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package be.unamur.inference.web.apache;

import java.util.Locale;

import org.apache.commons.lang3.time.DateParser;

import com.google.common.base.Splitter;
import com.google.common.collect.ImmutableMap;
import com.google.code.regexp.Matcher;
import com.google.code.regexp.Pattern;

/**
 * This class is used to generate regular expression {@link Pattern}s to parse
 * Apache web log entries. The patterns are built using groups names by the
 * different static Strings declared in this class. The usage of this class is
 * to get the singleton instance using getInstance() method and to call the
 * buildPattern method on this object using one of the constants defining a
 * format: COMMON_LOG_FORMAT, COMBINED_LOG_FORMAT, REQUEST_FORMAT, or
 * DATE_FORMAT. The returned {@link Pattern} is used to match a given string and
 * the resulting {@link Matcher} object may return the different groups of the
 * used pattern using the names defined in the _DIRECTIVE constants (see
 * http://httpd.apache.org/docs/ for the different log formats). Example:
 * 
 *  * {
 * 	@code
 * 	Pattern pattern = getInstance().buildPattern(COMMON_LOG_FORMAT);
 * 	Matcher match = pattern.matcher(logLine);
 * 	String request = match.group(REQUEST_DIRECTIVE);
 * 	String host = match.group(HOST_DIRECTIVE);
 * }
 * 
 * 
 * @author Xavier Devroey - [email protected]
 * 
 */
public class ApacheLogFormatPatternBuilder {

	/**
	 * The host directive group name.
	 */
	public static final String HOST_DIRECTIVE = "h";
	/**
	 * The identity directive group name.
	 */
	public static final String IDENTITY_DIRECTIVE = "l";
	/**
	 * The user directive group name.
	 */
	public static final String USER_DIRECTIVE = "u";
	/**
	 * The time directive group name.
	 */
	public static final String TIME_DIRECTIVE = "t";
	/**
	 * The request directive groupe name.
	 */
	public static final String REQUEST_DIRECTIVE = "r";
	/**
	 * The status code directive group name.
	 */
	public static final String STATUS_CODE_DIRECTIVE = "s";
	/**
	 * The size directive group name.
	 */
	public static final String SIZE_DIRECTIVE = "b";
	/**
	 * The referrer directive group name.
	 */
	public static final String REFERRER_DIRECTIVE = "i";
	/**
	 * The user agent directive group name.
	 */
	public static final String USER_AGENT_DIRECTIVE = "a";

	/**
	 * The request method directive group name.
	 */
	public static final String REQUEST_METHOD_DIRECTIVE = "m";
	/**
	 * The request query path directive group name.
	 */
	public static final String REQUEST_QUERY_PATH_DIRECTIVE = "q";
	/**
	 * The request query parameters directive group name.
	 */
	public static final String REQUEST_QUERY_PARAMETERS_DIRECTIVE = "c";
	/**
	 * The request protocole directive group name.
	 */
	public static final String REQUEST_PROTOCOL_DIRECTIVE = "p";

	/**
	 * The common Apache web log format regular expression.
	 */
	public static final String COMMON_LOG_FORMAT = String.format(
			"%s%s\\ %s%s\\ %s%s\\ %s%s\\ %s%s\\ %s%s\\ %s%s", "%", HOST_DIRECTIVE, "%",
			IDENTITY_DIRECTIVE, "%", USER_DIRECTIVE, "%", TIME_DIRECTIVE, "%",
			REQUEST_DIRECTIVE, "%", STATUS_CODE_DIRECTIVE, "%", SIZE_DIRECTIVE);

	/**
	 * The combined Apache web log format regular expression.
	 */
	public static final String COMBINED_LOG_FORMAT = String.format(
			"%s%s\\ %s%s\\ %s%s\\ %s%s\\ %s%s\\ %s%s\\ %s%s\\ %s%s\\ %s%s", "%",
			HOST_DIRECTIVE, "%", IDENTITY_DIRECTIVE, "%", USER_DIRECTIVE, "%",
			TIME_DIRECTIVE, "%", REQUEST_DIRECTIVE, "%", STATUS_CODE_DIRECTIVE, "%",
			SIZE_DIRECTIVE, "%", REFERRER_DIRECTIVE, "%", USER_AGENT_DIRECTIVE);

	/**
	 * The Apache request format regular expression.
	 */
	public static final String REQUEST_FORMAT = String.format(
			"%s%s\\ %s%s(\\?%s%s)?\\ %s%s", "%", REQUEST_METHOD_DIRECTIVE, "%",
			REQUEST_QUERY_PATH_DIRECTIVE, "%", REQUEST_QUERY_PARAMETERS_DIRECTIVE, "%",
			REQUEST_PROTOCOL_DIRECTIVE, "%");

	/**
	 * Date format used in Apache logs.
	 */
	public static final String DATE_FORMAT = "dd/MMM/yyyy:hh:mm:ss Z";

	/**
	 * The {@link Locale} value used in the dates of the log. This value has to
	 * be provided to {@link DateParser} objects.
	 */
	public static final Locale DATE_LOCALE = Locale.ENGLISH;

	/**
	 * The instance of this singleton class.
	 */
	private static ApacheLogFormatPatternBuilder instance;

	/**
	 * Return the instance of this singleton class.
	 */
	public static ApacheLogFormatPatternBuilder getInstance() {
		return instance == null ? instance = new ApacheLogFormatPatternBuilder()
				: instance;
	}

	/**
	 * The dirrecrives and their regular expressions.
	 */
	private final ImmutableMap directives = new ImmutableMap.Builder()
			.put(HOST_DIRECTIVE,
					"(?<"
							+ HOST_DIRECTIVE
							+ ">([0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+)|(([0-9a-z-A-Z\\-]+.)*[0-9a-z-A-Z\\-]+))")
			.put(IDENTITY_DIRECTIVE,
					"(?<" + IDENTITY_DIRECTIVE + ">(\\-)|([a-zA-Z0-9\\-\\_\\.]+))")
			.put(USER_DIRECTIVE,
					"(?<" + USER_DIRECTIVE + ">(\\-)|(\\\"\\\")|([a-zA-Z0-9\\-\\_\\.]+))")
			.put(TIME_DIRECTIVE,
					"(?<"
							+ TIME_DIRECTIVE
							+ ">\\[\\d{2}/[A-Za-z]{3}/\\d{4}:\\d{2}:\\d{2}:\\d{2} (\\+|\\-)\\d{4}\\])")
			.put(REQUEST_DIRECTIVE, "(?<" + REQUEST_DIRECTIVE + ">\\\"[^\\\"]*\\\")")
			.put(STATUS_CODE_DIRECTIVE, "(?<" + STATUS_CODE_DIRECTIVE + ">\\d\\d\\d)")
			.put(SIZE_DIRECTIVE, "(?<" + SIZE_DIRECTIVE + ">(\\d+)|(\\-))")
			.put(REFERRER_DIRECTIVE, "(?<" + REFERRER_DIRECTIVE + ">\\\"[^\\\"]*\\\")")
			.put(USER_AGENT_DIRECTIVE,
					"(?<" + USER_AGENT_DIRECTIVE + ">\\\"[^\\\"]*\\\")")
			.put(REQUEST_METHOD_DIRECTIVE,
					"(?<" + REQUEST_METHOD_DIRECTIVE + ">HEAD|POST|GET)")
			.put(REQUEST_QUERY_PATH_DIRECTIVE,
					"(?<" + REQUEST_QUERY_PATH_DIRECTIVE + ">[^ \\t\\?]+)")
			.put(REQUEST_QUERY_PARAMETERS_DIRECTIVE,
					"(?<" + REQUEST_QUERY_PARAMETERS_DIRECTIVE + ">[^ \\t]*)")
			.put(REQUEST_PROTOCOL_DIRECTIVE,
					"(?<" + REQUEST_PROTOCOL_DIRECTIVE + ">[^ \\t]+)").build();

	private ApacheLogFormatPatternBuilder() {
	}

	/**
	 * Return a pattern corresponding to the given regular expression string.
	 * 
	 * @param format The format of the regular expression.
	 * @return A {@link Pattern} corresponding tot the given regular expression
	 *         string.
	 */
	public Pattern buildPattern(String format) {
		StringBuffer buff = new StringBuffer();
		char directive;
		String element;
		for (String str : Splitter.on('%').omitEmptyStrings().split(format)) {
			directive = str.charAt(0);
			element = str.replace(Character.toString(directive),
					directives.get(Character.toString(directive)));
			buff.append(element);
		}
		return Pattern.compile(buff.toString());
	}

}