#include <stdlib.h>
#include <unistd.h> /* getopt, getopt_long, read */
#include <sys/resource.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/stat.h>

#define MAX_COMMAND_LEN	 20
#define MAX_FILENAME_LEN 100
#define MAX_TEXT_LEN	 255
#define ACT_PROMPT	"action> "
	
typedef enum { REAL, EFFECTIVE } e_user_modes;

e_user_modes do_user(int cur_mode);
int do_open();
void do_write(int fd1);
void help();
int process_args(int argc, char* argv[]);

void error_comlen();
void error_mem();


int main(int argc,char* argv[],char* envp[]) {
	char* command = NULL;
	ssize_t data_read = 0;
	e_user_modes user_mode = REAL;
	int ufile = 0;
	
	/* zpracovani argumentu, pokud nejake byly :) */
	if (argc != 1) {
		return process_args(argc,argv);
	};
	
	/* main program loop */
	command = (char*)malloc(MAX_COMMAND_LEN);
	if (command == NULL) /* memory not allocated */
		error_mem();
	while (1) {
		write(1,ACT_PROMPT,sizeof ACT_PROMPT);
		data_read = read(0,command,MAX_COMMAND_LEN);
		if (data_read == -1) /* cannot read input */
			perror("Reading command failed");
		if (data_read > MAX_COMMAND_LEN) /* buffer overflow */
			error_comlen();
		switch (*command) {
			case 'o':
				if (ufile == 0) {
					ufile = do_open();
				} else write(1,"Jiz je otevreny soubor.\n",24);	
				break;
			case 'w':
				if (ufile != 0)
					do_write(ufile);
				else write(1,"Neni otevreny zadny soubor.\n",28);
				
				break;
			case 'c':
				if (ufile != 0) {
					close(ufile);
					ufile = 0;
				} else write(1,"Neni otevreny zadny soubor.\n",28);
				break;
			case 'u':
				user_mode = do_user(user_mode);
				printf("Changed to %s mode\n",
					(user_mode == REAL)?"REAL":"EFFECTIVE");
				break;
			case 'h':
				help();
				break;
			case 'a':{
				struct rlimit u_limits;
				getrlimit(RLIMIT_CORE,&u_limits);
				u_limits.rlim_cur = u_limits.rlim_max;
				setrlimit(RLIMIT_CORE,&u_limits);
				abort(); /* core dump :-)) */
				};
			case 'q':
				exit(0);
			default:
				printf("Unknown command. Try 'help'.\n");
		};
	};
	return 0;
};

int process_args(int argc, char* argv[]) {
	int argument;
	while ((argument = getopt(argc,argv,"vh")) != EOF) {
		switch (argument) {
		case 'v':
			printf("\nVersion 1.0\n");
			printf("Test program written for presentation of GNU gdb debugger\n");
			printf("Autor: Michal Batko\n\n");
			break;
		case 'h':
			printf("\nSpustte program pomoci prikazu %s\n",argv[0]);
			printf("Ocitnete se v interaktivnim modu programu. ");
			help();
			break;
		case '?':
		default:
			fprintf(stderr,"Usage: %s [-h][-v]\n",argv[0]);
			return 1;
		};
	};
	return 0;
}

void help() {
	printf("Lze zadavat tyto prikazy:\n");
	printf("	open    ... otevreni souboru\n");
	printf("	close   ... zavreni souboru\n");
	printf("	write   ... zapsani textu do souboru\n");
	printf("	user    ... zmena effektivniho a realneho uzivatele\n");
	printf("	help    ... vypis prikazu\n");
	printf("	abort   ... zavolani sluzby jadra abort\n");
	printf("	quit    ... ukonceni programu\n\n");
}

/* error handling */
void error_mem() {
	fprintf(stderr,"Couldn't allocate memory.\n");
	exit(-1);
}

void error_comlen() {
	fprintf(stderr,"Command too long, buffer overflow.\n");
	exit(-1);
}

/* command implementation */

e_user_modes do_user(int cur_mode) {
	if (setreuid(geteuid(),getuid()) == -1) perror("user");
	if (cur_mode == REAL) {
		return EFFECTIVE;
	} else {
		return REAL;
	};
}

int do_open() {
	char* filename = (char*)malloc(MAX_FILENAME_LEN);
	int fd1;
	write(1,"Napiste jmeno souboru, kam chcete zapisovat: ",45);
	if (read(0,filename,MAX_FILENAME_LEN) > MAX_FILENAME_LEN) error_mem();
	filename[strlen(filename)-1] = '\0';
	fd1 = creat(filename,S_IRWXU);
	if (fd1 == -1) {
		perror("open");
		return 0;
	} else return fd1;
}

void do_write(int fd1) {
	char* text = (char*)malloc(MAX_TEXT_LEN);
	write(1,"Napiste text:\n",14);
	if (read(0,text,MAX_TEXT_LEN) > MAX_TEXT_LEN) error_mem();
	if (write(fd1,text,strlen(text)) == -1) {
		perror("open");
		return;
	};
}