// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// http://code.google.com/p/protobuf/
//
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// modification, are permitted provided that the following conditions are
// met:
//
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// notice, this list of conditions and the following disclaimer.
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// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
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package com.google.protobuf;

import java.io.UnsupportedEncodingException;

/**
 * The classes contained within are used internally by the Protocol Buffer
 * library and generated message implementations. They are public only because
 * those generated messages do not reside in the {@code protobuf} package.
 * Others should not use this class directly.
 *
 * @author kenton@google.com (Kenton Varda)
 */
public class Internal {
  /**
   * Helper called by generated code to construct default values for string
   * fields.
   * <p>
   * The protocol compiler does not actually contain a UTF-8 decoder -- it
   * just pushes UTF-8-encoded text around without touching it.  The one place
   * where this presents a problem is when generating Java string literals.
   * Unicode characters in the string literal would normally need to be encoded
   * using a Unicode escape sequence, which would require decoding them.
   * To get around this, protoc instead embeds the UTF-8 bytes into the
   * generated code and leaves it to the runtime library to decode them.
   * <p>
   * It gets worse, though.  If protoc just generated a byte array, like:
   *   new byte[] {0x12, 0x34, 0x56, 0x78}
   * Java actually generates *code* which allocates an array and then fills
   * in each value.  This is much less efficient than just embedding the bytes
   * directly into the bytecode.  To get around this, we need another
   * work-around.  String literals are embedded directly, so protoc actually
   * generates a string literal corresponding to the bytes.  The easiest way
   * to do this is to use the ISO-8859-1 character set, which corresponds to
   * the first 256 characters of the Unicode range.  Protoc can then use
   * good old CEscape to generate the string.
   * <p>
   * So we have a string literal which represents a set of bytes which
   * represents another string.  This function -- stringDefaultValue --
   * converts from the generated string to the string we actually want.  The
   * generated code calls this automatically.
   */
  public static String stringDefaultValue(String bytes) {
    try {
      return new String(bytes.getBytes("ISO-8859-1"), "UTF-8");
    } catch (UnsupportedEncodingException e) {
      // This should never happen since all JVMs are required to implement
      // both of the above character sets.
      throw new IllegalStateException(
          "Java VM does not support a standard character set.", e);
    }
  }

  /**
   * Helper called by generated code to construct default values for bytes
   * fields.
   * <p>
   * This is a lot like {@link #stringDefaultValue}, but for bytes fields.
   * In this case we only need the second of the two hacks -- allowing us to
   * embed raw bytes as a string literal with ISO-8859-1 encoding.
   */
  public static ByteString bytesDefaultValue(String bytes) {
    try {
      return ByteString.copyFrom(bytes.getBytes("ISO-8859-1"));
    } catch (UnsupportedEncodingException e) {
      // This should never happen since all JVMs are required to implement
      // ISO-8859-1.
      throw new IllegalStateException(
          "Java VM does not support a standard character set.", e);
    }
  }

  /**
   * Helper called by generated code to determine if a byte array is a valid
   * UTF-8 encoded string such that the original bytes can be converted to
   * a String object and then back to a byte array round tripping the bytes
   * without loss.  More precisely, returns {@code true} whenever:
   * <pre>   {@code
   * Arrays.equals(byteString.toByteArray(),
   *     new String(byteString.toByteArray(), "UTF-8").getBytes("UTF-8"))
   * }</pre>
   *
   * <p>This method rejects "overlong" byte sequences, as well as
   * 3-byte sequences that would map to a surrogate character, in
   * accordance with the restricted definition of UTF-8 introduced in
   * Unicode 3.1.  Note that the UTF-8 decoder included in Oracle's
   * JDK has been modified to also reject "overlong" byte sequences,
   * but currently (2011) still accepts 3-byte surrogate character
   * byte sequences.
   *
   * <p>See the Unicode Standard,</br>
   * Table 3-6. <em>UTF-8 Bit Distribution</em>,</br>
   * Table 3-7. <em>Well Formed UTF-8 Byte Sequences</em>.
   *
   * <p>As of 2011-02, this method simply returns the result of {@link
   * ByteString#isValidUtf8()}.  Calling that method directly is preferred.
   *
   * @param byteString the string to check
   * @return whether the byte array is round trippable
   */
  public static boolean isValidUtf8(ByteString byteString) {
    return byteString.isValidUtf8();
  }

  /**
   * Interface for an enum value or value descriptor, to be used in FieldSet.
   * The lite library stores enum values directly in FieldSets but the full
   * library stores EnumValueDescriptors in order to better support reflection.
   */
  public interface EnumLite {
    int getNumber();
  }

  /**
   * Interface for an object which maps integers to {@link EnumLite}s.
   * {@link Descriptors.EnumDescriptor} implements this interface by mapping
   * numbers to {@link Descriptors.EnumValueDescriptor}s.  Additionally,
   * every generated enum type has a static method internalGetValueMap() which
   * returns an implementation of this type that maps numbers to enum values.
   */
  public interface EnumLiteMap<T extends EnumLite> {
    T findValueByNumber(int number);
  }
}