/*
 * Copyright (c) 2011, 2021 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Oracle - initial API and implementation
//
package org.eclipse.persistence.jpa.jpql.tools.model.query;

import java.io.IOException;
import java.util.List;
import org.eclipse.persistence.jpa.jpql.parser.ResultVariable;
import org.eclipse.persistence.jpa.jpql.parser.SelectExpressionBNF;
import static org.eclipse.persistence.jpa.jpql.parser.AbstractExpression.*;

/**
 * A result variable may be used to name a select item in the query result.
 *
 * <div><p><b>BNF:</b> <code>select_item ::= select_expression [[AS] result_variable]</code></p></div>
 *
 * @see ResultVariable
 *
 * @version 2.4
 * @since 2.4
 * @author Pascal Filion
 */
@SuppressWarnings({"nls", "unused"}) // unused used for the import statement: see bug 330740
public class ResultVariableStateObject extends AbstractStateObject {

    /**
     * Flag used to determine if the <code><b>AS</b></code> identifier is used or not.
     */
    private boolean as;

    /**
     * The result variable identifies the select expression, which can be used in the
     * <code><b>ORDER BY</b></code> clause.
     */
    private IdentificationVariableStateObject resultVariable;

    /**
     * The state object representing the select expression that is named with a result variable.
     */
    private StateObject stateObject;

    /**
     * Notifies the visibility of the <code><b>AS</b></code> identifier has changed.
     */
    public static final String AS_PROPERTY = "as";

    /**
     * Notifies the result variable property has changed.
     */
    public static final String RESULT_VARIABLE_PROPERTY = "resultVariable";

    /**
     * Notifies the select state object property has changed.
     */
    public static final String STATE_OBJECT_PROPERTY = "selectStateObject";

    /**
     * Creates a new <code>ResultVariableStateObject</code>.
     *
     * @param parent The parent of this state object, which cannot be <code>null</code>
     * @exception NullPointerException The given parent cannot be <code>null</code>
     */
    public ResultVariableStateObject(SelectClauseStateObject parent) {
        super(parent);
    }

    /**
     * Creates a new <code>ResultVariableStateObject</code>.
     *
     * @param parent The parent of this state object, which cannot be <code>null</code>
     * @param stateObject The {@link StateObject} representing the select item
     * @param as Determines whether the <code><b>AS</b></code> identifier is used or not
     * @param resultVariable The variable identifying the select item
     * @exception NullPointerException The given parent cannot be <code>null</code>
     */
    public ResultVariableStateObject(SelectClauseStateObject parent,
                                     StateObject stateObject,
                                     boolean as,
                                     String resultVariable) {

        super(parent);
        this.as             = as;
        this.stateObject    = parent(stateObject);
        this.resultVariable.setTextInternally(resultVariable);
    }

    /**
     * Creates a new <code>ResultVariableStateObject</code>.
     *
     * @param parent The parent of this state object, which cannot be <code>null</code>
     * @param stateObject The {@link StateObject} representing the select item
     * @param resultVariable The variable identifying the select item
     * @exception NullPointerException The given parent cannot be <code>null</code>
     */
    public ResultVariableStateObject(SelectClauseStateObject parent,
                                     StateObject stateObject,
                                     String resultVariable) {

        this(parent, stateObject, false, resultVariable);
    }

    @Override
    public void accept(StateObjectVisitor visitor) {
        visitor.visit(this);
    }

    /**
     * Makes sure the <code><b>AS</b></code> identifier is used.
     *
     * @return This object
     */
    public ResultVariableStateObject addAs() {
        if (!as) {
            setAs(true);
        }
        return this;
    }

    @Override
    protected void addChildren(List<StateObject> children) {
        super.addChildren(children);
        if (stateObject != null) {
            children.add(stateObject);
        }
        children.add(resultVariable);
    }

    @Override
    public ResultVariable getExpression() {
        return (ResultVariable) super.getExpression();
    }

    @Override
    public SelectClauseStateObject getParent() {
        return (SelectClauseStateObject) super.getParent();
    }

    /**
     * Returns the result variable identifies the select expression, which can be used in the
     * <code><b>ORDER BY</b></code> clause.
     *
     * @return The unique identifier declaring the select expression
     */
    public String getResultVariable() {
        return resultVariable.getText();
    }

    /**
     * Returns the {@link StateObject} representing a single select expression.
     *
     * @return The {@link StateObject} representing a single select expression
     */
    public StateObject getStateObject() {
        return stateObject;
    }

    /**
     * Determines whether the <code><b>AS</b></code> identifier is used.
     *
     * @return <code>true</code> if the <code><b>AS</b></code> identifier is used; <code>false</code>
     * otherwise
     */
    public boolean hasAs() {
        return as;
    }

    /**
     * Determines whether the result variable has been defined.
     *
     * @return <code>true</code> if the result variable is defined; <code>false</code> otherwise
     */
    public boolean hasResultVariable() {
        return resultVariable.hasText();
    }

    /**
     * Determines whether the select item has been defined.
     *
     * @return <code>true</code> if there the selected expression has been defined; <code>false</code>
     * if it's missing
     */
    public boolean hasStateObject() {
        return stateObject != null;
    }

    @Override
    protected void initialize() {
        super.initialize();
        resultVariable = new IdentificationVariableStateObject(this);
    }

    @Override
    public boolean isEquivalent(StateObject stateObject) {

        if (super.isEquivalent(stateObject)) {
            ResultVariableStateObject resultVariable = (ResultVariableStateObject) stateObject;
            return as == resultVariable.as &&
                   resultVariable.isEquivalent(resultVariable.resultVariable) &&
                   areEquivalent(stateObject, resultVariable.stateObject);
        }

        return false;
    }

    /**
     * Parses the given JPQL fragment, which represents a single select expression, and creates the
     * {@link StateObject}.
     *
     * @param jpqlFragment The portion of the query representing a single select expression
     */
    public void parse(String jpqlFragment) {
        StateObject stateObject = buildStateObject(jpqlFragment, SelectExpressionBNF.ID);
        setStateObject(stateObject);
    }

    /**
     * Makes sure the <code><b>AS</b></code> identifier is not used.
     */
    public void removeAs() {
        if (as) {
            setAs(true);
        }
    }

    /**
     * Sets whether the <code><b>AS</b></code> identifier should be used.
     *
     * @param as <code>true</code> if the <code><b>AS</b></code> identifier should be used part;
     * <code>false</code> otherwise
     */
    public void setAs(boolean as) {
        boolean oldAs = this.as;
        this.as = as;
        firePropertyChanged(AS_PROPERTY, oldAs, as);
    }

    /**
     * Keeps a reference of the {@link ResultVariable parsed object} object, which should only be
     * done when this object is instantiated during the conversion of a parsed JPQL query into
     * {@link StateObject StateObjects}.
     *
     * @param expression The {@link ResultVariable parsed object} representing a result variable
     * expression
     */
    public void setExpression(ResultVariable expression) {
        super.setExpression(expression);
    }

    /**
     * Sets the result variable that identifies the select expression, which can be used in the
     * <code><b>ORDER BY</b></code> clause.
     *
     * @param resultVariable The unique identifier declaring the select expression
     */
    public void setResultVariable(String resultVariable) {
        String oldResultVariable = getResultVariable();
        this.resultVariable.setText(resultVariable);
        firePropertyChanged(RESULT_VARIABLE_PROPERTY, oldResultVariable, resultVariable);
    }

    /**
     * Sets the {@link StateObject} representing a single select expression.
     *
     * @param stateObject The {@link StateObject} representing a single select expression
     */
    public void setStateObject(StateObject stateObject) {
        StateObject oldStateObject = this.stateObject;
        this.stateObject = parent(stateObject);
        firePropertyChanged(STATE_OBJECT_PROPERTY, oldStateObject, stateObject);
    }

    /**
     * Toggles the visibility of the <code><b>AS</b></code> identifier; either adds it if it's not
     * present otherwise removes it if it's present.
     */
    public void toggleAs() {
        setAs(!as);
    }

    @Override
    protected void toTextInternal(Appendable writer) throws IOException {

        if (stateObject != null) {
            stateObject.toString(writer);
            writer.append(SPACE);
        }

        if (as) {
            writer.append(AS);
        }

        if (hasResultVariable()) {
            writer.append(SPACE);
            resultVariable.toTextInternal(writer);
        }
    }
}