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package org.scijava.annotations;

import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.HashSet;
import java.util.Set;
import java.util.jar.Attributes.Name;
import java.util.jar.JarFile;
import java.util.jar.Manifest;

import org.scijava.Context;
import org.scijava.util.FileUtils;

/**
 * Helps Eclipse's lack of support for annotation processing in incremental
 * build mode.
 * <p>
 * Eclipse has a very, let's say, "creative" way to interpret the Java
 * specifications when it comes to annotation processing: while Java mandates
 * that annotation processors need to be run after compiling Java classes,
 * Eclipse cops out of that because it poses a challenge to its incremental
 * compilation (and especially to Eclipse's attempt at compiling .class files
 * even from .java sources that contain syntax errors).
 * </p>
 * <p>
 * So we need to do something about this. Our strategy is to detect when the
 * annotation index was not updated properly and just do it ourselves, whenever
 * {@link Index#load(Class)} is called.
 * </p>
 * <p>
 * Since our aim here is to compensate for Eclipse's shortcoming, we need only
 * care about the scenario where the developer launches either a Java main class
 * or a unit test from within Eclipse, and even then only when the annotation
 * index is to be accessed.
 * </p>
 * <p>
 * The way Eclipse launches Java main classes or unit tests, it makes a single
 * {@link URLClassLoader} with all the necessary class path elements. Crucially,
 * the class path elements corresponding to Eclipse projects will never point to
 * {@code .jar} files but to directories. This allows us to assume that the
 * annotation classes as well as the annotated classes can be loaded using that
 * exact class loader, too.
 * </p>
 * <p>
 * It is quite possible that a developer may launch a main class in a different
 * project than the one which needs annotation indexing, therefore we need to
 * inspect all class path elements.
 * </p>
 * <p>
 * To provide at least a semblance of a performant component, before going all
 * out and indexing the annotations, we verify that the {@code META-INF/json/}
 * directory has an outdated timestamp relative to the {@code .class} files. If
 * that is not the case, we may safely assume that the annotation indexes are
 * up-to-date.
 * </p>
 * <p>
 * To avoid indexing class path elements over and over again which simply do not
 * contain indexable annotations, we make the {@code META-INF/json/} directory
 * nevertheless, updating the timestamp to reflect that we indexed the
 * annotations.
 * </p>
 * 
 * @author Johannes Schindelin
 */
public class EclipseHelper extends DirectoryIndexer {

	private static final String FORCE_ANNOTATION_INDEX_PROPERTY = "force.annotation.index";
	static Set<URL> indexed = new HashSet<>();
	private boolean bannerShown;

	private static boolean debug =
		"debug".equals(System.getProperty("scijava.log.level"));
	private boolean autoDetectEclipse = true;

	private static void debug(final String message) {
		if (debug) {
			System.err.println(message);
		}
	}

	/**
	 * Updates the annotation index in the current Eclipse project.
	 * <p>
	 * The assumption is that Eclipse -- after failing to run the annotation
	 * processors correctly -- will launch any tests or main classes with a class
	 * path that contains the project's output directory with the {@code .class}
	 * files (as opposed to a {@code .jar} file). We only need to update that
	 * first class path element (or for tests, the first two), and only if it is a
	 * local directory.
	 * </p>
	 * 
	 * @param loader the class loader whose class path to inspect
	 */
	public static void updateAnnotationIndex(final ClassLoader loader) {
		debug("Checking class loader: " + loader);
		if (loader == null ||
			!(loader instanceof URLClassLoader))
		{
			debug("Not an URLClassLoader: " + loader);
			return;
		}
		EclipseHelper helper = new EclipseHelper();
		if (Boolean.getBoolean(FORCE_ANNOTATION_INDEX_PROPERTY)) {
			helper.autoDetectEclipse = false;
		}
		boolean first = true;
		for (final URL url : ((URLClassLoader) loader).getURLs()) {
			debug("Checking URL: " + url);
			if (helper.autoDetectEclipse && first) {
				if (!"file".equals(url.getProtocol()) ||
					(!url.getPath().endsWith("/") && !url.getPath().contains("surefire")))
				{
					debug("Not Eclipse because first entry is: " + url);
					return;
				}
				first = false;
			}
			if (url.toString().endsWith("/./")) {
				// Eclipse never adds "." to the class path
				break;
			}
			helper.maybeIndex(url, loader);
		}
		updateAnnotationIndex(loader.getParent());
	}

	private void maybeIndex(final URL url, final ClassLoader loader) {
		synchronized (indexed) {
			if (indexed.contains(url)) {
				return;
			}
			indexed.add(url);
		}
		if (!"file".equals(url.getProtocol())) {
			debug("Not a file URL: " + url);
			return;
		}
		File file = FileUtils.urlToFile(url);
		if (autoDetectEclipse && !file.isAbsolute()) {
			debug("Not an absolute file URL: " + url);
			return;
		}
		final String name = file.getName();
		if (name.endsWith(".jar")) {
			if (!file.isFile()) {
				debug("Not a file: " + file);
				return;
			}
			/*
			 * To support mixed development with Eclipse and Maven, let's handle
			 * the case where Eclipse compiled classes, did not run the annotation
			 * processors, then the developer called "mvn test". In this case, we
			 * have a surefirebooter.jar whose manifest contains the dependencies,
			 * but crucially also the target/classes/ and target/test-classes/
			 * directories which may need to be indexed.
			 */
			if (!autoDetectEclipse || url.toString().matches(".*/target/surefire/surefirebooter[0-9]*\\.jar")) try {
				final JarFile jar = new JarFile(file);
				Manifest manifest = jar.getManifest();
				if (manifest != null) {
					final String classPath =
						manifest.getMainAttributes().getValue(Name.CLASS_PATH);
					if (classPath != null) {
						for (final String element : classPath.split(" +"))
							try {
								maybeIndex(new URL(url, element), loader);
							}
							catch (MalformedURLException e) {
								e.printStackTrace();
							}
					}
				}
			}
			catch (final IOException e) {
				System.err.println("Warning: could not index annotations due to ");
				e.printStackTrace();
			}
			return;
		}
		if (!file.isDirectory()) {
			return;
		}
		index(file, loader);
	}

	private void index(File directory, ClassLoader loader) {
		debug("Directory: " + directory);
		if (!directory.canWrite() || upToDate(directory) || isIJ1(directory)) {
			debug("can write: " + directory.canWrite() + ", up-to-date: " +
				upToDate(directory) + ", : is IJ1: " + isIJ1(directory));
			return;
		}
		final File jsonDirectory = new File(directory, Index.INDEX_PREFIX);
		try {
			discoverAnnotations(directory, "", loader);
			if (!jsonDirectory.exists() && !foundAnnotations()) return;
			if (!bannerShown) {
				System.err.println("[ECLIPSE HELPER] Indexing annotations...");
				bannerShown = true;
			}
			write(directory);
		}
		catch (IOException e) {
			e.printStackTrace();
		}
		// update the timestamp of META-INF/json/
		if (jsonDirectory.isDirectory()) {
			jsonDirectory.setLastModified(System.currentTimeMillis());
		}
		else {
			jsonDirectory.mkdirs();
		}
	}

	/**
	 * A hacky way of detecting whether the given directory is the root of an
	 * ImageJ1 codebase containing unpacked ImageJ1 classes.
	 */
	private boolean isIJ1(File directory) {
		return new File(directory, "IJ_Props.txt").exists();
	}

	private boolean upToDate(final File directory) {
		final File jsonDirectory = new File(directory, Index.INDEX_PREFIX);
		if (!jsonDirectory.isDirectory()) {
			return false;
		}
		return upToDate(directory, jsonDirectory.lastModified());
	}

	private boolean upToDate(File directory, long lastModified) {
		if (directory.lastModified() > lastModified) {
			return false;
		}
		final File[] list = directory.listFiles();
		if (list != null) {
			for (final File file : list) {
				if (file.isFile()) {
					if (file.lastModified() > lastModified) {
						return false;
					}
				}
				else if (file.isDirectory()) {
					if (!upToDate(file, lastModified)) {
						return false;
					}
				}
			}
		}
		return true;
	}

	/**
	 * Updates the annotation index in the current Eclipse project.
	 * <p>
	 * The assumption is that Eclipse -- after failing to run the annotation
	 * processors correctly -- will launch any tests or main classes with a class
	 * path that contains the project's output directory with the {@code .class}
	 * files (as opposed to a {@code .jar} file). We only need to update that
	 * first class path element (or for tests, the first two), and only if it is a
	 * local directory.
	 * </p>
	 */
	public static void main(final String... args) {
		System.setProperty(FORCE_ANNOTATION_INDEX_PROPERTY, "true");
		updateAnnotationIndex(Context.getClassLoader());
	}

}
