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Truffle is a multi-language framework for executing dynamic languages that achieves high performance when combined with Graal.
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/*
 * Copyright (c) 2017, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package com.oracle.truffle.api.source;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

/**
 * Copied from {@link StringReader} JDK class. But uses {@link CharSequence} instead.
 */
final class CharSequenceReader extends Reader {

    private CharSequence seq;
    private int length;
    private int next = 0;
    private int mark = 0;

    CharSequenceReader(CharSequence s) {
        this.seq = s;
        this.length = s.length();
    }

    private void ensureOpen() throws IOException {
        if (seq == null) {
            throw new IOException("Stream closed");
        }
    }

    @Override
    public int read() throws IOException {
        synchronized (lock) {
            ensureOpen();
            if (next >= length) {
                return -1;
            }
            return seq.charAt(next++);
        }
    }

    @Override
    public int read(char[] cbuf, int off, int len) throws IOException {
        synchronized (lock) {
            ensureOpen();
            if ((off < 0) || (off > cbuf.length) || (len < 0) ||
                            ((off + len) > cbuf.length) || ((off + len) < 0)) {
                throw new IndexOutOfBoundsException();
            } else if (len == 0) {
                return 0;
            }
            if (next >= length) {
                return -1;
            }
            int n = Math.min(length - next, len);
            // this was adapted from the original StringReader code.
            for (int i = 0; i < n; i++) {
                cbuf[off + i] = seq.charAt(next + i);
            }
            next += n;
            return n;
        }
    }

    @Override
    public long skip(long ns) throws IOException {
        synchronized (lock) {
            ensureOpen();
            if (next >= length) {
                return 0;
            }
            // Bound skip by beginning and end of the source
            long n = Math.min(length - next, ns);
            n = Math.max(-next, n);
            next += n;
            return n;
        }
    }

    @Override
    public boolean ready() throws IOException {
        synchronized (lock) {
            ensureOpen();
            return true;
        }
    }

    @Override
    public boolean markSupported() {
        return true;
    }

    @Override
    public void mark(int readAheadLimit) throws IOException {
        if (readAheadLimit < 0) {
            throw new IllegalArgumentException("Read-ahead limit < 0");
        }
        synchronized (lock) {
            ensureOpen();
            mark = next;
        }
    }

    @Override
    public void reset() throws IOException {
        synchronized (lock) {
            ensureOpen();
            next = mark;
        }
    }

    @Override
    public void close() {
        seq = null;
    }
}