#include <errno.h> /* errno */
#include <stdio.h> /* fprintf(3), getc(3), putc(3), stderr, stdin, stdout, EOF,
                    * NULL */
#include <stdlib.h> /* size_t */
#include <string.h> /* strerror(3) */
#if !defined EX_OK || !defined EX_OSERR || !defined EX_USAGE
#	include <sysexits.h>
#endif
#include <termios.h> /* tcgetattr(3), tcsetattr(3), struct termios, ECHO */
#include <unistd.h> /* dup(2), execvp(3), fork(2), getopt(3), isatty(3),
                     * pipe(2), STDIN_FILENO */

static char *program_name = "peek";

int main(int argc, char *argv[]){
	int c;
	int eof;
	size_t i;
	char include_eof;
	FILE *outputs[] = {
		NULL /* stdout */,
		NULL /* stderr */,
		NULL /* -p */
	};
	int p[2] = {0, 0};
	struct termios t;

	if(argc < 1)
		goto usage;

	eof = EOF;
	include_eof = 0;
	while((c = getopt(argc, argv, "1enopt")) != -1)
		switch(c){
		case '1': eof = '\n';          break;
		case 'n': include_eof = 1;     break;
		case 'o': outputs[0] = stdout; break;
		case 'e': outputs[1] = stderr; break;
		case 'p':
			if(pipe(p) != 0)
				goto die;
			else if((outputs[2] = fdopen(p[1], "ab")) == NULL)
				goto die;
			break;
		case 't':
			if(isatty(STDIN_FILENO) != 1){
				fprintf(stderr, "%s: Must be run in a terminal"
					" (option -t specified)\n", argv[0]);
				return EX_USAGE;
			}
		default:  goto usage;
		}

	/* If -p is used there must be additional arguments. Getopt(3) wouldn't
	 * work for this because optarg would have to be one string to give to
	 * system(3) or an equivalent and it would be a mess of parsing and
	 * security issues. Any intended usage works with this slightly funkier
	 * argument parsing, unintended usages work as happy coincidence. */
	if((argc > optind) == (outputs[2] == 0)){
usage:		fprintf(stderr, "Usage: %s (-1enot)"
			" (-p [program [arguments...]])\n",
			argv[0] == NULL ? program_name : argv[0]);
		return EX_USAGE;
	}

	if(outputs[2] != 0)
		switch(fork()){
		case 0:
			if(close(p[1]) == 0
					&& dup2(p[0], STDIN_FILENO)
						== STDIN_FILENO)
				execvp(argv[optind], argv + optind);
		case -1:
			goto die;
		default:
			if(close(p[0]) != 0)
				goto die;
		}

	/* terminal echo */
	tcgetattr(STDIN_FILENO, &t);
	t.c_lflag ^= ECHO;
	tcsetattr(STDIN_FILENO, TCSAFLUSH, &t);

	do{	if((c = getc(stdin)) != eof || include_eof)
			for(i = 0; i < (sizeof outputs)/(sizeof *outputs); ++i)
				if(outputs[i] != NULL
						&& putc(c, outputs[i]) == EOF){
					if(i == 2)
						fclose(outputs[i]);
					outputs[i] = 0;
				}
	}while(c != eof);

	tcgetattr(STDIN_FILENO, &t);
	t.c_lflag |= ECHO;
	tcsetattr(STDIN_FILENO, TCSAFLUSH, &t);

	return EX_OK;

die:	fprintf(stderr, "%s: %s\n", argv[0], strerror(errno));
	return EX_OSERR;
}