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
18package android.filterfw.io;
19
20import java.util.regex.Matcher;
21import java.util.regex.Pattern;
22
23/**
24 * @hide
25 */
26public 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