/*
  * Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg 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
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 

 #include "config.h"
 
 #if HAVE_UNISTD_H

 #include <unistd.h>

 #endif

 #include <fcntl.h>

 #include <math.h>
 #include <time.h>

 #include <string.h>

 #include "avassert.h"

 #include "timer.h"
 #include "random_seed.h"

 #include "sha.h"
 #include "intreadwrite.h"
 
 #ifndef TEST
 #define TEST 0
 #endif

 static int read_random(uint32_t *dst, const char *file)
 {

 #if HAVE_UNISTD_H

     int fd = open(file, O_RDONLY);
     int err = -1;
 
     if (fd == -1)
         return -1;

     err = read(fd, dst, sizeof(*dst));

     close(fd);
 
     return err;

 #else
     return -1;
 #endif

 }
 

 static uint32_t get_generic_seed(void)
 {

     uint8_t tmp[120];

     struct AVSHA *sha = (void*)tmp;

     clock_t last_t  = 0;

     static uint64_t i = 0;
     static uint32_t buffer[512] = {0};
     unsigned char digest[32];
     uint64_t last_i = i;

     av_assert0(sizeof(tmp) >= av_sha_size);
 

     if(TEST){
         memset(buffer, 0, sizeof(buffer));
         last_i = i = 0;
     }else{
 #ifdef AV_READ_TIME
         buffer[13] ^= AV_READ_TIME();
         buffer[41] ^= AV_READ_TIME()>>32;
 #endif
     }
 
     for (;;) {

         clock_t t = clock();

 
         if(last_t == t){
             buffer[i&511]++;
         }else{
             buffer[++i&511]+= (t-last_t) % 3294638521U;
             if(last_i && i-last_i > 4 || i-last_i > 64 || TEST && i-last_i > 8)
                 break;

         }

         last_t = t;

     }
 

     if(TEST)
         buffer[0] = buffer[1] = 0;

     av_sha_init(sha, 160);
     av_sha_update(sha, (uint8_t*)buffer, sizeof(buffer));
     av_sha_final(sha, digest);
     return AV_RB32(digest) + AV_RB32(digest+32);

 }
 

 uint32_t av_get_random_seed(void)

 {
     uint32_t seed;

     if (read_random(&seed, "/dev/urandom") == sizeof(seed))
         return seed;
     if (read_random(&seed, "/dev/random")  == sizeof(seed))

         return seed;

     return get_generic_seed();

 }

 #if TEST

 #undef printf
 #define N 256
 #include <stdio.h>
 
 int main(void)
 {
     int i, j, retry;
     uint32_t seeds[N];
 
     for (retry=0; retry<3; retry++){
         for (i=0; i<N; i++){
             seeds[i] = av_get_random_seed();
             for (j=0; j<i; j++)
                 if (seeds[j] == seeds[i])
                     goto retry;
         }
         printf("seeds OK\n");
         return 0;
         retry:;
     }
     printf("FAIL at %d with %X\n", j, seeds[j]);
     return 1;
 }
 #endif