/**
 * @file    fmemopen.c
 * @brief   Implementation of fmemopen for old MacOSX and Windows.
 * @author  Hanno Rein <hanno@hanno-rein.de>
 * 
 * @section LICENSE
 * Copyright (c) 2023 Hanno Rein
 * 
 * This file is part of rebound.
 *
 * rebound 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.
 *
 * rebound 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 rebound.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Most of the code below is taken from glibc. 
 * See https://github.com/lattera/glibc/blob/master/libio/fmemopen.c
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include "fmemopen.h"

#ifdef __MACH__

// This code here is a workaround for old MacOS versions which do 
// not come with fmemopen. (Note that as a result of fmemopen 
// missing, conda-forge builds fail).
// The following code has been slightly modified from
// https://raw.githubusercontent.com/Cibiv/PDA/master/fmemopen.c

struct fmem {
    size_t pos;
    size_t size;
    char *buffer;
};

static int readfn(void *handler, char *buf, int size) {
    struct fmem *mem = handler;
    size_t available = mem->size - mem->pos;

    if (size > available) {
        size = available;
    }
    memcpy(buf, mem->buffer + mem->pos, sizeof(char) * size);
    mem->pos += size;

    return size;
}

static int writefn(void *handler, const char *buf, int size) {
    struct fmem *mem = handler;
    size_t available = mem->size - mem->pos;

    if (size > available) {
        size = available;
    }
    memcpy(mem->buffer + mem->pos, buf, sizeof(char) * size);
    mem->pos += size;

    return size;
}

static fpos_t seekfn(void *handler, fpos_t offset, int whence) {
    size_t pos;
    struct fmem *mem = handler;

    switch (whence) {
        case SEEK_SET: pos = offset; break;
        case SEEK_CUR: pos = mem->pos + offset; break;
        case SEEK_END: pos = mem->size + offset; break;
        default: return -1;
    }

    if (pos > mem->size) {
        return -1;
    }

    mem->pos = pos;
    return (fpos_t)pos;
}

static int closefn(void *handler) {
    free(handler);
    return 0;
}

FILE *reb_fmemopen(void *buf, size_t size, const char *mode) {
    // This data is released on fclose.
    struct fmem* mem = (struct fmem *) malloc(sizeof(struct fmem));

    // Zero-out the structure.
    memset(mem, 0, sizeof(struct fmem));

    mem->size = size;
    mem->buffer = buf;

    // funopen's man page: https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man3/funopen.3.html
    return funopen(mem, readfn, writefn, seekfn, closefn);
}

#elif defined _WIN32

// Fmemopen does not exist on Windows. 
// This workaround is using temporary files.
// This works but it is SLOW!

#define WIN32_LEAN_AND_MEAN
#include <Windows.h>
#include <share.h>
#include <io.h>
#include <sys/stat.h>
// Source: https://github.com/Arryboom/fmemopen_windows
FILE *reb_fmemopen(void *buf, size_t len, const char *type) {
    int fd;
    FILE *fp;
    char tp[MAX_PATH - 13];
    char fn[MAX_PATH + 1];
    int * pfd = &fd;
    int retner = -1;
    char tfname[] = "MemTF_";
    if (!GetTempPathA(sizeof(tp), tp))
        return NULL;
    if (!GetTempFileNameA(tp, tfname, 0, fn))
        return NULL;
    retner = _sopen_s(pfd, fn, _O_CREAT | _O_SHORT_LIVED | _O_TEMPORARY | _O_RDWR | _O_BINARY | _O_NOINHERIT, _SH_DENYRW, _S_IREAD | _S_IWRITE);
    if (retner != 0)
        return NULL;
    if (fd == -1)
        return NULL;
    fp = _fdopen(fd, "wb+");
    if (!fp) {
        _close(fd);
        return NULL;
    }
    /*File descriptors passed into _fdopen are owned by the returned FILE * stream.If _fdopen is successful, do not call _close on the file descriptor.Calling fclose on the returned FILE * also closes the file descriptor.*/
    fwrite(buf, len, 1, fp);
    rewind(fp);
    return fp;
}

#else
// Just an alias for everyone else
FILE *reb_fmemopen(void *buf, size_t len, const char *type){
    return fmemopen(buf, len, type);
}

#endif