g502.c

// Based on this program for G600:
// https://github.com/mafik/logitech-g600-linux
// It's 99% the same program except for the fact that it looks for a G502 instead of G600, and some other minor changes I couldn't be bothered to write down.

#include <linux/input.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

struct input_event events[256];
const char kDir[] = "/dev/input/by-id/";
const char kPrefix[] = "usb-Logitech_Gaming_Mouse_G502_";
const char kSuffix[] = "-if01-event-kbd";

// ADD KEY->COMMAND MAPPINGS HERE:
const char *downCommands[] = {
	//[scancode] = "command to run",
	[4] = "xdotool mousedown 8", // G4 (mouse button 4 / backward)
	[5] = "xdotool mousedown 9", // G5 (mouse button 5 / forward)
	[6] = "xdotool key ctrl+w", // G7
	[7] = "xdotool key ctrl+t", // G8
	[8] = "xdotool mousedown 6", // Scroll left (not useful in current state)
	[9] = "xdotool mousedown 7", // Scroll right (not useful in current state)
	//[10] = "", // G+G4 (not practical)
	//[11] = "", // G+G5 (not practical)
	//[12] = "", // G+G7
	[13] = "xdotool key ctrl+shift+t", // G+G8
	[14] = "xdotool key ctrl+shift+Tab", // G+Scroll left
	[15] = "xdotool key ctrl+Tab", // G+Scroll right
};
const char *upCommands[] = {
	//[scancode] = "command to run",
	[4] = "xdotool mouseup 8", // G4
	[5] = "xdotool mouseup 9", // G5
	[8] = "xdotool mouseup 6", // Scroll left (not useful in current state)
	[9] = "xdotool mouseup 7", // Scroll right (not useful in current state)
};

int starts_with(const char* haystack, const char* prefix) {
	size_t prefix_length = strlen(prefix), haystack_length = strlen(haystack);
	if (haystack_length < prefix_length) return 0;
	return strncmp(prefix, haystack, prefix_length) == 0;
}

int ends_with(const char* haystack, const char* suffix) {
	size_t suffix_length = strlen(suffix), haystack_length = strlen(haystack);
	if (haystack_length < suffix_length) return 0;
	size_t haystack_end = haystack + haystack_length - suffix_length;
	return strncmp(suffix, haystack_end, suffix_length) == 0;
}

// Returns non-0 on error.
int find_g600(char *path) {
	//*path = kDir;
	DIR *dir;
	struct dirent *ent;
	if (!(dir = opendir(kDir))) {
		return 1;
	}
	while ((ent = readdir(dir))) {
		if (starts_with(ent->d_name, kPrefix) && ends_with(ent->d_name, kSuffix)) {
			strcpy(path, kDir);
			strcat(path, ent->d_name);

			printf("full path is %s\n", path);

			//*path += ent->d_name;
			closedir(dir);
			return 0;
		}
	}
	closedir(dir);
	return 2;
}

int main() {
	printf("Starting G502 Linux controller.\n\n");
	printf("It's a good idea to configure G502 with Logitech Gaming Software before running this program:\n");
	printf(" - assign left, right, middle mouse button and vertical mouse wheel to their normal functions\n");
	printf(" - assign the G-Shift button to \"G-Shift\"\n");
	printf(" - assign all other keys (including horizontal mouse wheel) to arbitrary (unique) keyboard keys\n");
	printf("\n");		
	char path[1024];
	int find_error = find_g600(&path);
	if (find_error) {
		printf("Error: Couldn't find G502 input device.\n");
		switch(find_error) {
		case 1: 
			printf("Suggestion: Maybe the expected directory (%s) is wrong. Check whether this directory exists and fix it by editing \"g600.c\".\n", kDir);
			break;
		case 2:
			printf("Suggestion: Maybe the expected device prefix (%s) is wrong. Check whether a device with this prefix exists in %s and fix it by editing \"g600.cpp\".\n", kPrefix, kDir);
			break;
		}
		printf("Suggestion: Maybe a permission is missing. Try running this program with with sudo.\n");
		return 1;
	}
	int fd = open(path, O_RDONLY);
	if (fd < 0) {
		printf("Error: Couldn't open \"%s\" for reading.\n", path);
		printf("Reason: %s.\n", strerror(errno));
		printf("Suggestion: Maybe a permission is missing. Try running this program with with sudo.\n");
		return 1;
	}

	ioctl(fd, EVIOCGRAB, 1);
	printf("G502 controller started successfully.\n\n");
	while (1) {
		size_t n = read(fd, events, sizeof(events));
		if (n <= 0) return 2;
		if (n < sizeof(struct input_event) % 2) continue;
		
		if (events[0].type != 4 || events[0].code != 4 || events[1].type != 1)
			continue;
		/*
		for (int i = 0; i < 2; i++) {
			printf("type %d, code %d, value %d (%d)\n", events[i].type, events[i].code, events[i].value, events[i].value & ~0x70000);
		}
		/*/
		int pressed = events[1].value;
		int scancode = events[0].value & ~0x70000;

		const char* actionStr = (pressed) ? "+" : "-";
		printf("%s %d.\n", actionStr, scancode);
		
		const char *downCommand = downCommands[scancode], *upCommand = upCommands[scancode];
		const char *cmdToRun = (pressed) ? downCommand : upCommand;
		if (!cmdToRun || !strlen(cmdToRun)) continue;

		printf("Executing: \"%s\"\n", cmdToRun);
		system(cmdToRun);
		//*/
	}
	
	close(fd);
}