// gcc cache2.c ../osdep/shmem.o -o cache2

// Initial draft of my new cache system...
// includes some simulation code, using usleep() to emulate limited bandwith
// TODO: seeking, data consistency checking

#define READ_SPEED 20
#define FILL_SPEED 10

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "../osdep/shmem.h"

typedef struct {
  // constats:
  void *buffer;      // base pointer of the alllocated buffer memory
  int buffer_size;   // size of the alllocated buffer memory
  int sector_size;   // size of a single sector (2048/2324)
     // Note: buffer_size should be N*sector_size, where N is integer...
  int back_size;  // we should keep back_size amount of old bytes for backward seek
  int fill_limit; // we should fill buffer if space>fill_limit
  // reader's pointers:
  int read_filepos;
  // filler's pointers:
  int min_filepos; // buffer contain only a part of the file, from min-max pos
  int max_filepos;
  int offset;      // filepos <-> bufferpos  offset value (filepos of the buffer's first byte)
  // commands/locking:
  int cmd_lock;   // 1 if we will seek/reset buffer, 2 if we are ready for cmd
  int fifo_flag;  // 1 if we should use FIFO to notice cache about buffer reads.
} cache_vars_t;

int min_fill=0;
int sleep_flag=0;

void cache_stats(cache_vars_t* s){
  int newb=s->max_filepos-s->read_filepos; // new bytes in the buffer
  printf("0x%06X  [0x%06X]  0x%06X   ",s->min_filepos,s->read_filepos,s->max_filepos);
  printf("%3d %%  (%3d%%)\n",100*newb/s->buffer_size,100*min_fill/s->buffer_size);
}

int cache_read(cache_vars_t* s,int size){
  int total=0;
  while(size>0){
    int pos,newb,len;
    
    pos=s->read_filepos - s->offset;
    if(pos<0) pos+=s->buffer_size; else
    if(pos>=s->buffer_size) pos-=s->buffer_size;
    
    newb=s->max_filepos-s->read_filepos; // new bytes in the buffer

    if(newb<min_fill) min_fill=newb; // statistics...

    if(newb<=0){
	// waiting for buffer fill...
	usleep(10000); // 10ms
	continue;
    }
    
//    printf("*** newb: %d bytes ***\n",newb);
    
    if(newb>s->buffer_size-pos) newb=s->buffer_size-pos; // handle wrap...
    if(newb>size) newb=size;
    
    // len=write(mem,newb)
    printf("Buffer read: %d bytes\n",newb);
    len=newb;usleep(len*READ_SPEED*sleep_flag);
    // ...
    
    s->read_filepos+=len;
    size-=len;
    total+=len;
    
  }
  return total;
}

int cache_fill(cache_vars_t* s){
  int read,back,newb,space,len,pos,endpos;
  
  read=s->read_filepos;
  
  // calc number of back-bytes:
  back=read - s->min_filepos;
  if(back<0) back=0; // strange...
  if(back>s->back_size) back=s->back_size;
  
  // calc number of new bytes:
  newb=s->max_filepos - read;
  if(newb<0) newb=0; // strange...

  // calc free buffer space:
  space=s->buffer_size - (newb+back);
  
  // calc bufferpos:
  pos=s->max_filepos - s->offset;
  if(pos>=s->buffer_size) pos-=s->buffer_size; // wrap-around
  
  if(space<s->fill_limit){
//    printf("Buffer is full (%d bytes free, limit: %d)\n",space,s->fill_limit);
    return 0; // no fill...
  }

//  printf("### read=0x%X  back=%d  newb=%d  space=%d  pos=%d\n",read,back,newb,space,pos);
     
  // reduce space if needed:
  if(space>s->buffer_size-pos) space=s->buffer_size-pos;
  
  if(space>32768) space=32768; // limit one-time block size
  
  s->min_filepos=read-back; // avoid seeking-back to temp area...
  
  // ....
  printf("Buffer fill: %d bytes of %d\n",space,s->buffer_size);
  len=space; usleep(len*FILL_SPEED*sleep_flag);
  // ....
  
  s->max_filepos+=len;
  if(pos+len>=s->buffer_size){
      // wrap...
      s->offset+=s->buffer_size;
  }
  
  return len;
  
}

cache_vars_t* cache_init(int size,int sector){
  int num;
  cache_vars_t* s=shmem_alloc(sizeof(cache_vars_t));
  memset(s,0,sizeof(cache_vars_t));
  num=size/sector;
  s->buffer_size=num*sector;
  s->sector_size=sector;
  s->buffer=shmem_alloc(s->buffer_size);
  s->fill_limit=8*sector;
  s->back_size=size/2;
  return s;
}

int main(){

  cache_vars_t* s=cache_init(1024*1024,2048);
  
//  while(cache_fill(s)){ }  // fill buffer:
  
  min_fill=s->buffer_size;
  sleep_flag=1; // start simulation
  
  if(fork()){
    while(1){
      if(!cache_fill(s)) usleep(10000); // wait 10ms for buffer space
      //cache_stats(s);
    }
  } else {
    srand(12345);
    while(1){
        int len=10+rand()&8191;
        cache_stats(s);
	cache_read(s,len);
    }
  }

}