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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, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * The Universal Permissive License (UPL), Version 1.0
 *
 * Subject to the condition set forth below, permission is hereby granted to any
 * person obtaining a copy of this software, associated documentation and/or
 * data (collectively the "Software"), free of charge and under any and all
 * copyright rights in the Software, and any and all patent rights owned or
 * freely licensable by each licensor hereunder covering either (i) the
 * unmodified Software as contributed to or provided by such licensor, or (ii)
 * the Larger Works (as defined below), to deal in both
 *
 * (a) the Software, and
 *
 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
 * one is included with the Software each a "Larger Work" to which the Software
 * is contributed by such licensors),
 *
 * without restriction, including without limitation the rights to copy, create
 * derivative works of, display, perform, and distribute the Software and make,
 * use, sell, offer for sale, import, export, have made, and have sold the
 * Software and the Larger Work(s), and to sublicense the foregoing rights on
 * either these or other terms.
 *
 * This license is subject to the following condition:
 *
 * The above copyright notice and either this complete permission notice or at a
 * minimum a reference to the UPL must be included in all copies or substantial
 * portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
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;
    }
}