Add a history class for the upcoming script interpreters

The newly-introduced History class maintains the history of most recently
executed statements and has functionality to persist and retrieve the list
from the preferences.

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

Author: dscho

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

@@ -0,0 +1,140 @@
+/*
+ * #%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 org.scijava.prefs.PrefService;
+import org.scijava.util.LastRecentlyUsed;
+
+/**
+ * Container for a script language's interpreter history.
+ * 
+ * @author Johannes Schindelin
+ */
+class History {
+
+	protected static final long serialVersionUID = 1L;
+
+	private static final String PREFIX = "History.";
+	private final int MAX_ENTRIES = 1000;
+
+	private final PrefService prefs;
+	private final String name;
+	private final LastRecentlyUsed<String> entries = new LastRecentlyUsed<String>(MAX_ENTRIES);
+	private int position = -1;
+
+	/**
+	 * Constructs a history object for a given scripting language.
+	 * 
+	 * @param name the name of the scripting language
+	 */
+	public History(final PrefService prefs, final String name) {
+		this.prefs = prefs;
+		this.name = name;
+	}
+
+	/**
+	 * Read back a persisted history.
+	 */
+	public void read() {
+		entries.clear();
+		for (final String item : prefs.getIterable(getClass(), PREFIX + name)) {
+			entries.addToEnd(item);
+		};
+	}
+
+	/**
+	 * Persist the history.
+	 * 
+	 * @see {@link Prefs}
+	 */
+	public void write() {
+		prefs.putIterable(getClass(), entries, PREFIX + name);
+	}
+
+	/**
+	 * Adds the most recently issued command.
+	 * 
+	 * @param command the most recent command to add to the history
+	 */
+	public void add(final String command) {
+		entries.add(command);
+		position = -1;
+	}
+
+	public boolean replace(final String currentCommand) {
+		if (position < 0) return false;
+		return entries.replace(position, currentCommand);
+	}
+
+	/**
+	 * Navigates to the next (more recent) command.
+	 * <p>
+	 * This method wraps around, i.e. it returns {@code null} when there is no
+	 * more-recent command in the history.
+	 * </p>
+	 * 
+	 * @return the next command
+	 */
+	public String next() {
+		position = entries.next(position);
+		return position < 0 ? null : entries.get(position);
+	}
+
+	/**
+	 * Navigates to the previous (i.e less recent) command.
+	 * <p>
+	 * This method wraps around, i.e. it returns {@code null} when there is no
+	 * less-recent command in the history.
+	 * </p>
+	 * 
+	 * @return the previous command
+	 */
+	public String previous() {
+		position = entries.previous(position);
+		return position < 0 ? null : entries.get(position);
+	}
+
+	@Override
+	public String toString() {
+		final StringBuilder builder = new StringBuilder();
+		int position = -1;
+		for (;;) {
+			position = entries.previous(position);
+			if (position < 0) break;
+			if (builder.length() > 0) builder.append(" -> ");
+			if (this.position == position) builder.append("[");
+			builder.append(entries.get(position));
+			if (this.position == position) builder.append("]");
+		}
+		return builder.toString();
+	}
+}