#include <bios.h>
#include <dos.h>
#include <errno.h>
#include <string.h>
#include "ddisk.h"

extern int errno;
int dwd=-1, cwd=-1, cwt=-1, cwh=-1;	/*	current working drive, track, head */
int numt=0, nums=0;
char dbuf[4608], tbuf[4608];

/*	sets the bytes-per-sector value (0=128,1=256,2=512,3=1024) */
void setbps(unsigned bpsval) {
	uchar far *dparm=MK_FP(0, 0x78);	/*	gets disk parm vector */

	dparm=MK_FP((dparm[3]<<8)|dparm[2], (dparm[1]<<8)|dparm[0]);
	dparm[3]=bpsval;
}

/*	initialise system to 256 byte sectors, reads directory track to
	memory and initialises tracks and sectors/track info
	returns 0 on success, -1 on error (setting errno) */
int dkinit(unsigned drive) {
	char buf[256];

	setbps(1);	/*	init to 256 bps */
	cwd=drive;
	if(dkrdabs(20, 1, buf)) {
		cwd=-1;
		return -1;
	}	/*	read t20,s1 (contains track info) */
	if((buf[252]+buf[254]+1)&0xff+0xff&(buf[253]+buf[255]+1)) {
		cwd=-1;
		errno=EINVFMT;
		return -1;
	}
	numt=buf[252];
	nums=buf[253];

	return 0;
}

/*	resets system to 512 byte sectors, ready for exiting */
void dktidy(void) {

	setbps(2);
}

/*	read absolute sector into buf.  sector is read from dbuf if directory
	track is specified.  track=0..  sector=1..
	returns 0 on success, -1 on error (setting errno) */
int dkrdabs(unsigned track, unsigned sector, uchar *buf) {
	char *mybuf=tbuf;
	int tready;
	/* references to sector after this point assume sector=0.. */

	sector--;
	tready=(track==cwt && sector/18==cwh);	/*	check mem */
	if(cwd<0) {
		errno=EINVDRV;
		return -1;
	}
	if(track==20 && sector<18) {
		mybuf=dbuf;
		if(dwd==cwd)
			tready=1;
		dwd=cwd;
	} else {
		if(track>=numt || sector>=nums) {
			errno=EFAULT;
			return -1;
		}
		cwt=track;  cwh=sector/18;
	}
	if(!tready) {
		int retry=2;

		do {
			if(!retry--) {
				cwt=-1;
				cwh=-1;
				errno=EINVFMT;
				return -1;
			}
		} while(biosdisk(2, cwd, sector/18, track, 1, 18, mybuf));
	}
	memcpy(buf, &mybuf[(sector%18)<<8], 0x0100);
	return 0;
}

/*	read sector by lsn (calls dkrdabs so same conditions)
	tracks and sectors/track info must be initialised by dkinit before a
	call to this function */
int dkrdlsn(unsigned lsn, uchar *buf) {

	return dkrdabs(lsn/nums, (lsn%nums)+1, buf);
}

/*	read a numbered (0-159) directory entry
	returns 0 on success, -1 on error */
int dkrdent(unsigned entno, dkent *ent) {
	char buf[256];

	if(entno>159) {
		errno=EFAULT;
		return -1;
	}
	dkrdabs(20, (entno/10)+3, buf);
	memcpy(ent, &buf[(entno%10)*25], 25);
	return 0;
}