Add the UI-agnostic part of the script interpreters

The newly-introduced ScriptInterpreter class provides all the
functionality of a script interpreter sans the graphical user interface.
It can execute statements and persists a history of most recently
executed statements.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

src/main/java/org/scijava/script/DefaultScriptInterpreter.java

@@ -0,0 +1,104 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2014 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.script;
+
+import javax.script.ScriptEngine;
+import javax.script.ScriptException;
+
+import org.scijava.prefs.PrefService;
+
+/**
+ * The default implementation of a {@link ScriptInterpreter}.
+ *  
+ * @author Johannes Schindelin
+ */
+public class DefaultScriptInterpreter implements ScriptInterpreter {
+
+	private ScriptEngine engine;
+	private History history;
+	private String currentCommand = "";
+
+	/**
+	 * Constructs a new {@link DefaultScriptInterpreter}.
+	 * 
+	 * @param scriptService the script service
+	 * @param engine the script engine
+	 */
+	public DefaultScriptInterpreter(final PrefService prefs, final ScriptService scriptService, final ScriptEngine engine) {
+		this.engine = engine;
+		history = new History(prefs, engine.getClass().getName());
+		readHistory();
+	}
+
+	@Override
+	public synchronized void readHistory() {
+		if (history == null) return;
+		history.read();
+	}
+
+	@Override
+	public synchronized void writeHistory() {
+		if (history == null) return;
+		history.write();
+	}
+
+	@Override
+	public synchronized String walkHistory(final String currentCommand, boolean forward) {
+		this.currentCommand = currentCommand;
+		if (history == null) return currentCommand;
+		history.replace(currentCommand);
+		return forward ? history.next() : history.previous();
+	}
+
+	/**
+	 * Evaluates a command.
+	 * 
+	 * @param command the command to evaluate
+	 * @throws ScriptException
+	 */
+	@Override
+	public void eval(String command) throws ScriptException {
+		if (history != null) history.add(command);
+		if (engine == null) throw new java.lang.IllegalArgumentException();
+		engine.eval(command);
+	}
+
+	/**
+	 * Returns the current script engine.
+	 * 
+	 * @return
+	 */
+	@Override
+	public ScriptEngine getEngine() {
+		return engine;
+	}
+
+}

src/main/java/org/scijava/script/ScriptInterpreter.java

@@ -0,0 +1,78 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2014 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.script;
+
+import javax.script.ScriptEngine;
+import javax.script.ScriptException;
+
+/**
+ * The contract for script interpreters.
+ * 
+ * @author Johannes Schindelin
+ */
+public interface ScriptInterpreter {
+
+	/**
+	 * Reads the persisted history of the current script interpreter.
+	 */
+	public void readHistory();
+
+	/**
+	 * Persists the history of the current script interpreter.
+	 */
+	public void writeHistory();
+
+	/**
+	 * Obtains the next/previous command in the command history.
+	 * 
+	 * @param currentCommand the current command (will be stored in the history)
+	 * @param forward if true, the next history entry is returned (more recent),
+	 *          if false, the previous one
+	 * @return the next/previous command
+	 */
+	public String walkHistory(final String currentCommand, boolean forward);
+
+	/**
+	 * Evaluates a command.
+	 * 
+	 * @param command the command to evaluate
+	 * @throws ScriptException
+	 */
+	public void eval(String command) throws ScriptException;
+
+	/**
+	 * Returns the associated {@link ScriptEngine}
+	 * 
+	 * @return the script engine
+	 */
+	public ScriptEngine getEngine();
+}