/*
 * 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.tsfile.external.commons.io;

import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.charset.UnsupportedCharsetException;
import java.util.Collections;
import java.util.SortedMap;
import java.util.TreeMap;

/**
 * Charsets required of every implementation of the Java platform.
 *
 * <p>From the Java documentation <a
 * href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard
 * charsets</a>:
 *
 * <p><cite>Every implementation of the Java platform is required to support the following character
 * encodings. Consult the release documentation for your implementation to see if any other
 * encodings are supported. Consult the release documentation for your implementation to see if any
 * other encodings are supported. </cite>
 *
 * <ul>
 *   <li>{@code US-ASCII}<br>
 *       Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the Basic Latin block of the Unicode character
 *       set.
 *   <li>{@code ISO-8859-1}<br>
 *       ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1.
 *   <li>{@code UTF-8}<br>
 *       Eight-bit Unicode Transformation Format.
 *   <li>{@code UTF-16BE}<br>
 *       Sixteen-bit Unicode Transformation Format, big-endian byte order.
 *   <li>{@code UTF-16LE}<br>
 *       Sixteen-bit Unicode Transformation Format, little-endian byte order.
 *   <li>{@code UTF-16}<br>
 *       Sixteen-bit Unicode Transformation Format, byte order specified by a mandatory initial
 *       byte-order mark (either order accepted on input, big-endian used on output.)
 * </ul>
 *
 * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard
 *     charsets</a>
 * @since 2.3
 */
public class Charsets {

  //
  // This class should only contain Charset instances for required encodings. This guarantees that
  // it will load
  // correctly and without delay on all Java platforms.
  //

  private static final SortedMap<String, Charset> STANDARD_CHARSET_MAP;

  static {
    final SortedMap<String, Charset> standardCharsetMap =
        new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
    standardCharsetMap.put(StandardCharsets.ISO_8859_1.name(), StandardCharsets.ISO_8859_1);
    standardCharsetMap.put(StandardCharsets.US_ASCII.name(), StandardCharsets.US_ASCII);
    standardCharsetMap.put(StandardCharsets.UTF_16.name(), StandardCharsets.UTF_16);
    standardCharsetMap.put(StandardCharsets.UTF_16BE.name(), StandardCharsets.UTF_16BE);
    standardCharsetMap.put(StandardCharsets.UTF_16LE.name(), StandardCharsets.UTF_16LE);
    standardCharsetMap.put(StandardCharsets.UTF_8.name(), StandardCharsets.UTF_8);
    STANDARD_CHARSET_MAP = Collections.unmodifiableSortedMap(standardCharsetMap);
  }

  /**
   * CharEncodingISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1.
   *
   * <p>Every implementation of the Java platform is required to support this character encoding.
   *
   * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard
   *     charsets</a>
   * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
   */
  @Deprecated public static final Charset ISO_8859_1 = StandardCharsets.ISO_8859_1;

  /**
   * Seven-bit ASCII, also known as ISO646-US, also known as the Basic Latin block of the Unicode
   * character set.
   *
   * <p>Every implementation of the Java platform is required to support this character encoding.
   *
   * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard
   *     charsets</a>
   * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
   */
  @Deprecated public static final Charset US_ASCII = StandardCharsets.US_ASCII;

  /**
   * Sixteen-bit Unicode Transformation Format, The byte order specified by a mandatory initial
   * byte-order mark (either order accepted on input, big-endian used on output)
   *
   * <p>Every implementation of the Java platform is required to support this character encoding.
   *
   * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard
   *     charsets</a>
   * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
   */
  @Deprecated public static final Charset UTF_16 = StandardCharsets.UTF_16;

  /**
   * Sixteen-bit Unicode Transformation Format, big-endian byte order.
   *
   * <p>Every implementation of the Java platform is required to support this character encoding.
   *
   * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard
   *     charsets</a>
   * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
   */
  @Deprecated public static final Charset UTF_16BE = StandardCharsets.UTF_16BE;

  /**
   * Sixteen-bit Unicode Transformation Format, little-endian byte order.
   *
   * <p>Every implementation of the Java platform is required to support this character encoding.
   *
   * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard
   *     charsets</a>
   * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
   */
  @Deprecated public static final Charset UTF_16LE = StandardCharsets.UTF_16LE;

  /**
   * Eight-bit Unicode Transformation Format.
   *
   * <p>Every implementation of the Java platform is required to support this character encoding.
   *
   * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard
   *     charsets</a>
   * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
   */
  @Deprecated public static final Charset UTF_8 = StandardCharsets.UTF_8;

  /**
   * Constructs a sorted map from canonical charset names to charset objects required of every
   * implementation of the Java platform.
   *
   * <p>From the Java documentation <a
   * href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard
   * charsets</a>:
   *
   * @return An immutable, case-insensitive map from canonical charset names to charset objects.
   * @see Charset#availableCharsets()
   * @since 2.5
   */
  public static SortedMap<String, Charset> requiredCharsets() {
    return STANDARD_CHARSET_MAP;
  }

  /**
   * Returns the given Charset or the default Charset if the given Charset is null.
   *
   * @param charset A charset or null.
   * @return the given Charset or the default Charset if the given Charset is null
   */
  public static Charset toCharset(final Charset charset) {
    return charset == null ? Charset.defaultCharset() : charset;
  }

  /**
   * Returns the given charset if non-null, otherwise return defaultCharset.
   *
   * @param charset The charset to test, may be null.
   * @param defaultCharset The charset to return if charset is null, may be null.
   * @return a Charset .
   * @since 2.12.0
   */
  public static Charset toCharset(final Charset charset, final Charset defaultCharset) {
    return charset == null ? defaultCharset : charset;
  }

  /**
   * Returns a Charset for the named charset. If the name is null, return the default Charset.
   *
   * @param charsetName The name of the requested charset, may be null.
   * @return a Charset for the named charset.
   * @throws UnsupportedCharsetException If the named charset is unavailable (unchecked exception).
   */
  public static Charset toCharset(final String charsetName) throws UnsupportedCharsetException {
    return toCharset(charsetName, Charset.defaultCharset());
  }

  /**
   * Returns a Charset for the named charset. If the name is null, return the given default Charset.
   *
   * @param charsetName The name of the requested charset, may be null.
   * @param defaultCharset The name charset to return if charsetName is null, may be null.
   * @return a Charset for the named charset.
   * @throws UnsupportedCharsetException If the named charset is unavailable (unchecked exception).
   * @since 2.12.0
   */
  public static Charset toCharset(final String charsetName, final Charset defaultCharset)
      throws UnsupportedCharsetException {
    return charsetName == null ? defaultCharset : Charset.forName(charsetName);
  }
}
