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/*
 * Licensed 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.
 *
 * Other licenses:
 * -----------------------------------------------------------------------------
 * Commercial licenses for this work are available. These replace the above
 * ASL 2.0 and offer limited warranties, support, maintenance, and commercial
 * database integrations.
 *
 * For more information, please visit: http://www.jooq.org/licenses
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */
package org.jooq;

import java.io.Serializable;
import java.util.function.Function;

import org.jooq.impl.SQLDataType;

/**
 * A Converter for data types.
 * 
 * A general data type conversion interface that can be provided to jOOQ at
 * various places in order to perform custom data type conversion. Conversion is
 * directed, this means that the Converter is used
 * 

 * to load database types converting them to user types "FROM" the database.
 * Hence, {@link #fromType()} is the type as defined in the database.
 * to store user types converting them to database types "TO" the database.
 * Hence, {@link #toType()} is the user-defined type
 * 
 * 
 * Note: In order to avoid unwanted side-effects, it is highly recommended (yet
 * not required) for {@link #from(Object)} and {@link #to(Object)} to be
 * reciprocal. The two methods are reciprocal, if for all
 * X and Y, it can be said that
 * 

 * if Y.equals(converter.from(X)), then
 * X.equals(converter.to(Y)).
 * 
 * X.equals(converter.from(converter.to(X)))
 * X.equals(converter.to(converter.from(X)))
 * 
 * 
 * Furthermore, it is recommended (yet not required) that
 * 

 * converter.from(null) == null
 * converter.to(null) == null
 * 
 *
 * @author Lukas Eder
 * @param  The database type - i.e. any type available from
 *            {@link SQLDataType}
 * @param  The user type
 */
public interface Converter extends Serializable {

    /**
     * Convert a database object to a user object
     *
     * @param databaseObject The database object
     * @return The user object
     */
    U from(T databaseObject);

    /**
     * Convert a user object to a database object
     *
     * @param userObject The user object
     * @return The database object
     */
    T to(U userObject);

    /**
     * The database type
     */
    Class fromType();

    /**
     * The user type
     */
    Class toType();



    /**
     * Inverse this converter.
     */
    default Converter inverse() {
        return Converters.inverse(this);
    }

    /**
     * Chain a converter to this converter.
     */
    default  Converter andThen(Converter converter) {
        return Converters.of(this, converter);
    }

    /**
     * Construct a new converter from functions.
     *
     * @param  the database type
     * @param  the user type
     * @param fromType The database type
     * @param toType The user type
     * @param from A function converting from T to U
     * @param to A function converting from U to T
     * @return The converter.
     * @see Converter
     */
    static  Converter of(
        Class fromType,
        Class toType,
        Function from,
        Function to
    ) {
        return new Converter() {

            /**
             * Generated UID
             */
            private static final long serialVersionUID = 8782437631959970693L;

            @Override
            public final U from(T t) {
                return from.apply(t);
            }

            @Override
            public final T to(U u) {
                return to.apply(u);
            }

            @Override
            public final Class fromType() {
                return fromType;
            }

            @Override
            public final Class toType() {
                return toType;
            }

            @Override
            public String toString() {
                return "Converter [ " + fromType.getName() + " -> " + toType.getName() + " ]";
            }
        };
    }

    /**
     * Construct a new converter from functions.
     * 
     * This works like {@link Converter#of(Class, Class, Function, Function)},
     * except that both conversion {@link Function}s are decorated with a
     * function that always returns null for null
     * inputs.
     * 

     * Example:
     * 

     * 
     * Converter converter =
     *   Converter.ofNullable(String.class, Integer.class, Integer::parseInt, Object::toString);
     *
     * // No exceptions thrown
     * assertNull(converter.from(null));
     * assertNull(converter.to(null));
     * 
     *
     * @param  the database type
     * @param  the user type
     * @param fromType The database type
     * @param toType The user type
     * @param from A function converting from T to U
     * @param to A function converting from U to T
     * @return The converter.
     * @see Converter
     */
    static  Converter ofNullable(
        Class fromType,
        Class toType,
        Function from,
        Function to
    ) {
        return of(
            fromType,
            toType,
            t -> t == null ? null : from.apply(t),
            u -> u == null ? null : to.apply(u)
        );
    }


}