/*
 * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package com.sun.tools.javac.parser;

import java.nio.*;
import java.util.List;
import java.util.ArrayList;

import com.sun.tools.javac.util.Position.LineMap;
import com.sun.tools.javac.parser.JavaTokenizer.*;

import static com.sun.tools.javac.parser.Tokens.*;

The lexical analyzer maps an input stream consisting of
 ASCII characters and Unicode escapes into a token sequence.
 
This is NOT part of any supported API.
 If you write code that depends on this, you do so at your own risk.
 This code and its internal interfaces are subject to change or
 deletion without notice.
/** The lexical analyzer maps an input stream consisting of
 *  ASCII characters and Unicode escapes into a token sequence.
 *
 *  <p><b>This is NOT part of any supported API.
 *  If you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 */
public class Scanner implements Lexer {

    private Tokens tokens;

    
The token, set by nextToken().
/** The token, set by nextToken().
     */
    private Token token;

    
The previous token, set by nextToken().
/** The previous token, set by nextToken().
     */
    private Token prevToken;

    
Buffer of saved tokens (used during lookahead)
/** Buffer of saved tokens (used during lookahead)
     */
    private List<Token> savedTokens = new ArrayList<>();

    private JavaTokenizer tokenizer;

    
Create a scanner from the input array. This method might modify the array. To avoid copying the input array, ensure that inputLength < input.length or input[input.length -1] is a white space character. 
Params:
fac – the factory which created this Scanner
buf – the input, might be modified
Must be positive and less than or equal to input.length./**
     * Create a scanner from the input array.  This method might
     * modify the array.  To avoid copying the input array, ensure
     * that {@code inputLength < input.length} or
     * {@code input[input.length -1]} is a white space character.
     *
     * @param fac the factory which created this Scanner
     * @param buf the input, might be modified
     * Must be positive and less than or equal to input.length.
     */
    protected Scanner(ScannerFactory fac, CharBuffer buf) {
        this(fac, new JavaTokenizer(fac, buf));
    }

    protected Scanner(ScannerFactory fac, char[] buf, int inputLength) {
        this(fac, new JavaTokenizer(fac, buf, inputLength));
    }

    protected Scanner(ScannerFactory fac, JavaTokenizer tokenizer) {
        this.tokenizer = tokenizer;
        tokens = fac.tokens;
        token = prevToken = DUMMY;
    }

    public Token token() {
        return token(0);
    }

    public Token token(int lookahead) {
        if (lookahead == 0) {
            return token;
        } else {
            ensureLookahead(lookahead);
            return savedTokens.get(lookahead - 1);
        }
    }
    //where
        private void ensureLookahead(int lookahead) {
            for (int i = savedTokens.size() ; i < lookahead ; i ++) {
                savedTokens.add(tokenizer.readToken());
            }
        }

    public Token prevToken() {
        return prevToken;
    }

    public void nextToken() {
        prevToken = token;
        if (!savedTokens.isEmpty()) {
            token = savedTokens.remove(0);
        } else {
            token = tokenizer.readToken();
        }
    }

    public Token split() {
        Token[] splitTokens = token.split(tokens);
        prevToken = splitTokens[0];
        token = splitTokens[1];
        return token;
    }

    public LineMap getLineMap() {
        return tokenizer.getLineMap();
    }

    public int errPos() {
        return tokenizer.errPos();
    }

    public void errPos(int pos) {
        tokenizer.errPos(pos);
    }
}