#define _XOPEN_SOURCE 700
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>
#include <sys/wait.h>

#define BUFF_SZ (4096*64)

void write_buffer(const char *buff, size_t buff_sz, const char *fname) {
	int fd = open(fname, O_CREAT | O_WRONLY | O_TRUNC, 0664);
	size_t n = 0;
	ssize_t r;
	if (!fd) {
		fprintf(stderr, "Failed to open(3) %s: %s\n", fname, strerror(errno));
		return;
	}

	do {
		r = write(fd, buff + n, buff_sz - n);
		if (r == -1) {
			if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
				continue;
			fprintf(stderr, "Failed to write(2): %s\n", strerror(errno));
			return;
		} else if (r == 0) {
			break;
		} else {
			n += r;
		}
	} while (n < buff_sz);
	close(fd);
}

void ptmx_slave_test(int pty, const char *line, size_t rsz) {
	char *buff = malloc(BUFF_SZ);
	size_t n = 0, nn;
	ssize_t r;
	int l, bad;
	struct timespec slen;

	if (!buff) {
		fprintf(stderr, "Failed to malloc(3): %s\n", strerror(errno));
		return;
	}

	do {
		r = read(pty, buff + n, rsz + n > BUFF_SZ ? BUFF_SZ - n : rsz);
		if (r == -1) {
			if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
				continue;
			fprintf(stderr, "Failed to read(2): %s\n", strerror(errno));
			return;
		} else if (r == 0) {
			if (n < BUFF_SZ)
				fprintf(stderr, "Read %zu bytes, expected %zu!\n", n, BUFF_SZ);
			break;
		} else {
			n += r;
		}
		memset(&slen, 0, sizeof(slen));
		nanosleep(&slen, NULL);
	} while (n < BUFF_SZ);
	nn = n;

	/* check buffer if it matches expected value... */
	r = strlen(line);
	l = 0;
	bad = 0;
	for (n = 0; n < BUFF_SZ; n += r+1) {
		l++;
		if (memcmp(buff + n, line, n + r < BUFF_SZ ? r : BUFF_SZ - n) != 0) {
			// TODO: determine position of breakage!
			fprintf(stderr, "Line data mismatch for line %d!\n", l);
			bad = 1;
			break;
		}
		if (n + r + 1 < BUFF_SZ && buff[n+r] != '\n') {
			fprintf(stderr, "Expecting '\\n' at end of line %d, but found 0x%hhx\n", l, buff[n+r]);
			bad = 1;
			break;
		}
	}

//	fprintf(stderr, "Buffer seen by slave is:\n");
//	fwrite(buff, BUFF_SZ, 1, stdout);
	if (bad)
		write_buffer(buff, nn, "/tmp/ptmx_out.txt");
}

void ptmx_master_test(int pty, const char *line, size_t wsz) {
	char *buff = malloc(BUFF_SZ);
	size_t n = 0;
	ssize_t r;

	if (!buff) {
		fprintf(stderr, "Failed to malloc(3): %s\n", strerror(errno));
		return;
	}

	/* initialize buffer */
	r = strlen(line);
	for (n = 0; n < BUFF_SZ; n += r+1) {
		memcpy(buff + n, line, n + r < BUFF_SZ ? r : BUFF_SZ - n);
		if (n + r + 1 < BUFF_SZ)
			buff[n+r] = '\n';
	}

	n = 0;
	do {
		r = write(pty, buff + n, wsz + n > BUFF_SZ ? BUFF_SZ - n : wsz);
		if (r == -1) {
			if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
				continue;
			fprintf(stderr, "Failed to write(2): %s\n", strerror(errno));
			return;
		} else if (r == 0) {
			break;
		} else {
			n += r;
		}
	} while (n < BUFF_SZ);
	close(pty);
	write_buffer(buff, BUFF_SZ, "/tmp/ptmx_in.txt");
}

int main() {
	const char *line = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
	const char *ptsdname = NULL;
	int pty, pid;
	size_t rsz = 128, wsz = 1024;


	pty = open("/dev/ptmx", O_RDWR | O_CLOEXEC);
	if (pty == -1) {
		fprintf(stderr, "Failed to open(3) /dev/ptmx: %s\n", strerror(errno));
		return 1;
	}

	ptsdname = ptsname(pty);
	if (!ptsdname) {
		fprintf(stderr, "Failed to ptsname(3): %s\n", strerror(errno));
		close(pty);
		return 1;
	}

	if (grantpt(pty) == -1) {
		fprintf(stderr, "Failed to grantpty(3): %s\n", strerror(errno));
		close(pty);
		return 1;
	}

	if (unlockpt(pty) == -1) {
		fprintf(stderr, "Failed to unlockpt(3): %s\n", strerror(errno));
		close(pty);
		return 1;
	}

	pid = fork();
	if (pid == -1) {
		fprintf(stderr, "Failed to fork(3): %s\n", strerror(errno));
		close(pty);
		return 1;
	} else if (pid == 0) {
		close(pty);

		pty = open(ptsdname, O_RDWR | O_CLOEXEC);
		if (pty == -1) {
			fprintf(stderr, "Failed to open(3) %s: %s\n", ptsdname, strerror(errno));
			return 1;
		}

		ptmx_slave_test(pty, line, rsz);
		close(pty);
		return 0;
	} else {
		int s;
		ptmx_master_test(pty, line, wsz);

		if (waitpid(pid, &s, 0) == -1) {
			fprintf(stderr, "Failed to waitpid(2) for %d: %s\n", pid, strerror(errno));
			return 1;
		}
		if (WIFEXITED(s) && WEXITSTATUS(s) == 0)
			return 0;
		if (WIFEXITED(s))
			fprintf(stderr, "Child exited with %d\n", WEXITSTATUS(s));
		else if (WIFSIGNALED(s))
			fprintf(stderr, "Child died with signal %d\n", WTERMSIG(s));
		else
			fprintf(stderr, "Child terminated in an unknown way with status %d\n", s);
		return 1;
	}
}