/* An implementation of getc, using MPMY functions.  */

#include <stddef.h>
#include <errno.h>
#include "Msgs.h"
#include "error.h"
#include "SDF-private.h"
#include "stdio.h"
#include "mpmy_io.h"

#define MYBUFSZ 4096

/* Assumption:  we can only have one header at a time being read.
   The header is opened, read anc closed, all during the course of SDFopen
   so we don't have to screw around with multiple open files, etc. */

static MPMYFile *fp;
static char buf[MYBUFSZ];
static char *ptr;
static char *endbuf;
static int buf_offset;


int SDF_Hdropen(const char *name){
    fp = MPMY_Fopen(name, MPMY_RDONLY|MPMY_SINGL);
    if( fp == NULL )
	return -1;
    endbuf = ptr = buf;
    buf_offset = 0;
    Msg("SDF", ("SDFhdropen:  return fp=%p\n", fp));
    return 0;
}

void SDF_Hdrclose(void){
    Msg("SDF", ("SDFhdrclose called\n"));
    MPMY_Fclose(fp);
    endbuf = ptr = NULL;
    fp = NULL;
    buf_offset = -1;
}

int SDF_Hdroffset(void){
    if( ptr == NULL )
	return -1;
    return buf_offset + (ptr - buf);
}

int SDF_Hdrgetc(){
    int nread;

    if( ptr == NULL ){
	Msgf(("SDFhdrgetc: Returning EOF, ptr==NULL\n"));
	return EOF;
    }

    if( ptr < endbuf ){
	if( *ptr == '\0' ){
	    SinglWarning("Returning NULL at char %d in SDFhdrio\n", (int)(ptr-buf));
	}
	Msgf(("SDF_hdrgetc:  %c\n", *ptr));
	return *ptr++;
    }

    nread = MPMY_Fread(buf, 1, MYBUFSZ, fp);
    {int i;
     int sum = 0;
     for(i=0; i<nread; i++){
	 sum ^= buf[i];
     }
     Msgf(("SDFhdrio Fread(%d), obtained %d, sum=%d\n", MYBUFSZ, nread, sum));
    }
    if(nread <= 0 ) {
	if( nread < 0 ){
	    SinglWarning("SDFhdrio: MPMY_Fread returns %d, errno=%d\n", nread, errno);
	}
	Msgf(("SDFhdrgetc:  Returning EOF, nread=%d, errno=%d\n", nread, errno));
	return EOF;		/* don't distinguish between error and EOF? */
    }
    buf_offset += endbuf - buf;
    ptr = buf;
    endbuf = ptr + nread;
    /* This tail recursion is guaranteed to terminate on the second try
       because we have guaranteed that endbuf>ptr */
    return SDF_Hdrgetc();
}