/*
 *  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 groovy.json;

import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.util.Locale;

/**
 * Escapes and unescapes <code>String</code>s for
 * Java, Java Script, HTML, XML, and SQL.
 * <p>
 * #ThreadSafe#
 * <p>
 * <b>Note that this version is a stripped down version from Commons Lang 2.6 with only necessary methods for
 * JSON builder</b>
 * @author Apache Software Foundation
 * @author Apache Jakarta Turbine
 * @author Purple Technology
 * @author <a href="mailto:alex@purpletech.com">Alexander Day Chaffee</a>
 * @author Antony Riley
 * @author Helge Tesgaard
 * @author <a href="sean@boohai.com">Sean Brown</a>
 * @author <a href="mailto:ggregory@seagullsw.com">Gary Gregory</a>
 * @author Phil Steitz
 * @author Pete Gieser
 * @since 2.0
 */
public class StringEscapeUtils {

    /**
     * <p><code>StringEscapeUtils</code> instances should NOT be constructed in
     * standard programming.
     *
     * <p>Instead, the class should be used as:
     * <pre>StringEscapeUtils.escapeJava("foo");</pre>
     *
     * <p>This constructor is public to permit tools that require a JavaBean
     * instance to operate.
     */
    public StringEscapeUtils() {
        super();
    }

    // Java and JavaScript
    //--------------------------------------------------------------------------
    /**
     * Escapes the characters in a <code>String</code> using Java String rules.
     * <p>
     * Deals correctly with quotes and control-chars (tab, backslash, cr, ff, etc.)
     * <p>
     * So a tab becomes the characters <code>'\\'</code> and <code>'t'</code>.
     * <p>
     * The only difference between Java strings and JavaScript strings
     * is that in JavaScript, a single quote must be escaped.
     * <p>
     * Example:
     * <pre>
     * input string: He didn't say, "Stop!"
     * output string: He didn't say, \"Stop!\"
     * </pre>
     *
     * @param str  String to escape values in, may be null
     * @return String with escaped values, <code>null</code> if null string input
     */
    public static String escapeJava(String str) {
        return escapeJavaStyleString(str, false, false);
    }

    /**
     * Escapes the characters in a <code>String</code> using Java String rules to
     * a <code>Writer</code>.
     * <p>
     * A <code>null</code> string input has no effect.
     *
     * @see #escapeJava(java.lang.String)
     * @param out  Writer to write escaped string into
     * @param str  String to escape values in, may be null
     * @throws IllegalArgumentException if the Writer is <code>null</code>
     * @throws IOException if error occurs on underlying Writer
     */
    public static void escapeJava(Writer out, String str) throws IOException {
        escapeJavaStyleString(out, str, false, false);
    }

    /**
     * Escapes the characters in a <code>String</code> using JavaScript String rules.
     * <p>
     * Escapes any values it finds into their JavaScript String form.
     * Deals correctly with quotes and control-chars (tab, backslash, cr, ff, etc.)
     * <p>
     * So a tab becomes the characters <code>'\\'</code> and <code>'t'</code>.
     * <p>
     * The only difference between Java strings and JavaScript strings
     * is that in JavaScript, a single quote must be escaped.
     * <p>
     * Example:
     * <pre>
     * input string: He didn't say, "Stop!"
     * output string: He didn\'t say, \"Stop!\"
     * </pre>
     *
     * @param str  String to escape values in, may be null
     * @return String with escaped values, <code>null</code> if null string input
     */
    public static String escapeJavaScript(String str) {
        return escapeJavaStyleString(str, true, true);
    }

    /**
     * Escapes the characters in a <code>String</code> using JavaScript String rules
     * to a <code>Writer</code>.
     * <p>
     * A <code>null</code> string input has no effect.
     * 
     * @see #escapeJavaScript(java.lang.String)
     * @param out  Writer to write escaped string into
     * @param str  String to escape values in, may be null
     * @throws IllegalArgumentException if the Writer is <code>null</code>
     * @throws IOException if error occurs on underlying Writer
     **/
    public static void escapeJavaScript(Writer out, String str) throws IOException {
        escapeJavaStyleString(out, str, true, true);
    }

    /**
     * Worker method for the {@link #escapeJavaScript(String)} method.
     *
     * @param str String to escape values in, may be null
     * @param escapeSingleQuotes escapes single quotes if <code>true</code>
     * @param escapeForwardSlash TODO
     * @return the escaped string
     */
    private static String escapeJavaStyleString(String str, boolean escapeSingleQuotes, boolean escapeForwardSlash) {
        if (str == null) {
            return null;
        }
        try {
            StringWriter writer = new StringWriter(str.length() * 2);
            escapeJavaStyleString(writer, str, escapeSingleQuotes, escapeForwardSlash);
            return writer.toString();
        } catch (IOException ioe) {
            // this should never ever happen while writing to a StringWriter
            throw new RuntimeException(ioe);
        }
    }

    /**
     * Worker method for the {@link #escapeJavaScript(String)} method.
     * 
     * @param out write to receieve the escaped string
     * @param str String to escape values in, may be null
     * @param escapeSingleQuote escapes single quotes if <code>true</code>
     * @param escapeForwardSlash TODO
     * @throws IOException if an IOException occurs
     */
    private static void escapeJavaStyleString(Writer out, String str, boolean escapeSingleQuote,
            boolean escapeForwardSlash) throws IOException {
        if (out == null) {
            throw new IllegalArgumentException("The Writer must not be null");
        }
        if (str == null) {
            return;
        }
        int sz;
        sz = str.length();
        for (int i = 0; i < sz; i++) {
            char ch = str.charAt(i);

            // handle unicode
            if (ch > 0xfff) {
                out.write("\\u" + hex(ch));
            } else if (ch > 0xff) {
                out.write("\\u0" + hex(ch));
            } else if (ch > 0x7f) {
                out.write("\\u00" + hex(ch));
            } else if (ch < 32) {
                switch (ch) {
                    case '\b':
                        out.write('\\');
                        out.write('b');
                        break;
                    case '\n':
                        out.write('\\');
                        out.write('n');
                        break;
                    case '\t':
                        out.write('\\');
                        out.write('t');
                        break;
                    case '\f':
                        out.write('\\');
                        out.write('f');
                        break;
                    case '\r':
                        out.write('\\');
                        out.write('r');
                        break;
                    default:
                        if (ch > 0xf) {
                            out.write("\\u00" + hex(ch));
                        } else {
                            out.write("\\u000" + hex(ch));
                        }
                        break;
                }
            } else {
                switch (ch) {
                    case '\'':
                        if (escapeSingleQuote) {
                            out.write('\\');
                        }
                        out.write('\'');
                        break;
                    case '"':
                        out.write('\\');
                        out.write('"');
                        break;
                    case '\\':
                        out.write('\\');
                        out.write('\\');
                        break;
                    case '/':
                        if (escapeForwardSlash) {
                            out.write('\\');
                        }
                        out.write('/');
                        break;
                    default:
                        out.write(ch);
                        break;
                }
            }
        }
    }

    /**
     * Returns an upper case hexadecimal <code>String</code> for the given
     * character.
     *
     * @param ch The character to convert.
     * @return An upper case hexadecimal <code>String</code>
     */
    private static String hex(char ch) {
        return Integer.toHexString(ch).toUpperCase(Locale.ENGLISH);
    }

    /**
     * Unescapes any Java literals found in the <code>String</code>.
     * For example, it will turn a sequence of <code>'\'</code> and
     * <code>'n'</code> into a newline character, unless the <code>'\'</code>
     * is preceded by another <code>'\'</code>.
     * 
     * @param str  the <code>String</code> to unescape, may be null
     * @return a new unescaped <code>String</code>, <code>null</code> if null string input
     */
    public static String unescapeJava(String str) {
        if (str == null) {
            return null;
        }
        try {
            StringWriter writer = new StringWriter(str.length());
            unescapeJava(writer, str);
            return writer.toString();
        } catch (IOException ioe) {
            // this should never ever happen while writing to a StringWriter
            throw new RuntimeException(ioe);
        }
    }

    /**
     * <p>Unescapes any Java literals found in the <code>String</code> to a
     * <code>Writer</code>.
     * <p>
     * For example, it will turn a sequence of <code>'\'</code> and
     * <code>'n'</code> into a newline character, unless the <code>'\'</code>
     * is preceded by another <code>'\'</code>.
     * <p>
     * A <code>null</code> string input has no effect.
     *
     * @param out  the <code>Writer</code> used to output unescaped characters
     * @param str  the <code>String</code> to unescape, may be null
     * @throws IllegalArgumentException if the Writer is <code>null</code>
     * @throws IOException if error occurs on underlying Writer
     */
    public static void unescapeJava(Writer out, String str) throws IOException {
        if (out == null) {
            throw new IllegalArgumentException("The Writer must not be null");
        }
        if (str == null) {
            return;
        }
        int sz = str.length();
        StringBuilder unicode = new StringBuilder(4);
        boolean hadSlash = false;
        boolean inUnicode = false;
        for (int i = 0; i < sz; i++) {
            char ch = str.charAt(i);
            if (inUnicode) {
                // if in unicode, then we're reading unicode
                // values in somehow
                unicode.append(ch);
                if (unicode.length() == 4) {
                    // unicode now contains the four hex digits
                    // which represents our unicode character
                    try {
                        int value = Integer.parseInt(unicode.toString(), 16);
                        out.write((char) value);
                        unicode.setLength(0);
                        inUnicode = false;
                        hadSlash = false;
                    } catch (NumberFormatException nfe) {
                        throw new RuntimeException("Unable to parse unicode value: " + unicode, nfe);
                    }
                }
                continue;
            }
            if (hadSlash) {
                // handle an escaped value
                hadSlash = false;
                switch (ch) {
                    case '\\':
                        out.write('\\');
                        break;
                    case '\'':
                        out.write('\'');
                        break;
                    case '\"':
                        out.write('"');
                        break;
                    case 'r':
                        out.write('\r');
                        break;
                    case 'f':
                        out.write('\f');
                        break;
                    case 't':
                        out.write('\t');
                        break;
                    case 'n':
                        out.write('\n');
                        break;
                    case 'b':
                        out.write('\b');
                        break;
                    case 'u':
                        {
                            // uh-oh, we're in unicode country....
                            inUnicode = true;
                            break;
                        }
                    default :
                        out.write(ch);
                        break;
                }
                continue;
            } else if (ch == '\\') {
                hadSlash = true;
                continue;
            }
            out.write(ch);
        }
        if (hadSlash) {
            // then we're in the weird case of a \ at the end of the
            // string, let's output it anyway.
            out.write('\\');
        }
    }

    /**
     * Unescapes any JavaScript literals found in the <code>String</code>.
     * <p>
     * For example, it will turn a sequence of <code>'\'</code> and <code>'n'</code>
     * into a newline character, unless the <code>'\'</code> is preceded by another
     * <code>'\'</code>.
     *
     * @see #unescapeJava(String)
     * @param str  the <code>String</code> to unescape, may be null
     * @return A new unescaped <code>String</code>, <code>null</code> if null string input
     */
    public static String unescapeJavaScript(String str) {
        return unescapeJava(str);
    }

    /**
     * Unescapes any JavaScript literals found in the <code>String</code> to a
     * <code>Writer</code>.
     * <p>
     * For example, it will turn a sequence of <code>'\'</code> and <code>'n'</code>
     * into a newline character, unless the <code>'\'</code> is preceded by another
     * <code>'\'</code>.
     * <p>
     * A <code>null</code> string input has no effect.
     *
     * @see #unescapeJava(Writer,String)
     * @param out  the <code>Writer</code> used to output unescaped characters
     * @param str  the <code>String</code> to unescape, may be null
     * @throws IllegalArgumentException if the Writer is <code>null</code>
     * @throws IOException if error occurs on underlying Writer
     */
    public static void unescapeJavaScript(Writer out, String str) throws IOException {
        unescapeJava(out, str);
    }
}
