math_shell/msh.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <string.h>

#include <readline/readline.h>
#include <readline/history.h>

#include "msh.h"

#define clear() printf("\033[H\033[J")

union pipe {
	int fileDesc[2];
	struct {
		int read;
		int write;
	};
};

static char *builtinFunctions[] = {
	"exit",
	"author"
};

int (*builtinFunc[]) (char *) = {
	&builtinExit,
	&builtinAuthor
};

int builtinExit() {
	exit(EXIT_SUCCESS);
}

int builtinAuthor() {
	static const char* message =
		"Author: Spencer\n"
		"Description: A shell to promote math!\n"
		"Ask for the source code!\n"
		"\n";
	printf("%s", message);
	return 0;
}

void failedTest() {
	static const char* message =
		"\n"
		"How can you expect to execute commands without knowing any math???\n"
		"\n";
	printf("%s", message);
	return;
}

int runCommand(char *command) {
	int status = 0;
	pid_t pid;

	pid = fork();
	if (pid == 0) { // Child process
		if(execlp("bash", "bash", "-c", command, NULL) == -1) {
			exit(EXIT_FAILURE);
		}
		exit(EXIT_SUCCESS);
	} else if (pid < 0) {
		printf("Error forking...\n");
		status = 1;
	} else { // Parent process
		do {
			waitpid(pid, &status, WUNTRACED);
		} while(!WIFEXITED(status) && !WIFSIGNALED(status));
	}

	return status;
}

int execCommand(char *command) {
	for (size_t i = 0; i < (sizeof(builtinFunctions) / sizeof(char *)); i++) {
		if (strcmp(command, builtinFunctions[i]) == 0) {
			return (*builtinFunc[i])(command);
		}
	}
	return runCommand(command);
}

void initShell() {
	FILE *fd;

	clear();
	using_history();

	// Setting random time seed
	srand(time(0));

	runCommand("uname -a");

	fd = fopen("/etc/motd", "r");
	if (fd != NULL) {
		char c;
		c = fgetc(fd);
		printf("\n");
		while (c != EOF) {
			printf("%c", c);
			c = fgetc(fd);
		}
		fclose(fd);
	} else {
		printf("MOTD is empty\n");
	}

	return;
}

char *getPrompt() {
	pid_t pid;
	union pipe input, output;
	FILE *outputFileD;
	size_t len = 0;
	int status = 0;

	static char *prompt = NULL;
	static size_t promptCap = 0;

	pipe(input.fileDesc);
	pipe(output.fileDesc);

	pid = fork();
	if (pid == 0) { // Child process
		close(input.write);
		close(output.read);

		dup2(input.read, STDIN_FILENO);
		dup2(output.write, STDOUT_FILENO);
		close(STDERR_FILENO); // Do not print errors to the screen

		execlp("bash", "bash", "-i", "-c", "\
			ver=$(bash --version | head -n 1 | awk \'{print $4}\' | grep -o \".\\..\");\
			check_ver=$(echo -e \"${ver}\n4.3\" | sort -V | head -n 1);\
			if [[ \"${ver}\" == \"${check_ver}\" ]]; then\
			  echo \"[${USER}]\";\
			else\
			  echo \"${PS1@P}\";\
			fi\
			", NULL);
	} else if (pid < 0) { // Error forking
		printf("Error forking\n");
	} else { // Parent process
		close(input.read);
		close(output.write);

		outputFileD = fdopen(output.read, "r");

		len = getline(&prompt, &promptCap, outputFileD);

		if (prompt[len - 1] == '\n') {
			prompt[len - 1] = '\0';
		}

		fclose(outputFileD);
		do {
			waitpid(pid, &status, WUNTRACED);
		} while(!WIFEXITED(status) && !WIFSIGNALED(status));
	}

	return prompt;
}

int randomNum(int limit) {
	int num = 0;
	if (limit != 0) {
		num = rand()%limit +1;
	} else {
		num = rand();
	}
	return num;
}

int mathTest() {
	int status = 0;
	int numAnswer = 0;
	int num1 = randomNum(10);
	int num2 = randomNum(10);
	char *numLine = NULL;
	printf("%d + %d = ", num1, num2);
	numLine = readline("");
	sscanf(numLine, "%d", &numAnswer);

	#ifdef RELEASEBUILD
	printf("Calculating");
	for (int i = 0; i < 3; i++){
		printf(".");
		fflush(stdout);
		sleep(2);
	}
	printf("\n");
	#endif

	if ((num1 + num2) != numAnswer) { // If wrong answer
		status = 1;
	}

	free(numLine);
	return status;
}


void startShell() {
	char *line = NULL;
	int status = 0;

	while ((line = readline(getPrompt())) != NULL) {
		if (strlen(line) != 0) { // Checking if prompt returns empty
			status = mathTest();
			if (status == 0) { // Passed math test
				add_history(line);
				execCommand(line);
			} else { // Failed math test
				failedTest();
			}
		}
		free(line);
	}
}

void handleBreak(){
	signal(SIGINT, handleBreak);
	printf("\n");
	rl_on_new_line();
	rl_replace_line("", 0);
	rl_redisplay();
}

int main() {
	initShell();
	signal(SIGINT, handleBreak);
	startShell();
	exit(EXIT_SUCCESS);
}