// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// http://code.google.com/p/protobuf/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package com.google.protobuf;

import com.google.protobuf.Descriptors.Descriptor;
import com.google.protobuf.Descriptors.FieldDescriptor;
import com.google.protobuf.Descriptors.EnumDescriptor;
import com.google.protobuf.Descriptors.EnumValueDescriptor;

import java.io.IOException;
import java.nio.CharBuffer;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Provide ascii text parsing and formatting support for proto2 instances.
 * The implementation largely follows google/protobuf/text_format.cc.
 *
 * @author wenboz@google.com Wenbo Zhu
 * @author kenton@google.com Kenton Varda
 */
public final class TextFormat {
  private TextFormat() {
  }

  /**
   * Outputs a textual representation of the Protocol Message supplied into
   * the parameter output. (This representation is the new version of the
   * classic "ProtocolPrinter" output from the original Protocol Buffer system)
   */
  public static void print(final Message message, final Appendable output)
                           throws IOException {
    final TextGenerator generator = new TextGenerator(output);
    print(message, generator);
  }

  /** Outputs a textual representation of {@code fields} to {@code output}. */
  public static void print(final UnknownFieldSet fields,
                           final Appendable output)
                           throws IOException {
    final TextGenerator generator = new TextGenerator(output);
    printUnknownFields(fields, generator);
  }

  /**
   * Like {@code print()}, but writes directly to a {@code String} and
   * returns it.
   */
  public static String printToString(final Message message) {
    try {
      final StringBuilder text = new StringBuilder();
      print(message, text);
      return text.toString();
    } catch (IOException e) {
      throw new RuntimeException(
        "Writing to a StringBuilder threw an IOException (should never " +
        "happen).", e);
    }
  }

  /**
   * Like {@code print()}, but writes directly to a {@code String} and
   * returns it.
   */
  public static String printToString(final UnknownFieldSet fields) {
    try {
      final StringBuilder text = new StringBuilder();
      print(fields, text);
      return text.toString();
    } catch (IOException e) {
      throw new RuntimeException(
        "Writing to a StringBuilder threw an IOException (should never " +
        "happen).", e);
    }
  }

  private static void print(final Message message,
                            final TextGenerator generator)
      throws IOException {
    for (final Map.Entry<FieldDescriptor, Object> field :
         message.getAllFields().entrySet()) {
      printField(field.getKey(), field.getValue(), generator);
    }
    printUnknownFields(message.getUnknownFields(), generator);
  }

  public static void printField(final FieldDescriptor field,
                                final Object value,
                                final Appendable output)
                                throws IOException {
    final TextGenerator generator = new TextGenerator(output);
    printField(field, value, generator);
  }

  public static String printFieldToString(final FieldDescriptor field,
                                          final Object value) {
    try {
      final StringBuilder text = new StringBuilder();
      printField(field, value, text);
      return text.toString();
    } catch (IOException e) {
      throw new RuntimeException(
        "Writing to a StringBuilder threw an IOException (should never " +
        "happen).", e);
    }
  }

  private static void printField(final FieldDescriptor field,
                                final Object value,
                                final TextGenerator generator)
                                throws IOException {
    if (field.isRepeated()) {
      // Repeated field.  Print each element.
      for (final Object element : (List) value) {
        printSingleField(field, element, generator);
      }
    } else {
      printSingleField(field, value, generator);
    }
  }

  private static void printSingleField(final FieldDescriptor field,
                                       final Object value,
                                       final TextGenerator generator)
                                       throws IOException {
    if (field.isExtension()) {
      generator.print("[");
      // We special-case MessageSet elements for compatibility with proto1.
      if (field.getContainingType().getOptions().getMessageSetWireFormat()
          && (field.getType() == FieldDescriptor.Type.MESSAGE)
          && (field.isOptional())
          // object equality
          && (field.getExtensionScope() == field.getMessageType())) {
        generator.print(field.getMessageType().getFullName());
      } else {
        generator.print(field.getFullName());
      }
      generator.print("]");
    } else {
      if (field.getType() == FieldDescriptor.Type.GROUP) {
        // Groups must be serialized with their original capitalization.
        generator.print(field.getMessageType().getName());
      } else {
        generator.print(field.getName());
      }
    }

    if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
      generator.print(" {\n");
      generator.indent();
    } else {
      generator.print(": ");
    }

    printFieldValue(field, value, generator);

    if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
      generator.outdent();
      generator.print("}");
    }
    generator.print("\n");
  }

  private static void printFieldValue(final FieldDescriptor field,
                                      final Object value,
                                      final TextGenerator generator)
                                      throws IOException {
    switch (field.getType()) {
      case INT32:
      case INT64:
      case SINT32:
      case SINT64:
      case SFIXED32:
      case SFIXED64:
      case FLOAT:
      case DOUBLE:
      case BOOL:
        // Good old toString() does what we want for these types.
        generator.print(value.toString());
        break;

      case UINT32:
      case FIXED32:
        generator.print(unsignedToString((Integer) value));
        break;

      case UINT64:
      case FIXED64:
        generator.print(unsignedToString((Long) value));
        break;

      case STRING:
        generator.print("\"");
        generator.print(escapeText((String) value));
        generator.print("\"");
        break;

      case BYTES:
        generator.print("\"");
        generator.print(escapeBytes((ByteString) value));
        generator.print("\"");
        break;

      case ENUM:
        generator.print(((EnumValueDescriptor) value).getName());
        break;

      case MESSAGE:
      case GROUP:
        print((Message) value, generator);
        break;
    }
  }

  private static void printUnknownFields(final UnknownFieldSet unknownFields,
                                         final TextGenerator generator)
                                         throws IOException {
    for (final Map.Entry<Integer, UnknownFieldSet.Field> entry :
         unknownFields.asMap().entrySet()) {
      final String prefix = entry.getKey().toString() + ": ";
      final UnknownFieldSet.Field field = entry.getValue();

      for (final long value : field.getVarintList()) {
        generator.print(entry.getKey().toString());
        generator.print(": ");
        generator.print(unsignedToString(value));
        generator.print("\n");
      }
      for (final int value : field.getFixed32List()) {
        generator.print(entry.getKey().toString());
        generator.print(": ");
        generator.print(String.format((Locale) null, "0x%08x", value));
        generator.print("\n");
      }
      for (final long value : field.getFixed64List()) {
        generator.print(entry.getKey().toString());
        generator.print(": ");
        generator.print(String.format((Locale) null, "0x%016x", value));
        generator.print("\n");
      }
      for (final ByteString value : field.getLengthDelimitedList()) {
        generator.print(entry.getKey().toString());
        generator.print(": \"");
        generator.print(escapeBytes(value));
        generator.print("\"\n");
      }
      for (final UnknownFieldSet value : field.getGroupList()) {
        generator.print(entry.getKey().toString());
        generator.print(" {\n");
        generator.indent();
        printUnknownFields(value, generator);
        generator.outdent();
        generator.print("}\n");
      }
    }
  }

  /** Convert an unsigned 32-bit integer to a string. */
  private static String unsignedToString(final int value) {
    if (value >= 0) {
      return Integer.toString(value);
    } else {
      return Long.toString(((long) value) & 0x00000000FFFFFFFFL);
    }
  }

  /** Convert an unsigned 64-bit integer to a string. */
  private static String unsignedToString(final long value) {
    if (value >= 0) {
      return Long.toString(value);
    } else {
      // Pull off the most-significant bit so that BigInteger doesn't think
      // the number is negative, then set it again using setBit().
      return BigInteger.valueOf(value & 0x7FFFFFFFFFFFFFFFL)
                       .setBit(63).toString();
    }
  }

  /**
   * An inner class for writing text to the output stream.
   */
  private static final class TextGenerator {
    private Appendable output;
    private boolean atStartOfLine = true;
    private final StringBuilder indent = new StringBuilder();

    private TextGenerator(final Appendable output) {
      this.output = output;
    }

    /**
     * Indent text by two spaces.  After calling Indent(), two spaces will be
     * inserted at the beginning of each line of text.  Indent() may be called
     * multiple times to produce deeper indents.
     */
    public void indent() {
      indent.append("  ");
    }

    /**
     * Reduces the current indent level by two spaces, or crashes if the indent
     * level is zero.
     */
    public void outdent() {
      final int length = indent.length();
      if (length == 0) {
        throw new IllegalArgumentException(
            " Outdent() without matching Indent().");
      }
      indent.delete(length - 2, length);
    }

    /**
     * Print text to the output stream.
     */
    public void print(final CharSequence text) throws IOException {
      final int size = text.length();
      int pos = 0;

      for (int i = 0; i < size; i++) {
        if (text.charAt(i) == '\n') {
          write(text.subSequence(pos, size), i - pos + 1);
          pos = i + 1;
          atStartOfLine = true;
        }
      }
      write(text.subSequence(pos, size), size - pos);
    }

    private void write(final CharSequence data, final int size)
                       throws IOException {
      if (size == 0) {
        return;
      }
      if (atStartOfLine) {
        atStartOfLine = false;
        output.append(indent);
      }
      output.append(data);
    }
  }

  // =================================================================
  // Parsing

  /**
   * Represents a stream of tokens parsed from a {@code String}.
   *
   * <p>The Java standard library provides many classes that you might think
   * would be useful for implementing this, but aren't.  For example:
   *
   * <ul>
   * <li>{@code java.io.StreamTokenizer}:  This almost does what we want -- or,
   *   at least, something that would get us close to what we want -- except
   *   for one fatal flaw:  It automatically un-escapes strings using Java
   *   escape sequences, which do not include all the escape sequences we
   *   need to support (e.g. '\x').
   * <li>{@code java.util.Scanner}:  This seems like a great way at least to
   *   parse regular expressions out of a stream (so we wouldn't have to load
   *   the entire input into a single string before parsing).  Sadly,
   *   {@code Scanner} requires that tokens be delimited with some delimiter.
   *   Thus, although the text "foo:" should parse to two tokens ("foo" and
   *   ":"), {@code Scanner} would recognize it only as a single token.
   *   Furthermore, {@code Scanner} provides no way to inspect the contents
   *   of delimiters, making it impossible to keep track of line and column
   *   numbers.
   * </ul>
   *
   * <p>Luckily, Java's regular expression support does manage to be useful to
   * us.  (Barely:  We need {@code Matcher.usePattern()}, which is new in
   * Java 1.5.)  So, we can use that, at least.  Unfortunately, this implies
   * that we need to have the entire input in one contiguous string.
   */
  private static final class Tokenizer {
    private final CharSequence text;
    private final Matcher matcher;
    private String currentToken;

    // The character index within this.text at which the current token begins.
    private int pos = 0;

    // The line and column numbers of the current token.
    private int line = 0;
    private int column = 0;

    // The line and column numbers of the previous token (allows throwing
    // errors *after* consuming).
    private int previousLine = 0;
    private int previousColumn = 0;

    // We use possesive quantifiers (*+ and ++) because otherwise the Java
    // regex matcher has stack overflows on large inputs.
    private static final Pattern WHITESPACE =
      Pattern.compile("(\\s|(#.*$))++", Pattern.MULTILINE);
    private static final Pattern TOKEN = Pattern.compile(
      "[a-zA-Z_][0-9a-zA-Z_+-]*+|" +                // an identifier
      "[.]?[0-9+-][0-9a-zA-Z_.+-]*+|" +             // a number
      "\"([^\"\n\\\\]|\\\\.)*+(\"|\\\\?$)|" +       // a double-quoted string
      "\'([^\'\n\\\\]|\\\\.)*+(\'|\\\\?$)",         // a single-quoted string
      Pattern.MULTILINE);

    private static final Pattern DOUBLE_INFINITY = Pattern.compile(
      "-?inf(inity)?",
      Pattern.CASE_INSENSITIVE);
    private static final Pattern FLOAT_INFINITY = Pattern.compile(
      "-?inf(inity)?f?",
      Pattern.CASE_INSENSITIVE);
    private static final Pattern FLOAT_NAN = Pattern.compile(
      "nanf?",
      Pattern.CASE_INSENSITIVE);

    /** Construct a tokenizer that parses tokens from the given text. */
    private Tokenizer(final CharSequence text) {
      this.text = text;
      this.matcher = WHITESPACE.matcher(text);
      skipWhitespace();
      nextToken();
    }

    /** Are we at the end of the input? */
    public boolean atEnd() {
      return currentToken.length() == 0;
    }

    /** Advance to the next token. */
    public void nextToken() {
      previousLine = line;
      previousColumn = column;

      // Advance the line counter to the current position.
      while (pos < matcher.regionStart()) {
        if (text.charAt(pos) == '\n') {
          ++line;
          column = 0;
        } else {
          ++column;
        }
        ++pos;
      }

      // Match the next token.
      if (matcher.regionStart() == matcher.regionEnd()) {
        // EOF
        currentToken = "";
      } else {
        matcher.usePattern(TOKEN);
        if (matcher.lookingAt()) {
          currentToken = matcher.group();
          matcher.region(matcher.end(), matcher.regionEnd());
        } else {
          // Take one character.
          currentToken = String.valueOf(text.charAt(pos));
          matcher.region(pos + 1, matcher.regionEnd());
        }

        skipWhitespace();
      }
    }

    /**
     * Skip over any whitespace so that the matcher region starts at the next
     * token.
     */
    private void skipWhitespace() {
      matcher.usePattern(WHITESPACE);
      if (matcher.lookingAt()) {
        matcher.region(matcher.end(), matcher.regionEnd());
      }
    }

    /**
     * If the next token exactly matches {@code token}, consume it and return
     * {@code true}.  Otherwise, return {@code false} without doing anything.
     */
    public boolean tryConsume(final String token) {
      if (currentToken.equals(token)) {
        nextToken();
        return true;
      } else {
        return false;
      }
    }

    /**
     * If the next token exactly matches {@code token}, consume it.  Otherwise,
     * throw a {@link ParseException}.
     */
    public void consume(final String token) throws ParseException {
      if (!tryConsume(token)) {
        throw parseException("Expected \"" + token + "\".");
      }
    }

    /**
     * Returns {@code true} if the next token is an integer, but does
     * not consume it.
     */
    public boolean lookingAtInteger() {
      if (currentToken.length() == 0) {
        return false;
      }

      final char c = currentToken.charAt(0);
      return ('0' <= c && c <= '9') ||
             c == '-' || c == '+';
    }

    /**
     * If the next token is an identifier, consume it and return its value.
     * Otherwise, throw a {@link ParseException}.
     */
    public String consumeIdentifier() throws ParseException {
      for (int i = 0; i < currentToken.length(); i++) {
        final char c = currentToken.charAt(i);
        if (('a' <= c && c <= 'z') ||
            ('A' <= c && c <= 'Z') ||
            ('0' <= c && c <= '9') ||
            (c == '_') || (c == '.')) {
          // OK
        } else {
          throw parseException("Expected identifier.");
        }
      }

      final String result = currentToken;
      nextToken();
      return result;
    }

    /**
     * If the next token is a 32-bit signed integer, consume it and return its
     * value.  Otherwise, throw a {@link ParseException}.
     */
    public int consumeInt32() throws ParseException {
      try {
        final int result = parseInt32(currentToken);
        nextToken();
        return result;
      } catch (NumberFormatException e) {
        throw integerParseException(e);
      }
    }

    /**
     * If the next token is a 32-bit unsigned integer, consume it and return its
     * value.  Otherwise, throw a {@link ParseException}.
     */
    public int consumeUInt32() throws ParseException {
      try {
        final int result = parseUInt32(currentToken);
        nextToken();
        return result;
      } catch (NumberFormatException e) {
        throw integerParseException(e);
      }
    }

    /**
     * If the next token is a 64-bit signed integer, consume it and return its
     * value.  Otherwise, throw a {@link ParseException}.
     */
    public long consumeInt64() throws ParseException {
      try {
        final long result = parseInt64(currentToken);
        nextToken();
        return result;
      } catch (NumberFormatException e) {
        throw integerParseException(e);
      }
    }

    /**
     * If the next token is a 64-bit unsigned integer, consume it and return its
     * value.  Otherwise, throw a {@link ParseException}.
     */
    public long consumeUInt64() throws ParseException {
      try {
        final long result = parseUInt64(currentToken);
        nextToken();
        return result;
      } catch (NumberFormatException e) {
        throw integerParseException(e);
      }
    }

    /**
     * If the next token is a double, consume it and return its value.
     * Otherwise, throw a {@link ParseException}.
     */
    public double consumeDouble() throws ParseException {
      // We need to parse infinity and nan separately because
      // Double.parseDouble() does not accept "inf", "infinity", or "nan".
      if (DOUBLE_INFINITY.matcher(currentToken).matches()) {
        final boolean negative = currentToken.startsWith("-");
        nextToken();
        return negative ? Double.NEGATIVE_INFINITY : Double.POSITIVE_INFINITY;
      }
      if (currentToken.equalsIgnoreCase("nan")) {
        nextToken();
        return Double.NaN;
      }
      try {
        final double result = Double.parseDouble(currentToken);
        nextToken();
        return result;
      } catch (NumberFormatException e) {
        throw floatParseException(e);
      }
    }

    /**
     * If the next token is a float, consume it and return its value.
     * Otherwise, throw a {@link ParseException}.
     */
    public float consumeFloat() throws ParseException {
      // We need to parse infinity and nan separately because
      // Float.parseFloat() does not accept "inf", "infinity", or "nan".
      if (FLOAT_INFINITY.matcher(currentToken).matches()) {
        final boolean negative = currentToken.startsWith("-");
        nextToken();
        return negative ? Float.NEGATIVE_INFINITY : Float.POSITIVE_INFINITY;
      }
      if (FLOAT_NAN.matcher(currentToken).matches()) {
        nextToken();
        return Float.NaN;
      }
      try {
        final float result = Float.parseFloat(currentToken);
        nextToken();
        return result;
      } catch (NumberFormatException e) {
        throw floatParseException(e);
      }
    }

    /**
     * If the next token is a boolean, consume it and return its value.
     * Otherwise, throw a {@link ParseException}.
     */
    public boolean consumeBoolean() throws ParseException {
      if (currentToken.equals("true")) {
        nextToken();
        return true;
      } else if (currentToken.equals("false")) {
        nextToken();
        return false;
      } else {
        throw parseException("Expected \"true\" or \"false\".");
      }
    }

    /**
     * If the next token is a string, consume it and return its (unescaped)
     * value.  Otherwise, throw a {@link ParseException}.
     */
    public String consumeString() throws ParseException {
      return consumeByteString().toStringUtf8();
    }

    /**
     * If the next token is a string, consume it, unescape it as a
     * {@link ByteString}, and return it.  Otherwise, throw a
     * {@link ParseException}.
     */
    public ByteString consumeByteString() throws ParseException {
      List<ByteString> list = new ArrayList<ByteString>();
      consumeByteString(list);
      while (currentToken.startsWith("'") || currentToken.startsWith("\"")) {
        consumeByteString(list);
      }
      return ByteString.copyFrom(list);
    }

    /**
     * Like {@link #consumeByteString()} but adds each token of the string to
     * the given list.  String literals (whether bytes or text) may come in
     * multiple adjacent tokens which are automatically concatenated, like in
     * C or Python.
     */
    private void consumeByteString(List<ByteString> list) throws ParseException {
      final char quote = currentToken.length() > 0 ? currentToken.charAt(0)
                                                   : '\0';
      if (quote != '\"' && quote != '\'') {
        throw parseException("Expected string.");
      }

      if (currentToken.length() < 2 ||
          currentToken.charAt(currentToken.length() - 1) != quote) {
        throw parseException("String missing ending quote.");
      }

      try {
        final String escaped =
            currentToken.substring(1, currentToken.length() - 1);
        final ByteString result = unescapeBytes(escaped);
        nextToken();
        list.add(result);
      } catch (InvalidEscapeSequenceException e) {
        throw parseException(e.getMessage());
      }
    }

    /**
     * Returns a {@link ParseException} with the current line and column
     * numbers in the description, suitable for throwing.
     */
    public ParseException parseException(final String description) {
      // Note:  People generally prefer one-based line and column numbers.
      return new ParseException(
        (line + 1) + ":" + (column + 1) + ": " + description);
    }

    /**
     * Returns a {@link ParseException} with the line and column numbers of
     * the previous token in the description, suitable for throwing.
     */
    public ParseException parseExceptionPreviousToken(
        final String description) {
      // Note:  People generally prefer one-based line and column numbers.
      return new ParseException(
        (previousLine + 1) + ":" + (previousColumn + 1) + ": " + description);
    }

    /**
     * Constructs an appropriate {@link ParseException} for the given
     * {@code NumberFormatException} when trying to parse an integer.
     */
    private ParseException integerParseException(
        final NumberFormatException e) {
      return parseException("Couldn't parse integer: " + e.getMessage());
    }

    /**
     * Constructs an appropriate {@link ParseException} for the given
     * {@code NumberFormatException} when trying to parse a float or double.
     */
    private ParseException floatParseException(final NumberFormatException e) {
      return parseException("Couldn't parse number: " + e.getMessage());
    }
  }

  /** Thrown when parsing an invalid text format message. */
  public static class ParseException extends IOException {
    private static final long serialVersionUID = 3196188060225107702L;

    public ParseException(final String message) {
      super(message);
    }
  }

  /**
   * Parse a text-format message from {@code input} and merge the contents
   * into {@code builder}.
   */
  public static void merge(final Readable input,
                           final Message.Builder builder)
                           throws IOException {
    merge(input, ExtensionRegistry.getEmptyRegistry(), builder);
  }

  /**
   * Parse a text-format message from {@code input} and merge the contents
   * into {@code builder}.
   */
  public static void merge(final CharSequence input,
                           final Message.Builder builder)
                           throws ParseException {
    merge(input, ExtensionRegistry.getEmptyRegistry(), builder);
  }

  /**
   * Parse a text-format message from {@code input} and merge the contents
   * into {@code builder}.  Extensions will be recognized if they are
   * registered in {@code extensionRegistry}.
   */
  public static void merge(final Readable input,
                           final ExtensionRegistry extensionRegistry,
                           final Message.Builder builder)
                           throws IOException {
    // Read the entire input to a String then parse that.

    // If StreamTokenizer were not quite so crippled, or if there were a kind
    // of Reader that could read in chunks that match some particular regex,
    // or if we wanted to write a custom Reader to tokenize our stream, then
    // we would not have to read to one big String.  Alas, none of these is
    // the case.  Oh well.

    merge(toStringBuilder(input), extensionRegistry, builder);
  }

  private static final int BUFFER_SIZE = 4096;

  // TODO(chrisn): See if working around java.io.Reader#read(CharBuffer)
  // overhead is worthwhile
  private static StringBuilder toStringBuilder(final Readable input)
      throws IOException {
    final StringBuilder text = new StringBuilder();
    final CharBuffer buffer = CharBuffer.allocate(BUFFER_SIZE);
    while (true) {
      final int n = input.read(buffer);
      if (n == -1) {
        break;
      }
      buffer.flip();
      text.append(buffer, 0, n);
    }
    return text;
  }

  /**
   * Parse a text-format message from {@code input} and merge the contents
   * into {@code builder}.  Extensions will be recognized if they are
   * registered in {@code extensionRegistry}.
   */
  public static void merge(final CharSequence input,
                           final ExtensionRegistry extensionRegistry,
                           final Message.Builder builder)
                           throws ParseException {
    final Tokenizer tokenizer = new Tokenizer(input);

    while (!tokenizer.atEnd()) {
      mergeField(tokenizer, extensionRegistry, builder);
    }
  }

  /**
   * Parse a single field from {@code tokenizer} and merge it into
   * {@code builder}.
   */
  private static void mergeField(final Tokenizer tokenizer,
                                 final ExtensionRegistry extensionRegistry,
                                 final Message.Builder builder)
                                 throws ParseException {
    FieldDescriptor field;
    final Descriptor type = builder.getDescriptorForType();
    ExtensionRegistry.ExtensionInfo extension = null;

    if (tokenizer.tryConsume("[")) {
      // An extension.
      final StringBuilder name =
          new StringBuilder(tokenizer.consumeIdentifier());
      while (tokenizer.tryConsume(".")) {
        name.append('.');
        name.append(tokenizer.consumeIdentifier());
      }

      extension = extensionRegistry.findExtensionByName(name.toString());

      if (extension == null) {
        throw tokenizer.parseExceptionPreviousToken(
          "Extension \"" + name + "\" not found in the ExtensionRegistry.");
      } else if (extension.descriptor.getContainingType() != type) {
        throw tokenizer.parseExceptionPreviousToken(
          "Extension \"" + name + "\" does not extend message type \"" +
          type.getFullName() + "\".");
      }

      tokenizer.consume("]");

      field = extension.descriptor;
    } else {
      final String name = tokenizer.consumeIdentifier();
      field = type.findFieldByName(name);

      // Group names are expected to be capitalized as they appear in the
      // .proto file, which actually matches their type names, not their field
      // names.
      if (field == null) {
        // Explicitly specify US locale so that this code does not break when
        // executing in Turkey.
        final String lowerName = name.toLowerCase(Locale.US);
        field = type.findFieldByName(lowerName);
        // If the case-insensitive match worked but the field is NOT a group,
        if (field != null && field.getType() != FieldDescriptor.Type.GROUP) {
          field = null;
        }
      }
      // Again, special-case group names as described above.
      if (field != null && field.getType() == FieldDescriptor.Type.GROUP &&
          !field.getMessageType().getName().equals(name)) {
        field = null;
      }

      if (field == null) {
        throw tokenizer.parseExceptionPreviousToken(
          "Message type \"" + type.getFullName() +
          "\" has no field named \"" + name + "\".");
      }
    }

    Object value = null;

    if (field.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
      tokenizer.tryConsume(":");  // optional

      final String endToken;
      if (tokenizer.tryConsume("<")) {
        endToken = ">";
      } else {
        tokenizer.consume("{");
        endToken = "}";
      }

      final Message.Builder subBuilder;
      if (extension == null) {
        subBuilder = builder.newBuilderForField(field);
      } else {
        subBuilder = extension.defaultInstance.newBuilderForType();
      }

      while (!tokenizer.tryConsume(endToken)) {
        if (tokenizer.atEnd()) {
          throw tokenizer.parseException(
            "Expected \"" + endToken + "\".");
        }
        mergeField(tokenizer, extensionRegistry, subBuilder);
      }

      value = subBuilder.build();

    } else {
      tokenizer.consume(":");

      switch (field.getType()) {
        case INT32:
        case SINT32:
        case SFIXED32:
          value = tokenizer.consumeInt32();
          break;

        case INT64:
        case SINT64:
        case SFIXED64:
          value = tokenizer.consumeInt64();
          break;

        case UINT32:
        case FIXED32:
          value = tokenizer.consumeUInt32();
          break;

        case UINT64:
        case FIXED64:
          value = tokenizer.consumeUInt64();
          break;

        case FLOAT:
          value = tokenizer.consumeFloat();
          break;

        case DOUBLE:
          value = tokenizer.consumeDouble();
          break;

        case BOOL:
          value = tokenizer.consumeBoolean();
          break;

        case STRING:
          value = tokenizer.consumeString();
          break;

        case BYTES:
          value = tokenizer.consumeByteString();
          break;

        case ENUM:
          final EnumDescriptor enumType = field.getEnumType();

          if (tokenizer.lookingAtInteger()) {
            final int number = tokenizer.consumeInt32();
            value = enumType.findValueByNumber(number);
            if (value == null) {
              throw tokenizer.parseExceptionPreviousToken(
                "Enum type \"" + enumType.getFullName() +
                "\" has no value with number " + number + '.');
            }
          } else {
            final String id = tokenizer.consumeIdentifier();
            value = enumType.findValueByName(id);
            if (value == null) {
              throw tokenizer.parseExceptionPreviousToken(
                "Enum type \"" + enumType.getFullName() +
                "\" has no value named \"" + id + "\".");
            }
          }

          break;

        case MESSAGE:
        case GROUP:
          throw new RuntimeException("Can't get here.");
      }
    }

    if (field.isRepeated()) {
      builder.addRepeatedField(field, value);
    } else {
      builder.setField(field, value);
    }
  }

  // =================================================================
  // Utility functions
  //
  // Some of these methods are package-private because Descriptors.java uses
  // them.

  /**
   * Escapes bytes in the format used in protocol buffer text format, which
   * is the same as the format used for C string literals.  All bytes
   * that are not printable 7-bit ASCII characters are escaped, as well as
   * backslash, single-quote, and double-quote characters.  Characters for
   * which no defined short-hand escape sequence is defined will be escaped
   * using 3-digit octal sequences.
   */
  static String escapeBytes(final ByteString input) {
    final StringBuilder builder = new StringBuilder(input.size());
    for (int i = 0; i < input.size(); i++) {
      final byte b = input.byteAt(i);
      switch (b) {
        // Java does not recognize \a or \v, apparently.
        case 0x07: builder.append("\\a" ); break;
        case '\b': builder.append("\\b" ); break;
        case '\f': builder.append("\\f" ); break;
        case '\n': builder.append("\\n" ); break;
        case '\r': builder.append("\\r" ); break;
        case '\t': builder.append("\\t" ); break;
        case 0x0b: builder.append("\\v" ); break;
        case '\\': builder.append("\\\\"); break;
        case '\'': builder.append("\\\'"); break;
        case '"' : builder.append("\\\""); break;
        default:
          if (b >= 0x20) {
            builder.append((char) b);
          } else {
            builder.append('\\');
            builder.append((char) ('0' + ((b >>> 6) & 3)));
            builder.append((char) ('0' + ((b >>> 3) & 7)));
            builder.append((char) ('0' + (b & 7)));
          }
          break;
      }
    }
    return builder.toString();
  }

  /**
   * Un-escape a byte sequence as escaped using
   * {@link #escapeBytes(ByteString)}.  Two-digit hex escapes (starting with
   * "\x") are also recognized.
   */
  static ByteString unescapeBytes(final CharSequence input)
      throws InvalidEscapeSequenceException {
    final byte[] result = new byte[input.length()];
    int pos = 0;
    for (int i = 0; i < input.length(); i++) {
      char c = input.charAt(i);
      if (c == '\\') {
        if (i + 1 < input.length()) {
          ++i;
          c = input.charAt(i);
          if (isOctal(c)) {
            // Octal escape.
            int code = digitValue(c);
            if (i + 1 < input.length() && isOctal(input.charAt(i + 1))) {
              ++i;
              code = code * 8 + digitValue(input.charAt(i));
            }
            if (i + 1 < input.length() && isOctal(input.charAt(i + 1))) {
              ++i;
              code = code * 8 + digitValue(input.charAt(i));
            }
            result[pos++] = (byte)code;
          } else {
            switch (c) {
              case 'a' : result[pos++] = 0x07; break;
              case 'b' : result[pos++] = '\b'; break;
              case 'f' : result[pos++] = '\f'; break;
              case 'n' : result[pos++] = '\n'; break;
              case 'r' : result[pos++] = '\r'; break;
              case 't' : result[pos++] = '\t'; break;
              case 'v' : result[pos++] = 0x0b; break;
              case '\\': result[pos++] = '\\'; break;
              case '\'': result[pos++] = '\''; break;
              case '"' : result[pos++] = '\"'; break;

              case 'x':
                // hex escape
                int code = 0;
                if (i + 1 < input.length() && isHex(input.charAt(i + 1))) {
                  ++i;
                  code = digitValue(input.charAt(i));
                } else {
                  throw new InvalidEscapeSequenceException(
                    "Invalid escape sequence: '\\x' with no digits");
                }
                if (i + 1 < input.length() && isHex(input.charAt(i + 1))) {
                  ++i;
                  code = code * 16 + digitValue(input.charAt(i));
                }
                result[pos++] = (byte)code;
                break;

              default:
                throw new InvalidEscapeSequenceException(
                  "Invalid escape sequence: '\\" + c + '\'');
            }
          }
        } else {
          throw new InvalidEscapeSequenceException(
            "Invalid escape sequence: '\\' at end of string.");
        }
      } else {
        result[pos++] = (byte)c;
      }
    }

    return ByteString.copyFrom(result, 0, pos);
  }

  /**
   * Thrown by {@link TextFormat#unescapeBytes} and
   * {@link TextFormat#unescapeText} when an invalid escape sequence is seen.
   */
  static class InvalidEscapeSequenceException extends IOException {
    private static final long serialVersionUID = -8164033650142593304L;

    InvalidEscapeSequenceException(final String description) {
      super(description);
    }
  }

  /**
   * Like {@link #escapeBytes(ByteString)}, but escapes a text string.
   * Non-ASCII characters are first encoded as UTF-8, then each byte is escaped
   * individually as a 3-digit octal escape.  Yes, it's weird.
   */
  static String escapeText(final String input) {
    return escapeBytes(ByteString.copyFromUtf8(input));
  }

  /**
   * Un-escape a text string as escaped using {@link #escapeText(String)}.
   * Two-digit hex escapes (starting with "\x") are also recognized.
   */
  static String unescapeText(final String input)
                             throws InvalidEscapeSequenceException {
    return unescapeBytes(input).toStringUtf8();
  }

  /** Is this an octal digit? */
  private static boolean isOctal(final char c) {
    return '0' <= c && c <= '7';
  }

  /** Is this a hex digit? */
  private static boolean isHex(final char c) {
    return ('0' <= c && c <= '9') ||
           ('a' <= c && c <= 'f') ||
           ('A' <= c && c <= 'F');
  }

  /**
   * Interpret a character as a digit (in any base up to 36) and return the
   * numeric value.  This is like {@code Character.digit()} but we don't accept
   * non-ASCII digits.
   */
  private static int digitValue(final char c) {
    if ('0' <= c && c <= '9') {
      return c - '0';
    } else if ('a' <= c && c <= 'z') {
      return c - 'a' + 10;
    } else {
      return c - 'A' + 10;
    }
  }

  /**
   * Parse a 32-bit signed integer from the text.  Unlike the Java standard
   * {@code Integer.parseInt()}, this function recognizes the prefixes "0x"
   * and "0" to signify hexidecimal and octal numbers, respectively.
   */
  static int parseInt32(final String text) throws NumberFormatException {
    return (int) parseInteger(text, true, false);
  }

  /**
   * Parse a 32-bit unsigned integer from the text.  Unlike the Java standard
   * {@code Integer.parseInt()}, this function recognizes the prefixes "0x"
   * and "0" to signify hexidecimal and octal numbers, respectively.  The
   * result is coerced to a (signed) {@code int} when returned since Java has
   * no unsigned integer type.
   */
  static int parseUInt32(final String text) throws NumberFormatException {
    return (int) parseInteger(text, false, false);
  }

  /**
   * Parse a 64-bit signed integer from the text.  Unlike the Java standard
   * {@code Integer.parseInt()}, this function recognizes the prefixes "0x"
   * and "0" to signify hexidecimal and octal numbers, respectively.
   */
  static long parseInt64(final String text) throws NumberFormatException {
    return parseInteger(text, true, true);
  }

  /**
   * Parse a 64-bit unsigned integer from the text.  Unlike the Java standard
   * {@code Integer.parseInt()}, this function recognizes the prefixes "0x"
   * and "0" to signify hexidecimal and octal numbers, respectively.  The
   * result is coerced to a (signed) {@code long} when returned since Java has
   * no unsigned long type.
   */
  static long parseUInt64(final String text) throws NumberFormatException {
    return parseInteger(text, false, true);
  }

  private static long parseInteger(final String text,
                                   final boolean isSigned,
                                   final boolean isLong)
                                   throws NumberFormatException {
    int pos = 0;

    boolean negative = false;
    if (text.startsWith("-", pos)) {
      if (!isSigned) {
        throw new NumberFormatException("Number must be positive: " + text);
      }
      ++pos;
      negative = true;
    }

    int radix = 10;
    if (text.startsWith("0x", pos)) {
      pos += 2;
      radix = 16;
    } else if (text.startsWith("0", pos)) {
      radix = 8;
    }

    final String numberText = text.substring(pos);

    long result = 0;
    if (numberText.length() < 16) {
      // Can safely assume no overflow.
      result = Long.parseLong(numberText, radix);
      if (negative) {
        result = -result;
      }

      // Check bounds.
      // No need to check for 64-bit numbers since they'd have to be 16 chars
      // or longer to overflow.
      if (!isLong) {
        if (isSigned) {
          if (result > Integer.MAX_VALUE || result < Integer.MIN_VALUE) {
            throw new NumberFormatException(
              "Number out of range for 32-bit signed integer: " + text);
          }
        } else {
          if (result >= (1L << 32) || result < 0) {
            throw new NumberFormatException(
              "Number out of range for 32-bit unsigned integer: " + text);
          }
        }
      }
    } else {
      BigInteger bigValue = new BigInteger(numberText, radix);
      if (negative) {
        bigValue = bigValue.negate();
      }

      // Check bounds.
      if (!isLong) {
        if (isSigned) {
          if (bigValue.bitLength() > 31) {
            throw new NumberFormatException(
              "Number out of range for 32-bit signed integer: " + text);
          }
        } else {
          if (bigValue.bitLength() > 32) {
            throw new NumberFormatException(
              "Number out of range for 32-bit unsigned integer: " + text);
          }
        }
      } else {
        if (isSigned) {
          if (bigValue.bitLength() > 63) {
            throw new NumberFormatException(
              "Number out of range for 64-bit signed integer: " + text);
          }
        } else {
          if (bigValue.bitLength() > 64) {
            throw new NumberFormatException(
              "Number out of range for 64-bit unsigned integer: " + text);
          }
        }
      }

      result = bigValue.longValue();
    }

    return result;
  }
}
