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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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/*
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 * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
 * Institute of Molecular Cell Biology and Genetics.
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 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
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package org.scijava.script;

import java.io.File;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.script.ScriptEngineFactory;

import org.scijava.log.LogService;
import org.scijava.util.ClassUtils;
import org.scijava.util.FileUtils;

/**
 * Data structure for managing registered scripting languages.
 * 
 * @author Johannes Schindelin
 * @author Curtis Rueden
 */
public class ScriptLanguageIndex extends ArrayList {

	private static final long serialVersionUID = 1L;

	private final Map byExtension =
		new HashMap<>();

	private final Map byName =
		new HashMap<>();

	private final LogService log;

	@Deprecated
	public ScriptLanguageIndex() {
		this(null);
	}

	/**
	 * Instantiates an index of the available script languages.
	 * 
	 * @param log the log service for errors and warnings
	 */
	public ScriptLanguageIndex(final LogService log) {
		this.log = log;
	}

	public boolean add(final ScriptEngineFactory factory, final boolean gently) {
		boolean result = false;

		final ScriptLanguage language = wrap(factory);

		// add language names
		result |= put("name", byName, language.getLanguageName(), language, gently);
		for (final String name : language.getNames()) {
			result |= put("name", byName, name, language, gently);
		}

		// add file extensions
		for (final String extension : language.getExtensions()) {
			if ("".equals(extension)) continue;
			result |= put("extension", byExtension, extension, language, gently);
		}

		result |= super.add(language);
		return result;
	}

	public ScriptLanguage getByExtension(final String extension) {
		return byExtension.get(extension);
	}

	public ScriptLanguage getByName(final String name) {
		return byName.get(name);
	}

	public String[] getFileExtensions(final ScriptLanguage language) {
		final List extensions = language.getExtensions();
		return extensions.toArray(new String[extensions.size()]);
	}

	public boolean canHandleFile(final File file) {
		final String extension = FileUtils.getExtension(file);
		if ("".equals(extension)) return false;
		return byExtension.containsKey(extension);
	}

	public boolean canHandleFile(final String fileName) {
		final String extension = FileUtils.getExtension(fileName);
		if ("".equals(extension)) return false;
		return byExtension.containsKey(extension);
	}

	// -- Collection methods --

	@Override
	public boolean add(final ScriptLanguage language) {
		return add(language, false);
	}

	// -- Helper methods --

	private boolean put(final String type, final Map map,
		final String key, final ScriptLanguage value, final boolean gently)
	{
		final ScriptLanguage existing = map.get(key);

		if (existing == value) {
			// Duplicate key/value pair; do not overwrite.
			if (log != null && log.isDebug()) {
				// In debug mode, warn about the duplicate (since it is atypical).
				log.debug(overwriteMessage(false, type, key, value, existing));
			}
			return false;
		}

		if (existing != null) {
			// Conflicting value; behavior depends on mode.
			if (gently) {
				// Do not overwrite the previous value.
				if (log != null && log.isWarn()) {
					log.warn(overwriteMessage(false, type, key, value, existing));
				}
				return false;
			}
			if (log != null && log.isDebug()) {
				// In debug mode, warn about overwriting.
				log.debug(overwriteMessage(true, type, key, value, existing));
			}
		}

		map.put(key, value);
		return true;
	}

	/** Helper method of {@link #add(ScriptEngineFactory, boolean)}. */
	private ScriptLanguage wrap(final ScriptEngineFactory factory) {
		if (factory instanceof ScriptLanguage) return (ScriptLanguage) factory;
		return new AdaptedScriptLanguage(factory);
	}

	/** Helper method of {@link #put}. */
	private String overwriteMessage(final boolean overwrite, final String type,
		final String key, final ScriptLanguage proposed,
		final ScriptLanguage existing)
	{
		return (overwrite ? "Overwriting " : "Not overwriting ") + //
			type + " '" + key + "':\n" + //
			"\tproposed = " + details(proposed) + "\n" +
			"\texisting = " + details(existing);
	}

	/** Helper method of {@link #overwriteMessage}. */
	private String details(final ScriptLanguage language) {
		final Class c = language.getClass();
		return c.getName() + " [" + ClassUtils.getLocation(c);
	}
}