/*
 * Copyright 2016 Google Inc.
 *
 * 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.palantir.javaformat.java.javadoc;

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

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

/**
 * String reader designed for use from the lexer. Callers invoke the {@link #tryConsume tryConsume*} methods to specify
 * what characters they expect and then {@link #readAndResetRecorded} to retrieve and consume the matched characters.
 * This is a slightly odd API -- why not just return the matched characters from tryConsume? -- but it is convenient for
 * the lexer.
 */
final class CharStream {
    String remaining;
    int toConsume;

    CharStream(String input) {
        this.remaining = checkNotNull(input);
    }

    boolean tryConsume(String expected) {
        if (!remaining.startsWith(expected)) {
            return false;
        }
        toConsume = expected.length();
        return true;
    }

    /*
     * @param pattern the pattern to search for, which must be anchored to match only at position 0
     */
    boolean tryConsumeRegex(Pattern pattern) {
        Matcher matcher = pattern.matcher(remaining);
        if (!matcher.find()) {
            return false;
        }
        checkArgument(matcher.start() == 0);
        toConsume = matcher.end();
        return true;
    }

    String readAndResetRecorded() {
        String result = remaining.substring(0, toConsume);
        remaining = remaining.substring(toConsume);
        toConsume = 0; // TODO(cpovirk): Set this to a bogus value here and in the constructor.
        return result;
    }

    boolean isExhausted() {
        return remaining.isEmpty();
    }
}
