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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.

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/*
 * #%L
 * SciJava Common shared library for SciJava software.
 * %%
 * Copyright (C) 2009 - 2016 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
 * Institute of Molecular Cell Biology and Genetics.
 * %%
 * 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
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * #L%
 */

package org.scijava.annotations;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;

import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.Filer;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.AnnotationMirror;
import javax.lang.model.element.AnnotationValue;
import javax.lang.model.element.Element;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.Name;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.type.TypeMirror;
import javax.lang.model.util.Elements;
import javax.lang.model.util.Types;
import javax.tools.Diagnostic.Kind;
import javax.tools.FileObject;
import javax.tools.StandardLocation;

import org.scijava.annotations.AbstractIndexWriter.StreamFactory;

/**
 * The annotation processor for use with Java 6 and above.
 * 
 * @author Johannes Schindelin
 */
@SupportedSourceVersion(SourceVersion.RELEASE_6)
@SupportedAnnotationTypes("*")
public class AnnotationProcessor extends AbstractProcessor {

	private RoundEnvironment roundEnv;

	@Override
	public boolean process(final Set elements,
		final RoundEnvironment env)
	{
		roundEnv = env;

		final Writer writer = new Writer();
		for (final TypeElement element : elements) {
			writer.add(element);
		}
		try {
			writer.write(writer);
		}
		catch (final IOException e) {
			final ByteArrayOutputStream out = new ByteArrayOutputStream();
			e.printStackTrace(new PrintStream(out));
			try {
				out.close();
				processingEnv.getMessager().printMessage(Kind.ERROR, out.toString());
			}
			catch (final IOException e2) {
				processingEnv.getMessager().printMessage(Kind.ERROR,
					e2.getMessage() + " while printing " + e.getMessage());
			}
		}
		return false;
	}

	private class Writer extends AbstractIndexWriter implements StreamFactory {

		private final Map> originatingElements =
			new HashMap<>();
		private final Filer filer = processingEnv.getFiler();
		private final Elements utils = processingEnv.getElementUtils();
		private final Types typeUtils = processingEnv.getTypeUtils();

		public void add(final TypeElement element) {
			final AnnotationMirror mirror = getMirror(element);
			if (mirror != null) {
				final String annotationName = utils.getBinaryName(element).toString();

				// remember originating elements
				List originating = originatingElements.get(annotationName);
				if (originating == null) {
					originating = new ArrayList<>();
					originatingElements.put(annotationName, originating);
				}

				for (final Element annotated : roundEnv
					.getElementsAnnotatedWith(element))
				{
					switch (annotated.getKind()) {
						case ANNOTATION_TYPE:
						case CLASS:
						case ENUM:
						case INTERFACE:
							final String className =
								utils.getBinaryName((TypeElement) annotated).toString();
							final Map values =
								adapt(annotated.getAnnotationMirrors(), element.asType());
							super.add(values, annotationName, className);
							originating.add(annotated);
							break;
						default:
							processingEnv.getMessager().printMessage(
								Kind.ERROR,
								"Cannot handle annotated element of kind " +
									annotated.getKind());
					}
				}
			}
			//
		}

		@SuppressWarnings("unchecked")
		private Map adapt(
			final List mirrors,
			final TypeMirror annotationType)
		{
			final Map result = new TreeMap<>();
			for (final AnnotationMirror mirror : mirrors) {
				if (typeUtils.isSameType(mirror.getAnnotationType(), annotationType)) {
					return (Map) adapt(mirror);
				}
			}
			return result;
		}

		@Override
		protected Object adapt(final Object o) {
			if (o instanceof AnnotationMirror) {
				final AnnotationMirror mirror = (AnnotationMirror) o;
				final Map result = new TreeMap<>();
				for (final Entry entry : mirror
					.getElementValues().entrySet())
				{
					final String key = entry.getKey().getSimpleName().toString();
					final Object value = adapt(entry.getValue().getValue());
					result.put(key, value);
				}
				return result;
			}
			else if (o instanceof List) {
				final List list = (List) o;
				final List result = new ArrayList<>(list.size());
				for (final Object item : list) {
					result.add(adapt(item));
				}
				return result;
			}
			else if (o instanceof TypeMirror) {
				final TypeMirror mirror = (TypeMirror) o;
				return utils.getBinaryName((TypeElement) typeUtils.asElement(mirror))
					.toString();
			}
			else if (o instanceof VariableElement) {
				final VariableElement element = (VariableElement) o;
				final Map result = new TreeMap<>();
				final String enumName =
					utils.getBinaryName((TypeElement) element.getEnclosingElement())
						.toString();
				final String valueName = element.getSimpleName().toString();
				result.put("enum", enumName);
				result.put("value", valueName);
				return result;
			}
			else {
				return super.adapt(o);
			}
		}

		private AnnotationMirror getMirror(final TypeElement element) {
			for (final AnnotationMirror candidate : utils
				.getAllAnnotationMirrors(element))
			{
				final Name binaryName =
					utils.getBinaryName((TypeElement) candidate.getAnnotationType()
						.asElement());
				if (binaryName.contentEquals(Indexable.class.getName())) {
					return candidate;
				}
			}
			return null;
		}

		@Override
		public InputStream openInput(final String annotationName)
			throws IOException
		{
			try {
				return filer.getResource(StandardLocation.CLASS_OUTPUT, "",
					Index.INDEX_PREFIX + annotationName).openInputStream();
			}
			catch (final FileNotFoundException e) {
				return null;
			}
		}

		@Override
		public OutputStream openOutput(final String annotationName)
			throws IOException
		{
			final List originating = originatingElements.get(annotationName);
			final String path = Index.INDEX_PREFIX + annotationName;
			final FileObject fileObject =
				filer.createResource(StandardLocation.CLASS_OUTPUT, "", path,
					originating.toArray(new Element[originating.size()]));

			// Verify that the generated file is in the META-INF/json/ subdirectory;
			// Despite our asking for it explicitly, the DefaultFileManager will
			// strip out the directory if javac was called without an explicit
			// output directory (i.e. without -d option).
			final String uri = fileObject.toUri().toString();
			if (uri != null && uri.endsWith("/" + path)) {
				return fileObject.openOutputStream();
			}
			final String prefix =
				uri == null ? "" : uri.substring(0, uri.length() -
					annotationName.length());
			final File file = new File(prefix + path);
			final File parent = file.getParentFile();
			if (parent != null && !parent.isDirectory() && !parent.mkdirs()) {
				throw new IOException("Could not create directory: " + parent);
			}
			return new FileOutputStream(file);
		}

		@Override
		public boolean isClassObsolete(final String className) {
			return false;
		}

	}
}