/*
 * Copyright (c) 2006, 2020 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.resolver;

import java.util.HashMap;
import java.util.Map;
import org.eclipse.persistence.jpa.jpql.tools.TypeHelper;
import org.eclipse.persistence.jpa.jpql.tools.spi.IManagedType;
import org.eclipse.persistence.jpa.jpql.tools.spi.IManagedTypeProvider;
import org.eclipse.persistence.jpa.jpql.tools.spi.IMapping;
import org.eclipse.persistence.jpa.jpql.tools.spi.IQuery;
import org.eclipse.persistence.jpa.jpql.tools.spi.IType;
import org.eclipse.persistence.jpa.jpql.tools.spi.ITypeDeclaration;
import org.eclipse.persistence.jpa.jpql.tools.spi.ITypeRepository;

/**
 * A <code>Resolver</code> is responsible to resolve a property by retrieving either the managed
 * type, the mapping, the type and the type declaration depending on the type of resolver.
 * <p>
 * Provisional API: This interface is part of an interim API that is still under development and
 * expected to change significantly before reaching stability. It is available at this early stage
 * to solicit feedback from pioneering adopters on the understanding that any code that uses this
 * API will almost certainly be broken (repeatedly) as the API evolves.
 *
 * @version 2.5
 * @since 2.3
 * @author Pascal Filion
 */
@SuppressWarnings("nls")
public abstract class Resolver {

    /**
     * This is only applicable to 1:1 relationships, and allows the target of the relationship to be
     * <code>null</code> if there is no corresponding relationship in the database.
     */
    private boolean nullAllowed;

    /**
     * The parent of this resolver, which is never <code>null</code>.
     */
    private final Resolver parent;

    /**
     * The cached {@link Resolver Resolvers} mapped with a variable name.
     */
    private Map<String, Resolver> resolvers;

    /**
     * The cached {@link IType} of the value to resolve.
     */
    private IType type;

    /**
     * The cached {@link ITypeDeclaration} of the value to resolve.
     */
    private ITypeDeclaration typeDeclaration;

    /**
     * Creates a new <code>Resolver</code>.
     *
     * @param parent The parent of this resolver, which is never <code>null</code>
     * @exception NullPointerException If the parent is <code>null</code>
     */
    protected Resolver(Resolver parent) {
        super();
        checkParent(parent);
        this.parent = parent;
    }

    /**
     * Caches the given {@link Resolver}.
     *
     * @param variableName The key used to cache the given {@link Resolver}
     * @param resolver The {@link Resolver} to cache
     */
    public final void addChild(String variableName, Resolver resolver) {

        if (resolvers == null) {
            resolvers = new HashMap<String, Resolver>();
        }

        resolvers.put(variableName, resolver);
    }

    /**
     * Resolves the {@link IType} of the property handled by this {@link Resolver}.
     *
     * @return Either the {@link IType} that was resolved by this {@link Resolver} or the {@link
     * IType} for {@link IType#UNRESOLVABLE_TYPE} if it could not be resolved
     */
    protected IType buildType() {
        return getTypeDeclaration().getType();
    }

    /**
     * Resolves the {@link ITypeDeclaration} of the property handled by this {@link Resolver}.
     *
     * @return Either the {@link ITypeDeclaration} that was resolved by this {@link Resolver} or the
     * {@link ITypeDeclaration} for {@link IType#UNRESOLVABLE_TYPE} if it could not be resolved
     */
    protected abstract ITypeDeclaration buildTypeDeclaration();

    protected void checkParent(Resolver parent) {
        if (parent == null) {
            throw new NullPointerException("The parent resolver cannot be null");
        }
    }

    /**
     * Retrieves the child of this {@link Resolver} that has the given variable name.
     *
     * @param variableName The name of the property that was cached
     * @return The cached {@link Resolver} mapped with the given property name; otherwise <code>null</code>
     */
    public final Resolver getChild(String variableName) {
        return (resolvers != null) ? resolvers.get(variableName) : null;
    }

    /**
     * Returns the {@link IManagedType} associated with the field handled by this {@link Resolver}.
     * If this {@link Resolver} does not handle a field that has a {@link IManagedType}, then
     * <code>null</code> should be returned.
     * <p>
     * For example: "<code><b>SELECT</b> e <b>FROM</b> Employee e</code>", the {@link Resolver} for
     * <i>e</i> would be returning the {@link IManagedType} for <i>Employee</i>.
     *
     * @return Either the {@link IManagedType}, if it could be resolved; <code>null</code> otherwise
     */
    public IManagedType getManagedType() {
        return null;
    }

    /**
     * Returns the {@link IMapping} for the wrapped field.
     *
     * @return Either the {@link IMapping} or <code>null</code> if none exists
     */
    public IMapping getMapping() {
        return null;
    }

    /**
     * Returns the parent of this {@link Resolver}.
     *
     * @return The parent of this {@link Resolver}
     */
    public Resolver getParent() {
        return parent;
    }

    /**
     * Returns the managed type of the parent resolver.
     *
     * @return The managed type of the parent resolver
     */
    public final IManagedType getParentManagedType() {
        return parent.getManagedType();
    }

    /**
     * Returns the {@link IMapping} of the parent resolver.
     *
     * @return The {@link IMapping} of the parent resolver
     */
    public final IMapping getParentMapping() {
        return parent.getMapping();
    }

    /**
     * Returns the type of the parent resolver.
     *
     * @return The type of the parent resolver
     */
    public final IType getParentType() {
        return parent.getType();
    }

    /**
     * Returns the type declaration of the parent resolver.
     *
     * @return The type declaration of the parent resolver
     */
    public final ITypeDeclaration getParentTypeDeclaration() {
        return parent.getTypeDeclaration();
    }

    /**
     * Returns the provider of managed types.
     *
     * @return The container holding the managed types
     */
    public final IManagedTypeProvider getProvider() {
        return getQuery().getProvider();
    }

    /**
     * Returns the external form representing the JPQL query.
     *
     * @return The external form of the JPQL query
     */
    public IQuery getQuery() {
        return parent.getQuery();
    }

    /**
     * Returns the {@link IType} of the field handled by this {@link Resolver}.
     *
     * @return Either the {@link IType} that was resolved by this {@link Resolver} or the {@link IType}
     * for {@link IType#UNRESOLVABLE_TYPE} if it could not be resolved
     */
    public final IType getType() {
        if (type == null) {
            type = buildType();
        }
        return type;
    }

    /**
     * Returns the {@link IType} of the given Java type.
     *
     * @param type The Java type for which its external form will be returned
     * @return The {@link IType} representing the given Java type
     */
    public final IType getType(Class<?> type) {
        return getTypeRepository().getType(type);
    }

    /**
     * Retrieves the external class for the given fully qualified class name.
     *
     * @param typeName The fully qualified class name of the class to retrieve
     * @return The external form of the class to retrieve
     */
    public final IType getType(String typeName) {
        return getTypeRepository().getType(typeName);
    }

    /**
     * Returns the {@link ITypeDeclaration} of the field handled by this {@link Resolver}.
     *
     * @return Either the {@link ITypeDeclaration} that was resolved by this {@link Resolver} or the
     * {@link ITypeDeclaration} for {@link IType#UNRESOLVABLE_TYPE} if it could not be resolved
     */
    public final ITypeDeclaration getTypeDeclaration() {
        if (typeDeclaration == null) {
            typeDeclaration = buildTypeDeclaration();
        }
        return typeDeclaration;
    }

    /**
     * Returns a helper that gives access to the most common {@link IType types}.
     *
     * @return A helper containing a collection of methods related to {@link IType}
     */
    public final TypeHelper getTypeHelper() {
        return getTypeRepository().getTypeHelper();
    }

    /**
     * Returns the type repository for the application.
     *
     * @return The repository of {@link IType ITypes}
     */
    public final ITypeRepository getTypeRepository() {
        return getQuery().getProvider().getTypeRepository();
    }

    /**
     * Determines whether the {@link org.eclipse.persistence.jpa.jpql.parser.Expression Expression}
     * to be created, which wraps the attribute or query key name allows the target of the 1:1
     * relationship to be <code>null</code> if there is no corresponding relationship in the database.
     *
     * @return <code>true</code> to allow <code>null</code> if the corresponding relationship in the
     * database does not exists; <code>false</code> otherwise
     */
    public boolean isNullAllowed() {
        return nullAllowed;
    }

    /**
     * Sets whether the {@link org.eclipse.persistence.jpa.jpql.parser.Expression Expression} to be
     * created, which wraps the attribute or query key name allows the target of the 1:1 relationship
     * to be <code>null</code> if there is no corresponding relationship in the database.
     *
     * @param nullAllowed <code>true</code> to allow <code>null</code> if the corresponding
     * relationship in the database does not exists; <code>false</code> otherwise
     */
    public void setNullAllowed(boolean nullAllowed) {
        this.nullAllowed = nullAllowed;
    }
}