#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h> /* TCP_NODELAY */
#include <arpa/inet.h>
#include <termios.h>

#define DATA_BUFLEN 128
#define DEV_PATH 32


/* Structures used for communication parameters. */
struct server_t {
	int socket; 					/* server socket */
	struct sockaddr_in address; 	/* server address information */
	unsigned int port;				/* server port in host byte order, practical reference */
};

struct client_t {
	int socket; 						/* client socket */
	struct sockaddr_in address; 		/* client address information */
	char ip_string[INET_ADDRSTRLEN]; 	/* client IP address as a string */
	char data[DATA_BUFLEN]; 			/* buffer for data received from client */
};

struct tty_t {
	int fd; 					/* tty file descriptor */
	struct termios ttyset;		/* tty termios settings */
	char path[DEV_PATH]; 		/* tty device path */
	char data[DATA_BUFLEN]; 	/* buffer for data received from tty */
};


/* Global variables used throughout the application. */
struct server_t server; 	/* main server structure */
struct client_t client; 	/* connected client structure */ //TODO working with only 1 client, this can be expanded into a list
struct tty_t tty_dev; 		/* connected tty device */


/* Functions handling server operation. */

/**
 * Sets up the server on specific port, binds to a socket and listens for client connections.
 *
 * Returns:
 * - 0 on success,
 * - negative errno value set appropriately by error in setup process
 */
int server_setup(struct server_t *server, unsigned int port);

/**
 * Closes the server socket.
 * 
 * Returns:
 * 0 always, but internally tries closing again if it fails.
 */
int server_close(struct server_t *server);

/**
 * Accepts incoming client connection.
 * 
 * Returns:
 * - 0 on success,
 * - negative errno value set appropriately by error in setup process
 */
int server_accept(struct server_t *server, struct client_t *accepted_client);

/**
 * Rejects incoming client connection.
 * 
 * Returns:
 * 0 always, errors with rejected client are ignored
 */
int server_reject(struct server_t *server);


/* Functions handling communication with clients. */

/**
 * Closes client connection.
 * 
 * Returns:
 * 0 always, but internally tries closing again if it fails.
 */
int client_close(struct client_t *client);

/**
 * Reads data from client into client data buffer.
 * 
 * Returns:
 * - number of read bytes on success,
 * - negative ENODATA value (-ENODATA) if client disconnected,
 * - negative errno value set appropriately by error in reading
 */
int client_read(struct client_t *client);

/**
 * Sends data from a buffer to client.
 * 
 * Returns:
 * - number of sent bytes on success,
 * - negative errno value set appropriately by error in sending
 */
int client_write(struct client_t *client, char *databuf, int datalen);


/* Functions handling details related to telnet protocol. */

/**
 * Tells client to go into "character" mode.
 * 
 * Returns:
 * - 0 on success
 * - negative value if error occurred
 */
int telnet_set_character_mode(struct client_t *client);

/**
 * Handles special characters in data buffer after receiving them from client.
 * Used to filter out handshake commands of telnet protocol.
 * 
 * Returns:
 * 0 always
 */
int telnet_handle_client_read(char *databuf, int *datalen);

/**
 * Handles special characters in data buffer before sending to client.
 * Used for echoing characters correctly to telnet client.
 * 
 * Returns:
 * 0 always
 */
int telnet_handle_client_write(char *databuf, int *datalen);


/* Functions handling communication with tty device. */

/* Opens the tty device and configures it. */
int tty_open(struct tty_t *tty_dev);
/* Closes the tty device. */
int tty_close(struct tty_t *tty_dev);
/* Reconfigures the tty device. */
int tty_reconfigure(struct tty_t *tty_dev, struct termios newttyset);
/* Reads incoming data from tty device to tty data buffer. */
int tty_read(struct tty_t *tty_dev);
/* Sends data from a buffer to tty device. */
int tty_write(struct tty_t *tty_dev, char *databuf, int datalen);
/* Main tty thread function */
void *tty_thread_func(void *arg);