/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.scxml2.model;

import java.util.HashSet;
import java.util.Set;

/**
 * The class in this SCXML object model that corresponds to the
 * simple &lt;transition&gt; SCXML element, without Transition rules for &quot;events&quot; or
 * &quot;guard-conditions&quot;. Used for &lt;history&gt; or &lt;history&gt; elements.
 *
 */
public class SimpleTransition extends Executable implements Observable {

    /**
     * Serial version UID.
     */
    private static final long serialVersionUID = 2L;

    /**
     * The id for this {@link Observable} which is unique within the SCXML state machine
     */
    private Integer observableId;

    /**
     * The Transition type: internal or external (default)
     * @see #isTypeInternal()
     */
    private TransitionType type;

    /**
     * The transition domain for this transition.
     * @see #getTransitionDomain()
     */
    private TransitionalState transitionDomain;

    /**
     * Internal flag indicating a null transitionDomain was derived to be the SCXML Document itself.
     */
    private boolean scxmlTransitionDomain;

    /**
     * Derived effective Transition type.
     * @see #isTypeInternal()
     */
    private Boolean typeInternal;

    /**
     * Optional property that specifies the new state(s) or parallel(s)
     * element to transition to. May be specified by reference or in-line.
     * If multiple state(s) are specified, they must belong to the regions
     * of the same parallel.
     */
    private final Set<TransitionTarget> targets;

    /**
     * The transition target ID
     */
    private String next;

    /**
     * Constructor.
     */
    public SimpleTransition() {
        this.targets = new HashSet<>();
    }

    private boolean isCompoundStateParent(TransitionalState ts) {
        return ts instanceof State && ((State)ts).isComposite();
    }

    /**
     * {@inheritDoc}
     */
    public final Integer getObservableId() {
        return observableId;
    }

    /**
     * Sets the observableId for this Observable, which must be unique within the SCXML state machine
     * @param observableId the observableId
     */
    public final void setObservableId(Integer observableId) {
        this.observableId = observableId;
    }

    /**
     * Get the TransitionalState (State or Parallel) parent.
     *
     * @return Returns the parent.
     */
    @Override
    public TransitionalState getParent() {
        return (TransitionalState)super.getParent();
    }

    /**
     * Set the TransitionalState (State or Parallel) parent
     * <p>
     * For transitions of Initial or History elements their TransitionalState parent must be set.
     * </p>
     *
     * @param parent The parent to set.
     */
    public final void setParent(final TransitionalState parent) {
        super.setParent(parent);
    }

    /**
     * @return true if Transition type == internal or false if type == external (default)
     */
    public final TransitionType getType() {
        return type;
    }

    /**
     * Sets the Transition type
     * @param type the Transition type
     */
    public final void setType(final TransitionType type) {
        this.type = type;
    }

    /**
     * Returns the effective Transition type.
     * <p>
     * A transition type is only effectively internal if:
     * </p>
     * <ul>
     *   <li>its {@link #getType()} == {@link TransitionType#internal}</li>
     *   <li>its source state {@link #getParent()} {@link State#isComposite()}</li>
     *   <li>all its {@link #getTargets()} are proper descendants of its {@link #getParent()}</li>
     * </ul>
     * <p>
     * Otherwise it is treated (for determining its exit states) as if it is of type {@link TransitionType#external}
     * </p>
     * @see <a href="https://www.w3.org/TR/2015/REC-scxml-20150901/#SelectingTransitions">
     *     https://www.w3.org/TR/2015/REC-scxml-20150901/#SelectingTransitions</a>
     * @return true if the effective Transition type is {@link TransitionType#internal}
     */
    public final boolean isTypeInternal() {
        if (typeInternal == null) {

            // derive typeInternal
            typeInternal = TransitionType.internal == type && isCompoundStateParent(getParent());

            if (typeInternal && targets.size() > 0) {
                for (TransitionTarget tt : targets) {
                    if (!tt.isDescendantOf(getParent())) {
                        typeInternal = false;
                        break;
                    }
                }
            }
        }
        return typeInternal;
    }

    /**
     * Returns the transition domain of this transition
     * <p>
     * If this transition is target-less OR if its transition domain is the SCXML document itself, null is returned.
     * </p>
     * <p>
     * This method therefore only is useful to be invoked if the transition has targets!
     * </p>
     * <p>
     * If the transition has targets then the transition domain is the compound State parent such that:
     * </p>
     * <ul>
     *   <li>all states that are exited or entered as a result of taking this transition are descendants of it</li>
     *   <li>no descendant of it has this property</li>
     * </ul>
     * <p>
     * If there is no such compound state parent, the transition domain effectively becomes the SCXML document itself,
     * which is not a (Transitional)State, and thus null will be returned instead.
     * </p>
     *
     * @return The transition domain of this transition
     */
    public TransitionalState getTransitionDomain() {
        TransitionalState ts = transitionDomain;
        if (ts == null && targets.size() > 0 && !scxmlTransitionDomain) {

            if (getParent() != null) {
                if (isTypeInternal()) {
                    transitionDomain = getParent();
                }
                else {
                    // findLCCA
                    for (int i = getParent().getNumberOfAncestors()-1; i > -1; i--) {
                        if (isCompoundStateParent(getParent().getAncestor(i))) {
                            boolean allDescendants = true;
                            for (TransitionTarget tt : targets) {
                                if (i >= tt.getNumberOfAncestors()) {
                                    i = tt.getNumberOfAncestors();
                                    allDescendants = false;
                                    break;
                                }
                                if (tt.getAncestor(i) != getParent().getAncestor(i)) {
                                    allDescendants = false;
                                    break;
                                }
                            }
                            if (allDescendants) {
                                transitionDomain = getParent().getAncestor(i);
                                break;
                            }
                        }
                    }
                }
            }
            ts = transitionDomain;
            if (ts == null) {
                scxmlTransitionDomain = true;
            }
        }
        return ts;
    }

    /**
     * Get the set of transition targets (may be an empty list).
     *
     * @return Returns the target(s) as specified in SCXML markup.
     * <p>Remarks: Is <code>empty</code> for &quot;stay&quot; transitions.
     *
     * @since 0.7
     */
    public final Set<TransitionTarget> getTargets() {
        return targets;
    }

    /**
     * Get the ID of the transition target (may be null, if, for example,
     * the target is specified inline).
     *
     * @return String Returns the transition target ID
     * @see #getTargets()
     */
    public final String getNext() {
        return next;
    }

    /**
     * Set the transition target by specifying its ID.
     *
     * @param next The the transition target ID
     */
    public final void setNext(final String next) {
        this.next = next;
    }
}