition previousTransition(Instant instant) {
            return null;
        }

        @Override
        public List<ZoneOffsetTransition> getTransitions() {
            return Collections.emptyList();
        }

        @Override
        public List<ZoneOffsetTransitionRule> getTransitionRules() {
            return Collections.emptyList();
        }

        //-----------------------------------------------------------------------
        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
               return true;
            }
            if (obj instanceof Fixed) {
                return offset.equals(((Fixed) obj).offset);
            }
            return false;
        }

        @Override
        public int hashCode() {
            return offset.hashCode() + 1;
        }
    }

}