/* LINUX DOCS: https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-power
 * (C) 2024 Tim Keller <tjkeller.xyz>
 * MIT License
 */

#include <libnotify/notify.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <dirent.h>

#define PERIOD 3 // number of seconds before each check
#define PSUPATH "/sys/class/power_supply" // number of seconds before each check
#define MAX_BATTERIES     8
#define MAX_PSU_NAME_LEN  8
#define MAX_PROP_PATH_LEN 64

// variables
static char batteries[MAX_BATTERIES][MAX_PSU_NAME_LEN];
static unsigned int num_batteries;
static FILE *fp;
static char prop_path[MAX_PROP_PATH_LEN];

// functions
void load_installed_batteries() {
	// search through "power supplies" for "status" property (only available on batteries)
	DIR *dir, *subdir;
	struct dirent *entry, *subentry;

	if ((dir = opendir(PSUPATH)) == NULL) {
		fprintf(stderr, "failed to see power supplies"); // TODO
		exit(EXIT_FAILURE);
	}

	// power supplies TODO warn user if max batteries exceeded
	num_batteries = 0;
	while ((entry = readdir(dir)) != NULL && num_batteries < MAX_BATTERIES) {
		if (entry->d_name[0] == '.')
			continue; // skip . and ..
		if (strlen(entry->d_name) > MAX_PSU_NAME_LEN) {
			fprintf(stderr, "the power supply name was too long: %s", entry->d_name);
			exit(EXIT_FAILURE);
		}

		// power supplies will always be a directory, no need to check beforehand :)
		snprintf(prop_path, MAX_PROP_PATH_LEN, PSUPATH "/%s", entry->d_name);

		if ((subdir = opendir(prop_path)) == NULL) {
			fprintf(stderr, "failed to see power supplies sub\n"); // TODO
			exit(EXIT_FAILURE);
		}

		// power supply properties
		while ((subentry = readdir(subdir)) != NULL) {
			// add to list of batteries if it has the status property
			if (strcmp(subentry->d_name, "status") == 0) {
				strncpy(batteries[num_batteries], entry->d_name, MAX_PSU_NAME_LEN);
				num_batteries++;
				break;
			}
		}
		closedir(subdir);
	}
	closedir(dir);
}

void notifysend(char *title, char *content, NotifyUrgency urgency) {
	NotifyNotification *notif;
	notify_init("lowbat");
	notif = notify_notification_new(title, content, NULL);

	notify_notification_set_timeout(notif, NOTIFY_EXPIRES_NEVER);
	notify_notification_set_urgency(notif, urgency);
	notify_notification_show(notif, NULL);
}

void read_prop(char *psu, char *prop, char *fmt, void *out) {
	/* this function is only designed to read one var at a time because all bat
	 * properties will only be one var */
	snprintf(prop_path, MAX_PROP_PATH_LEN, PSUPATH "/%s/%s", psu, prop);

	if ((fp = fopen(prop_path, "r")) != NULL) {
		fscanf(fp, fmt, out);
		fclose(fp);
	}
	else {
		printf("failed to read fmt '%s' from property %s\n", fmt, prop_path); // TODO fprintf me plz
		exit(EXIT_FAILURE);
	}
}

int get_total_capacity() {
	unsigned long int energy_full = 0, energy_now = 0, x;
	int i;

	for (i = 0; i < num_batteries; i++) {
		read_prop(batteries[i], "energy_full", "%ld", &x);
		energy_full += x;
		read_prop(batteries[i], "energy_now",  "%ld", &x);
		energy_now += x;
	}

	return energy_now * 100 / energy_full;
}

int is_discharging() {
	char status[12]; // valid values: "Unknown", "Charging", "Discharging", "Not charging", "Full"
	int i;

	for (i = 0; i < num_batteries; i++) {
		read_prop(batteries[i], "status", "%s", &status);
		if (strcmp(status, "Discharging") != 0)
			return 0;
	}

	return 1;
}

int main() {
	int discharging, capacity;
	int w_lowbat = 0, w_lowbat_crit = 0; // 1 if warned already
	char msg[32];

	load_installed_batteries();
	if (!num_batteries) {
		fprintf(stderr, "no batteries installed in system. exiting...\n"); // TODO
		exit(EXIT_FAILURE);
	}

	while (1) {
		load_installed_batteries();
		discharging = is_discharging();
		capacity = get_total_capacity();

		if (discharging) {
			if (capacity <= 5 && !w_lowbat_crit) {
				sprintf(msg, "%d%% remains", capacity); // TODO snprintf me plz
				notifysend("Critical Low Battery Warning", msg, NOTIFY_URGENCY_CRITICAL);

				w_lowbat_crit = w_lowbat = 1;
			} else if (capacity <= 20 && !w_lowbat) {
				sprintf(msg, "%d%% remains", capacity);
				notifysend("Low Battery Warning", msg, NOTIFY_URGENCY_NORMAL);

				w_lowbat = 1;
			}
		} else {
			w_lowbat_crit = w_lowbat = 0;  // clear conditions
		}

		printf("\r%s %d%%", discharging ? "Discharging" : "Charging", capacity);
		fflush(stdout);
		sleep(PERIOD);
	}

	return 0;
}