Dépôt officiel du code source de l'ERP OpenConcerto

/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.

 *

 * Copyright 2011 OpenConcerto, by ILM Informatique. All rights reserved.

 *

 * The contents of this file are subject to the terms of the GNU General Public License Version 3

 * only ("GPL"). You may not use this file except in compliance with the License. You can obtain a

 * copy of the License at http://www.gnu.org/licenses/gpl-3.0.html See the License for the specific

 * language governing permissions and limitations under the License.

 *

 * When distributing the software, include this License Header Notice in each file.

 */

 package org.openconcerto.utils;

import org.openconcerto.utils.cc.I2ExnFactory;

import java.util.Map;

import java.util.function.Supplier;

/**

 * Null can be ambiguous, e.g. {@link Map#get(Object)}. This class allows to avoid the problem.

 *

 * @author Sylvain

 * @param <V> type of value.

 */

public abstract class Value<V> {

    @SuppressWarnings("rawtypes")

    static private final Value NONE = new Value(false) {

        @Override

        public Object getValue() {

            throw new IllegalStateException(this.toString());

        }

        @Override

        public String toString() {

            return "No Value";

        }

    };

    /**

     * I.e. {@link Map#containsKey(Object)} is <code>false</code>.

     *

     * @return the no value instance, i.e. {@link Value#hasValue()} <code>false</code>.

     */

    @SuppressWarnings("unchecked")

    public static <V> Value<V> getNone() {

        return NONE;

    }

    @SuppressWarnings("rawtypes")

    static private final Value NULL_VALUE = new Value.Some<>(null);

    /**

     * Return an instance with a <code>null</code> value.

     *

     * @return the <code>null</code> {@link #getValue() value} instance, i.e.

     *         {@link Value#hasValue()} <code>true</code>.

     */

    @SuppressWarnings("unchecked")

    public static <V> Value<V> getNullValue() {

        return NULL_VALUE;

    }

    static private final class Some<V> extends Value<V> {

        private final V val;

        public Some(final V val) {

            super(true);

            this.val = val;

        }

        @Override

        public V getValue() {

            return this.val;

        }

        @Override

        public String toString() {

            return "Value <" + this.getValue() + '>';

        }

        @Override

        public int hashCode() {

            final int prime = 31;

            int result = super.hashCode();

            result = prime * result + ((this.val == null) ? 0 : this.val.hashCode());

            return result;

        }

        @Override

        public boolean equals(Object obj) {

            if (this == obj)

                return true;

            if (!super.equals(obj))

                return false;

            final Some<?> other = (Some<?>) obj;

            return CompareUtils.equals(this.val, other.val);

        }

    };

    /**

     * I.e. {@link Map#containsKey(Object)} is <code>true</code>.

     *

     * @param value e.g. the value contained in the Map, possibly <code>null</code>.

     * @return a instance with {@link #hasValue()} <code>true</code>.

     */

    public static <V> Value<V> getSome(final V value) {

        // less memory

        return value == null ? Value.<V> getNullValue() : new Value.Some<V>(value);

    }

    public static final boolean hasValue(final Value<?> v) {

        return v != null && v.hasValue();

    }

    /**

     * Usefull if <code>null</code> value actually means none, i.e. the map cannot contain

     * <code>null</code>.

     *

     * @param value the value.

     * @return {@link #getNone()} if <code>value</code> is <code>null</code>,

     *         {@link #getSome(Object)} otherwise.

     */

    public static <V> Value<V> fromNonNull(final V value) {

        return value == null ? Value.<V> getNone() : getSome(value);

    }

    private final boolean hasValue;

    private Value(boolean hasValue) {

        super();

        this.hasValue = hasValue;

    }

    public final boolean hasValue() {

        return this.hasValue;

    }

    /**

     * Return our value if any.

     *

     * @return our value if this {@link #hasValue()}, can be <code>null</code>.

     * @throws IllegalStateException if not {@link #hasValue()}.

     */

    public abstract V getValue() throws IllegalStateException;

    /**

     * Return the value if {@link #hasValue()}, otherwise the passed one, never throws an exception.

     *

     * @param def the default value.

     * @return either {@link #getValue()} or <code>def</code>.

     */

    public final V getValue(final V def) {

        if (this.hasValue())

            return this.getValue();

        else

            return def;

    }

    public final Value<V> asSome(final V def) {

        if (this.hasValue())

            return this;

        else

            return getSome(def);

    }

    // Same method names as Optional

    public final V orElse(final V def) {

        return this.getValue(def);

    }

    public final V orGet(final Supplier<? extends V> def) {

        if (this.hasValue())

            return this.getValue();

        else

            return def.get();

    }

    public final <X extends Exception, X2 extends Exception> V orThrowingGet(final I2ExnFactory<? extends V, X, X2> def) throws X, X2 {

        if (this.hasValue())

            return this.getValue();

        else

            return def.createChecked();

    }

    /**

     * Return <code>null</code> if and only if this has no value.

     *

     * @return non <code>null</code> {@link #getValue()} if {@link #hasValue()}, otherwise

     *         <code>null</code>.

     * @throws IllegalStateException if {@link #getValue()} is <code>null</code>.

     * @see #fromNonNull(Object)

     */

    public final V toNonNull() throws IllegalStateException {

        if (!this.hasValue())

            return null;

        final V res = this.getValue();

        if (res == null)

            throw new IllegalStateException("Null value");

        return res;

    }

    @SuppressWarnings("unchecked")

    public final <T> Value<T> cast(final Class<T> clazz) {

        if (this.hasValue())

            clazz.cast(this.getValue());

        return (Value<T>) this;

    }

    @Override

    public int hashCode() {

        return this.hasValue ? 1231 : 1237;

    }

    @Override

    public boolean equals(Object obj) {

        if (this == obj)

            return true;

        if (obj == null)

            return false;

        if (getClass() != obj.getClass())

            return false;

        return this.hasValue == ((Value<?>) obj).hasValue;

    }

}