/*
 * =============================================================================
 * 
 *   Copyright (c) 2014-2017, The UNBESCAPE team (http://www.unbescape.org)
 * 
 *   Licensed 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.unbescape.json;

import java.io.IOException;
import java.io.Reader;
import java.io.Writer;


/**
 * <p>
 *   Utility class for performing JSON escape/unescape operations.
 * </p>
 *
 * <strong><u>Configuration of escape/unescape operations</u></strong>
 *
 * <p>
 *   <strong>Escape</strong> operations can be (optionally) configured by means of:
 * </p>
 * <ul>
 *   <li><em>Level</em>, which defines how deep the escape operation must be (what
 *       chars are to be considered eligible for escaping, depending on the specific
 *       needs of the scenario). Its values are defined by the {@link JsonEscapeLevel}
 *       enum.</li>
 *   <li><em>Type</em>, which defines whether escaping should be performed by means of SECs
 *       (Single Escape Characters like <tt>&#92;n</tt>) or additionally by means of u-based
 *       hexadecimal references (<tt>&#92;u00E1</tt>).
 *       Its values are defined by the {@link JsonEscapeType} enum.</li>
 * </ul>
 * <p>
 *   <strong>Unescape</strong> operations need no configuration parameters. Unescape operations
 *   will always perform <em>complete</em> unescape of SECs (<tt>&#92;n</tt>)
 *   and u-based (<tt>&#92;u00E1</tt>) hexadecimal escapes.
 * </p>
 *
 * <strong><u>Features</u></strong>
 *
 * <p>
 *   Specific features of the JSON escape/unescape operations performed by means of this class:
 * </p>
 * <ul>
 *   <li>The JSON basic escape set is supported. This <em>basic set</em> consists of:
 *         <ul>
 *           <li>The <em>Single Escape Characters</em>:
 *               <tt>&#92;b</tt> (<tt>U+0008</tt>),
 *               <tt>&#92;t</tt> (<tt>U+0009</tt>),
 *               <tt>&#92;n</tt> (<tt>U+000A</tt>),
 *               <tt>&#92;f</tt> (<tt>U+000C</tt>),
 *               <tt>&#92;r</tt> (<tt>U+000D</tt>),
 *               <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
 *               <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
 *               <tt>&#92;&#47;</tt> (<tt>U+002F</tt>).
 *               Note that <tt>&#92;&#47;</tt> is optional, and will only be used when the <tt>&#47;</tt>
 *               symbol appears after <tt>&lt;</tt>, as in <tt>&lt;&#47;</tt>. This is to avoid accidentally
 *               closing <tt>&lt;script&gt;</tt> tags in HTML.
 *           </li>
 *           <li>
 *               Two ranges of non-displayable, control characters (some of which are already part of the
 *               <em>single escape characters</em> list): <tt>U+0000</tt> to <tt>U+001F</tt> (required
 *               by the JSON spec) and <tt>U+007F</tt> to <tt>U+009F</tt> (additional).
 *           </li>
 *         </ul>
 *   </li>
 *   <li>U-based hexadecimal escapes (a.k.a. <em>unicode escapes</em>) are supported both in escape
 *       and unescape operations: <tt>&#92;u00E1</tt>.</li>
 *   <li>Support for the whole Unicode character set: <tt>&#92;u0000</tt> to <tt>&#92;u10FFFF</tt>, including
 *       characters not representable by only one <tt>char</tt> in Java (<tt>&gt;&#92;uFFFF</tt>).</li>
 * </ul>
 *
 * <strong><u>Input/Output</u></strong>
 *
 * <p>
 *   There are four different input/output modes that can be used in escape/unescape operations:
 * </p>
 * <ul>
 *   <li><em><tt>String</tt> input, <tt>String</tt> output</em>: Input is specified as a <tt>String</tt> object
 *       and output is returned as another. In order to improve memory performance, all escape and unescape
 *       operations <u>will return the exact same input object as output if no escape/unescape modifications
 *       are required</u>.</li>
 *   <li><em><tt>String</tt> input, <tt>java.io.Writer</tt> output</em>: Input will be read from a String
 *       and output will be written into the specified <tt>java.io.Writer</tt>.</li>
 *   <li><em><tt>java.io.Reader</tt> input, <tt>java.io.Writer</tt> output</em>: Input will be read from a Reader
 *       and output will be written into the specified <tt>java.io.Writer</tt>.</li>
 *   <li><em><tt>char[]</tt> input, <tt>java.io.Writer</tt> output</em>: Input will be read from a char array
 *       (<tt>char[]</tt>) and output will be written into the specified <tt>java.io.Writer</tt>.
 *       Two <tt>int</tt> arguments called <tt>offset</tt> and <tt>len</tt> will be
 *       used for specifying the part of the <tt>char[]</tt> that should be escaped/unescaped. These methods
 *       should be called with <tt>offset = 0</tt> and <tt>len = text.length</tt> in order to process
 *       the whole <tt>char[]</tt>.</li>
 * </ul>
 *
 * <strong><u>Glossary</u></strong>
 *
 * <dl>
 *   <dt>SEC</dt>
 *     <dd>Single Escape Character:
 *               <tt>&#92;b</tt> (<tt>U+0008</tt>),
 *               <tt>&#92;t</tt> (<tt>U+0009</tt>),
 *               <tt>&#92;n</tt> (<tt>U+000A</tt>),
 *               <tt>&#92;f</tt> (<tt>U+000C</tt>),
 *               <tt>&#92;r</tt> (<tt>U+000D</tt>),
 *               <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
 *               <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
 *               <tt>&#92;&#47;</tt> (<tt>U+002F</tt>) (optional, only in <tt>&lt;&#47;</tt>).
 *     </dd>
 *   <dt>UHEXA escapes</dt>
 *     <dd>Also called <em>u-based hexadecimal escapes</em> or simply <em>unicode escapes</em>:
 *         complete representation of unicode codepoints up to <tt>U+FFFF</tt>, with <tt>&#92;u</tt>
 *         followed by exactly four hexadecimal figures: <tt>&#92;u00E1</tt>. Unicode codepoints &gt;
 *         <tt>U+FFFF</tt> can be represented in JSON by mean of two UHEXA escapes (a
 *         <em>surrogate pair</em>).</dd>
 *   <dt>Unicode Codepoint</dt>
 *     <dd>Each of the <tt>int</tt> values conforming the Unicode code space.
 *         Normally corresponding to a Java <tt>char</tt> primitive value (codepoint &lt;= <tt>&#92;uFFFF</tt>),
 *         but might be two <tt>char</tt>s for codepoints <tt>&#92;u10000</tt> to <tt>&#92;u10FFFF</tt> if the
 *         first <tt>char</tt> is a high surrogate (<tt>&#92;uD800</tt> to <tt>&#92;uDBFF</tt>) and the
 *         second is a low surrogate (<tt>&#92;uDC00</tt> to <tt>&#92;uDFFF</tt>).</dd>
 * </dl>
 *
 * <strong><u>References</u></strong>
 *
 * <p>
 *   The following references apply:
 * </p>
 * <ul>
 *   <li><a href="http://www.ietf.org/rfc/rfc4627.txt" target="_blank">RFC4627: The application/json
 *       Media Type for JavaScript Object Notation (JSON)</a>
 *       [ietf.org]</li>
 *   <li><a href="http://timelessrepo.com/json-isnt-a-javascript-subset" target="_blank">JSON:
 *       The JavaScript subset that isn't</a> [timelessrepo.com]</li>
 *   <li><a href="http://benalman.com/news/2010/03/theres-no-such-thing-as-a-json/" target="_blank">There
 *       is no such thing as a &quot;JSON Object&quot;</a> [benalman.com]</li>
 * </ul>
 *
 *
 * @author Daniel Fern&aacute;ndez
 *
 * @since 1.0.0
 *
 */
public final class JsonEscape {


    /**
     * <p>
     *   Perform a JSON level 1 (only basic set) <strong>escape</strong> operation
     *   on a <tt>String</tt> input.
     * </p>
     * <p>
     *   <em>Level 1</em> means this method will only escape the JSON basic escape set:
     * </p>
     * <ul>
     *   <li>The <em>Single Escape Characters</em>:
     *       <tt>&#92;b</tt> (<tt>U+0008</tt>),
     *       <tt>&#92;t</tt> (<tt>U+0009</tt>),
     *       <tt>&#92;n</tt> (<tt>U+000A</tt>),
     *       <tt>&#92;f</tt> (<tt>U+000C</tt>),
     *       <tt>&#92;r</tt> (<tt>U+000D</tt>),
     *       <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
     *       <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
     *       <tt>&#92;&#47;</tt> (<tt>U+002F</tt>).
     *       Note that <tt>&#92;&#47;</tt> is optional, and will only be used when the <tt>&#47;</tt>
     *       symbol appears after <tt>&lt;</tt>, as in <tt>&lt;&#47;</tt>. This is to avoid accidentally
     *       closing <tt>&lt;script&gt;</tt> tags in HTML.
     *   </li>
     *   <li>
     *       Two ranges of non-displayable, control characters (some of which are already part of the
     *       <em>single escape characters</em> list): <tt>U+0000</tt> to <tt>U+001F</tt> (required
     *       by the JSON spec) and <tt>U+007F</tt> to <tt>U+009F</tt> (additional).
     *   </li>
     * </ul>
     * <p>
     *   This method calls {@link #escapeJson(String, JsonEscapeType, JsonEscapeLevel)}
     *   with the following preconfigured values:
     * </p>
     * <ul>
     *   <li><tt>type</tt>:
     *       {@link JsonEscapeType#SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA}</li>
     *   <li><tt>level</tt>:
     *       {@link JsonEscapeLevel#LEVEL_1_BASIC_ESCAPE_SET}</li>
     * </ul>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>String</tt> to be escaped.
     * @return The escaped result <tt>String</tt>. As a memory-performance improvement, will return the exact
     *         same object as the <tt>text</tt> input argument if no escaping modifications were required (and
     *         no additional <tt>String</tt> objects will be created during processing). Will
     *         return <tt>null</tt> if input is <tt>null</tt>.
     */
    public static String escapeJsonMinimal(final String text) {
        return escapeJson(text,
                JsonEscapeType.SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA,
                JsonEscapeLevel.LEVEL_1_BASIC_ESCAPE_SET);
    }


    /**
     * <p>
     *   Perform a JSON level 2 (basic set and all non-ASCII chars) <strong>escape</strong> operation
     *   on a <tt>String</tt> input.
     * </p>
     * <p>
     *   <em>Level 2</em> means this method will escape:
     * </p>
     * <ul>
     *   <li>The JSON basic escape set:
     *         <ul>
     *           <li>The <em>Single Escape Characters</em>:
     *               <tt>&#92;b</tt> (<tt>U+0008</tt>),
     *               <tt>&#92;t</tt> (<tt>U+0009</tt>),
     *               <tt>&#92;n</tt> (<tt>U+000A</tt>),
     *               <tt>&#92;f</tt> (<tt>U+000C</tt>),
     *               <tt>&#92;r</tt> (<tt>U+000D</tt>),
     *               <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
     *               <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
     *               <tt>&#92;&#47;</tt> (<tt>U+002F</tt>).
     *               Note that <tt>&#92;&#47;</tt> is optional, and will only be used when the <tt>&#47;</tt>
     *               symbol appears after <tt>&lt;</tt>, as in <tt>&lt;&#47;</tt>. This is to avoid accidentally
     *               closing <tt>&lt;script&gt;</tt> tags in HTML.
     *           </li>
     *           <li>
     *               Two ranges of non-displayable, control characters (some of which are already part of the
     *               <em>single escape characters</em> list): <tt>U+0000</tt> to <tt>U+001F</tt> (required
     *               by the JSON spec) and <tt>U+007F</tt> to <tt>U+009F</tt> (additional).
     *           </li>
     *         </ul>
     *   </li>
     *   <li>All non ASCII characters.</li>
     * </ul>
     * <p>
     *   This escape will be performed by using the Single Escape Chars whenever possible. For escaped
     *   characters that do not have an associated SEC, default to <tt>&#92;uFFFF</tt>
     *   Hexadecimal Escapes.
     * </p>
     * <p>
     *   This method calls {@link #escapeJson(String, JsonEscapeType, JsonEscapeLevel)}
     *   with the following preconfigured values:
     * </p>
     * <ul>
     *   <li><tt>type</tt>:
     *       {@link JsonEscapeType#SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA}</li>
     *   <li><tt>level</tt>:
     *       {@link JsonEscapeLevel#LEVEL_2_ALL_NON_ASCII_PLUS_BASIC_ESCAPE_SET}</li>
     * </ul>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>String</tt> to be escaped.
     * @return The escaped result <tt>String</tt>. As a memory-performance improvement, will return the exact
     *         same object as the <tt>text</tt> input argument if no escaping modifications were required (and
     *         no additional <tt>String</tt> objects will be created during processing). Will
     *         return <tt>null</tt> if input is <tt>null</tt>.
     */
    public static String escapeJson(final String text) {
        return escapeJson(text,
                JsonEscapeType.SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA,
                JsonEscapeLevel.LEVEL_2_ALL_NON_ASCII_PLUS_BASIC_ESCAPE_SET);
    }


    /**
     * <p>
     *   Perform a (configurable) JSON <strong>escape</strong> operation on a <tt>String</tt> input.
     * </p>
     * <p>
     *   This method will perform an escape operation according to the specified
     *   {@link JsonEscapeType} and
     *   {@link JsonEscapeLevel} argument values.
     * </p>
     * <p>
     *   All other <tt>String</tt>-based <tt>escapeJson*(...)</tt> methods call this one with preconfigured
     *   <tt>type</tt> and <tt>level</tt> values.
     * </p>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>String</tt> to be escaped.
     * @param type the type of escape operation to be performed, see
     *             {@link JsonEscapeType}.
     * @param level the escape level to be applied, see {@link JsonEscapeLevel}.
     * @return The escaped result <tt>String</tt>. As a memory-performance improvement, will return the exact
     *         same object as the <tt>text</tt> input argument if no escaping modifications were required (and
     *         no additional <tt>String</tt> objects will be created during processing). Will
     *         return <tt>null</tt> if input is <tt>null</tt>.
     */
    public static String escapeJson(final String text,
                                    final JsonEscapeType type, final JsonEscapeLevel level) {

        if (type == null) {
            throw new IllegalArgumentException("The 'type' argument cannot be null");
        }

        if (level == null) {
            throw new IllegalArgumentException("The 'level' argument cannot be null");
        }

        return JsonEscapeUtil.escape(text, type, level);

    }




    /**
     * <p>
     *   Perform a JSON level 1 (only basic set) <strong>escape</strong> operation
     *   on a <tt>String</tt> input, writing results to a <tt>Writer</tt>.
     * </p>
     * <p>
     *   <em>Level 1</em> means this method will only escape the JSON basic escape set:
     * </p>
     * <ul>
     *   <li>The <em>Single Escape Characters</em>:
     *       <tt>&#92;b</tt> (<tt>U+0008</tt>),
     *       <tt>&#92;t</tt> (<tt>U+0009</tt>),
     *       <tt>&#92;n</tt> (<tt>U+000A</tt>),
     *       <tt>&#92;f</tt> (<tt>U+000C</tt>),
     *       <tt>&#92;r</tt> (<tt>U+000D</tt>),
     *       <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
     *       <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
     *       <tt>&#92;&#47;</tt> (<tt>U+002F</tt>).
     *       Note that <tt>&#92;&#47;</tt> is optional, and will only be used when the <tt>&#47;</tt>
     *       symbol appears after <tt>&lt;</tt>, as in <tt>&lt;&#47;</tt>. This is to avoid accidentally
     *       closing <tt>&lt;script&gt;</tt> tags in HTML.
     *   </li>
     *   <li>
     *       Two ranges of non-displayable, control characters (some of which are already part of the
     *       <em>single escape characters</em> list): <tt>U+0000</tt> to <tt>U+001F</tt> (required
     *       by the JSON spec) and <tt>U+007F</tt> to <tt>U+009F</tt> (additional).
     *   </li>
     * </ul>
     * <p>
     *   This method calls {@link #escapeJson(String, Writer, JsonEscapeType, JsonEscapeLevel)}
     *   with the following preconfigured values:
     * </p>
     * <ul>
     *   <li><tt>type</tt>:
     *       {@link JsonEscapeType#SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA}</li>
     *   <li><tt>level</tt>:
     *       {@link JsonEscapeLevel#LEVEL_1_BASIC_ESCAPE_SET}</li>
     * </ul>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>String</tt> to be escaped.
     * @param writer the <tt>java.io.Writer</tt> to which the escaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @throws IOException if an input/output exception occurs
     *
     * @since 1.1.2
     */
    public static void escapeJsonMinimal(final String text, final Writer writer)
            throws IOException {
        escapeJson(text, writer,
                JsonEscapeType.SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA,
                JsonEscapeLevel.LEVEL_1_BASIC_ESCAPE_SET);
    }


    /**
     * <p>
     *   Perform a JSON level 2 (basic set and all non-ASCII chars) <strong>escape</strong> operation
     *   on a <tt>String</tt> input, writing results to a <tt>Writer</tt>.
     * </p>
     * <p>
     *   <em>Level 2</em> means this method will escape:
     * </p>
     * <ul>
     *   <li>The JSON basic escape set:
     *         <ul>
     *           <li>The <em>Single Escape Characters</em>:
     *               <tt>&#92;b</tt> (<tt>U+0008</tt>),
     *               <tt>&#92;t</tt> (<tt>U+0009</tt>),
     *               <tt>&#92;n</tt> (<tt>U+000A</tt>),
     *               <tt>&#92;f</tt> (<tt>U+000C</tt>),
     *               <tt>&#92;r</tt> (<tt>U+000D</tt>),
     *               <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
     *               <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
     *               <tt>&#92;&#47;</tt> (<tt>U+002F</tt>).
     *               Note that <tt>&#92;&#47;</tt> is optional, and will only be used when the <tt>&#47;</tt>
     *               symbol appears after <tt>&lt;</tt>, as in <tt>&lt;&#47;</tt>. This is to avoid accidentally
     *               closing <tt>&lt;script&gt;</tt> tags in HTML.
     *           </li>
     *           <li>
     *               Two ranges of non-displayable, control characters (some of which are already part of the
     *               <em>single escape characters</em> list): <tt>U+0000</tt> to <tt>U+001F</tt> (required
     *               by the JSON spec) and <tt>U+007F</tt> to <tt>U+009F</tt> (additional).
     *           </li>
     *         </ul>
     *   </li>
     *   <li>All non ASCII characters.</li>
     * </ul>
     * <p>
     *   This escape will be performed by using the Single Escape Chars whenever possible. For escaped
     *   characters that do not have an associated SEC, default to <tt>&#92;uFFFF</tt>
     *   Hexadecimal Escapes.
     * </p>
     * <p>
     *   This method calls {@link #escapeJson(String, Writer, JsonEscapeType, JsonEscapeLevel)}
     *   with the following preconfigured values:
     * </p>
     * <ul>
     *   <li><tt>type</tt>:
     *       {@link JsonEscapeType#SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA}</li>
     *   <li><tt>level</tt>:
     *       {@link JsonEscapeLevel#LEVEL_2_ALL_NON_ASCII_PLUS_BASIC_ESCAPE_SET}</li>
     * </ul>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>String</tt> to be escaped.
     * @param writer the <tt>java.io.Writer</tt> to which the escaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @throws IOException if an input/output exception occurs
     *
     * @since 1.1.2
     */
    public static void escapeJson(final String text, final Writer writer)
            throws IOException {
        escapeJson(text, writer,
                JsonEscapeType.SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA,
                JsonEscapeLevel.LEVEL_2_ALL_NON_ASCII_PLUS_BASIC_ESCAPE_SET);
    }


    /**
     * <p>
     *   Perform a (configurable) JSON <strong>escape</strong> operation on a <tt>String</tt> input,
     *   writing results to a <tt>Writer</tt>.
     * </p>
     * <p>
     *   This method will perform an escape operation according to the specified
     *   {@link JsonEscapeType} and
     *   {@link JsonEscapeLevel} argument values.
     * </p>
     * <p>
     *   All other <tt>String</tt>/<tt>Writer</tt>-based <tt>escapeJson*(...)</tt> methods call this one with preconfigured
     *   <tt>type</tt> and <tt>level</tt> values.
     * </p>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>String</tt> to be escaped.
     * @param writer the <tt>java.io.Writer</tt> to which the escaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @param type the type of escape operation to be performed, see
     *             {@link JsonEscapeType}.
     * @param level the escape level to be applied, see {@link JsonEscapeLevel}.
     * @throws IOException if an input/output exception occurs
     *
     * @since 1.1.2
     */
    public static void escapeJson(final String text, final Writer writer,
                                  final JsonEscapeType type, final JsonEscapeLevel level)
            throws IOException {

        if (writer == null) {
            throw new IllegalArgumentException("Argument 'writer' cannot be null");
        }

        if (type == null) {
            throw new IllegalArgumentException("The 'type' argument cannot be null");
        }

        if (level == null) {
            throw new IllegalArgumentException("The 'level' argument cannot be null");
        }

        JsonEscapeUtil.escape(new InternalStringReader(text), writer, type, level);

    }




    /**
     * <p>
     *   Perform a JSON level 1 (only basic set) <strong>escape</strong> operation
     *   on a <tt>Reader</tt> input, writing results to a <tt>Writer</tt>.
     * </p>
     * <p>
     *   <em>Level 1</em> means this method will only escape the JSON basic escape set:
     * </p>
     * <ul>
     *   <li>The <em>Single Escape Characters</em>:
     *       <tt>&#92;b</tt> (<tt>U+0008</tt>),
     *       <tt>&#92;t</tt> (<tt>U+0009</tt>),
     *       <tt>&#92;n</tt> (<tt>U+000A</tt>),
     *       <tt>&#92;f</tt> (<tt>U+000C</tt>),
     *       <tt>&#92;r</tt> (<tt>U+000D</tt>),
     *       <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
     *       <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
     *       <tt>&#92;&#47;</tt> (<tt>U+002F</tt>).
     *       Note that <tt>&#92;&#47;</tt> is optional, and will only be used when the <tt>&#47;</tt>
     *       symbol appears after <tt>&lt;</tt>, as in <tt>&lt;&#47;</tt>. This is to avoid accidentally
     *       closing <tt>&lt;script&gt;</tt> tags in HTML.
     *   </li>
     *   <li>
     *       Two ranges of non-displayable, control characters (some of which are already part of the
     *       <em>single escape characters</em> list): <tt>U+0000</tt> to <tt>U+001F</tt> (required
     *       by the JSON spec) and <tt>U+007F</tt> to <tt>U+009F</tt> (additional).
     *   </li>
     * </ul>
     * <p>
     *   This method calls {@link #escapeJson(Reader, Writer, JsonEscapeType, JsonEscapeLevel)}
     *   with the following preconfigured values:
     * </p>
     * <ul>
     *   <li><tt>type</tt>:
     *       {@link JsonEscapeType#SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA}</li>
     *   <li><tt>level</tt>:
     *       {@link JsonEscapeLevel#LEVEL_1_BASIC_ESCAPE_SET}</li>
     * </ul>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param reader the <tt>Reader</tt> reading the text to be escaped.
     * @param writer the <tt>java.io.Writer</tt> to which the escaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @throws IOException if an input/output exception occurs
     *
     * @since 1.1.2
     */
    public static void escapeJsonMinimal(final Reader reader, final Writer writer)
            throws IOException {
        escapeJson(reader, writer,
                JsonEscapeType.SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA,
                JsonEscapeLevel.LEVEL_1_BASIC_ESCAPE_SET);
    }


    /**
     * <p>
     *   Perform a JSON level 2 (basic set and all non-ASCII chars) <strong>escape</strong> operation
     *   on a <tt>Reader</tt> input, writing results to a <tt>Writer</tt>.
     * </p>
     * <p>
     *   <em>Level 2</em> means this method will escape:
     * </p>
     * <ul>
     *   <li>The JSON basic escape set:
     *         <ul>
     *           <li>The <em>Single Escape Characters</em>:
     *               <tt>&#92;b</tt> (<tt>U+0008</tt>),
     *               <tt>&#92;t</tt> (<tt>U+0009</tt>),
     *               <tt>&#92;n</tt> (<tt>U+000A</tt>),
     *               <tt>&#92;f</tt> (<tt>U+000C</tt>),
     *               <tt>&#92;r</tt> (<tt>U+000D</tt>),
     *               <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
     *               <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
     *               <tt>&#92;&#47;</tt> (<tt>U+002F</tt>).
     *               Note that <tt>&#92;&#47;</tt> is optional, and will only be used when the <tt>&#47;</tt>
     *               symbol appears after <tt>&lt;</tt>, as in <tt>&lt;&#47;</tt>. This is to avoid accidentally
     *               closing <tt>&lt;script&gt;</tt> tags in HTML.
     *           </li>
     *           <li>
     *               Two ranges of non-displayable, control characters (some of which are already part of the
     *               <em>single escape characters</em> list): <tt>U+0000</tt> to <tt>U+001F</tt> (required
     *               by the JSON spec) and <tt>U+007F</tt> to <tt>U+009F</tt> (additional).
     *           </li>
     *         </ul>
     *   </li>
     *   <li>All non ASCII characters.</li>
     * </ul>
     * <p>
     *   This escape will be performed by using the Single Escape Chars whenever possible. For escaped
     *   characters that do not have an associated SEC, default to <tt>&#92;uFFFF</tt>
     *   Hexadecimal Escapes.
     * </p>
     * <p>
     *   This method calls {@link #escapeJson(Reader, Writer, JsonEscapeType, JsonEscapeLevel)}
     *   with the following preconfigured values:
     * </p>
     * <ul>
     *   <li><tt>type</tt>:
     *       {@link JsonEscapeType#SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA}</li>
     *   <li><tt>level</tt>:
     *       {@link JsonEscapeLevel#LEVEL_2_ALL_NON_ASCII_PLUS_BASIC_ESCAPE_SET}</li>
     * </ul>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param reader the <tt>Reader</tt> reading the text to be escaped.
     * @param writer the <tt>java.io.Writer</tt> to which the escaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @throws IOException if an input/output exception occurs
     *
     * @since 1.1.2
     */
    public static void escapeJson(final Reader reader, final Writer writer)
            throws IOException {
        escapeJson(reader, writer,
                JsonEscapeType.SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA,
                JsonEscapeLevel.LEVEL_2_ALL_NON_ASCII_PLUS_BASIC_ESCAPE_SET);
    }


    /**
     * <p>
     *   Perform a (configurable) JSON <strong>escape</strong> operation on a <tt>Reader</tt> input,
     *   writing results to a <tt>Writer</tt>.
     * </p>
     * <p>
     *   This method will perform an escape operation according to the specified
     *   {@link JsonEscapeType} and
     *   {@link JsonEscapeLevel} argument values.
     * </p>
     * <p>
     *   All other <tt>Reader</tt>/<tt>Writer</tt>-based <tt>escapeJson*(...)</tt> methods call this one with preconfigured
     *   <tt>type</tt> and <tt>level</tt> values.
     * </p>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param reader the <tt>Reader</tt> reading the text to be escaped.
     * @param writer the <tt>java.io.Writer</tt> to which the escaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @param type the type of escape operation to be performed, see
     *             {@link JsonEscapeType}.
     * @param level the escape level to be applied, see {@link JsonEscapeLevel}.
     * @throws IOException if an input/output exception occurs
     *
     * @since 1.1.2
     */
    public static void escapeJson(final Reader reader, final Writer writer,
                                  final JsonEscapeType type, final JsonEscapeLevel level)
            throws IOException {

        if (writer == null) {
            throw new IllegalArgumentException("Argument 'writer' cannot be null");
        }

        if (type == null) {
            throw new IllegalArgumentException("The 'type' argument cannot be null");
        }

        if (level == null) {
            throw new IllegalArgumentException("The 'level' argument cannot be null");
        }

        JsonEscapeUtil.escape(reader, writer, type, level);

    }




    /**
     * <p>
     *   Perform a JSON level 1 (only basic set) <strong>escape</strong> operation
     *   on a <tt>char[]</tt> input.
     * </p>
     * <p>
     *   <em>Level 1</em> means this method will only escape the JSON basic escape set:
     * </p>
     * <ul>
     *   <li>The <em>Single Escape Characters</em>:
     *       <tt>&#92;b</tt> (<tt>U+0008</tt>),
     *       <tt>&#92;t</tt> (<tt>U+0009</tt>),
     *       <tt>&#92;n</tt> (<tt>U+000A</tt>),
     *       <tt>&#92;f</tt> (<tt>U+000C</tt>),
     *       <tt>&#92;r</tt> (<tt>U+000D</tt>),
     *       <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
     *       <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
     *       <tt>&#92;&#47;</tt> (<tt>U+002F</tt>).
     *       Note that <tt>&#92;&#47;</tt> is optional, and will only be used when the <tt>&#47;</tt>
     *       symbol appears after <tt>&lt;</tt>, as in <tt>&lt;&#47;</tt>. This is to avoid accidentally
     *       closing <tt>&lt;script&gt;</tt> tags in HTML.
     *   </li>
     *   <li>
     *       Two ranges of non-displayable, control characters (some of which are already part of the
     *       <em>single escape characters</em> list): <tt>U+0000</tt> to <tt>U+001F</tt> (required
     *       by the JSON spec) and <tt>U+007F</tt> to <tt>U+009F</tt> (additional).
     *   </li>
     * </ul>
     * <p>
     *   This method calls
     *   {@link #escapeJson(char[], int, int, java.io.Writer, JsonEscapeType, JsonEscapeLevel)}
     *   with the following preconfigured values:
     * </p>
     * <ul>
     *   <li><tt>type</tt>:
     *       {@link JsonEscapeType#SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA}</li>
     *   <li><tt>level</tt>:
     *       {@link JsonEscapeLevel#LEVEL_1_BASIC_ESCAPE_SET}</li>
     * </ul>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>char[]</tt> to be escaped.
     * @param offset the position in <tt>text</tt> at which the escape operation should start.
     * @param len the number of characters in <tt>text</tt> that should be escaped.
     * @param writer the <tt>java.io.Writer</tt> to which the escaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @throws IOException if an input/output exception occurs
     */
    public static void escapeJsonMinimal(final char[] text, final int offset, final int len, final Writer writer)
                                         throws IOException {
        escapeJson(text, offset, len, writer,
                   JsonEscapeType.SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA,
                   JsonEscapeLevel.LEVEL_1_BASIC_ESCAPE_SET);
    }


    /**
     * <p>
     *   Perform a JSON level 2 (basic set and all non-ASCII chars) <strong>escape</strong> operation
     *   on a <tt>char[]</tt> input.
     * </p>
     * <p>
     *   <em>Level 2</em> means this method will escape:
     * </p>
     * <ul>
     *   <li>The JSON basic escape set:
     *         <ul>
     *           <li>The <em>Single Escape Characters</em>:
     *               <tt>&#92;b</tt> (<tt>U+0008</tt>),
     *               <tt>&#92;t</tt> (<tt>U+0009</tt>),
     *               <tt>&#92;n</tt> (<tt>U+000A</tt>),
     *               <tt>&#92;f</tt> (<tt>U+000C</tt>),
     *               <tt>&#92;r</tt> (<tt>U+000D</tt>),
     *               <tt>&#92;&quot;</tt> (<tt>U+0022</tt>),
     *               <tt>&#92;&#92;</tt> (<tt>U+005C</tt>) and
     *               <tt>&#92;&#47;</tt> (<tt>U+002F</tt>).
     *               Note that <tt>&#92;&#47;</tt> is optional, and will only be used when the <tt>&#47;</tt>
     *               symbol appears after <tt>&lt;</tt>, as in <tt>&lt;&#47;</tt>. This is to avoid accidentally
     *               closing <tt>&lt;script&gt;</tt> tags in HTML.
     *           </li>
     *           <li>
     *               Two ranges of non-displayable, control characters (some of which are already part of the
     *               <em>single escape characters</em> list): <tt>U+0000</tt> to <tt>U+001F</tt> (required
     *               by the JSON spec) and <tt>U+007F</tt> to <tt>U+009F</tt> (additional).
     *           </li>
     *         </ul>
     *   </li>
     *   <li>All non ASCII characters.</li>
     * </ul>
     * <p>
     *   This escape will be performed by using the Single Escape Chars whenever possible. For escaped
     *   characters that do not have an associated SEC, default to <tt>&#92;uFFFF</tt>
     *   Hexadecimal Escapes.
     * </p>
     * <p>
     *   This method calls
     *   {@link #escapeJson(char[], int, int, java.io.Writer, JsonEscapeType, JsonEscapeLevel)}
     *   with the following preconfigured values:
     * </p>
     * <ul>
     *   <li><tt>type</tt>:
     *       {@link JsonEscapeType#SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA}</li>
     *   <li><tt>level</tt>:
     *       {@link JsonEscapeLevel#LEVEL_2_ALL_NON_ASCII_PLUS_BASIC_ESCAPE_SET}</li>
     * </ul>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>char[]</tt> to be escaped.
     * @param offset the position in <tt>text</tt> at which the escape operation should start.
     * @param len the number of characters in <tt>text</tt> that should be escaped.
     * @param writer the <tt>java.io.Writer</tt> to which the escaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @throws IOException if an input/output exception occurs
     */
    public static void escapeJson(final char[] text, final int offset, final int len, final Writer writer)
                                  throws IOException {
        escapeJson(text, offset, len, writer,
                   JsonEscapeType.SINGLE_ESCAPE_CHARS_DEFAULT_TO_UHEXA,
                   JsonEscapeLevel.LEVEL_2_ALL_NON_ASCII_PLUS_BASIC_ESCAPE_SET);
    }


    /**
     * <p>
     *   Perform a (configurable) JSON <strong>escape</strong> operation on a <tt>char[]</tt> input.
     * </p>
     * <p>
     *   This method will perform an escape operation according to the specified
     *   {@link JsonEscapeType} and
     *   {@link JsonEscapeLevel} argument values.
     * </p>
     * <p>
     *   All other <tt>char[]</tt>-based <tt>escapeJson*(...)</tt> methods call this one with preconfigured
     *   <tt>type</tt> and <tt>level</tt> values.
     * </p>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>char[]</tt> to be escaped.
     * @param offset the position in <tt>text</tt> at which the escape operation should start.
     * @param len the number of characters in <tt>text</tt> that should be escaped.
     * @param writer the <tt>java.io.Writer</tt> to which the escaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @param type the type of escape operation to be performed, see
     *             {@link JsonEscapeType}.
     * @param level the escape level to be applied, see {@link JsonEscapeLevel}.
     * @throws IOException if an input/output exception occurs
     */
    public static void escapeJson(final char[] text, final int offset, final int len, final Writer writer,
                                  final JsonEscapeType type, final JsonEscapeLevel level)
                                  throws IOException {

        if (writer == null) {
            throw new IllegalArgumentException("Argument 'writer' cannot be null");
        }

        if (type == null) {
            throw new IllegalArgumentException("The 'type' argument cannot be null");
        }

        if (level == null) {
            throw new IllegalArgumentException("The 'level' argument cannot be null");
        }

        final int textLen = (text == null? 0 : text.length);

        if (offset < 0 || offset > textLen) {
            throw new IllegalArgumentException(
                    "Invalid (offset, len). offset=" + offset + ", len=" + len + ", text.length=" + textLen);
        }

        if (len < 0 || (offset + len) > textLen) {
            throw new IllegalArgumentException(
                    "Invalid (offset, len). offset=" + offset + ", len=" + len + ", text.length=" + textLen);
        }

        JsonEscapeUtil.escape(text, offset, len, writer, type, level);

    }








    /**
     * <p>
     *   Perform a JSON <strong>unescape</strong> operation on a <tt>String</tt> input.
     * </p>
     * <p>
     *   No additional configuration arguments are required. Unescape operations
     *   will always perform <em>complete</em> JSON unescape of SECs and u-based escapes.
     * </p>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>String</tt> to be unescaped.
     * @return The unescaped result <tt>String</tt>. As a memory-performance improvement, will return the exact
     *         same object as the <tt>text</tt> input argument if no unescaping modifications were required (and
     *         no additional <tt>String</tt> objects will be created during processing). Will
     *         return <tt>null</tt> if input is <tt>null</tt>.
     */
    public static String unescapeJson(final String text) {
        if (text == null) {
            return null;
        }
        if (text.indexOf('\\') < 0) {
            // Fail fast, avoid more complex (and less JIT-table) method to execute if not needed
            return text;
        }
        return JsonEscapeUtil.unescape(text);
    }


    /**
     * <p>
     *   Perform a JSON <strong>unescape</strong> operation on a <tt>String</tt> input, writing
     *   results to a <tt>Writer</tt>.
     * </p>
     * <p>
     *   No additional configuration arguments are required. Unescape operations
     *   will always perform <em>complete</em> JSON unescape of SECs and u-based escapes.
     * </p>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>String</tt> to be unescaped.
     * @param writer the <tt>java.io.Writer</tt> to which the unescaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @throws IOException if an input/output exception occurs
     *
     * @since 1.1.2
     */
    public static void unescapeJson(final String text, final Writer writer)
            throws IOException {

        if (writer == null) {
            throw new IllegalArgumentException("Argument 'writer' cannot be null");
        }
        if (text == null) {
            return;
        }
        if (text.indexOf('\\') < 0) {
            // Fail fast, avoid more complex (and less JIT-table) method to execute if not needed
            writer.write(text);
            return;
        }

        JsonEscapeUtil.unescape(new InternalStringReader(text), writer);

    }


    /**
     * <p>
     *   Perform a JSON <strong>unescape</strong> operation on a <tt>Reader</tt> input, writing
     *   results to a <tt>Writer</tt>.
     * </p>
     * <p>
     *   No additional configuration arguments are required. Unescape operations
     *   will always perform <em>complete</em> JSON unescape of SECs and u-based escapes.
     * </p>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param reader the <tt>Reader</tt> reading the text to be unescaped.
     * @param writer the <tt>java.io.Writer</tt> to which the unescaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @throws IOException if an input/output exception occurs
     *
     * @since 1.1.2
     */
    public static void unescapeJson(final Reader reader, final Writer writer)
            throws IOException {

        if (writer == null) {
            throw new IllegalArgumentException("Argument 'writer' cannot be null");
        }

        JsonEscapeUtil.unescape(reader, writer);

    }


    /**
     * <p>
     *   Perform a JSON <strong>unescape</strong> operation on a <tt>char[]</tt> input.
     * </p>
     * <p>
     *   No additional configuration arguments are required. Unescape operations
     *   will always perform <em>complete</em> JSON unescape of SECs and u-based escapes.
     * </p>
     * <p>
     *   This method is <strong>thread-safe</strong>.
     * </p>
     *
     * @param text the <tt>char[]</tt> to be unescaped.
     * @param offset the position in <tt>text</tt> at which the unescape operation should start.
     * @param len the number of characters in <tt>text</tt> that should be unescaped.
     * @param writer the <tt>java.io.Writer</tt> to which the unescaped result will be written. Nothing will
     *               be written at all to this writer if input is <tt>null</tt>.
     * @throws IOException if an input/output exception occurs
     */
    public static void unescapeJson(final char[] text, final int offset, final int len, final Writer writer)
                                    throws IOException {

        if (writer == null) {
            throw new IllegalArgumentException("Argument 'writer' cannot be null");
        }

        final int textLen = (text == null? 0 : text.length);

        if (offset < 0 || offset > textLen) {
            throw new IllegalArgumentException(
                    "Invalid (offset, len). offset=" + offset + ", len=" + len + ", text.length=" + textLen);
        }

        if (len < 0 || (offset + len) > textLen) {
            throw new IllegalArgumentException(
                    "Invalid (offset, len). offset=" + offset + ", len=" + len + ", text.length=" + textLen);
        }

        JsonEscapeUtil.unescape(text, offset, len, writer);

    }




    private JsonEscape() {
        super();
    }



    /*
     * This is basically a very simplified, thread-unsafe version of StringReader that should
     * perform better than the original StringReader by removing all synchronization structures.
     *
     * Note the only implemented methods are those that we know are really used from within the
     * stream-based escape/unescape operations.
     */
    private static final class InternalStringReader extends Reader {

        private String str;
        private int length;
        private int next = 0;

        public InternalStringReader(final String s) {
            super();
            this.str = s;
            this.length = s.length();
        }

        @Override
        public int read() throws IOException {
            if (this.next >= length) {
                return -1;
            }
            return this.str.charAt(this.next++);
        }

        @Override
        public int read(final char[] cbuf, final int off, final int len) throws IOException {
            if ((off < 0) || (off > cbuf.length) || (len < 0) ||
                    ((off + len) > cbuf.length) || ((off + len) < 0)) {
                throw new IndexOutOfBoundsException();
            } else if (len == 0) {
                return 0;
            }
            if (this.next >= this.length) {
                return -1;
            }
            int n = Math.min(this.length - this.next, len);
            this.str.getChars(this.next, this.next + n, cbuf, off);
            this.next += n;
            return n;
        }

        @Override
        public void close() throws IOException {
            this.str = null; // Just set the reference to null, help the GC
        }

    }


}