/*
 * #%L
 * SciJava Common shared library for SciJava software.
 * %%
 * Copyright (C) 2009 - 2017 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
 * Institute of Molecular Cell Biology and Genetics, University of
 * Konstanz, and KNIME GmbH.
 * %%
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 * POSSIBILITY OF SUCH DAMAGE.
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package org.scijava.convert;

import java.lang.reflect.Type;

import org.scijava.Priority;
import org.scijava.plugin.Plugin;
import org.scijava.util.Types;

/**
 * {@link Converter} implementation for handling {@code null} values. Performs
 * basic casting when given a {@code null} source and returns {@code null}
 * directly when given a {@code null} destination.
 * <p>
 * By running at {@link Priority#FIRST}, other converters should
 * not need to worry about {@code null} source or destination parameters.
 * </p>
 * <p>
 * NB: if a {@link Class} source is queried for the {@link #canConvert},
 * this converter will always return false (as there is no way of knowing
 * if the source object will be null or not).
 * </p>
 *
 * @author Mark Hiner
 */
@Plugin(type = Converter.class, priority = Priority.FIRST)
public class NullConverter extends AbstractConverter<Object, Object> {

	@Override
	public boolean canConvert(final ConversionRequest request) {
		if (request == null) return false;
		return (request.destType() == null && request.destClass() == null) ||
			(request.sourceObject() == null && request.sourceClass() == null);
	}

	@Override
	public boolean canConvert(final Object src, final Type dest) {
		return src == null || dest == null;
	}

	@Override
	public boolean canConvert(final Object src, final Class<?> dest) {
		return src == null || dest == null;
	}

	@Override
	public boolean canConvert(final Class<?> src, final Class<?> dest) {
		if (src == null) return false;
		return dest == null;
	}

	@Override
	public <T> T convert(final Object src, final Class<T> dest) {
		if (dest == null) return null;
		if (src == null) return Types.nullValue(dest);

		throw new IllegalArgumentException("Attempting non-null conversion: " +
			src + " > " + dest + " using NullConverter.");
	}

	@Override
	public Class<Object> getOutputType() {
		return Object.class;
	}

	@Override
	public Class<Object> getInputType() {
		return Object.class;
	}

}
