Implement a parser for dates

In order to parse user specified strings containing date and time info
a thread-safe parser is implemented. This is needed for example to
interpret configuration parameters (e.g. gc.pruneexpire where need to
parse strings like "2 weeks ago"). The parser is thread-safe by caching
SimpleDateFormat instances in a ThreadLocal cache.

Native git has a parser called approxidate which is able to interpret a
huge number of formats ("1 year ago", "tea time", ...). Ideally JGit
should be able to parse the same strings as native git but for now this
parser understands the following subset:

"now"
"yesterday"
"(x) years|months|weeks|days|hours|minutes|seconds ago"
"yyyy-MM-dd HH:mm:ss Z" (ISO)
"EEE, dd MMM yyyy HH:mm:ss Z" (RFC)
"yyyy-MM-dd"
"yyyy.MM.dd"
"MM/dd/yyyy"
"dd.MM.yyyy"
"EEE MMM dd HH:mm:ss yyyy Z" (DEFAULT)
"EEE MMM dd HH:mm:ss yyyy" (LOCAL)

Change-Id: Iccb66dadb60da13104e73140e53d5e2de068369c

2 files changed, 240 insertions, 2 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/GitDateParser.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/GitDateParser.java
new file mode 100644
index 0000000000..04ef553b05
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/GitDateParser.java
@@ -0,0 +1,233 @@
+/*
+ * Copyright (C) 2012 Christian Halstrick
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - 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.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * 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 OWNER 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.
+ */
+package org.eclipse.jgit.util;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.GregorianCalendar;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Parses strings with time and date specifications into {@link Date}.
+ *
+ * When git needs to parse strings specified by the user this parser can be
+ * used. One example is the parsing of the config parameter gc.pruneexpire. The
+ * parser can handle only subset of what native gits approxidate parser
+ * understands.
+ */
+public class GitDateParser {
+	// Since SimpleDateFormat instances are expensive to instantiate they should
+	// be cached. Since they are also not threadsafe they are cached using
+	// ThreadLocal.
+	private static ThreadLocal<Map<ParseableSimpleDateFormat, SimpleDateFormat>> formatCache = new ThreadLocal<Map<ParseableSimpleDateFormat, SimpleDateFormat>>() {
+		protected Map<ParseableSimpleDateFormat, SimpleDateFormat> initialValue() {
+			return new HashMap<ParseableSimpleDateFormat, SimpleDateFormat>();
+		}
+	};
+
+	// Gets an instance of a SimpleDateFormat. If there is not already an
+	// appropriate instance in the (ThreadLocal) cache the create one and put in
+	// into the cache
+	private static SimpleDateFormat getDateFormat(ParseableSimpleDateFormat f) {
+		Map<ParseableSimpleDateFormat, SimpleDateFormat> map = formatCache
+				.get();
+		SimpleDateFormat dateFormat = map.get(f);
+		if (dateFormat != null)
+			return dateFormat;
+		SimpleDateFormat df = SystemReader.getInstance().getSimpleDateFormat(
+				f.formatStr);
+		map.put(f, df);
+		return df;
+	}
+
+	// An enum of all those formats which this parser can parse with the help of
+	// a SimpleDateFormat. There are other formats (e.g. the relative formats
+	// like "yesterday" or "1 week ago") which this parser can parse but which
+	// are not listed here because they are parsed without the help of a
+	// SimpleDateFormat.
+	enum ParseableSimpleDateFormat {
+		ISO("yyyy-MM-dd HH:mm:ss Z"), //
+		RFC("EEE, dd MMM yyyy HH:mm:ss Z"), //
+		SHORT("yyyy-MM-dd"), //
+		SHORT_WITH_DOTS_REVERSE("dd.MM.yyyy"), //
+		SHORT_WITH_DOTS("yyyy.MM.dd"), //
+		SHORT_WITH_SLASH("MM/dd/yyyy"), //
+		DEFAULT("EEE MMM dd HH:mm:ss yyyy Z"), //
+		LOCAL("EEE MMM dd HH:mm:ss yyyy");
+
+		String formatStr;
+
+		private ParseableSimpleDateFormat(String formatStr) {
+			this.formatStr = formatStr;
+		}
+	}
+
+	/**
+	 * Parses a string into a {@link Date}. Since this parser also supports
+	 * relative formats (e.g. "yesterday") the caller can specify the reference
+	 * date. These types of strings can be parsed:
+	 * <ul>
+	 * <li>"now"</li>
+	 * <li>"yesterday"</li>
+	 * <li>"(x) years|months|weeks|days|hours|minutes|seconds ago"<br>
+	 * Multiple specs can be combined like in "2 weeks 3 days ago". Instead of
+	 * ' ' one can use '.' to seperate the words</li>
+	 * <li>"yyyy-MM-dd HH:mm:ss Z" (ISO)</li>
+	 * <li>"EEE, dd MMM yyyy HH:mm:ss Z" (RFC)</li>
+	 * <li>"yyyy-MM-dd"</li>
+	 * <li>"yyyy.MM.dd"</li>
+	 * <li>"MM/dd/yyyy",</li>
+	 * <li>"dd.MM.yyyy"</li>
+	 * <li>"EEE MMM dd HH:mm:ss yyyy Z" (DEFAULT)</li>
+	 * <li>"EEE MMM dd HH:mm:ss yyyy" (LOCAL)</li>
+	 * </ul>
+	 *
+	 * @param dateStr
+	 *            the string to be parsed
+	 * @param now
+	 *            the base date which is used for the calculation of relative
+	 *            formats. E.g. if baseDate is "25.8.2012" then parsing of the
+	 *            string "1 week ago" would result in a date corresponding to
+	 *            "18.8.2012". This is used when a JGit command calls this
+	 *            parser often but wants a consistent starting point for calls.<br>
+	 *            If set to <code>null</code> then the current time will be used
+	 *            instead.
+	 * @return the parsed {@link Date} or <code>null</code> if this string was
+	 *         not parseable.
+	 */
+	public static Date parse(String dateStr, Calendar now) {
+		dateStr = dateStr.trim();
+		Date ret;
+		ret = parse_relative(dateStr, now);
+		if (ret != null)
+			return ret;
+		for (ParseableSimpleDateFormat f : ParseableSimpleDateFormat.values()) {
+			ret = parse_simple(dateStr, f);
+			if (ret != null)
+				return ret;
+		}
+		return null;
+	}
+
+	// tries to parse a string with the formats supported by SimpleDateFormat
+	private static Date parse_simple(String dateStr, ParseableSimpleDateFormat f) {
+		SimpleDateFormat dateFormat = getDateFormat(f);
+		try {
+			dateFormat.setLenient(false);
+			return dateFormat.parse(dateStr);
+		} catch (ParseException e) {
+			return null;
+		}
+	}
+
+	// tries to parse a string with a relative time specification
+	private static Date parse_relative(String dateStr, Calendar now) {
+		Calendar cal;
+		SystemReader sysRead = SystemReader.getInstance();
+
+		// check for the static words "yesterday" or "now"
+		if ("now".equals(dateStr)) {
+			return ((now == null) ? new Date(sysRead.getCurrentTime()) : now
+					.getTime());
+		}
+
+		if (now == null) {
+			cal = new GregorianCalendar(sysRead.getTimeZone(),
+					sysRead.getLocale());
+			cal.setTimeInMillis(sysRead.getCurrentTime());
+		} else
+			cal = (Calendar) now.clone();
+
+		if ("yesterday".equals(dateStr)) {
+			cal.add(Calendar.DATE, -1);
+			cal.set(Calendar.HOUR_OF_DAY, 0);
+			cal.set(Calendar.MINUTE, 0);
+			cal.set(Calendar.SECOND, 0);
+			cal.set(Calendar.MILLISECOND, 0);
+			cal.set(Calendar.MILLISECOND, 0);
+			return cal.getTime();
+		}
+
+		// parse constructs like "3 days ago", "5.week.2.day.ago"
+		String[] parts = dateStr.split("\\.| ");
+		int partsLength = parts.length;
+		// check we have an odd number of parts (at least 3) and that the last
+		// part is "ago"
+		if (partsLength < 3 || (partsLength & 1) == 0
+				|| !"ago".equals(parts[parts.length - 1]))
+			return null;
+		int number;
+		for (int i = 0; i < parts.length - 2; i += 2) {
+			try {
+				number = Integer.parseInt(parts[i]);
+			} catch (NumberFormatException e) {
+				return null;
+			}
+			if ("year".equals(parts[i + 1]) || "years".equals(parts[i + 1]))
+				cal.add(Calendar.YEAR, -number);
+			else if ("month".equals(parts[i + 1])
+					|| "months".equals(parts[i + 1]))
+				cal.add(Calendar.MONTH, -number);
+			else if ("week".equals(parts[i + 1])
+					|| "weeks".equals(parts[i + 1]))
+				cal.add(Calendar.WEEK_OF_YEAR, -number);
+			else if ("day".equals(parts[i + 1]) || "days".equals(parts[i + 1]))
+				cal.add(Calendar.DATE, -number);
+			else if ("hour".equals(parts[i + 1])
+					|| "hours".equals(parts[i + 1]))
+				cal.add(Calendar.HOUR_OF_DAY, -number);
+			else if ("minute".equals(parts[i + 1])
+					|| "minutes".equals(parts[i + 1]))
+				cal.add(Calendar.MINUTE, -number);
+			else if ("second".equals(parts[i + 1])
+					|| "seconds".equals(parts[i + 1]))
+				cal.add(Calendar.SECOND, -number);
+			else
+				return null;
+		}
+		return cal.getTime();
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java
index 7cddccc292..e9d9953f4d 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java
@@ -68,7 +68,7 @@ import org.eclipse.jgit.storage.file.FileBasedConfig;
  * </p>
  */
 public abstract class SystemReader {
-	private static SystemReader INSTANCE = new SystemReader() {
+	private static SystemReader DEFAULT = new SystemReader() {
 		private volatile String hostname;
 
 		public String getenv(String variable) {
@@ -128,6 +128,8 @@ public abstract class SystemReader {
 		}
 	};
 
+	private static SystemReader INSTANCE = DEFAULT;
+
 	/** @return the live instance to read system properties. */
 	public static SystemReader getInstance() {
 		return INSTANCE;
@@ -138,7 +140,10 @@ public abstract class SystemReader {
 	 *            the new instance to use when accessing properties.
 	 */
 	public static void setInstance(SystemReader newReader) {
-		INSTANCE = newReader;
+		if (newReader == null)
+			INSTANCE = DEFAULT;
+		else
+			INSTANCE = newReader;
 	}
 
 	/**