/**
    *
    * 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.hadoop.hbase.filter;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.KeyValue;
  import org.apache.hadoop.hbase.filter.CompareFilter.CompareOp;
  import org.apache.hadoop.hbase.util.Bytes;
  
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.nio.ByteBuffer;
  import java.nio.charset.CharacterCodingException;
  import java.nio.charset.StandardCharsets;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.EmptyStackException;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.regex.Pattern;
  import java.util.Set;
  import java.util.Stack;
  
  /**
   * This class allows a user to specify a filter via a string
   * The string is parsed using the methods of this class and
   * a filter object is constructed. This filter object is then wrapped
   * in a scanner object which is then returned
   * <p>
   * This class addresses the HBASE-4168 JIRA. More documentation on this
   * Filter Language can be found at: https://issues.apache.org/jira/browse/HBASE-4176
   */
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public class ParseFilter {
    private static final Log LOG = LogFactory.getLog(ParseFilter.class);
  
    private static HashMap<ByteBuffer, Integer> operatorPrecedenceHashMap;
    private static HashMap<String, String> filterHashMap;
  
    static {
      // Registers all the filter supported by the Filter Language
      filterHashMap = new HashMap<String, String>();
      filterHashMap.put("KeyOnlyFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "KeyOnlyFilter");
      filterHashMap.put("FirstKeyOnlyFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "FirstKeyOnlyFilter");
      filterHashMap.put("PrefixFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "PrefixFilter");
      filterHashMap.put("ColumnPrefixFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "ColumnPrefixFilter");
      filterHashMap.put("MultipleColumnPrefixFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "MultipleColumnPrefixFilter");
      filterHashMap.put("ColumnCountGetFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "ColumnCountGetFilter");
      filterHashMap.put("PageFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "PageFilter");
      filterHashMap.put("ColumnPaginationFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "ColumnPaginationFilter");
      filterHashMap.put("InclusiveStopFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "InclusiveStopFilter");
      filterHashMap.put("TimestampsFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "TimestampsFilter");
      filterHashMap.put("RowFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "RowFilter");
      filterHashMap.put("FamilyFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "FamilyFilter");
      filterHashMap.put("QualifierFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "QualifierFilter");
      filterHashMap.put("ValueFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "ValueFilter");
      filterHashMap.put("ColumnRangeFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "ColumnRangeFilter");
      filterHashMap.put("SingleColumnValueFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "SingleColumnValueFilter");
      filterHashMap.put("SingleColumnValueExcludeFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "SingleColumnValueExcludeFilter");
      filterHashMap.put("DependentColumnFilter", ParseConstants.FILTER_PACKAGE + "." +
                        "DependentColumnFilter");
  
     // Creates the operatorPrecedenceHashMap
     operatorPrecedenceHashMap = new HashMap<ByteBuffer, Integer>();
     operatorPrecedenceHashMap.put(ParseConstants.SKIP_BUFFER, 1);
     operatorPrecedenceHashMap.put(ParseConstants.WHILE_BUFFER, 1);
     operatorPrecedenceHashMap.put(ParseConstants.AND_BUFFER, 2);
     operatorPrecedenceHashMap.put(ParseConstants.OR_BUFFER, 3);
   }
 
   /**
    * Parses the filterString and constructs a filter using it
    * <p>
    * @param filterString filter string given by the user
    * @return filter object we constructed
    */
   public Filter parseFilterString (String filterString)
     throws CharacterCodingException {
     return parseFilterString(Bytes.toBytes(filterString));
   }
 
   /**
    * Parses the filterString and constructs a filter using it
    * <p>
    * @param filterStringAsByteArray filter string given by the user
    * @return filter object we constructed
    */
   public Filter parseFilterString (byte [] filterStringAsByteArray)
     throws CharacterCodingException {
     // stack for the operators and parenthesis
     Stack <ByteBuffer> operatorStack = new Stack<ByteBuffer>();
     // stack for the filter objects
     Stack <Filter> filterStack = new Stack<Filter>();
 
     Filter filter = null;
     for (int i=0; i<filterStringAsByteArray.length; i++) {
       if (filterStringAsByteArray[i] == ParseConstants.LPAREN) {
         // LPAREN found
         operatorStack.push(ParseConstants.LPAREN_BUFFER);
       } else if (filterStringAsByteArray[i] == ParseConstants.WHITESPACE ||
                  filterStringAsByteArray[i] == ParseConstants.TAB) {
         // WHITESPACE or TAB found
         continue;
       } else if (checkForOr(filterStringAsByteArray, i)) {
         // OR found
         i += ParseConstants.OR_ARRAY.length - 1;
         reduce(operatorStack, filterStack, ParseConstants.OR_BUFFER);
         operatorStack.push(ParseConstants.OR_BUFFER);
       } else if (checkForAnd(filterStringAsByteArray, i)) {
         // AND found
         i += ParseConstants.AND_ARRAY.length - 1;
         reduce(operatorStack, filterStack, ParseConstants.AND_BUFFER);
         operatorStack.push(ParseConstants.AND_BUFFER);
       } else if (checkForSkip(filterStringAsByteArray, i)) {
         // SKIP found
         i += ParseConstants.SKIP_ARRAY.length - 1;
         reduce(operatorStack, filterStack, ParseConstants.SKIP_BUFFER);
         operatorStack.push(ParseConstants.SKIP_BUFFER);
       } else if (checkForWhile(filterStringAsByteArray, i)) {
         // WHILE found
         i += ParseConstants.WHILE_ARRAY.length - 1;
         reduce(operatorStack, filterStack, ParseConstants.WHILE_BUFFER);
         operatorStack.push(ParseConstants.WHILE_BUFFER);
       } else if (filterStringAsByteArray[i] == ParseConstants.RPAREN) {
         // RPAREN found
         if (operatorStack.empty()) {
           throw new IllegalArgumentException("Mismatched parenthesis");
         }
         ByteBuffer argumentOnTopOfStack = operatorStack.peek();
         if (argumentOnTopOfStack.equals(ParseConstants.LPAREN_BUFFER)) {
           operatorStack.pop();
           continue;
         }
         while (!(argumentOnTopOfStack.equals(ParseConstants.LPAREN_BUFFER))) {
           filterStack.push(popArguments(operatorStack, filterStack));
           if (operatorStack.empty()) {
             throw new IllegalArgumentException("Mismatched parenthesis");
           }
           argumentOnTopOfStack = operatorStack.pop();
         }
       } else {
         // SimpleFilterExpression found
         byte [] filterSimpleExpression = extractFilterSimpleExpression(filterStringAsByteArray, i);
         i+= (filterSimpleExpression.length - 1);
         filter = parseSimpleFilterExpression(filterSimpleExpression);
         filterStack.push(filter);
       }
     }
 
     // Finished parsing filterString
     while (!operatorStack.empty()) {
       filterStack.push(popArguments(operatorStack, filterStack));
     }
     if (filterStack.empty()) {
         throw new IllegalArgumentException("Incorrect Filter String");
     }
     filter = filterStack.pop();
     if (!filterStack.empty()) {
       throw new IllegalArgumentException("Incorrect Filter String");
     }
     return filter;
   }
 
 /**
  * Extracts a simple filter expression from the filter string given by the user
  * <p>
  * A simpleFilterExpression is of the form: FilterName('arg', 'arg', 'arg')
  * The user given filter string can have many simpleFilterExpressions combined
  * using operators.
  * <p>
  * This function extracts a simpleFilterExpression from the
  * larger filterString given the start offset of the simpler expression
  * <p>
  * @param filterStringAsByteArray filter string given by the user
  * @param filterExpressionStartOffset start index of the simple filter expression
  * @return byte array containing the simple filter expression
  */
   public byte [] extractFilterSimpleExpression (byte [] filterStringAsByteArray,
                                                 int filterExpressionStartOffset)
     throws CharacterCodingException {
     int quoteCount = 0;
     for (int i=filterExpressionStartOffset; i<filterStringAsByteArray.length; i++) {
       if (filterStringAsByteArray[i] == ParseConstants.SINGLE_QUOTE) {
         if (isQuoteUnescaped(filterStringAsByteArray, i)) {
           quoteCount ++;
         } else {
           // To skip the next quote that has been escaped
           i++;
         }
       }
       if (filterStringAsByteArray[i] == ParseConstants.RPAREN && (quoteCount %2 ) == 0) {
         byte [] filterSimpleExpression = new byte [i - filterExpressionStartOffset + 1];
         Bytes.putBytes(filterSimpleExpression, 0, filterStringAsByteArray,
                        filterExpressionStartOffset, i-filterExpressionStartOffset + 1);
         return filterSimpleExpression;
       }
     }
     throw new IllegalArgumentException("Incorrect Filter String");
   }
 
 /**
  * Constructs a filter object given a simple filter expression
  * <p>
  * @param filterStringAsByteArray filter string given by the user
  * @return filter object we constructed
  */
   public Filter parseSimpleFilterExpression (byte [] filterStringAsByteArray)
     throws CharacterCodingException {
 
     String filterName = Bytes.toString(getFilterName(filterStringAsByteArray));
     ArrayList<byte []> filterArguments = getFilterArguments(filterStringAsByteArray);
     if (!filterHashMap.containsKey(filterName)) {
       throw new IllegalArgumentException("Filter Name " + filterName + " not supported");
     }
     try {
       filterName = filterHashMap.get(filterName);
       Class<?> c = Class.forName(filterName);
       Class<?>[] argTypes = new Class [] {ArrayList.class};
       Method m = c.getDeclaredMethod("createFilterFromArguments", argTypes);
       return (Filter) m.invoke(null,filterArguments);
     } catch (ClassNotFoundException e) {
       e.printStackTrace();
     } catch (NoSuchMethodException e) {
       e.printStackTrace();
     } catch (IllegalAccessException e) {
       e.printStackTrace();
     } catch (InvocationTargetException e) {
       e.printStackTrace();
     }
     throw new IllegalArgumentException("Incorrect filter string " +
         new String(filterStringAsByteArray, StandardCharsets.UTF_8));
   }
 
 /**
  * Returns the filter name given a simple filter expression
  * <p>
  * @param filterStringAsByteArray a simple filter expression
  * @return name of filter in the simple filter expression
  */
   public static byte [] getFilterName (byte [] filterStringAsByteArray) {
     int filterNameStartIndex = 0;
     int filterNameEndIndex = 0;
 
     for (int i=filterNameStartIndex; i<filterStringAsByteArray.length; i++) {
       if (filterStringAsByteArray[i] == ParseConstants.LPAREN ||
           filterStringAsByteArray[i] == ParseConstants.WHITESPACE) {
         filterNameEndIndex = i;
         break;
       }
     }
 
     if (filterNameEndIndex == 0) {
       throw new IllegalArgumentException("Incorrect Filter Name");
     }
 
     byte [] filterName = new byte[filterNameEndIndex - filterNameStartIndex];
     Bytes.putBytes(filterName, 0, filterStringAsByteArray, 0,
                    filterNameEndIndex - filterNameStartIndex);
     return filterName;
   }
 
 /**
  * Returns the arguments of the filter from the filter string
  * <p>
  * @param filterStringAsByteArray filter string given by the user
  * @return an ArrayList containing the arguments of the filter in the filter string
  */
   public static ArrayList<byte []> getFilterArguments (byte [] filterStringAsByteArray) {
     int argumentListStartIndex = KeyValue.getDelimiter(filterStringAsByteArray, 0,
                                                        filterStringAsByteArray.length,
                                                        ParseConstants.LPAREN);
     if (argumentListStartIndex == -1) {
       throw new IllegalArgumentException("Incorrect argument list");
     }
 
     int argumentStartIndex = 0;
     int argumentEndIndex = 0;
     ArrayList<byte []> filterArguments = new ArrayList<byte []>();
 
     for (int i = argumentListStartIndex + 1; i<filterStringAsByteArray.length; i++) {
 
       if (filterStringAsByteArray[i] == ParseConstants.WHITESPACE ||
           filterStringAsByteArray[i] == ParseConstants.COMMA ||
           filterStringAsByteArray[i] == ParseConstants.RPAREN) {
         continue;
       }
 
       // The argument is in single quotes - for example 'prefix'
       if (filterStringAsByteArray[i] == ParseConstants.SINGLE_QUOTE) {
         argumentStartIndex = i;
         for (int j = argumentStartIndex+1; j < filterStringAsByteArray.length; j++) {
           if (filterStringAsByteArray[j] == ParseConstants.SINGLE_QUOTE) {
             if (isQuoteUnescaped(filterStringAsByteArray,j)) {
               argumentEndIndex = j;
               i = j+1;
               byte [] filterArgument = createUnescapdArgument(filterStringAsByteArray,
                                                               argumentStartIndex, argumentEndIndex);
               filterArguments.add(filterArgument);
               break;
             } else {
               // To jump over the second escaped quote
               j++;
             }
           } else if (j == filterStringAsByteArray.length - 1) {
             throw new IllegalArgumentException("Incorrect argument list");
           }
         }
       } else {
         // The argument is an integer, boolean, comparison operator like <, >, != etc
         argumentStartIndex = i;
         for (int j = argumentStartIndex; j < filterStringAsByteArray.length; j++) {
           if (filterStringAsByteArray[j] == ParseConstants.WHITESPACE ||
               filterStringAsByteArray[j] == ParseConstants.COMMA ||
               filterStringAsByteArray[j] == ParseConstants.RPAREN) {
             argumentEndIndex = j - 1;
             i = j;
             byte [] filterArgument = new byte [argumentEndIndex - argumentStartIndex + 1];
             Bytes.putBytes(filterArgument, 0, filterStringAsByteArray,
                            argumentStartIndex, argumentEndIndex - argumentStartIndex + 1);
             filterArguments.add(filterArgument);
             break;
           } else if (j == filterStringAsByteArray.length - 1) {
             throw new IllegalArgumentException("Incorrect argument list");
           }
         }
       }
     }
     return filterArguments;
   }
 
 /**
  * This function is called while parsing the filterString and an operator is parsed
  * <p>
  * @param operatorStack the stack containing the operators and parenthesis
  * @param filterStack the stack containing the filters
  * @param operator the operator found while parsing the filterString
  */
   public void reduce(Stack<ByteBuffer> operatorStack,
                      Stack<Filter> filterStack,
                      ByteBuffer operator) {
     while (!operatorStack.empty() &&
            !(ParseConstants.LPAREN_BUFFER.equals(operatorStack.peek())) &&
            hasHigherPriority(operatorStack.peek(), operator)) {
       filterStack.push(popArguments(operatorStack, filterStack));
     }
   }
 
   /**
    * Pops an argument from the operator stack and the number of arguments required by the operator
    * from the filterStack and evaluates them
    * <p>
    * @param operatorStack the stack containing the operators
    * @param filterStack the stack containing the filters
    * @return the evaluated filter
    */
   public static Filter popArguments (Stack<ByteBuffer> operatorStack, Stack <Filter> filterStack) {
     ByteBuffer argumentOnTopOfStack = operatorStack.peek();
 
     if (argumentOnTopOfStack.equals(ParseConstants.OR_BUFFER)) {
       // The top of the stack is an OR
       try {
         ArrayList<Filter> listOfFilters = new ArrayList<Filter>();
         while (!operatorStack.empty() && operatorStack.peek().equals(ParseConstants.OR_BUFFER)) {
           Filter filter = filterStack.pop();
           listOfFilters.add(0, filter);
           operatorStack.pop();
         }
         Filter filter = filterStack.pop();
         listOfFilters.add(0, filter);
         Filter orFilter = new FilterList(FilterList.Operator.MUST_PASS_ONE, listOfFilters);
         return orFilter;
       } catch (EmptyStackException e) {
         throw new IllegalArgumentException("Incorrect input string - an OR needs two filters");
       }
 
     } else if (argumentOnTopOfStack.equals(ParseConstants.AND_BUFFER)) {
       // The top of the stack is an AND
       try {
         ArrayList<Filter> listOfFilters = new ArrayList<Filter>();
         while (!operatorStack.empty() && operatorStack.peek().equals(ParseConstants.AND_BUFFER)) {
           Filter filter = filterStack.pop();
           listOfFilters.add(0, filter);
           operatorStack.pop();
         }
         Filter filter = filterStack.pop();
         listOfFilters.add(0, filter);
         Filter andFilter = new FilterList(FilterList.Operator.MUST_PASS_ALL, listOfFilters);
         return andFilter;
       } catch (EmptyStackException e) {
         throw new IllegalArgumentException("Incorrect input string - an AND needs two filters");
       }
 
     } else if (argumentOnTopOfStack.equals(ParseConstants.SKIP_BUFFER)) {
       // The top of the stack is a SKIP
       try {
         Filter wrappedFilter = filterStack.pop();
         Filter skipFilter = new SkipFilter(wrappedFilter);
         operatorStack.pop();
         return skipFilter;
       } catch (EmptyStackException e) {
         throw new IllegalArgumentException("Incorrect input string - a SKIP wraps a filter");
       }
 
     } else if (argumentOnTopOfStack.equals(ParseConstants.WHILE_BUFFER)) {
       // The top of the stack is a WHILE
       try {
         Filter wrappedFilter = filterStack.pop();
         Filter whileMatchFilter = new WhileMatchFilter(wrappedFilter);
         operatorStack.pop();
         return whileMatchFilter;
       } catch (EmptyStackException e) {
         throw new IllegalArgumentException("Incorrect input string - a WHILE wraps a filter");
       }
 
     } else if (argumentOnTopOfStack.equals(ParseConstants.LPAREN_BUFFER)) {
       // The top of the stack is a LPAREN
       try {
         Filter filter  = filterStack.pop();
         operatorStack.pop();
         return filter;
       } catch (EmptyStackException e) {
         throw new IllegalArgumentException("Incorrect Filter String");
       }
 
     } else {
       throw new IllegalArgumentException("Incorrect arguments on operatorStack");
     }
   }
 
 /**
  * Returns which operator has higher precedence
  * <p>
  * If a has higher precedence than b, it returns true
  * If they have the same precedence, it returns false
  */
   public boolean hasHigherPriority(ByteBuffer a, ByteBuffer b) {
     if ((operatorPrecedenceHashMap.get(a) - operatorPrecedenceHashMap.get(b)) < 0) {
       return true;
     }
     return false;
   }
 
 /**
  * Removes the single quote escaping a single quote - thus it returns an unescaped argument
  * <p>
  * @param filterStringAsByteArray filter string given by user
  * @param argumentStartIndex start index of the argument
  * @param argumentEndIndex end index of the argument
  * @return returns an unescaped argument
  */
   public static byte [] createUnescapdArgument (byte [] filterStringAsByteArray,
                                                 int argumentStartIndex, int argumentEndIndex) {
     int unescapedArgumentLength = 2;
     for (int i = argumentStartIndex + 1; i <= argumentEndIndex - 1; i++) {
       unescapedArgumentLength ++;
       if (filterStringAsByteArray[i] == ParseConstants.SINGLE_QUOTE &&
           i != (argumentEndIndex - 1) &&
           filterStringAsByteArray[i+1] == ParseConstants.SINGLE_QUOTE) {
         i++;
         continue;
       }
     }
 
     byte [] unescapedArgument = new byte [unescapedArgumentLength];
     int count = 1;
     unescapedArgument[0] = '\'';
     for (int i = argumentStartIndex + 1; i <= argumentEndIndex - 1; i++) {
       if (filterStringAsByteArray [i] == ParseConstants.SINGLE_QUOTE &&
           i != (argumentEndIndex - 1) &&
           filterStringAsByteArray [i+1] == ParseConstants.SINGLE_QUOTE) {
         unescapedArgument[count++] = filterStringAsByteArray [i+1];
         i++;
       }
       else {
         unescapedArgument[count++] = filterStringAsByteArray [i];
       }
     }
     unescapedArgument[unescapedArgumentLength - 1] = '\'';
     return unescapedArgument;
   }
 
 /**
  * Checks if the current index of filter string we are on is the beginning of the keyword 'OR'
  * <p>
  * @param filterStringAsByteArray filter string given by the user
  * @param indexOfOr index at which an 'O' was read
  * @return true if the keyword 'OR' is at the current index
  */
   public static boolean checkForOr (byte [] filterStringAsByteArray, int indexOfOr)
     throws CharacterCodingException, ArrayIndexOutOfBoundsException {
 
     try {
       if (filterStringAsByteArray[indexOfOr] == ParseConstants.O &&
           filterStringAsByteArray[indexOfOr+1] == ParseConstants.R &&
           (filterStringAsByteArray[indexOfOr-1] == ParseConstants.WHITESPACE ||
            filterStringAsByteArray[indexOfOr-1] == ParseConstants.RPAREN) &&
           (filterStringAsByteArray[indexOfOr+2] == ParseConstants.WHITESPACE ||
            filterStringAsByteArray[indexOfOr+2] == ParseConstants.LPAREN)) {
         return true;
       } else {
         return false;
       }
     } catch (ArrayIndexOutOfBoundsException e) {
       return false;
     }
   }
 
 /**
  * Checks if the current index of filter string we are on is the beginning of the keyword 'AND'
  * <p>
  * @param filterStringAsByteArray filter string given by the user
  * @param indexOfAnd index at which an 'A' was read
  * @return true if the keyword 'AND' is at the current index
  */
   public static boolean checkForAnd (byte [] filterStringAsByteArray, int indexOfAnd)
     throws CharacterCodingException {
 
     try {
       if (filterStringAsByteArray[indexOfAnd] == ParseConstants.A &&
           filterStringAsByteArray[indexOfAnd+1] == ParseConstants.N &&
           filterStringAsByteArray[indexOfAnd+2] == ParseConstants.D &&
           (filterStringAsByteArray[indexOfAnd-1] == ParseConstants.WHITESPACE ||
            filterStringAsByteArray[indexOfAnd-1] == ParseConstants.RPAREN) &&
           (filterStringAsByteArray[indexOfAnd+3] == ParseConstants.WHITESPACE ||
            filterStringAsByteArray[indexOfAnd+3] == ParseConstants.LPAREN)) {
         return true;
       } else {
         return false;
       }
     } catch (ArrayIndexOutOfBoundsException e) {
       return false;
     }
   }
 
 /**
  * Checks if the current index of filter string we are on is the beginning of the keyword 'SKIP'
  * <p>
  * @param filterStringAsByteArray filter string given by the user
  * @param indexOfSkip index at which an 'S' was read
  * @return true if the keyword 'SKIP' is at the current index
  */
   public static boolean checkForSkip (byte [] filterStringAsByteArray, int indexOfSkip)
     throws CharacterCodingException {
 
     try {
       if (filterStringAsByteArray[indexOfSkip] == ParseConstants.S &&
           filterStringAsByteArray[indexOfSkip+1] == ParseConstants.K &&
           filterStringAsByteArray[indexOfSkip+2] == ParseConstants.I &&
           filterStringAsByteArray[indexOfSkip+3] == ParseConstants.P &&
           (indexOfSkip == 0 ||
            filterStringAsByteArray[indexOfSkip-1] == ParseConstants.WHITESPACE ||
            filterStringAsByteArray[indexOfSkip-1] == ParseConstants.RPAREN ||
            filterStringAsByteArray[indexOfSkip-1] == ParseConstants.LPAREN) &&
           (filterStringAsByteArray[indexOfSkip+4] == ParseConstants.WHITESPACE ||
            filterStringAsByteArray[indexOfSkip+4] == ParseConstants.LPAREN)) {
         return true;
       } else {
         return false;
       }
     } catch (ArrayIndexOutOfBoundsException e) {
       return false;
     }
   }
 
 /**
  * Checks if the current index of filter string we are on is the beginning of the keyword 'WHILE'
  * <p>
  * @param filterStringAsByteArray filter string given by the user
  * @param indexOfWhile index at which an 'W' was read
  * @return true if the keyword 'WHILE' is at the current index
  */
   public static boolean checkForWhile (byte [] filterStringAsByteArray, int indexOfWhile)
     throws CharacterCodingException {
 
     try {
       if (filterStringAsByteArray[indexOfWhile] == ParseConstants.W &&
           filterStringAsByteArray[indexOfWhile+1] == ParseConstants.H &&
           filterStringAsByteArray[indexOfWhile+2] == ParseConstants.I &&
           filterStringAsByteArray[indexOfWhile+3] == ParseConstants.L &&
           filterStringAsByteArray[indexOfWhile+4] == ParseConstants.E &&
           (indexOfWhile == 0 || filterStringAsByteArray[indexOfWhile-1] == ParseConstants.WHITESPACE
            || filterStringAsByteArray[indexOfWhile-1] == ParseConstants.RPAREN ||
            filterStringAsByteArray[indexOfWhile-1] == ParseConstants.LPAREN) &&
           (filterStringAsByteArray[indexOfWhile+5] == ParseConstants.WHITESPACE ||
            filterStringAsByteArray[indexOfWhile+5] == ParseConstants.LPAREN)) {
         return true;
       } else {
         return false;
       }
     } catch (ArrayIndexOutOfBoundsException e) {
       return false;
     }
   }
 
 /**
  * Returns a boolean indicating whether the quote was escaped or not
  * <p>
  * @param array byte array in which the quote was found
  * @param quoteIndex index of the single quote
  * @return returns true if the quote was unescaped
  */
   public static boolean isQuoteUnescaped (byte [] array, int quoteIndex) {
     if (array == null) {
       throw new IllegalArgumentException("isQuoteUnescaped called with a null array");
     }
 
     if (quoteIndex == array.length - 1 || array[quoteIndex+1] != ParseConstants.SINGLE_QUOTE) {
       return true;
     }
     else {
       return false;
     }
   }
 
 /**
  * Takes a quoted byte array and converts it into an unquoted byte array
  * For example: given a byte array representing 'abc', it returns a
  * byte array representing abc
  * <p>
  * @param quotedByteArray the quoted byte array
  * @return Unquoted byte array
  */
   public static byte [] removeQuotesFromByteArray (byte [] quotedByteArray) {
     if (quotedByteArray == null ||
         quotedByteArray.length < 2 ||
         quotedByteArray[0] != ParseConstants.SINGLE_QUOTE ||
         quotedByteArray[quotedByteArray.length - 1] != ParseConstants.SINGLE_QUOTE) {
       throw new IllegalArgumentException("removeQuotesFromByteArray needs a quoted byte array");
     } else {
       byte [] targetString = new byte [quotedByteArray.length - 2];
       Bytes.putBytes(targetString, 0, quotedByteArray, 1, quotedByteArray.length - 2);
       return targetString;
     }
   }
 
 /**
  * Converts an int expressed in a byte array to an actual int
  * <p>
  * This doesn't use Bytes.toInt because that assumes
  * that there will be {@link Bytes#SIZEOF_INT} bytes available.
  * <p>
  * @param numberAsByteArray the int value expressed as a byte array
  * @return the int value
  */
   public static int convertByteArrayToInt (byte [] numberAsByteArray) {
 
     long tempResult = ParseFilter.convertByteArrayToLong(numberAsByteArray);
 
     if (tempResult > Integer.MAX_VALUE) {
       throw new IllegalArgumentException("Integer Argument too large");
     } else if (tempResult < Integer.MIN_VALUE) {
       throw new IllegalArgumentException("Integer Argument too small");
     }
 
     int result = (int) tempResult;
     return result;
   }
 
 /**
  * Converts a long expressed in a byte array to an actual long
  * <p>
  * This doesn't use Bytes.toLong because that assumes
  * that there will be {@link Bytes#SIZEOF_INT} bytes available.
  * <p>
  * @param numberAsByteArray the long value expressed as a byte array
  * @return the long value
  */
   public static long convertByteArrayToLong (byte [] numberAsByteArray) {
     if (numberAsByteArray == null) {
       throw new IllegalArgumentException("convertByteArrayToLong called with a null array");
     }
 
     int i = 0;
     long result = 0;
     boolean isNegative = false;
 
     if (numberAsByteArray[i] == ParseConstants.MINUS_SIGN) {
       i++;
       isNegative = true;
     }
 
     while (i != numberAsByteArray.length) {
       if (numberAsByteArray[i] < ParseConstants.ZERO ||
           numberAsByteArray[i] > ParseConstants.NINE) {
         throw new IllegalArgumentException("Byte Array should only contain digits");
       }
       result = result*10 + (numberAsByteArray[i] - ParseConstants.ZERO);
       if (result < 0) {
         throw new IllegalArgumentException("Long Argument too large");
       }
       i++;
     }
 
     if (isNegative) {
       return -result;
     } else {
       return result;
     }
   }
 
 /**
  * Converts a boolean expressed in a byte array to an actual boolean
  *<p>
  * This doesn't used Bytes.toBoolean because Bytes.toBoolean(byte [])
  * assumes that 1 stands for true and 0 for false.
  * Here, the byte array representing "true" and "false" is parsed
  * <p>
  * @param booleanAsByteArray the boolean value expressed as a byte array
  * @return the boolean value
  */
   public static boolean convertByteArrayToBoolean (byte [] booleanAsByteArray) {
     if (booleanAsByteArray == null) {
       throw new IllegalArgumentException("convertByteArrayToBoolean called with a null array");
     }
 
     if (booleanAsByteArray.length == 4 &&
         (booleanAsByteArray[0] == 't' || booleanAsByteArray[0] == 'T') &&
         (booleanAsByteArray[1] == 'r' || booleanAsByteArray[1] == 'R') &&
         (booleanAsByteArray[2] == 'u' || booleanAsByteArray[2] == 'U') &&
         (booleanAsByteArray[3] == 'e' || booleanAsByteArray[3] == 'E')) {
       return true;
     }
     else if (booleanAsByteArray.length == 5 &&
              (booleanAsByteArray[0] == 'f' || booleanAsByteArray[0] == 'F') &&
              (booleanAsByteArray[1] == 'a' || booleanAsByteArray[1] == 'A') &&
              (booleanAsByteArray[2] == 'l' || booleanAsByteArray[2] == 'L') &&
              (booleanAsByteArray[3] == 's' || booleanAsByteArray[3] == 'S') &&
              (booleanAsByteArray[4] == 'e' || booleanAsByteArray[4] == 'E')) {
       return false;
     }
     else {
       throw new IllegalArgumentException("Incorrect Boolean Expression");
     }
   }
 
 /**
  * Takes a compareOperator symbol as a byte array and returns the corresponding CompareOperator
  * <p>
  * @param compareOpAsByteArray the comparatorOperator symbol as a byte array
  * @return the Compare Operator
  */
   public static CompareFilter.CompareOp createCompareOp (byte [] compareOpAsByteArray) {
     ByteBuffer compareOp = ByteBuffer.wrap(compareOpAsByteArray);
     if (compareOp.equals(ParseConstants.LESS_THAN_BUFFER))
       return CompareOp.LESS;
     else if (compareOp.equals(ParseConstants.LESS_THAN_OR_EQUAL_TO_BUFFER))
       return CompareOp.LESS_OR_EQUAL;
     else if (compareOp.equals(ParseConstants.GREATER_THAN_BUFFER))
       return CompareOp.GREATER;
     else if (compareOp.equals(ParseConstants.GREATER_THAN_OR_EQUAL_TO_BUFFER))
       return CompareOp.GREATER_OR_EQUAL;
     else if (compareOp.equals(ParseConstants.NOT_EQUAL_TO_BUFFER))
       return CompareOp.NOT_EQUAL;
     else if (compareOp.equals(ParseConstants.EQUAL_TO_BUFFER))
       return CompareOp.EQUAL;
     else
       throw new IllegalArgumentException("Invalid compare operator");
   }
 
 /**
  * Parses a comparator of the form comparatorType:comparatorValue form and returns a comparator
  * <p>
  * @param comparator the comparator in the form comparatorType:comparatorValue
  * @return the parsed comparator
  */
   public static ByteArrayComparable createComparator (byte [] comparator) {
     if (comparator == null)
       throw new IllegalArgumentException("Incorrect Comparator");
     byte [][] parsedComparator = ParseFilter.parseComparator(comparator);
     byte [] comparatorType = parsedComparator[0];
     byte [] comparatorValue = parsedComparator[1];
 
 
     if (Bytes.equals(comparatorType, ParseConstants.binaryType))
       return new BinaryComparator(comparatorValue);
     else if (Bytes.equals(comparatorType, ParseConstants.binaryPrefixType))
       return new BinaryPrefixComparator(comparatorValue);
     else if (Bytes.equals(comparatorType, ParseConstants.regexStringType))
       return new RegexStringComparator(new String(comparatorValue, StandardCharsets.UTF_8));
     else if (Bytes.equals(comparatorType, ParseConstants.regexStringNoCaseType))
       return new RegexStringComparator(new String(comparatorValue, StandardCharsets.UTF_8),
                                        Pattern.CASE_INSENSITIVE | Pattern.DOTALL);
     else if (Bytes.equals(comparatorType, ParseConstants.substringType))
       return new SubstringComparator(new String(comparatorValue, StandardCharsets.UTF_8));
     else
       throw new IllegalArgumentException("Incorrect comparatorType");
   }
 
 /**
  * Splits a column in comparatorType:comparatorValue form into separate byte arrays
  * <p>
  * @param comparator the comparator
  * @return the parsed arguments of the comparator as a 2D byte array
  */
   public static byte [][] parseComparator (byte [] comparator) {
     final int index = KeyValue.getDelimiter(comparator, 0, comparator.length, ParseConstants.COLON);
     if (index == -1) {
       throw new IllegalArgumentException("Incorrect comparator");
     }
 
     byte [][] result = new byte [2][0];
     result[0] = new byte [index];
     System.arraycopy(comparator, 0, result[0], 0, index);
 
     final int len = comparator.length - (index + 1);
     result[1] = new byte[len];
     System.arraycopy(comparator, index + 1, result[1], 0, len);
 
     return result;
   }
 
 /**
  * Return a Set of filters supported by the Filter Language
  */
   public Set<String> getSupportedFilters () {
     return filterHashMap.keySet();
   }
 
   /**
    * Returns all known filters
    * @return an unmodifiable map of filters
    */
   public static Map<String, String> getAllFilters() {
     return Collections.unmodifiableMap(filterHashMap);
   }
 
   /**
    * Register a new filter with the parser.  If the filter is already registered,
    * an IllegalArgumentException will be thrown.
    *
    * @param name a name for the filter
    * @param filterClass fully qualified class name
    */
   public static void registerFilter(String name, String filterClass) {
     if(LOG.isInfoEnabled())
       LOG.info("Registering new filter " + name);
 
     filterHashMap.put(name, filterClass);
   }
 }