module os

// file descriptor based operations:

// close filedescriptor
pub fn fd_close(fd int) int {
    if fd == -1 {
        return 0
    }
    return C.close(fd)
}

pub fn fd_write(fd int, s string) {
    if fd == -1 {
        return
    }
    mut sp := s.str
    mut remaining := s.len
    for remaining > 0 {
        written := C.write(fd, sp, remaining)
        if written < 0 {
            return
        }
        remaining = remaining - written
        sp = unsafe { voidptr(sp + written) }
    }
}

// read from filedescriptor, block until data
pub fn fd_slurp(fd int) []string {
    mut res := []string{}
    if fd == -1 {
        return res
    }
    for {
        s, b := fd_read(fd, 4096)
        if b <= 0 {
            break
        }
        res << s
    }
    return res
}

// read from filedescriptor, don't block
// return [bytestring,nrbytes]
pub fn fd_read(fd int, maxbytes int) (string, int) {
    if fd == -1 {
        return '', 0
    }
    unsafe {
        mut buf := malloc_noscan(maxbytes + 1)
        nbytes := C.read(fd, buf, maxbytes)
        if nbytes < 0 {
            free(buf)
            return '', nbytes
        }
        buf[nbytes] = 0
        return tos(buf, nbytes), nbytes
    }
}