//
// aegis - project change supervisor
// Copyright (C) 2005, 2006, 2008, 2012 Peter Miller
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or (at
// your option) any later version.
//
// This program 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 for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//

#include <common/ac/assert.h>

#include <common/nstring.h>


nstring
nstring::substr(long start, long nbytes)
    const
{
    //
    // If start is negative, measure from the end instead of the beginning.
    //
    if (start < 0)
    {
        start += size();
    }

    //
    // If nbytes is negative, measure to the left instead of to the right.
    //
    if (nbytes < 0)
    {
        start += nbytes;
        nbytes = -nbytes;
    }

    //
    // If the start of the string is negative, pretend the negative part
    // is empty.
    //
    if (start < 0)
    {
        nbytes += start;
        start = 0;
    }

    //
    // If, after all that, the substring is still to the left of the
    // content, return the empty string.
    //
    assert(start >= 0);
    if (start + nbytes < 0)
        return "";
    assert(nbytes >= 0);

    //
    // If the bumber of bytes would project beynd the end of the string,
    // truncate them.
    //
    assert(start + nbytes >= 0);
    if ((size_t)(start + nbytes) > size())
        nbytes = size() - start;

    //
    // Build the substring.
    //
    return nstring(c_str() + start, nbytes);
}


// vim: set ts=8 sw=4 et :