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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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 * 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
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 * 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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package org.scijava.script;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.Writer;

import javax.script.ScriptContext;
import javax.script.ScriptEngine;
import javax.script.ScriptException;

import org.scijava.Context;
import org.scijava.Contextual;
import org.scijava.NullContextException;
import org.scijava.convert.ConvertService;
import org.scijava.log.LogService;
import org.scijava.module.AbstractModule;
import org.scijava.module.Module;
import org.scijava.module.ModuleItem;
import org.scijava.plugin.Parameter;
import org.scijava.script.process.ScriptCallback;

/**
 * A {@link Module} which executes a script.
 * 
 * @author Curtis Rueden
 * @author Johannes Schindelin
 */
public class ScriptModule extends AbstractModule implements Contextual {

	public static final String RETURN_VALUE = "result";

	private final ScriptInfo info;

	@Parameter
	private Context context;

	@Parameter
	private ScriptService scriptService;

	@Parameter
	private ConvertService conversionService;

	@Parameter
	private LogService log;

	/** Script engine with which the script should be executed. */
	private ScriptEngine scriptEngine;

	/** Destination for standard output during script execution. */
	private Writer output;

	/** Destination for standard error during script execution. */
	private Writer error;

	private Object returnValue;

	public ScriptModule(final ScriptInfo info) {
		this.info = info;
	}

	// -- ScriptModule methods --

	/** Sets the writer used to record the standard output stream. */
	public void setOutputWriter(final Writer output) {
		this.output = output;
	}

	/** Sets the writer used to record the standard error stream. */
	public void setErrorWriter(final Writer error) {
		this.error = error;
	}

	/** Gets the script engine used to execute the script. */
	public ScriptEngine getEngine() {
		if (scriptEngine == null) {
			scriptEngine = getInfo().getLanguage().getScriptEngine();
		}
		return scriptEngine;
	}

	/** Gets the return value of the script. */
	public Object getReturnValue() {
		return returnValue;
	}

	// -- Module methods --

	@Override
	public ScriptInfo getInfo() {
		return info;
	}

	// -- Runnable methods --

	@Override
	public void run() {
		final ScriptEngine engine = getEngine();
		final String path = getInfo().getPath();

		// initialize the script engine
		engine.put(ScriptEngine.FILENAME, path);
		engine.put(ScriptModule.class.getName(), this);
		final ScriptContext scriptContext = engine.getContext();
		if (output != null) scriptContext.setWriter(output);
		final PrintWriter errorPrinter;
		if (error != null) {
			scriptContext.setErrorWriter(error);
			errorPrinter = new PrintWriter(error);
		}
		else {
			errorPrinter = null;
		}

		// populate bindings with the input values
		for (final ModuleItem item : getInfo().inputs()) {
			final String name = item.getName();
			engine.put(name, getInput(name));
		}

		returnValue = null;
		try {
			// invoke the callbacks
			for (final ScriptCallback c : getInfo().callbacks()) {
				c.invoke(this);
			}

			// execute script!
			returnValue = engine.eval(getInfo().getProcessedScript());
		}
		catch (Throwable e) {
			while (e instanceof ScriptException && e.getCause() != null) {
				e = e.getCause();
			}
			if (error == null) log.error(e);
			else e.printStackTrace(errorPrinter);
		}

		// populate output values
		final ScriptLanguage language = getInfo().getLanguage();
		for (final ModuleItem item : getInfo().outputs()) {
			final String name = item.getName();
			final Object value;
			if (RETURN_VALUE.equals(name) && getInfo().isReturnValueAppended()) {
				// NB: This is the special implicit return value output!
				value = returnValue;
			}
			else value = engine.get(name);
			final Object decoded = language.decode(value);
			final Object typed = conversionService.convert(decoded, item.getType());
			setOutput(name, typed);
		}

		// flush output and error streams
		if (output != null) {
			try {
				output.flush();
			}
			catch (final IOException e) {
				if (error == null) log.error(e);
				else e.printStackTrace(errorPrinter);
			}
		}
		if (errorPrinter != null) errorPrinter.flush();
	}

	// -- Contextual methods --

	@Override
	public Context context() {
		if (context == null) throw new NullContextException();
		return context;
	}

	@Override
	public Context getContext() {
		return context;
	}

	@Override
	public void setContext(final Context context) {
		context.inject(this);
	}

	// -- Deprecated methods --

	/** @deprecated Use {@link ScriptInfo#getLanguage()} instead. */
	@Deprecated
	public ScriptLanguage getLanguage() {
		return getInfo().getLanguage();
	}

	/** @deprecated Use {@link ScriptInfo#setLanguage(ScriptLanguage)} instead. */
	@Deprecated
	public void setLanguage(final ScriptLanguage scriptLanguage) {
		getInfo().setLanguage(scriptLanguage);
	}
}