#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

#define LISTEN_PORT  1234  // Port we accept connections on
#define BUFFER_SIZE  1024  // Size of buffer for receiving data

/* Name:         createTcpSocket
 * Description:  Creates a new, unconnected TCP socket
 * Parameters:   sock - buffer to receive socket
 * Return code:  true if successful
 *               false if an error occurred
 */
bool createTcpSocket(int *sock)
{
	bool failed = false;

	*sock = socket(AF_INET, SOCK_STREAM, 0);
	if (*sock == -1)
	{
		fprintf(stderr, "Couldn't create socket: %s\n", strerror(errno));
		failed = true;
	}

	return !failed;
}

/* Name:         bindTcpSocket
 * Description:  Binds a TCP socket to a specific port on all interfaces
 * Parameters:   sock - socket to bind
 *               port - port to bind socket to
 * Return code:  true if successful
 *               false if an error occurred
 */
bool bindTcpSocket(int sock, unsigned short port)
{
	bool result = false;

	struct sockaddr_in saddr;
	saddr.sin_family = AF_INET;
	saddr.sin_port = htons(port);
	saddr.sin_addr.s_addr = INADDR_ANY;

	printf("Binding to %s:%u...", inet_ntoa(saddr.sin_addr), port);
	fflush(stdout);
	if (bind(sock, (struct sockaddr*) &saddr, sizeof(saddr)) == 0)
	{
		printf(" OK.\n");
		result = true;
	}
	else
	{
		printf(" FAILED.\n");
		fprintf(stderr, "Couldn't bind socket: %s\n", strerror(errno));
	}

	return result;
}

/* Name:         setSocketToListenMode
 * Description:  Sets a bound TCP socket to listen mode
 * Parameters:   sock - socket to set to listen mode
 * Return code:  true if successful
 *               false if an error occurred
 */
bool setSocketToListenMode(int sock)
{
	bool failed = false;

	if (listen(sock, 3) == -1)
	{
		fprintf(stderr, "Couldn't set socket to listen mode: %s\n", strerror(errno));
		failed = true;
	}

	return !failed;
}

/* Name:         acceptClient
 * Description:  Accepts a new client on a socket in listen mode
 * Parameters:   sock - socket in listen mode
 *               client - buffer for socket of new client
 * Return code:  true if successful
 *               false if an error occurred
 */
bool acceptClient(int sock, int *client)
{
	bool result = false;

	struct sockaddr_in saddr;
	socklen_t size = sizeof(saddr);
	*client = accept(sock, (struct sockaddr*) &saddr, &size);
	if (*client >= 0)
	{
		printf("Got a new client from %s:%u.\n", inet_ntoa(saddr.sin_addr), ntohs(saddr.sin_port));
		result = true;
	}
	else
	{
		fprintf(stderr, "Accepting client failed: %s\n", strerror(errno));
	}

	return result;
}

/* Name:         receiveString
 * Description:  Receives and prints a string from a connected socket
 * Parameters:   sock - socket to read from
 * Return code:  true if successful
 *               false if an error occurred
 */
bool receiveString(int sock)
{
	int total = 0;
	bool done = false;
	bool failed = false;
	char buffer[BUFFER_SIZE];

	while (!done && !failed)
	{
		int bytes = recv(sock, buffer + total, sizeof(buffer) - total - 1, 0);
		if (bytes > 0)
		{
			total += bytes;
			buffer[total] = '\0';
		}
		else if (bytes == 0)
		{
			done = true;
		}
		else if (bytes == -1)
		{
			fprintf(stderr, "Couldn't read from socket: %s\n", strerror(errno));
			failed = true;
		}
	}

	if (!failed)
	{
		printf("Received %i bytes: <%s>\n", total, buffer);
	}

	return !failed;
}

/* Name:         safeCloseSocket
 * Description:  Checks if a socket is valid, closes it. The socket is
 *               set to an invalid value to avoid double free errors.
 * Parameters:   sock - socket to communicate with
 * Return code:  none
 */
void safeCloseSocket(int *sock)
{
	if (*sock != -1)
	{
		close(*sock);
		*sock = -1;
	}
}

int main(void)
{
	int sock = -1;
	bool good = createTcpSocket(&sock);

	if (good)
		good = bindTcpSocket(sock, LISTEN_PORT);

	if (good)
		good = setSocketToListenMode(sock);

	int client = -1;
	if (good)
		good = acceptClient(sock, &client);

	if (good)
		good = receiveString(client);

	safeCloseSocket(&client);
	safeCloseSocket(&sock);

	return good ? EXIT_SUCCESS : EXIT_FAILURE;
}