#include <stdio.h>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <errno.h>

#include "common.h"

/* Send and receive blocks on demand from a remote. See doc/blksrv.
*/

/* Maximum number of read()==EAGAIN until we consider a timeout */
#define TIMEOUTCNT 10000

static volatile int isrunning = 1;
static int fd;
static FILE *fp;

void intHandler(int dummy) {
fprintf(stderr, "Shutting down\n");
isrunning = 0;
}

static int readn(void *buf, size_t count) {
ssize_t n, ntot=0;
for (int i=0; i<TIMEOUTCNT; i++) {
n = read(fd, buf, count-ntot);
if (n < 0) {
if (errno == EAGAIN) continue;
fprintf(stderr, "read() error, %d\n", errno);
return 1;
}
ntot += n;
buf += n;
if (ntot == count) return 0;
i = 0;
}
fprintf(stderr, "readn() timeout\n");
return 1;
}

static int writen(void *buf, size_t count) {
ssize_t n, ntot=0;
for (int i=0; i<TIMEOUTCNT; i++) {
n = write(fd, buf, count-ntot);
if (n < 0) {
if (errno == EAGAIN) continue;
fprintf(stderr, "write() error, %d\n", errno);
return 1;
}
ntot += n;
buf += n;
if (ntot == count) return 0;
i = 0;
}
fprintf(stderr, "writen() timeout\n");
return 1;
}

static int read16(int *dest) {
char buf[5];

if (readn(buf, 4) != 0) return 1;
buf[4] = 0;
*dest = strtol(buf, NULL, 16);
return 0;
}

static int write16(int n) {
char buf[5];

snprintf(buf, 5, "%04x", n);
return writen(buf, 4);
}

static int blksum(char *buf) {
int s = 0;
for (int i=0; i<1024; i++) s += buf[i];
return s & 0xffff;
}

static int readblkid() {
int blkid;

if (read16(&blkid) != 0) return 1;
fprintf(stderr, "blkid: %d\n", blkid);
if (fseek(fp, blkid*1024, SEEK_SET) < 0) {
fprintf(stderr, "seek error for blkid %d\n", blkid);
return 1;
}
return 0;
}

static int recvblk() {
char buf[1024];
int csum;

if (readn(buf, 1024) != 0) return 1;
if (read16(&csum) != 0) return 1;
if (blksum(buf) != csum) return 1;
if (fwrite(buf, 1024, 1, fp) != 1) return 1;
fflush(fp);
return 0;
}

static int sendblk() {
char buf[1024] = {' '};

if (fread(buf, 1024, 1, fp) != 1) return 1;
if (writen(buf, 1024) != 0) return 1;
return write16(blksum(buf));
}

int main(int argc, char **argv) {
char c;
ssize_t n;
if (argc != 3) {
fprintf(stderr, "Usage: ./blksrv device blkfs\n");
return 1;
}
fp = fopen(argv[2], "r+");
if (!fp) {
fprintf(stderr, "Could not open %s\n", argv[2]);
return 1;
}
fd = ttyopen(argv[1]);
if (fd < 0) {
fclose(fp);
fprintf(stderr, "Could not open %s\n", argv[1]);
return 1;
}
set_blocking(fd, 0);
signal(SIGINT, intHandler);
while (isrunning) {
n = read(fd, &c, 1);
if (n < 1) {
if ((n==0) || (errno == EAGAIN)) {
usleep(1000); // don't consume 100% CPU
continue;
}
fprintf(stderr, "read() error, %d\n", errno);
break;
}
fprintf(stderr, "new cmd: %c\n", c);
if (c == 'G') {
if (readblkid() != 0) continue;
if (sendblk() != 0) {
fprintf(stderr, "sendblk() error\n", c);
continue;
}
fprintf(stderr, "sendblk() complete\n", c);
} else if (c == 'P') {
if (readblkid() != 0) continue;
if (recvblk() != 0) {
fprintf(stderr, "recvblk() error\n", c);
continue;
}
fprintf(stderr, "recvblk() complete\n", c);
}
}
close(fd);
fclose(fp);
}