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/*
 * Copyright (C) 2009 The Guava Authors
 *
 * 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 com.signalfx.shaded.google.common.net;

import com.signalfx.shaded.google.common.annotations.GwtCompatible;
import com.signalfx.shaded.google.common.escape.Escaper;

/**
 * {@code Escaper} instances suitable for strings to be included in particular sections of URLs.
 *
 * If the resulting URLs are inserted into an HTML or XML document, they will require additional
 * escaping with {@link com.signalfx.shaded.google.common.html.HtmlEscapers} or {@link
 * com.signalfx.shaded.google.common.xml.XmlEscapers}.
 *
 * @author David Beaumont
 * @author Chris Povirk
 * @since 15.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public final class UrlEscapers {
  private UrlEscapers() {}

  // For each xxxEscaper() method, please add links to external reference pages
  // that are considered authoritative for the behavior of that escaper.

  static final String URL_FORM_PARAMETER_OTHER_SAFE_CHARS = "-_.*";

  static final String URL_PATH_OTHER_SAFE_CHARS_LACKING_PLUS =
      "-._~" // Unreserved characters.
          + "!$'()*,;&=" // The subdelim characters (excluding '+').
          + "@:"; // The gendelim characters permitted in paths.

  /**
   * Returns an {@link Escaper} instance that escapes strings so they can be safely included in URL form parameter names and values. Escaping is performed
   * with the UTF-8 character encoding. The caller is responsible for replacing any unpaired carriage return or line feed characters
   * with a CR+LF pair on any non-file inputs before escaping them with this escaper.
   *
   * 
When escaping a String, the following rules apply:
   *
   * 

   *   The alphanumeric characters "a" through "z", "A" through "Z" and "0" through "9" remain
   *       the same.
   *   
The special characters ".", "-", "*", and "_" remain the same.
   *   
The space character " " is converted into a plus sign "+".
   *   
All other characters are converted into one or more bytes using UTF-8 encoding and each
   *       byte is then represented by the 3-character string "%XY", where "XY" is the two-digit,
   *       uppercase, hexadecimal representation of the byte value.
   * 
   *
   * This escaper is suitable for escaping parameter names and values even when using the non-standard semicolon, rather than the ampersand, as
   * a parameter delimiter. Nevertheless, we recommend using the ampersand unless you must
   * interoperate with systems that require semicolons.
   *
   * 
Note: Unlike other escapers, URL escapers produce uppercase hexadecimal sequences.
   *
   */
  public static Escaper urlFormParameterEscaper() {
    return URL_FORM_PARAMETER_ESCAPER;
  }

  private static final Escaper URL_FORM_PARAMETER_ESCAPER =
      new PercentEscaper(URL_FORM_PARAMETER_OTHER_SAFE_CHARS, true);

  /**
   * Returns an {@link Escaper} instance that escapes strings so they can be safely included in URL path segments. The returned escaper escapes all non-ASCII
   * characters, even though many of these are accepted in modern
   * URLs. (If the escaper were to leave these characters
   * unescaped, they would be escaped by the consumer at parse time, anyway.) Additionally, the
   * escaper escapes the slash character ("/"). While slashes are acceptable in URL paths, they are
   * considered by the specification to be separators between "path segments." This implies that, if
   * you wish for your path to contain slashes, you must escape each segment separately and then
   * join them.
   *
   * 
When escaping a String, the following rules apply:
   *
   * 

   *   The alphanumeric characters "a" through "z", "A" through "Z" and "0" through "9" remain
   *       the same.
   *   
The unreserved characters ".", "-", "~", and "_" remain the same.
   *   
The general delimiters "@" and ":" remain the same.
   *   
The subdelimiters "!", "$", "&", "'", "(", ")", "*", "+", ",", ";", and "=" remain
   *       the same.
   *   
The space character " " is converted into %20.
   *   
All other characters are converted into one or more bytes using UTF-8 encoding and each
   *       byte is then represented by the 3-character string "%XY", where "XY" is the two-digit,
   *       uppercase, hexadecimal representation of the byte value.
   * 
   *
   * Note: Unlike other escapers, URL escapers produce uppercase hexadecimal sequences.
   */
  public static Escaper urlPathSegmentEscaper() {
    return URL_PATH_SEGMENT_ESCAPER;
  }

  private static final Escaper URL_PATH_SEGMENT_ESCAPER =
      new PercentEscaper(URL_PATH_OTHER_SAFE_CHARS_LACKING_PLUS + "+", false);

  /**
   * Returns an {@link Escaper} instance that escapes strings so they can be safely included in a URL fragment. The returned escaper escapes all non-ASCII
   * characters, even though many of these are accepted in modern
   * URLs.
   *
   * 
When escaping a String, the following rules apply:
   *
   * 

   *   The alphanumeric characters "a" through "z", "A" through "Z" and "0" through "9" remain
   *       the same.
   *   
The unreserved characters ".", "-", "~", and "_" remain the same.
   *   
The general delimiters "@" and ":" remain the same.
   *   
The subdelimiters "!", "$", "&", "'", "(", ")", "*", "+", ",", ";", and "=" remain
   *       the same.
   *   
The space character " " is converted into %20.
   *   
Fragments allow unescaped "/" and "?", so they remain the same.
   *   
All other characters are converted into one or more bytes using UTF-8 encoding and each
   *       byte is then represented by the 3-character string "%XY", where "XY" is the two-digit,
   *       uppercase, hexadecimal representation of the byte value.
   * 
   *
   * Note: Unlike other escapers, URL escapers produce uppercase hexadecimal sequences.
   */
  public static Escaper urlFragmentEscaper() {
    return URL_FRAGMENT_ESCAPER;
  }

  private static final Escaper URL_FRAGMENT_ESCAPER =
      new PercentEscaper(URL_PATH_OTHER_SAFE_CHARS_LACKING_PLUS + "+/?", false);
}