/*
 * Copyright (C) 2013  Internet Systems Consortium, Inc. ("ISC")
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

#include <windows.h>
#include <stdio.h>
#include <io.h>

#include "pread.h"

static CRITICAL_SECTION preadsc;

/* http://stackoverflow.com/a/2390626/1392778 */

#ifdef _MSC_VER

#pragma section(".CRT$XCU",read)

#define INITIALIZER(f)                                                  \
    static void __cdecl f(void);                                        \
    __declspec(allocate(".CRT$XCU")) void(__cdecl * f ## _) (void) = f; \
    static void __cdecl f(void)

#elif defined(__GNUC__)

#define INITIALIZER(f)                                \
    static void f(void) __attribute__((constructor)); \
    static void f(void)

#endif


#ifdef _WIN64
int pread(int fd, void *buf, unsigned int nbyte, __int64 offset)
{
    int cc = -1;
    __int64 prev = (__int64) - 1L;

    EnterCriticalSection(&preadsc);
    prev = _lseeki64(fd, 0L, SEEK_CUR);
    if (prev == (__int64) - 1L) {
        goto done;
    }
    if (_lseeki64(fd, offset, SEEK_SET) != offset) {
        goto done;
    }
    cc = _read(fd, buf, nbyte);

 done:
    if (prev != (__int64) - 1L) {
        (void)_lseeki64(fd, prev, SEEK_SET);
    }
    LeaveCriticalSection(&preadsc);

    return cc;
}
#else
int pread(int fd, void *buf, unsigned int nbyte, long offset)
{
    int cc = -1;
    long prev = -1L;

    EnterCriticalSection(&preadsc);
    prev = _lseek(fd, 0L, SEEK_CUR);
    if (prev == -1L) {
        goto done;
    }
    if (_lseek(fd, offset, SEEK_SET) != offset) {
        goto done;
    }
    cc = _read(fd, buf, nbyte);

 done:
    if (prev != -1L) {
        (void)_lseek(fd, prev, SEEK_SET);
    }
    LeaveCriticalSection(&preadsc);

    return cc;
}
#endif

static void deinitialize(void)
{
    DeleteCriticalSection(&preadsc);
}

INITIALIZER(initialize){
    InitializeCriticalSection(&preadsc);
    atexit(deinitialize);
}
