/*------------------------------------------------------------------------------
NAME
       iwlist - Get more detailed wireless information from a wireless interface

SYNOPSIS
       iwlist [interface] scanning

DESCRIPTION
       Iwlist  is used to display some additional information from a wireless
	   network interface that is not displayed
       by iwconfig(8).  The main argument is used to select a category of
	   information, iwlist  displays  in  detailed
       form all information related to this category, including information
	   already shown by iwconfig(8).

PARAMETERS
scan[ning]
	  Give  the  list of Access Points and Ad-Hoc cells in range, and optionally
	  a whole bunch of information
	  about them (ESSID, Quality, Frequency, Mode...). The type of information
	  returned depends on  what  the card supports.
	  Triggering scanning is a privileged operation (root only) and normal users
	  can only read left-over scan
	  results. By default, the way scanning is done (the scope of the scan) is
	  dependant on the card and card settings.
	  This command takes optional arguments, however most drivers will ignore
	  those. The option essid is used
	  to specify a scan on a specific ESSID. With some card/driver, this enables
	  to see hidden networks.  The
	  option last does not trigger a scan and read left-over scan results.

SEE ALSO
       iwconfig(8), iwspy(8).  iwevent(8), iwpriv(8), wireless(7).

https://www.centurylink.com/home/help/internet/wireless/which-frequency-should-you-use.html

	Standard	Frequency	Theoretical Speed 		Real World Speed
	802.11g		2.4Ghz		54 Mbps					10 -29 Mbps
	802.11n		2.4Ghz		300 Mpbs				150 Mbps
	802.11n		5Ghz		900 Mbps				450Mbps
	802.11ac	5Ghz		433 Mbps - 1.7 Gbps		210 Mbps - 1 G

------------------------------------------------------------------------------*/
#include <math.h>
#include <stdio.h>	//	Input/output
#include <stdlib.h>	//	General utilities
#include <string.h>	//	String handling
/*------------------------------------------------------------------------------

------------------------------------------------------------------------------*/
typedef struct wifi_channel_data
{
	double signal_level_dB;
	double frequency;
	double metric;
	char SSID_string[256];
	char quality_string[256];
	int quality_out_of_70;
	int channel;
}
CHANNEL_DATA;
/*-----------------------------------------------------------------------------
		compare two channel entries
-----------------------------------------------------------------------------*/
int compare_channels(const void *channel_a, const void *channel_b)
{
	int comparison;

	if(((CHANNEL_DATA*)channel_a)->metric
	== ((CHANNEL_DATA*)channel_b)->metric)
	{
		comparison = 0;
	}
	else
	if(((CHANNEL_DATA*)channel_a)->metric
	 < ((CHANNEL_DATA*)channel_b)->metric)
	{
		comparison = +1;
	}
	else
	{
		comparison = -1;
	}

	return comparison;
}
/*------------------------------------------------------------------------------

------------------------------------------------------------------------------*/
void report_error(char *error)
{
	printf("error\t: %s\n", error);
	printf("WiFi scan failed\n");
	getchar();
	exit(EXIT_FAILURE);
}
/*------------------------------------------------------------------------------

------------------------------------------------------------------------------*/
void print_channel_data(CHANNEL_DATA *channel_data_list)
{
	CHANNEL_DATA *channel_data;
	int count = 0;

	puts("");

	channel_data = channel_data_list;

	while(channel_data->quality_out_of_70 > 0 && channel_data->channel != -1)
	{
		count++;
		printf
		(
			"\t%2d \tSSID %-20s %3.0lfdB\t\tchannel %3d\tmetric %6.1lf\n",
			count,
			channel_data->SSID_string,
			channel_data->signal_level_dB,
			channel_data->channel,
			channel_data->metric
		);
		channel_data++;
	}
}
/*------------------------------------------------------------------------------
	a rather crude parsing of the output from iwlist
------------------------------------------------------------------------------*/
void parse_the_scan_line(char *scan_line, char *ssid, CHANNEL_DATA **channel_data)
{
	char *position;

	if((position = strstr(scan_line, "Quality=")) != NULL)
	{
		// obtain both quality and signal strength
		// which are on the same line
		strcpy((*channel_data)->quality_string, scan_line);
		(*channel_data)->quality_out_of_70 = atoi(position + strlen("Quality="));
		//printf("quality_out_of_70\t: %3d\n", (*channel_data)->quality_out_of_70);

		if((position = strstr(scan_line, "Signal level=")) != NULL)
		{
			(*channel_data)->signal_level_dB = atof(position + strlen("Signal level="));
		}
		else
		{
			(*channel_data)->signal_level_dB = -100;
		}
		//printf("signal_level_dB\t\t: %3.0lfdB\n", (*channel_data)->signal_level_dB);
	}
	else
	if((position = strstr(scan_line, "Frequency:")) != NULL)
	{
		//printf("\n\t\"%s\"\n", scan_line);
		(*channel_data)->frequency = atof(position + strlen("Frequency:"));
		//printf("frequency\t\t: %7.3lf GHz\n", (*channel_data)->frequency);

		if((position = strstr(scan_line, "Channel:")) != NULL)
		{
			(*channel_data)->channel = atoi(position + strlen("Channel:"));
			//printf("\nchannel\t\t\t: %3d\n", (*channel_data)->channel);
		}
	}
	else
	if((position = strstr(scan_line, "Channel:")) != NULL)
	{
		(*channel_data)->channel = atoi(position + strlen("Channel:"));
		//printf("\nchannel\t\t\t: %3d\n", (*channel_data)->channel);
	}
	else
	if((position = strstr(scan_line, "ESSID:")) != NULL)
	{
		strcpy((*channel_data)->SSID_string, position + strlen("ESSID:"));
		//printf("SSID_string\t\t: %s\n", (*channel_data)->SSID_string);

		if(strcasecmp((*channel_data)->SSID_string, ssid) == 0)
		{
/*
	Calculate a 'utility' metric based on signal strength and real world data rate.
	The balance between the two characteristics can be debated. The choice here
	is between a 5GHz channel at 450 Mbps and 2.4 GHz at ~20 Mbps.
	The power of the signal (in dBm) is logarithmic and can easily dominate
	the metric.
*/
			if((*channel_data)->channel > 14)
			{
				//	Standard	Frequency	Real World Speed
				//	802.11n		5 GHz		450 Mbps
				(*channel_data)->metric = 450 * 1000000 * pow(10, (*channel_data)->signal_level_dB / 10.0);
			}
			else
			{
				//	Standard	Frequency	Real World Speed
				//	802.11g		2.4 GHz		10 - 29 Mbps
				(*channel_data)->metric =  10 * 1000000 * pow(10, (*channel_data)->signal_level_dB / 10.0);
			}

			//printf("\tour SSID %s\n", (*channel_data)->SSID_string);
			(*channel_data)++;	// move on
		}
		else
		{
			// don't move on, not our SSID
			//printf("\tnot our SSID %s\n", (*channel_data)->SSID_string);
		}
	}
	else
	{
		printf("\n\t\"%s\"\n", scan_line);
		report_error("is not a recognized string in wifi_scan.txt");
	}
}
/*------------------------------------------------------------------------------

------------------------------------------------------------------------------*/
int main(int argc, char **argv)
{
	CHANNEL_DATA channel_data_list[256];
	CHANNEL_DATA *channel_data;
	FILE *fptr;
	char scan_line[256];
	char command[256];
	int count;
	char *ssid		= "\"clive\"";	// <-- set your SSD here
	//char *interface = "wlp1s0";		// <-- set your WiFi interface here
	char *interface = "wlp0s20f3";		// <-- set your WiFi interface here

	sprintf
	(
		command,
		"iwlist scan | grep -e completed"
	);

	printf("%s\n", command);
	system(command);			// this reveals the WiFi interface

	sprintf
	(
		command,
		"iwlist scan | "
		"grep -e ESSID -e Quality -e rate -e Channel "
		"> wifi_scan.txt"
	);

	printf("\n%s\n", command);

	/*
		Gathers the iwlist channel information.
		Does not work if does not have super-user permissions.
	*/
	//system(command);

    if((fptr = fopen("wifi_scan.txt", "rt")) == NULL)
	{
		report_error("can't open wifi_scan.txt");
	}
	else
	{
		channel_data = channel_data_list;
		while(!feof(fptr))
		{
			fscanf(fptr, " %[^\r\n]s", scan_line);
			parse_the_scan_line(scan_line, ssid, &channel_data);
		}
	}
	fclose(fptr);

	channel_data->channel = -1;	// terminate the list

	count = channel_data - channel_data_list - 1;

	print_channel_data(channel_data_list);
	qsort
	(
		(void *)channel_data_list,
		count, sizeof(CHANNEL_DATA),
		compare_channels	// by utility metric
	);
	print_channel_data(channel_data_list);

	// connect to the 'best' AP available using iwconfig
	sprintf
	(
		command,
		"iwconfig %s channel %d", interface, channel_data_list->channel
	);
	printf("\n%s\n", command);
	//system(command);		// un-comment this to make the change

	print_channel_data(channel_data_list);

	printf("\nWiFi scan is done\n");
	getchar();
	return EXIT_SUCCESS;
}
/*------------------------------------------------------------------------------

------------------------------------------------------------------------------*/