#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <sys/shm.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/types.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <signal.h>
#include <sys/select.h>

#include "dll.h"
#include "mac-list.h"
#include "routing-table.h"
#include "sync.h"

#define MAX_CLIENTS 32
#define OP_LEN 128
#define MAX_MASK 32

extern int store_IP(const char* mac, const char* ip);

int synchronized; // indicates if server has finished sending current updates
int connection_socket; // socket to establish connections with new clients
int loop = 1; // indicates if server is still running to clients


/*
* Server's copies of network data structures
*/

dll_t* routing_table;
dll_t* mac_list;

/*
* An array of File descriptors which the server process is maintaining in order 
* to talk with connected clients. Master skt FD is also a member of this array.
*/

int monitored_fd_set[MAX_CLIENTS];
pid_t client_pid_set[MAX_CLIENTS]; // array of client process id's.

/*
* Remove all the FDs and client pid's, if any, from the array.
*/

void initialize_monitor_fd_and_client_pid_set() {
	int i = 0;

	for (; i < MAX_CLIENTS; i++) {
		monitored_fd_set[i] = -1;
		client_pid_set[i] = -1;
	}
}

/*
* Add a new FD to the monitored_fd_set.
*/

void add_to_monitored_fd_set(int skt_fd) {
	int i = 0;
	for (; i < MAX_CLIENTS; i++) {
		if (monitored_fd_set[i] != -1)
			continue;

		monitored_fd_set[i] = skt_fd;
		break;
	}
}

/*
* Add a new pid to the client_pid_set array
*/

void add_to_client_pid_set(pid_t pid) {

	int i = 0;
	for (; i < MAX_CLIENTS; i++) {
		if (client_pid_set[i] != -1)
			continue;
		client_pid_set[i] = pid;
		break;
	}
}


/*Remove the FD from monitored_fd_set array*/
void remove_from_monitored_fd_set(int skt_fd) {
	int i = 0;
	for (; i < MAX_CLIENTS; i++) {
		if (monitored_fd_set[i] != skt_fd)
			continue;
		monitored_fd_set[i] = -1;
		break;
	}
}

/*Remove the pid from client_pid_set array*/
void remove_from_client_pid_set(int pid) {
	int i = 0;
	for (; i < MAX_CLIENTS; i++) {
		if (monitored_fd_set[i] != pid)
			continue;
		client_pid_set[i] = -1;
		break;
	}
}

/*
* Clone all the fds in monitored_fd_set array into fd_set 
* Data structure.
*/
void refresh_fd_set(fd_set* fd_set_ptr) {

	FD_ZERO(fd_set_ptr);
	int i = 0;
	for (; i < MAX_CLIENTS; i++) {
		if (monitored_fd_set[i] != -1) {
			FD_SET(monitored_fd_set[i], fd_set_ptr);
		}
	}
}

/*
* Inform clients to flush their routing tables and mac lists.
*/

void flush_clients() {
	int i;
	for (i = 0; i < MAX_CLIENTS; i++) {
		int pid = client_pid_set[i];
		if (pid != -1) {
			kill(pid, SIGUSR1);
		}
	}
}

/*
* Helper function for isValidMask.
*/
int digits_only(const char* s) {

	while (*s) {
		if (isdigit(*s++) == 0)return 0;
	}

	return 1;
}

/*
* Checks if IP address is Valid.
*/
int isValidIP(const char* addr) {
	struct sockaddr_in sa;
	return addr && inet_pton(AF_INET, addr, &(sa.sin_addr)) != 0;
}

/*
* Mask is valid if it is a string that can be
* converted to an integer within [0,32].
*/

int isValidMask(const char* mask) {
	return digits_only(mask) && atoi(mask) <= 32;
}

/*
* Check if a given string represents a valid mac address
*  in the format XX:XX:XX:XX:XX:XX, where each X represents
*  a hexadecimal digit 0-9 or a-f.
*/
int isValidMAC(const char* addr) {
	if (!addr)
		return 0;

	int i;
	for (i = 0; i < MAC_ADDR_LEN - 1; i++) {
		if (i % 3 != 2 && !isdigit(addr[i])) {
			return 0;
		}

		if (i % 3 == 2 && addr[i] != ':')
			return 0;

	}

	return addr[i] == '\0';
}


/*
* Get the numerical max value among all fds which server
* is monitoring.
*/

int get_max_fd() {
	int i = 0;
	int max = -1;

	for (; i < MAX_CLIENTS; i++) {
		if (monitored_fd_set[i] > max)
			max = monitored_fd_set[i];
	}

	return max;
}

/*
* Parses a string command, in the format
* <Opcode, Dest, Mask, GW, OIF> or <Opcode, MAC>
* with each field seperated by a space, to create
* a sync message for clients, instructing them on 
* how to update their copies of the routing table.
* The silent parameter indicates whether the server
* is actively inputting a command for MAC list via
* stdin or a client is replicating a command sent by
* the server. Returns 0 on success and -1 on any 
* failure.
*/


int create_sync_message(char* operation, sync_msg_t* sync_msg, int silent) {

	char* token = strtok(operation, " ");

	if (token) {
		switch (token[0]) {
		case 'C':
			sync_msg->op_code = CREATE;
			break;

		case 'U':
			sync_msg->op_code = UPDATE;
			break;

		case 'D':
			sync_msg->op_code = DELETE;
			break;
		
		case 'S':
			sync_msg->op_code = NONE;
			display_routing_table(routing_table);
			display_mac_list(mac_list);
			return 0;
		
		case 'F':
			sync_msg->op_code = NONE;

			flush_clients();
			deinit_dll(routing_table);
			deinit_dll(mac_list);

			routing_table = init_dll();
			mac_list = init_dll();
			return 0;

		default:

			fprintf(stderr, "Invalid operation: unknown op code\n");
			return -1;
		}
	}
	else {
		fprintf(stderr, "Invalid operation: missing op code\n");
		return -1;
	}

	token = strtok(NULL, " ");

	if (isValidIP(token)) {
		sync_msg->l_code = L3;
		memcpy(sync_msg->msg_body.routing_table_entry.dest, token, strlen(token));
	}
	else if (isValidMAC(token)) {
		sync_msg->l_code = L2;
		memcpy(sync_msg->msg_body.mac_list_entry.mac, token, strlen(token));

		if (!silent && sync_msg->op_code == CREATE) {

			printf("Enter an IP address:\n");
			char ip[IP_ADDR_LEN];
			int ret = read(0, ip, IP_ADDR_LEN);

			ip[strcspn(ip, "\r\n")] = 0;

			if (ret < 0 || store_IP(sync_msg->msg_body.mac_list_entry.mac, ip) == -1) {
				fprintf(stderr, "Failed to store ip address\n");
				return -1;
			}
		}

		return 0;
	}
	else {
		fprintf(stderr, "Invalid operation: invalid or missing destination IP/MAC address\n");
		return -1;
	}

	token = strtok(NULL, " ");
	if (isValidMask(token)) {
		sync_msg->msg_body.routing_table_entry.mask = atoi(token);
	}
	else {
		fprintf(stderr, "Invalid operation: invalid or missing subnet mask/IP address\n");
		return -1;
	}

	/*
	* Only CREATE and UPDATE require a gw and oif.
	*/

	if (sync_msg->op_code == CREATE || sync_msg->op_code == UPDATE) {
		token = strtok(NULL, " ");
		
		if (isValidIP(token)) {
			memcpy(sync_msg->msg_body.routing_table_entry.gw, token, strlen(token));
		}
		else {
			fprintf(stderr, "Invalid operation: invalid or missing gateway IP\n");
			return -1;
		}

		token = strtok(NULL, " ");
		if (token) {
			memcpy(sync_msg->msg_body.routing_table_entry.oif, token, strlen(token));
		}
		else {
			fprintf(stderr, "Invalid operation: missing OIF\n");
			return -1;
		}
	}

	return 0;
}

/*
* Break out of main infinite loop and inform clients of
* shutdown to exit clearly.
*/

void signal_handler(int signal_num) {

	if (signal_num == SIGINT) {
		int i, synchronized = WAIT, loop = 0;
		sync_msg_t sync_msg;
		sync_msg.op_code = NONE;

		for (i = 2; i < MAX_CLIENTS; i++) {
			int comm_socket_fd = monitored_fd_set[i];

			if (comm_socket_fd != -1) {
				write(comm_socket_fd, &sync_msg, sizeof(sync_msg_t));
				write(comm_socket_fd, &synchronized, sizeof(int));
				write(comm_socket_fd, &loop, sizeof(int));
			}
		}

		/*
		* Clean up resources.
		*/

		int shm_fd;
		mac_list_entry_t* entry;

		ITERATE_DLL(mac_list, entry, mac_list_entry_t)

			shm_fd = shm_open(entry->mac,
				O_CREAT | O_RDONLY,
				0660);

			shm_unlink(entry->mac);
			close(shm_fd);
		ITERATE_DLL_END()

		deinit_dll(routing_table);
		deinit_dll(mac_list);
		close(connection_socket);
		remove_from_monitored_fd_set(connection_socket);
		unlink(SOCKET_NAME);
		exit(0);
	}
}


/*
* Send newly client all necessary CREATE commands to replicate
* the server's copies of the current routing table or MAC list.
*/

void update_new_client(int data_socket, LCODE l_code, char* op, sync_msg_t* sync_msg) {
	
	dll_node_t* head = l_code == L3 ? routing_table->head : mac_list->head;
	dll_node_t* curr = head->next;

	while (curr != head) {
		routing_table_entry_t rt_entry = *((routing_table_entry_t*)curr->data);
		
		mac_list_entry_t ml_entry = *((mac_list_entry_t*)curr->data);

		sync_msg->op_code = CREATE;

		if (l_code == L3) {
			sprintf(op, "C %s %u %s %s", 
				rt_entry.dest, 
				rt_entry.mask, 
				rt_entry.gw, 
				rt_entry.oif);
		}
		else {

			sprintf(op, "C %s", ml_entry.mac);
		}

		create_sync_message(op, sync_msg, 1);

		write(data_socket, sync_msg, sizeof(sync_msg_t));
		write(data_socket, &synchronized, sizeof(int));
		write(data_socket, &loop, sizeof(int));
		
		curr = curr->next;
	}

	/*
	* Send dummy sync message to inform client that all
	* current updates have been sent.
	*/

	sync_msg->op_code = NONE;
	write(data_socket, sync_msg, sizeof(sync_msg_t));
	synchronized = l_code == L3 ? RT : ML;
	write(data_socket, &synchronized, sizeof(int));
	write(data_socket, &loop, sizeof(int));
}

int main() {

	struct sockaddr_un name;
	int ret;
	int data_socket;
	fd_set readfds;

	routing_table = init_dll();
	mac_list = init_dll();

	initialize_monitor_fd_and_client_pid_set();
	add_to_monitored_fd_set(0);

	unlink(SOCKET_NAME); //In case the program exited inadvertently on the last run, remove the socket.

	/*
	* Master socket for accepting connections
	* from client
	*/

	connection_socket = socket(AF_UNIX, SOCK_STREAM, 0);
	if (connection_socket == -1) {
		perror("socket");
		exit(1);
	}

	/*
	* Initialize
	*/

	memset(&name, 0, sizeof(struct sockaddr_un));

	/*
	* Specify the socket Credentials
	*/
	name.sun_family = AF_UNIX;
	strncpy(name.sun_path, SOCKET_NAME, sizeof(name.sun_path) - 1);

	/*
	* Bind socket to socket name
	*/

	ret = bind(connection_socket, (const struct sockaddr*) &name,
		sizeof(struct sockaddr_un));

	if (ret == -1) {
		perror("bind");
		exit(1);
	}

	/*
	* Prepare for accepting connections.
	*/

	ret = listen(connection_socket, 20);
	if (ret == -1) {
		perror("listen");
		exit(1);
	}

	add_to_monitored_fd_set(connection_socket);

	signal(SIGINT, signal_handler); //register signal handler

	/*
	* The server continuously checks for new clients connections, monitors
	* existing connections (i.e. incoming messages and inactive connections,
	* modifies the routing table or MAC list if need be, and broadcasts to
	* clients.
	*/

	while (1) {
		char op[OP_LEN];
		sync_msg_t* sync_msg = calloc(1, sizeof(sync_msg_t));
		synchronized = 0;

		refresh_fd_set(&readfds); /*Copy the entire monitored FDs to readfds*/

		printf("Please select from the following options:\n");
		printf("1.CREATE <Destination IP> <Mask (0-32)> <Gateway IP> <OIF>\n");
		printf("2.UPDATE <Destination IP> <Mask (0-32)> <New Gateway IP> <New OIF>\n");
		printf("3.DELETE <Destination IP> <Mask (0-32)>\n");
		printf("4.CREATE <MAC>\n");
		printf("5.DELETE <MAC>\n");
		printf("6.SHOW\n");
		printf("7.FLUSH\n");

		select(get_max_fd() + 1, &readfds, NULL, NULL, NULL); /* Wait for incoming connections*/

		/* New Connection : send entire routing table and mac list states to newly connected clients*/
		if (FD_ISSET(connection_socket, &readfds)) {
			data_socket = accept(connection_socket, NULL, NULL);
			if (data_socket == -1) {
				perror("accept");
				exit(1);
			}

			pid_t pid;
			if (read(data_socket, &pid, sizeof(pid_t)) == -1) {
				perror("read");
				exit(1);
			}

			add_to_monitored_fd_set(data_socket);
			add_to_client_pid_set(pid);

			update_new_client(data_socket, L3, op, sync_msg);
			update_new_client(data_socket, L2, op, sync_msg);

		}
		else if (FD_ISSET(0, &readfds)) { // server stdin

			ret = read(0, op, OP_LEN - 1);

			op[strcspn(op, "\r\n")] = 0; //flush new line

			if (ret == -1) {
				perror("read");
				return 1;
			}

			op[ret] = 0;


			if (!create_sync_message(op, sync_msg, 0)) {
				//Update server's tables

				if (sync_msg->l_code == L3) {
					process_sync_mesg(routing_table, sync_msg);
					synchronized = RT;
				}
				else {
					process_sync_mesg(mac_list, sync_msg);
					synchronized = ML;
				}

				// Notify existing clients of change.
				int i, comm_socket_fd;
				for (i = 2; i < MAX_CLIENTS; i++) {
					//Start at 2 since 0 and 1 are for server's stdin and stdout
					comm_socket_fd = monitored_fd_set[i];
					if (comm_socket_fd != -1) {
						write(comm_socket_fd, sync_msg, sizeof(sync_msg_t));
						write(comm_socket_fd, &synchronized, sizeof(int));
						write(comm_socket_fd, &loop, sizeof(int));
					}
				}
			}
		}
		else {
			/*
			* Check active status of clients.
			*/

			int i;
			for (i = 2; i < MAX_CLIENTS; i++) {
				if (FD_ISSET(monitored_fd_set[i], &readfds)) {
					int done;
					int comm_socket_fd = monitored_fd_set[i];

					ret = read(comm_socket_fd, &done, sizeof(int));
					if (done == 1) {
						//this client is disconnecting
						close(comm_socket_fd);
						remove_from_monitored_fd_set(comm_socket_fd);
					}
					else if (ret == -1) {
						perror("read");
						exit(1);
					}
					else {
						printf("%i\n", done);
					}
				}
			}
		}
	}
	
	exit(0);
}