package org.simantics.scl.compiler.completions.parsing;

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

/**
 * Based on java.io.StringReader.
 */

public class SubstringReader extends Reader {

    private String str;
    private int end;
    private int pos;
    private int mark;

    public SubstringReader(String str, int begin, int end) {
        this.str = str;
        this.pos = begin;
        this.mark = begin;
        this.end = end;
    }

    public int read() throws IOException {
        if (pos >= end)
            return -1;
        return str.charAt(pos++);
    }

    public int read(char cbuf[], int off, int len) throws IOException {
        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 (pos >= end)
            return -1;
        int n = Math.min(end - pos, len);
        str.getChars(pos, pos + n, cbuf, off);
        pos += n;
        return n;
    }

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

    public boolean ready() throws IOException {
        return true;
    }

    public boolean markSupported() {
        return true;
    }

    public void mark(int readAheadLimit) throws IOException {
        if (readAheadLimit < 0)
            throw new IllegalArgumentException("Read-ahead limit < 0");
        mark = pos;
    }

    public void reset() throws IOException {
        pos = mark;
    }

    public void close() {
    }
}