/*
 * The contents of this file are subject to the terms of the Common Development and
 * Distribution License (the License). You may not use this file except in compliance with the
 * License.
 *
 * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
 * specific language governing permission and limitations under the License.
 *
 * When distributing Covered Software, include this CDDL Header Notice in each file and include
 * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
 * Header, with the fields enclosed by brackets [] replaced by your own identifying
 * information: "Portions Copyright [year] [name of copyright owner]".
 *
 * Copyright 2013-2014 Manuel Gaupp
 * Portions Copyright 2014-2016 ForgeRock AS.
 */
package org.opends.server.protocols.asn1;

import static org.forgerock.util.Reject.*;
import static org.opends.messages.ProtocolMessages.*;

import java.math.BigInteger;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.forgerock.i18n.LocalizableMessage;

/**
 * This class implements a parser for strings which are encoded using the
 * Generic String Encoding Rules (GSER) defined in RFC 3641.
 *
 * @see <a href="http://tools.ietf.org/html/rfc3641">RFC 3641 -
 *      Generic String Encoding Rules (GSER) for ASN.1 Types
 *      </a>
 */
public class GSERParser
{

  private String gserValue;
  private int pos;
  private int length;

  /**
   * Pattern to match an identifier defined in RFC 3641, section 3.4.
   * <pre>
   * An &lt;identifier&gt; conforms to the definition of an identifier in ASN.1
   * notation (Clause 11.3 of X.680 [8]).  It begins with a lowercase
   * letter and is followed by zero or more letters, digits, and hyphens.
   * A hyphen is not permitted to be the last character, nor is it to be
   * followed by another hyphen.  The case of letters in an identifier is
   * always significant.
   *
   *    identifier    = lowercase *alphanumeric *(hyphen 1*alphanumeric)
   *    alphanumeric  = uppercase / lowercase / decimal-digit
   *    uppercase     = %x41-5A  ; "A" to "Z"
   *    lowercase     = %x61-7A  ; "a" to "z"
   *    decimal-digit = %x30-39  ; "0" to "9"
   *    hyphen        = "-"
   * </pre>
   */
  private static Pattern GSER_IDENTIFIER = Pattern
          .compile("^([a-z]([A-Za-z0-9]|(-[A-Za-z0-9]))*)");

  /**
   * Pattern to match the identifier part (including the colon) of an
   * IdentifiedChoiceValue defined in RFC 3641, section 3.12.
   * <pre>
   *    IdentifiedChoiceValue = identifier ":" Value
   * </pre>
   */
  private static Pattern GSER_CHOICE_IDENTIFIER = Pattern
          .compile("^([a-z]([A-Za-z0-9]|(-[A-Za-z0-9]))*:)");



  /**
   * Pattern to match "sp", containing zero, one or more space characters.
   * <pre>
   *    sp = *%x20  ; zero, one or more space characters
   * </pre>
   */
  private static Pattern GSER_SP = Pattern.compile("^( *)");



  /**
   * Pattern to match "msp", containing at least one space character.
   * <pre>
   *    msp = 1*%x20  ; one or more space characters
   * </pre>
   */
  private static Pattern GSER_MSP = Pattern.compile("^( +)");



  /**
   * Pattern to match an Integer value.
   */
  private static Pattern GSER_INTEGER = Pattern.compile("^(\\d+)");



  /**
   * Pattern to match a GSER StringValue, defined in RFC 3641, section 3.2:
   * <pre>
   * Any embedded double quotes in the resulting UTF-8 character string
   * are escaped by repeating the double quote characters.
   *
   * [...]
   *
   *    StringValue       = dquote *SafeUTF8Character dquote
   *    dquote            = %x22 ; &quot; (double quote)
   * </pre>
   */
  private static Pattern GSER_STRING = Pattern
          .compile("^(\"([^\"]|(\"\"))*\")");



  /**
   * Pattern to match the beginning of a GSER encoded Sequence.
   * <pre>
   *    SequenceValue = ComponentList
   *    ComponentList = "{" [ sp NamedValue *( "," sp NamedValue) ] sp "}"
   * </pre>
   */
  private static Pattern GSER_SEQUENCE_START = Pattern.compile("^(\\{)");



  /**
   * Pattern to match the end of a GSER encoded Sequence.
   * <pre>
   *    SequenceValue = ComponentList
   *    ComponentList = "{" [ sp NamedValue *( "," sp NamedValue) ] sp "}"
   * </pre>
   */
  private static Pattern GSER_SEQUENCE_END = Pattern.compile("^(\\})");



  /**
   * Pattern to match the separator used in GSER encoded sequences.
   */
  private static Pattern GSER_SEP = Pattern.compile("^(,)");



  /**
   * Creates a new GSER Parser.
   *
   * @param value the GSER encoded String value
   */
  public GSERParser(String value)
  {
    ifNull(value);
    this.gserValue = value;
    this.pos = 0;
    this.length = value.length();
  }



  /**
   * Determines if the GSER String contains at least one character to be read.
   *
   * @return <code>true</code> if there is at least one remaining character or
   *         <code>false</code> otherwise.
   */
  public boolean hasNext()
  {
    return pos < length;
  }



  /**
   * Determines if the remaining GSER String matches the provided pattern.
   *
   * @param pattern the pattern to search for
   *
   * @return <code>true</code> if the remaining string matches the pattern or
   *         <code>false</code> otherwise.
   */
  private boolean hasNext(Pattern pattern)
  {
    if (!hasNext())
    {
      return false;
    }

    Matcher matcher = pattern.matcher(gserValue.substring(pos,length));

    return matcher.find();
  }



  /**
   * Returns the String matched by the first capturing group of the pattern.
   * The parser advances past the input matched by the first capturing group.
   *
   * @param pattern the pattern to search for
   *
   * @return the String matched by the first capturing group of the pattern
   *
   * @throws GSERException
   *           If no match could be found
   */
  private String next(Pattern pattern) throws GSERException
  {
    Matcher matcher = pattern.matcher(gserValue.substring(pos,length));
    if (matcher.find() &&  matcher.groupCount() >= 1)
    {
      pos += matcher.end(1);
      return matcher.group(1);
    }
    else
    {
      LocalizableMessage msg = ERR_GSER_PATTERN_NO_MATCH.get(pattern.pattern(),
                      gserValue.substring(pos,length));
      throw new GSERException(msg);
    }
  }



  /**
   * Skips the input matched by the first capturing group.
   *
   * @param pattern the pattern to search for
   *
   * @throws GSERException
   *           If no match could be found
   */
  private void skip(Pattern pattern) throws GSERException
  {
    Matcher matcher = pattern.matcher(gserValue.substring(pos,length));

    if (matcher.find() && matcher.groupCount() >= 1)
    {
      pos += matcher.end(1);
    }
    else
    {
      LocalizableMessage msg = ERR_GSER_PATTERN_NO_MATCH.get(pattern.pattern(),
                      gserValue.substring(pos,length));
      throw new GSERException(msg);
    }
  }



  /**
   * Skips the input matching zero, one or more space characters.
   *
   * @return reference to this GSERParser
   *
   * @throws GSERException
   *           If no match could be found
   */
  public GSERParser skipSP() throws GSERException
  {
    skip(GSER_SP);
    return this;
  }



  /**
   * Skips the input matching one or more space characters.
   *
   * @return reference to this GSERParser
   *
   * @throws GSERException
   *           If no match could be found
   */
  public GSERParser skipMSP() throws GSERException
  {
    skip(GSER_MSP);
    return this;
  }



  /**
   * Skips the input matching the start of a sequence and subsequent space
   * characters.
   *
   * @return reference to this GSERParser
   *
   * @throws GSERException
   *           If the input does not match the start of a sequence
   */
  public GSERParser readStartSequence() throws GSERException
  {
    next(GSER_SEQUENCE_START);
    skip(GSER_SP);
    return this;
  }



  /**
   * Skips the input matching the end of a sequence and preceding space
   * characters.
   *
   * @return reference to this GSERParser
   *
   * @throws GSERException
   *           If the input does not match the end of a sequence
   */
  public GSERParser readEndSequence() throws GSERException
  {
    skip(GSER_SP);
    next(GSER_SEQUENCE_END);
    return this;
  }


  /**
   * Skips the input matching the separator pattern (",") and subsequenct space
   * characters.
   *
   * @return reference to this GSERParser
   *
   * @throws GSERException
   *           If the input does not match the separator pattern.
   */
  public GSERParser skipSeparator() throws GSERException
  {
    if (!hasNext(GSER_SEP))
    {
      LocalizableMessage msg = ERR_GSER_NO_VALID_SEPARATOR.get(gserValue
                      .substring(pos,length));
      throw new GSERException(msg);
    }
    skip(GSER_SEP);
    skip(GSER_SP);
    return this;
  }



  /**
   * Returns the next element as a String.
   *
   * @return the input matching the String pattern
   *
   * @throws GSERException
   *           If the input does not match the string pattern.
   */
  public String nextString() throws GSERException
  {
    if (!hasNext(GSER_STRING))
    {
      LocalizableMessage msg = ERR_GSER_NO_VALID_STRING.get(gserValue
                      .substring(pos,length));
      throw new GSERException(msg);
    }

    String str = next(GSER_STRING);

    // Strip leading and trailing dquotes; unescape double dquotes
    return str.substring(1, str.length() - 1).replace("\"\"","\"");
  }


  /**
   * Returns the next element as an Integer.
   *
   * @return the input matching the integer pattern
   *
   * @throws GSERException
   *           If the input does not match the integer pattern
   */
  public int nextInteger() throws GSERException
  {
    if (!hasNext(GSER_INTEGER))
    {
      LocalizableMessage msg = ERR_GSER_NO_VALID_INTEGER.get(gserValue
                      .substring(pos,length));
      throw new GSERException(msg);
    }
    return Integer.valueOf(next(GSER_INTEGER)).intValue();
  }



  /**
   * Returns the next element as a BigInteger.
   *
   * @return the input matching the integer pattern
   *
   * @throws GSERException
   *           If the input does not match the integer pattern
   */
  public BigInteger nextBigInteger() throws GSERException
  {
    if (!hasNext(GSER_INTEGER))
    {
      LocalizableMessage msg = ERR_GSER_NO_VALID_INTEGER.get(gserValue
                      .substring(pos,length));
      throw new GSERException(msg);
    }
    return new BigInteger(next(GSER_INTEGER));
  }


  /**
   * Returns the identifier of the next NamedValue element.
   *
   * @return the identifier of the NamedValue element
   *
   * @throws GSERException
   *           If the input does not match the identifier pattern of a
   *           NamedValue
   */
  public String nextNamedValueIdentifier() throws GSERException
  {
    if (!hasNext(GSER_IDENTIFIER))
    {
      LocalizableMessage msg = ERR_GSER_NO_VALID_IDENTIFIER.get(gserValue
                      .substring(pos,length));
      throw new GSERException(msg);
    }
    String identifier = next(GSER_IDENTIFIER);
    if (!hasNext(GSER_MSP))
    {
      LocalizableMessage msg = ERR_GSER_SPACE_CHAR_EXPECTED.get(gserValue
                      .substring(pos,length));
      throw new GSERException(msg);
    }
    skipMSP();
    return identifier;
  }


  /**
   * Return the identifier of the next IdentifiedChoiceValue element.
   *
   * @return the identifier of the IdentifiedChoiceValue element
   *
   * @throws GSERException
   *           If the input does not match the identifier pattern of an
   *           IdentifiedChoiceValue
   */
  public String nextChoiceValueIdentifier() throws GSERException
  {
    if (!hasNext(GSER_CHOICE_IDENTIFIER))
    {
      LocalizableMessage msg = ERR_GSER_NO_VALID_IDENTIFIEDCHOICE.get(gserValue
                      .substring(pos,length));
      throw new GSERException(msg);
    }
    String identifier = next(GSER_CHOICE_IDENTIFIER);

    // Remove the colon at the end of the identifier
    return identifier.substring(0, identifier.length() - 1);
  }


}