#include <getopt.h>
#include <signal.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/time.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <unistd.h>
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <stddef.h>

#define PROC_NET_DEV "/proc/net/dev"

struct iface {
	char interface[IFNAMSIZ];
	struct timeval timestamp;
	unsigned long long rx_bytes;
	unsigned long long tx_bytes;
};


volatile bool q = false;
bool use_bits = false;
struct iface *interfaces = NULL;
size_t no_iface = 0;

void endHandler(int signum) {
	q = true;
}

void print_bps(double bytesPerSecond) {
	const char* prefixes[] = { "", "k", "M", "G", "T", "P", "E", "Z", "Y" };

	// Calculate the value
	double value;
	const char* unit;
	if(use_bits) {
		value = bytesPerSecond * 8;
		unit = "b/s";
	}
	else {
		value = bytesPerSecond;
		unit = "B/s";
	}

	// Choose the prefix
	unsigned prefix = 0;
	while (prefix < (sizeof(prefixes) / sizeof(const char*)) && value > 1000.) {
		value /= 1000.;
		++prefix;
	}

	// Format the string
	printf("%.2f %s%s", value, prefixes[prefix], unit);

}

void print_stats() {
	// Open /proc/net/dev
	FILE *dev = fopen(PROC_NET_DEV, "r");
	if (!dev) {
		fprintf(stderr, "cannot open %s - %s\n", PROC_NET_DEV, strerror(errno));
		exit(EXIT_FAILURE);
	}

	// Read /proc/dev/net
	while (!feof(dev)) {
		char buf[512];
		char *name, *statistics_string;
		long long unsigned rx_bytes, tx_bytes;
		struct timezone unused_timezone;
		struct timeval timestamp;

		// Read a line
		fgets(buf, sizeof(buf), dev);

		// get timestamp
		gettimeofday(&timestamp, &unused_timezone);

		// Find the colon separating the name from the statistics
		statistics_string = strchr(buf, ':');
		if (!statistics_string) continue;

		// Get a pointer to the statistics
		*statistics_string = 0;
		++statistics_string;

		// Remove leading whitespace from the name
		name = buf;
		ptrdiff_t len = 0;
		while (*name == ' ' || *name == '\t') {
			++name;
		}
		len = name - buf;

		// Parse the statistics, alls well, then get this shit going, otherwise f it.
		if (sscanf(statistics_string, "%Lu %*Lu %*Lu %*Lu %*Lu %*Lu %*Lu %*Lu %Lu",
					&rx_bytes, &tx_bytes) == 2) {

			size_t i = 0;
			bool found = false;
			if(interfaces == NULL) {
				goto skip;
			}
			for(i = 0; i < no_iface; i++) {
				// if it exists in our interfaces, great. reuse the iface struct
				if(strncmp(name, interfaces[i].interface, len) == 0) {
					found = true;
					break;
				}
			}
skip:
			if(found) {
				double timeDelta, rx_speed, tx_speed = 0;

				// print our new speeds
				timeDelta = (timestamp.tv_sec  - interfaces[i].timestamp.tv_sec) * 1.0 +
					(timestamp.tv_usec - interfaces[i].timestamp.tv_usec) * .000001;

				rx_speed = (rx_bytes - interfaces[i].rx_bytes) / timeDelta;
				tx_speed = (tx_bytes - interfaces[i].tx_bytes) / timeDelta;

				printf("%s (", interfaces[i].interface);
				print_bps(rx_speed);
				printf(", ");
				print_bps(tx_speed);
				printf(")\t");

				// update our interface
				strcpy(interfaces[i].interface, name);
				interfaces[i].rx_bytes = rx_bytes;
				interfaces[i].timestamp = timestamp;
				interfaces[i].tx_bytes = tx_bytes;
			} 
			else {
				interfaces = realloc(interfaces, sizeof(struct iface) * (no_iface + 1));
				if(interfaces == NULL) {
					fprintf(stderr, "Error: %s\n", strerror(errno));
					exit(1);
				}
				strcpy(interfaces[no_iface].interface, name);
				interfaces[no_iface].rx_bytes = rx_bytes;
				interfaces[no_iface].tx_bytes = tx_bytes;
				no_iface++;
			}

		}

	}
	// Close the file
	fclose(dev);

}

int main(int argc, char **argv) {

	// parse the command line
	int c; 

	int interval = 10 * 100000;

	while ((c = getopt (argc, argv, "bi:hv")) != -1) 
		switch (c)
		{
			case 'b':
				use_bits = true;
				break;
			case 'i':
				// Magic numbers? fuck it that's not a magic number, that's a 'real' number.
				interval = atoi(optarg) * 100000;
				break;
			case 'h':
				printf("USAGE: fsbm, -b specifies bits, -i sets interval in 10ths of seconds, 1 sec default\n");
				exit(EXIT_SUCCESS);
				break;
			case 'v':
				printf("Version 1\n");
				exit(EXIT_SUCCESS);
				break;
			case '?':
				fprintf(stderr,"bad flag\n");
				break;
			default:  
				exit(EXIT_FAILURE);
		}

	// Catch SIGINT
	signal(SIGINT, endHandler);

	// populate first.
	print_stats();
	while (!q) {
		print_stats();
		printf("\n");
		usleep(interval);
	}

	return EXIT_SUCCESS;
}