com.google.gerrit.server.util.RegexListSearcher.java Source code

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Here is the source code for com.google.gerrit.server.util.RegexListSearcher.java

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// Copyright (C) 2014 The Android Open Source Project
//
// Licensed 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 com.google.gerrit.server.util;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Function;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.primitives.Chars;
import dk.brics.automaton.Automaton;
import dk.brics.automaton.RegExp;
import dk.brics.automaton.RunAutomaton;
import java.util.Collections;
import java.util.List;

/** Helper to search sorted lists for elements matching a regex. */
public abstract class RegexListSearcher<T> implements Function<T, String> {
    public static RegexListSearcher<String> ofStrings(String re) {
        return new RegexListSearcher<String>(re) {
            @Override
            public String apply(String in) {
                return in;
            }
        };
    }

    private final RunAutomaton pattern;

    private final String prefixBegin;
    private final String prefixEnd;
    private final int prefixLen;
    private final boolean prefixOnly;

    public RegexListSearcher(String re) {
        if (re.startsWith("^")) {
            re = re.substring(1);
        }

        if (re.endsWith("$") && !re.endsWith("\\$")) {
            re = re.substring(0, re.length() - 1);
        }

        Automaton automaton = new RegExp(re).toAutomaton();
        prefixBegin = automaton.getCommonPrefix();
        prefixLen = prefixBegin.length();

        if (0 < prefixLen) {
            char max = Chars.checkedCast(prefixBegin.charAt(prefixLen - 1) + 1);
            prefixEnd = prefixBegin.substring(0, prefixLen - 1) + max;
            prefixOnly = re.equals(prefixBegin + ".*");
        } else {
            prefixEnd = "";
            prefixOnly = false;
        }

        pattern = prefixOnly ? null : new RunAutomaton(automaton);
    }

    public Iterable<T> search(List<T> list) {
        checkNotNull(list);
        int begin;
        int end;

        if (0 < prefixLen) {
            // Assumes many consecutive elements may have the same prefix, so the cost
            // of two binary searches is less than iterating to find the endpoints.
            begin = find(list, prefixBegin);
            end = find(list, prefixEnd);
        } else {
            begin = 0;
            end = list.size();
        }

        if (prefixOnly) {
            return begin < end ? list.subList(begin, end) : ImmutableList.<T>of();
        }

        return Iterables.filter(list.subList(begin, end), x -> pattern.run(apply(x)));
    }

    public boolean hasMatch(List<T> list) {
        return !Iterables.isEmpty(search(list));
    }

    private int find(List<T> list, String p) {
        int r = Collections.binarySearch(Lists.transform(list, this), p);
        return r < 0 ? -(r + 1) : r;
    }
}