package org.simantics.db.layer0.genericrelation;


/**
 * This class contains utilities related to queries made into Lucene indexes,
 * such as escaping search terms.
 * 
 * @author Tuukka Lehtonen
 */
public class IndexQueries {

	/**
	 * Same as calling {@link #escape(String, boolean, boolean)} with
	 * escapeKeywords set to <code>true</code>.
	 * 
	 * @param s
	 * @param escapeWildcards
	 * @return escaped string
	 */
	public static String escape(String s, boolean escapeWildcards) {
		return escape(s, escapeWildcards, true);
	}

	/**
	 * Returns a String where those characters that QueryParser expects to be
	 * escaped are escaped by a preceding <code>\</code>.
	 * 
	 * Copied from
	 * {@link org.apache.lucene.queryParser.QueryParser#escape(String)} but
	 * disabled escaping of wildcard characters '*' and '?'. Clients must escape
	 * wildcards themselves to allow use of wildcards in queries.
	 * 
	 * @param s
	 *            lucene query to escape
	 * @param escapeWildcards
	 *            <code>true</code> to escape also wildcard characters
	 * @param escapeKeywords
	 *            <code>true</code> to escape keywords like AND, OR, etc.
	 * @return escaped string
	 */
	public static String escape(String s, boolean escapeWildcards, boolean escapeKeywords) {
		if (!needsEscaping(s, escapeWildcards, escapeKeywords))
			return s;

		StringBuilder sb = new StringBuilder(s.length() + 8);
		int len = s.length();
		// The beginning of the line is the same as the last character being
		// whitespace.
		boolean lastWhitespace = true;
		for (int i = 0; i < len;) {
			char c = s.charAt(i);
			// These characters are part of the query syntax and must be escaped
			if (c == '\\' || c == '+' || c == '-' || c == '!' || c == '(' || c == ')' || c == ':'
					|| c == '^' || c == '[' || c == ']' || c == '\"' || c == '{' || c == '}' || c == '~'
					|| c == '|' || c == '&' || c == '/' || (escapeWildcards && (c == '*' || c == '?'))) {
				sb.append('\\');
				sb.append(c);
				lastWhitespace = false;
			} else if (Character.isWhitespace(c)) {
				sb.append(c);
				lastWhitespace = true;
			} else {
				if (escapeKeywords && lastWhitespace) {
					int reslen = processReservedWords(s, i, sb);
					if (reslen > 0) {
						i += reslen;
						lastWhitespace = false;
						continue;
					}
				}
				sb.append(c);
				lastWhitespace = false;
			}
			++i;
		}
		return sb.toString();
	}

	/**
	 * Same logic as in {@link #escape(String, boolean, boolean)} but this one
	 * simply checks whether the input string needs escaping at all or not.
	 * 
	 * @param s
	 * @param escapeWildcards
	 * @param escapeKeywords
	 * @return
	 */
	private static boolean needsEscaping(String s, boolean escapeWildcards, boolean escapeKeywords) {
		int len = s.length();
		// The beginning of the line is the same as the last character being
		// whitespace.
		boolean lastWhitespace = true;
		for (int i = 0; i < len;) {
			char c = s.charAt(i);
			// These characters are part of the query syntax and must be escaped
			if (c == '\\' || c == '+' || c == '-' || c == '!' || c == '(' || c == ')' || c == ':'
					|| c == '^' || c == '[' || c == ']' || c == '\"' || c == '{' || c == '}' || c == '~'
					|| c == '|' || c == '&' || c == '/' || (escapeWildcards && (c == '*' || c == '?'))) {
				return true;
			} else if (Character.isWhitespace(c)) {
				lastWhitespace = true;
			} else {
				if (escapeKeywords && lastWhitespace) {
					int reslen = processReservedWords(s, i, null);
					if (reslen > 0)
						return true;
				}
				lastWhitespace = false;
			}
			++i;
		}
		return false;
	}

	private static final String[] RESERVED_WORDS = {
		"AND", "and",
		"OR", "or"
	};

	/**
	 * Lucene reserved words are case-sensitive for its query parser. Therefore
	 * only case-sensitive hits need to be looked for.
	 * 
	 * @param s
	 * @param fromIndex
	 * @return length of the reserved word in the input or 0 if no reserved word
	 *         in the input
	 */
	private static int processReservedWords(String s, int fromIndex, StringBuilder sb) {
		final int total = RESERVED_WORDS.length;
		for (int w = 0; w < total; w += 2) {
			String word = RESERVED_WORDS[w];
			int len = word.length();
			if (s.regionMatches(false, fromIndex, word, 0, len)) {
				if (sb != null) {
					String replacement = RESERVED_WORDS[w+1];
					sb.append(replacement);
				}
				return len;
			}
		}
		return 0;
	}

	/**
	 * Returns a String where those characters that QueryParser expects to be
	 * escaped are escaped by a preceding <code>\</code>.
	 */
	public static String escape(String s) {
		return escape(s, false);
	}

	public static StringBuilder escapeTerm(String field, String term, boolean escapeWildcards, StringBuilder result) {
		if (field != null)
			result.append(field).append(':');
		result.append( escape(term, escapeWildcards) );
		return result;
	}

	public static String escapeTerm(String field, String term, boolean escapeWildcards) {
		StringBuilder sb = new StringBuilder();
		return escapeTerm(field, term, escapeWildcards, sb).toString();
	}

//	public static void main(String[] args) {
//		System.out.println("esc: " + escape("AND01", true, true));
//		System.out.println("esc: " + escape("AND 01", true, true));
//		System.out.println("esc: " + escape(" AND 01", true, true));
//	}

}