/* gcc -o KernelTtyTest KernelTtyTest.c -Wall -O2 -lutil */
#define _GNU_SOURCE 1
#include <stdio.h>
#include <pty.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <signal.h>
#include <poll.h>
#include <setjmp.h>
#include <ctype.h>

#define POLL_TIMEOUT (10*1000)  /* in milliseconds */
#define LASTBUFSZ  10000
#define CMDBUFSZ 10000

#define SIGINT_LONGJMP 0
#define SIGINT_VAR 1
static void putstr(char *str, FILE *out)
{
	int c;
	for (c = *str++; c; c = *str++) {
		if (iscntrl(c)) {
			putc('\\', out);
			switch(c) {
			case '\n':  putc('n', out); break;
			case '\r':  putc('r', out); break;
			default: printf("%03o", c); break;
			}
		} else {
			putc(c, out);
		}
	}
}

static void print_lastbytes(char *lastbytes, size_t totalbytes, FILE *out)
{
	char *start = lastbytes;
	if (totalbytes < LASTBUFSZ)
		start = &lastbytes[LASTBUFSZ - totalbytes];
	fprintf(out, "lastbytes: '");
	putstr(start, out);
	fprintf(out, "'");
}
static void expect(int masterfd, char *str, size_t len)
{
	char lastbytes[LASTBUFSZ + 1];
	size_t totalbytes = 0;

	memset(lastbytes, sizeof(lastbytes), 0);

	for (;;) {
	  	char buf[1];
		ssize_t bytes;
		int ret;
		struct pollfd fds = {
			.fd = masterfd,
			.events = POLLIN | POLLERR | POLLHUP,
			.revents = 0,
		};
		ret = poll(&fds, 1, POLL_TIMEOUT);
		if (ret == 0) {
			fprintf(stderr, "Timeout while waiting for '");
			putstr(str, stderr);
			fprintf(stderr, "' ");
			print_lastbytes(lastbytes, totalbytes, stderr);
			fprintf(stderr,"\n");
			exit(5);
		}
		else if (ret < 0) {
			fprintf(stderr, "poll failed: %s\n", strerror(errno));
			exit(4);
		}
		bytes = read(masterfd, buf, 1);
		if (bytes == 1) {
			totalbytes++;
			memmove(lastbytes, lastbytes +1, LASTBUFSZ);
			lastbytes[LASTBUFSZ - 1] = buf[0];
			lastbytes[LASTBUFSZ] = '\0';
			if (memcmp(&lastbytes[LASTBUFSZ - len], str, len) == 0)
				return;
		}
		else if (bytes < 0) {
			fprintf(stderr, "read failed: %s\n",
				strerror(errno));
			print_lastbytes(lastbytes, totalbytes, stderr);
			fprintf(stderr,"\n");
			abort();
			exit(3);
		}
	}
}

static void resync(int masterfd)
{
	static unsigned count;
	char cookie[100];
	char cmd[1000];
	char reply[1000];
	ssize_t written, bytes;

	snprintf(cookie, sizeof(cookie), "_%u_", ++count);
	bytes = snprintf(cmd, sizeof(cmd), "echo %s\n", cookie);
	written = 0;
	while (bytes) {
		ssize_t sent;
		sent = write(masterfd, cmd + written, bytes);
		if (sent >= 0) {
			written += sent;
			bytes -= sent;
		} else if ((errno != EAGAIN) && (errno != EINTR)) {
			fprintf(stderr, "Write to child failed: %s\n", strerror(errno));
			exit(2);  
		}
	}
	snprintf(reply, sizeof(reply), "\n%s", cookie);
	expect(masterfd, reply, strlen(reply));
}

#if SIGINT_VAR
static volatile sig_atomic_t saw_sigint;
#endif

static void process_cmd(void)
{
	char cmdbuf[CMDBUFSZ];
	size_t cmdlen;
	char buf[1];

	cmdlen = 0;
	for (;;) {
		ssize_t bytes;
#if SIGINT_VAR
		if (saw_sigint) {
			saw_sigint = 0;
			printf("^C\n");
			fflush(stdout);
			return;
		}
#endif
		bytes = read(STDIN_FILENO, buf, 1);
		if (bytes == 1) {
			cmdbuf[cmdlen] = '\0';
			putchar(buf[0]);
			fflush(stdout);
			if (buf[0] == '\n') {
				if (cmdlen == 0) {
					printf("> ");
					fflush(stdout);
				}
				else if (memcmp("echo ", cmdbuf, 5) == 0) {
				  	printf("%s\n", cmdbuf + 5);
					fflush(stdout);
					return;
				} else {
					fprintf(stdout, "unknown cmd: '");
					putstr(cmdbuf, stdout);
					printf("'\n");
					fflush(stdout);
					return;
				}
			}
			cmdlen += 1;
			if (cmdlen >= CMDBUFSZ) {
				fprintf(stderr, "command too long!\n");
				_exit(3);
			}
			cmdbuf[cmdlen - 1] = buf[0];
			cmdbuf[cmdlen] = '\0';
		}
		if (bytes == 0) {
			/* EOF terminate */
			_exit(0);
		}
		if (bytes < 0) {
			fprintf(stderr, "%s read failed: %s\n",
				__func__, strerror(errno));
			_exit(4);
		}
	}
}

#if SIGINT_LONGJMP
static sigjmp_buf sigint_dest;
#endif
static void sigint_handler(int signum)
{
#if SIGINT_LONGJMP
	siglongjmp(sigint_dest, 1);
#endif
#if SIGINT_VAR
	saw_sigint = 1;
#endif

}

static void process_cmds(void)
{
	sigset_t signal_set;
#if 1
	struct sigaction act;
#endif

	sigemptyset( &signal_set);
	sigaddset( &signal_set, SIGINT);

	/* Block sigint until I reinstall the handler */
	sigprocmask(SIG_BLOCK, &signal_set, NULL);
#if 0
	signal(SIGINT, sigint_handler);
#else
	memset(&act, sizeof(act), 0);
	act.sa_handler = &sigint_handler;
	act.sa_flags = SA_NODEFER;
	sigaction(SIGINT, &act, NULL);
#endif
#if SIGINT_LONGJMP
	if (sigsetjmp(sigint_dest, 1)) {
		printf("^C\n");
		fflush(stdout);
	}
#endif
	sigprocmask(SIG_UNBLOCK, &signal_set, NULL);
	for (;;)
		process_cmd();
}

int main(int argc, char *argv[], char *environ[])
{
	pid_t pid;
	int masterfd;
	struct winsize terminal_size;
	int i;

	terminal_size.ws_row = 80;
	terminal_size.ws_col = 25;
	terminal_size.ws_xpixel = 0;
	terminal_size.ws_ypixel = 0;

	pid = forkpty(&masterfd, NULL, NULL, &terminal_size);
	if (pid == 0) { /* child */
		char *args[] = {  "/bin/sh",  NULL };
		char *env[] = { NULL };
#if 0
		execve("/bin/bash", args, env);
#endif
#if 1
		process_cmds();
#endif
		_exit(1);
	}
	resync(masterfd);
#if 1
	for (i = 0; i < 10; i++) {
		usleep(100);
		kill(pid, SIGINT);
	}
#endif
#if 0
	usleep(1000);
#endif
	resync(masterfd);
	return 0;
}