/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.table.codegen.util;

/**
 * Utilities for converting SQL {@code LIKE} and {@code SIMILAR} operators
 * to regular expressions.
 *
 * <p>Copy to Flink from Calcite is to expose some private method.
 */
public class FlinkLike {
	private static final String JAVA_REGEX_SPECIALS = "[]()|^-+*?{}$\\";
	private static final String SQL_SIMILAR_SPECIALS = "[]()|^-+*_%?{}";
	private static final String[] REG_CHAR_CLASSES = {
			"[:ALPHA:]", "\\p{Alpha}",
			"[:alpha:]", "\\p{Alpha}",
			"[:UPPER:]", "\\p{Upper}",
			"[:upper:]", "\\p{Upper}",
			"[:LOWER:]", "\\p{Lower}",
			"[:lower:]", "\\p{Lower}",
			"[:DIGIT:]", "\\d",
			"[:digit:]", "\\d",
			"[:SPACE:]", " ",
			"[:space:]", " ",
			"[:WHITESPACE:]", "\\s",
			"[:whitespace:]", "\\s",
			"[:ALNUM:]", "\\p{Alnum}",
			"[:alnum:]", "\\p{Alnum}"
	};

	private FlinkLike() {
	}

	/**
	 * Translates a SQL LIKE pattern to Java regex pattern, with optional
	 * escape string.
	 */
	public static String sqlToRegexLike(
			String sqlPattern,
			CharSequence escapeStr) {
		final char escapeChar;
		if (escapeStr != null) {
			if (escapeStr.length() != 1) {
				throw invalidEscapeCharacter(escapeStr.toString());
			}
			escapeChar = escapeStr.charAt(0);
		} else {
			escapeChar = 0;
		}
		return sqlToRegexLike(sqlPattern, escapeChar);
	}

	/**
	 * Translates a SQL LIKE pattern to Java regex pattern.
	 */
	static String sqlToRegexLike(
			String sqlPattern,
			char escapeChar) {
		int i;
		final int len = sqlPattern.length();
		final StringBuilder javaPattern = new StringBuilder(len + len);
		for (i = 0; i < len; i++) {
			char c = sqlPattern.charAt(i);
			if (JAVA_REGEX_SPECIALS.indexOf(c) >= 0) {
				javaPattern.append('\\');
			}
			if (c == escapeChar) {
				if (i == (sqlPattern.length() - 1)) {
					throw invalidEscapeSequence(sqlPattern, i);
				}
				char nextChar = sqlPattern.charAt(i + 1);
				if ((nextChar == '_')
						|| (nextChar == '%')
						|| (nextChar == escapeChar)) {
					javaPattern.append(nextChar);
					i++;
				} else {
					throw invalidEscapeSequence(sqlPattern, i);
				}
			} else if (c == '_') {
				javaPattern.append('.');
			} else if (c == '%') {
				javaPattern.append("(?s:.*)");
			} else {
				javaPattern.append(c);
			}
		}
		return javaPattern.toString();
	}

	public static RuntimeException invalidEscapeCharacter(String s) {
		return new RuntimeException(
				"Invalid escape character '" + s + "'");
	}

	public static RuntimeException invalidEscapeSequence(String s, int i) {
		return new RuntimeException(
				"Invalid escape sequence '" + s + "', " + i);
	}

	private static void similarEscapeRuleChecking(
			String sqlPattern,
			char escapeChar) {
		if (escapeChar == 0) {
			return;
		}
		if (SQL_SIMILAR_SPECIALS.indexOf(escapeChar) >= 0) {
			// The the escape character is a special character
			// SQL 2003 Part 2 Section 8.6 General Rule 3.b
			for (int i = 0; i < sqlPattern.length(); i++) {
				if (sqlPattern.charAt(i) == escapeChar) {
					if (i == (sqlPattern.length() - 1)) {
						throw invalidEscapeSequence(sqlPattern, i);
					}
					char c = sqlPattern.charAt(i + 1);
					if ((SQL_SIMILAR_SPECIALS.indexOf(c) < 0)
							&& (c != escapeChar)) {
						throw invalidEscapeSequence(sqlPattern, i);
					}
				}
			}
		}

		// SQL 2003 Part 2 Section 8.6 General Rule 3.c
		if (escapeChar == ':') {
			int position;
			position = sqlPattern.indexOf("[:");
			if (position >= 0) {
				position = sqlPattern.indexOf(":]");
			}
			if (position < 0) {
				throw invalidEscapeSequence(sqlPattern, position);
			}
		}
	}

	private static RuntimeException invalidRegularExpression(
			String pattern, int i) {
		return new RuntimeException(
				"Invalid regular expression '" + pattern + "'");
	}

	private static int sqlSimilarRewriteCharEnumeration(
			String sqlPattern,
			StringBuilder javaPattern,
			int pos,
			char escapeChar) {
		int i;
		for (i = pos + 1; i < sqlPattern.length(); i++) {
			char c = sqlPattern.charAt(i);
			if (c == ']') {
				return i - 1;
			} else if (c == escapeChar) {
				i++;
				char nextChar = sqlPattern.charAt(i);
				if (SQL_SIMILAR_SPECIALS.indexOf(nextChar) >= 0) {
					if (JAVA_REGEX_SPECIALS.indexOf(nextChar) >= 0) {
						javaPattern.append('\\');
					}
					javaPattern.append(nextChar);
				} else if (escapeChar == nextChar) {
					javaPattern.append(nextChar);
				} else {
					throw invalidRegularExpression(sqlPattern, i);
				}
			} else if (c == '-') {
				javaPattern.append('-');
			} else if (c == '^') {
				javaPattern.append('^');
			} else if (sqlPattern.startsWith("[:", i)) {
				int numOfRegCharSets = REG_CHAR_CLASSES.length / 2;
				boolean found = false;
				for (int j = 0; j < numOfRegCharSets; j++) {
					if (sqlPattern.startsWith(REG_CHAR_CLASSES[j + j], i)) {
						javaPattern.append(REG_CHAR_CLASSES[j + j + 1]);

						i += REG_CHAR_CLASSES[j + j].length() - 1;
						found = true;
						break;
					}
				}
				if (!found) {
					throw invalidRegularExpression(sqlPattern, i);
				}
			} else if (SQL_SIMILAR_SPECIALS.indexOf(c) >= 0) {
				throw invalidRegularExpression(sqlPattern, i);
			} else {
				javaPattern.append(c);
			}
		}
		return i - 1;
	}

	/**
	 * Translates a SQL SIMILAR pattern to Java regex pattern, with optional
	 * escape string.
	 */
	static String sqlToRegexSimilar(
			String sqlPattern,
			CharSequence escapeStr) {
		final char escapeChar;
		if (escapeStr != null) {
			if (escapeStr.length() != 1) {
				throw invalidEscapeCharacter(escapeStr.toString());
			}
			escapeChar = escapeStr.charAt(0);
		} else {
			escapeChar = 0;
		}
		return sqlToRegexSimilar(sqlPattern, escapeChar);
	}

	/**
	 * Translates SQL SIMILAR pattern to Java regex pattern.
	 */
	static String sqlToRegexSimilar(
			String sqlPattern,
			char escapeChar) {
		similarEscapeRuleChecking(sqlPattern, escapeChar);

		boolean insideCharacterEnumeration = false;
		final StringBuilder javaPattern =
				new StringBuilder(sqlPattern.length() * 2);
		final int len = sqlPattern.length();
		for (int i = 0; i < len; i++) {
			char c = sqlPattern.charAt(i);
			if (c == escapeChar) {
				if (i == (len - 1)) {
					// It should never reach here after the escape rule
					// checking.
					throw invalidEscapeSequence(sqlPattern, i);
				}
				char nextChar = sqlPattern.charAt(i + 1);
				if (SQL_SIMILAR_SPECIALS.indexOf(nextChar) >= 0) {
					// special character, use \ to replace the escape char.
					if (JAVA_REGEX_SPECIALS.indexOf(nextChar) >= 0) {
						javaPattern.append('\\');
					}
					javaPattern.append(nextChar);
				} else if (nextChar == escapeChar) {
					javaPattern.append(nextChar);
				} else {
					// It should never reach here after the escape rule
					// checking.
					throw invalidEscapeSequence(sqlPattern, i);
				}
				i++; // we already process the next char.
			} else {
				switch (c) {
					case '_':
						javaPattern.append('.');
						break;
					case '%':
						javaPattern.append("(?s:.*)");
						break;
					case '[':
						javaPattern.append('[');
						insideCharacterEnumeration = true;
						i = sqlSimilarRewriteCharEnumeration(
								sqlPattern,
								javaPattern,
								i,
								escapeChar);
						break;
					case ']':
						if (!insideCharacterEnumeration) {
							throw invalidRegularExpression(sqlPattern, i);
						}
						insideCharacterEnumeration = false;
						javaPattern.append(']');
						break;
					case '\\':
						javaPattern.append("\\\\");
						break;
					case '$':

						// $ is special character in java regex, but regular in
						// SQL regex.
						javaPattern.append("\\$");
						break;
					default:
						javaPattern.append(c);
				}
			}
		}
		if (insideCharacterEnumeration) {
			throw invalidRegularExpression(sqlPattern, len);
		}

		return javaPattern.toString();
	}
}