#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>

char *questions[] = {".*food.*", "^nons", "-E ^.?r..k.?$"};
char* getoutput(char* command);

char* get_result(char *pattern){
	char command[256];
	printf("We're about to run:  \n%s\n", command);
	if(strlen(pattern) > 192){
		printf("Maximum pattern length exceeded\n");
		exit(1);
	}
	snprintf(command, 128, "grep %s /usr/share/dict/american-english", pattern);
	return getoutput(command);
}

int main(int argc, char ** argv){
	if(argc == 1){
		printf("Usage:  %s questionnumber [grep_pattern]\n", argv[0]);
		return 1;
	}
	unsigned qnum = atoi(argv[1]);
	char *correct_result = get_result(questions[qnum - 1]);
	if(argc == 2){
		puts(correct_result);
		goto out_and_free;
	}	
	char *users_result = get_result(argv[2]);
	if(!strcmp(correct_result, users_result)){
		printf("You got it!\n");
	} else {
		puts("Sorry, results differ.  Your command generated:  ");
		puts(users_result);
	}
	free(users_result);
out_and_free:
	free(correct_result);
	if(argc > 3)
		printf("Extra parameter detected:  %s\n", argv[3]);
	return 0;
}

char* getoutput(char* command){
	// We'll need a pipe to put the output into
	// The command will have to run, and put output into the pipe
	// We'll have to read from the pipe
	int pipe_fds[2];
	char *buffer = malloc(16);
	pipe(pipe_fds);
	pid_t child = fork();

	if(!child){
		// Command part:
		// 	1.  Do plumbing as needed to send output into the pipe
		// 	2.  Run the command
		dup2(pipe_fds[1], 1);
		execl("/bin/sh", "sh", "-c", command, (char *) 0);
	} else {
		// Capture part:
		// 	1.  Wait for the command to run
		// 	2.  Collect the output from the pipe
		// while there's more to read:
		// 	read more stuff
		size_t sofar = 0;
		close(pipe_fds[1]);
		for(;;) {
			ssize_t readlen = read(pipe_fds[0], buffer + sofar, 16);
			if(readlen <= 0)
				break;
			sofar += readlen;
			buffer = realloc(buffer, sofar + 16);
		}
		buffer[sofar] = 0;
//		printf("We read:  %s\n", buffer);
		return buffer;
	}
}