#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#if (defined SOLARIS || defined POSIX)

#include <unistd.h>
#include <sys/mman.h>
#include <fcntl.h>

#ifdef __cplusplus
extern "C" {
#endif
   int shm_open(const char *, int, mode_t);
#ifdef __cplusplus
}
#endif

#else
#include <sys/types.h>
#include <sys/shm.h>
#endif


/*    format of the data buffer area header   */

#define NBLOCKS 64                     /*  current number of buffers used - must be 2**n */
#define MAX_BUFFERS 128                /*  unchangeable maximum because of header structure */

typedef struct s_buffer_header {
    int buffer_offset;                 /*    offset to first buffer */
    int buffer_number;                 /*    number of buffers */
    int buffer_length;                 /*    length of buffers */
    int buffer_next;                   /*    next buffer to be written */
    int buffer_max;                    /*    MAX_BUFFERS */
    int buffer_spare1;
    int buffer_spare2;
    int buffer_spare3;
    long long buffer_currentage;
    long long buffer_age[MAX_BUFFERS];
}  BUFFER_HEADER;  

#define SHM_KEY 110205

short * shm_bufferarea=NULL;

static short DataBuffer[(32*1024)+16];    //   maximum length is 64Kbyte + allow for 32 byte header later
int debug=0;

void initialise ()
{


#if (defined SOLARIS || defined POSIX)
   int shmid;
   int shmkey = SHM_KEY;
   char object_name[16];
#else
   int shmid;
   key_t shmkey = SHM_KEY;
#endif


   /*   Open the shared memory object   */

#if (defined SOLARIS || defined POSIX)

   sprintf( object_name, "/SHM_%d", shmkey );

   shmid = shm_open( object_name, O_RDONLY, ( mode_t ) 0 );
   /*--> Just check that we have opened the segment ok            <--*/
   if ( shmid == -1 ) {perror( "shm_open " ); exit( 1 );}

#else

    shmid = shmget(shmkey, 0, SHM_R);
    if (shmid == -1) {perror("shmget"); exit(1);}
    
#endif

#if (defined SOLARIS || defined POSIX)

   /*--> Now attach the memory segment                            <--*/

   shm_bufferarea = (short *)mmap( ( caddr_t ) NULL, 
                   ( size_t ) 0x401000,
                   PROT_READ,
                   MAP_SHARED,
                   shmid,
                   0 );
   
   /*--> Now check that we have attached it correctly             <--*/
   if ( shm_bufferarea == ( void *) MAP_FAILED )
    {
     perror( "mmap" );
     exit ( 1 );
    }
   /*--> Close the shared memory segment                          <--*/
   close( shmid );

#else

    shm_bufferarea = shmat(shmid, (void *) 0, SHM_RDONLY);
    if (shm_bufferarea == (void *) -1) {perror("shmat"); exit(1);}
    
#endif

}

short *get_block (int *New, int *runinfo)
{

    int offset, number, length, next, max;
    int i;
    
    unsigned long long cage;
    static unsigned long long age =0;
    
    BUFFER_HEADER * baseaddress;
    short * bufferaddress  =0;
  
  if (shm_bufferarea == NULL) {

      initialise ();
 
      if(debug)
      {
         printf("midasTS : Shared buffer area located at 0x%p\n", shm_bufferarea);
      }

      baseaddress = (BUFFER_HEADER *) shm_bufferarea;
      age = baseaddress->buffer_currentage;    /* start at the next new buffer */
  }
 
 baseaddress = (BUFFER_HEADER *) shm_bufferarea;
 cage = baseaddress->buffer_currentage;
 number = baseaddress->buffer_number;
 next = baseaddress->buffer_next;
 max = baseaddress->buffer_max;
 offset = baseaddress->buffer_offset;
 length = baseaddress->buffer_length;

 *runinfo = length;

 if (debug)
  {
    printf ("current control information: ");
    printf ("offset=%d number=%d length=%d next=%d max=%d age=%lld\n", offset, number, length, next, max, cage);
  }
 
 i = ( next - 1 ) & ( number - 1 );
 
 if ( baseaddress->buffer_age[i] != 0 )
 {
    bufferaddress = (short *) ((char *)shm_bufferarea + offset + (length * i));

    if (debug)
    {
     printf( "midasTS :index=%d   age  = %lld        : cage = %lld\n", i, age, cage );
    }

   /*--> Check to see the age of the data block ....          <--*/
    if ( cage > age )
    {
     /*-->  found a new buffer                      <--*/
       age  = cage;
     /*    copy the buffer   */
       memcpy (&DataBuffer[12], bufferaddress, baseaddress->buffer_length);
       bufferaddress = &DataBuffer[12];

       *New = 1;         /* a new buffer */
       if (debug)
       {
          printf( "midasTS :New buffer: index=%d   age  = %lld\n", i, age);
       }
    } else {
     /*--> So this buffer is the same as the last one ....  <--*/
      *New = 0;    /* no buffer available */
    }
  } else {
      *New = 0;    /* no buffer available */
  }
   
 return  bufferaddress;
}