/*
 *  Copyright 2001-2009 Stephen Colebourne
 *
 *  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.
 */
package org.joda.time.field;

import java.io.Serializable;
import java.util.HashMap;

import org.joda.time.DurationField;
import org.joda.time.DurationFieldType;

/**
 * A placeholder implementation to use when a duration field is not supported.
 * <p>
 * UnsupportedDurationField is thread-safe and immutable.
 *
 * @author Brian S O'Neill
 * @since 1.0
 */
public final class UnsupportedDurationField extends DurationField implements Serializable {

    /** Serialization lock. */
    private static final long serialVersionUID = -6390301302770925357L;

    /** The cache of unsupported duration field instances */
    private static HashMap<DurationFieldType, UnsupportedDurationField> cCache;

    /**
     * Gets an instance of UnsupportedDurationField for a specific named field.
     * The returned instance is cached.
     * 
     * @param type  the type to obtain
     * @return the instance
     */
    public static synchronized UnsupportedDurationField getInstance(DurationFieldType type) {
        UnsupportedDurationField field;
        if (cCache == null) {
            cCache = new HashMap<DurationFieldType, UnsupportedDurationField>(7);
            field = null;
        } else {
            field = cCache.get(type);
        }
        if (field == null) {
            field = new UnsupportedDurationField(type);
            cCache.put(type, field);
        }
        return field;
    }

    /** The name of the field */
    private final DurationFieldType iType;

    /**
     * Constructor.
     * 
     * @param type  the type to use
     */
    private UnsupportedDurationField(DurationFieldType type) {
        iType = type;
    }

    //-----------------------------------------------------------------------
    // Design note: Simple Accessors return a suitable value, but methods
    // intended to perform calculations throw an UnsupportedOperationException.

    @Override
    public final DurationFieldType getType() {
        return iType;
    }

    @Override
    public String getName() {
        return iType.getName();
    }

    /**
     * This field is not supported.
     *
     * @return false always
     */
    @Override
    public boolean isSupported() {
        return false;
    }

    /**
     * This field is precise.
     * 
     * @return true always
     */
    @Override
    public boolean isPrecise() {
        return true;
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public int getValue(long duration) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public long getValueAsLong(long duration) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public int getValue(long duration, long instant) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public long getValueAsLong(long duration, long instant) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public long getMillis(int value) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public long getMillis(long value) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException as this is not supported
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public long getMillis(int value, long instant) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public long getMillis(long value, long instant) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public long add(long instant, int value) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public long add(long instant, long value) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public int getDifference(long minuendInstant, long subtrahendInstant) {
        throw unsupported();
    }

    /**
     * Always throws UnsupportedOperationException
     *
     * @throws UnsupportedOperationException as this is not supported
     */
    @Override
    public long getDifferenceAsLong(long minuendInstant, long subtrahendInstant) {
        throw unsupported();
    }

    /**
     * Always returns zero.
     *
     * @return zero always
     */
    @Override
    public long getUnitMillis() {
        return 0;
    }

    /**
     * Always returns zero, indicating that sort order is not relevant.
     *
     * @return zero always
     */
    public int compareTo(DurationField durationField) {
        return 0;
    }

    //------------------------------------------------------------------------
    /**
     * Compares this duration field to another.
     * 
     * @param obj  the object to compare to
     * @return true if equal
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        } else if (obj instanceof UnsupportedDurationField) {
            UnsupportedDurationField other = (UnsupportedDurationField) obj;
            if (other.getName() == null) {
                return (getName() == null);
            }
            return (other.getName().equals(getName()));
        }
        return false;
    }

    /**
     * Gets a suitable hashcode.
     * 
     * @return the hashcode
     */
    @Override
    public int hashCode() {
        return getName().hashCode();
    }

    /**
     * Get a suitable debug string.
     * 
     * @return debug string
     */
    @Override
    public String toString() {
        return "UnsupportedDurationField[" + getName() + ']';
    }

    /**
     * Ensure proper singleton serialization
     */
    private Object readResolve() {
        return getInstance(iType);
    }

    private UnsupportedOperationException unsupported() {
        return new UnsupportedOperationException(iType + " field is unsupported");
    }

}
