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      1 /*
      2  * Copyright (C) 2011 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 
     18 package android.filterfw.io;
     19 
     20 import java.util.regex.Matcher;
     21 import java.util.regex.Pattern;
     22 
     23 /**
     24  * @hide
     25  */
     26 public class PatternScanner {
     27 
     28     private String mInput;
     29     private Pattern mIgnorePattern;
     30     private int mOffset = 0;
     31     private int mLineNo = 0;
     32     private int mStartOfLine = 0;
     33 
     34     public PatternScanner(String input) {
     35         mInput = input;
     36     }
     37 
     38     public PatternScanner(String input, Pattern ignorePattern) {
     39         mInput = input;
     40         mIgnorePattern = ignorePattern;
     41         skip(mIgnorePattern);
     42     }
     43 
     44     public String tryEat(Pattern pattern) {
     45         // Skip ignore pattern
     46         if (mIgnorePattern != null) {
     47             skip(mIgnorePattern);
     48         }
     49 
     50         // Create the matcher
     51         Matcher matcher = pattern.matcher(mInput);
     52         matcher.region(mOffset, mInput.length());
     53 
     54         // Attempt to match
     55         String result = null;
     56         if (matcher.lookingAt()) {
     57             updateLineCount(mOffset, matcher.end());
     58             mOffset = matcher.end();
     59             result = mInput.substring(matcher.start(), matcher.end());
     60         }
     61 
     62         // Skip ignore pattern
     63         if (result != null && mIgnorePattern != null) {
     64             skip(mIgnorePattern);
     65         }
     66 
     67         return result;
     68     }
     69 
     70     public String eat(Pattern pattern, String tokenName) {
     71         String result = tryEat(pattern);
     72         if (result == null) {
     73             throw new RuntimeException(unexpectedTokenMessage(tokenName));
     74         }
     75         return result;
     76     }
     77 
     78     public boolean peek(Pattern pattern) {
     79         // Skip ignore pattern
     80         if (mIgnorePattern != null) {
     81             skip(mIgnorePattern);
     82         }
     83 
     84         // Create the matcher
     85         Matcher matcher = pattern.matcher(mInput);
     86         matcher.region(mOffset, mInput.length());
     87 
     88         // Attempt to match
     89         return matcher.lookingAt();
     90     }
     91 
     92     public void skip(Pattern pattern) {
     93         Matcher matcher = pattern.matcher(mInput);
     94         matcher.region(mOffset, mInput.length());
     95         if (matcher.lookingAt()) {
     96             updateLineCount(mOffset, matcher.end());
     97             mOffset = matcher.end();
     98         }
     99     }
    100 
    101     public boolean atEnd() {
    102         return mOffset >= mInput.length();
    103     }
    104 
    105     public int lineNo() {
    106         return mLineNo;
    107     }
    108 
    109     public String unexpectedTokenMessage(String tokenName) {
    110         String line = mInput.substring(mStartOfLine, mOffset);
    111         return "Unexpected token on line " + (mLineNo + 1) + " after '" + line + "' <- Expected " +
    112                 tokenName + "!";
    113     }
    114 
    115     public void updateLineCount(int start, int end) {
    116         for (int i = start; i < end; ++i) {
    117             if (mInput.charAt(i) == '\n') {
    118                 ++mLineNo;
    119                 mStartOfLine = i + 1;
    120             }
    121         }
    122     }
    123 }
    124