// control charging of battery on apple M1
// tested on macbook pro 2021 model
// works on linux

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include <syslog.h>

enum charge_mode {
	CHARGE_AUTO,
	CHARGE_INHIBIT_CHARGE,
	CHARGE_FORCE_DISCHARGE,
};

static const char *chargemodes[] = {
	"auto",
	"inhibit-charge",
	"force-discharge",
};

#define CAPACITY_FILE \
	"/sys/class/power_supply/macsmc-battery/capacity"
#define CHARGE_BEHAVIOR_FILE \
	"/sys/class/power_supply/macsmc-battery/charge_behaviour"

#define LOWER_CHARGE	70
#define UPPER_CHARGE	90

static enum charge_mode last_mode = -1;

static void set_charge_mode(enum charge_mode mode)
{
	char *logname = "charge-ctl";
	FILE *cb;

	if (mode == last_mode)
		return;

	cb = fopen(CHARGE_BEHAVIOR_FILE, "w");
	if (!cb) {
		perror("fopen");
		exit(EXIT_FAILURE);
	}
	fprintf(cb, "%s", chargemodes[mode]);
	fclose(cb);
	last_mode = mode;
	openlog(logname, LOG_PID, LOG_USER);
	syslog(LOG_USER | LOG_INFO, chargemodes[mode]);
}

int main(int argc, char **argv)
{
	int option, limit = UPPER_CHARGE;
	pid_t pid, sid;

	while ((option = getopt(argc, argv, "l:uh")) != -1) {
		switch (option) {
		case 'h':
			puts("help");
			puts("-l limit capacity");
			exit(EXIT_SUCCESS);
		case 'l':
			limit = atoi(optarg);
			printf("limit: %d\n", limit);
			break;
		default:                          /* '?' */
			puts("unknown option");
			exit(EXIT_FAILURE);
		}
	}

	pid = fork();
	if (pid < 0)
		exit(EXIT_FAILURE);
	if (pid > 0)
		exit(EXIT_SUCCESS);

	umask(0);
	sid = setsid();
	if (sid < 0)
		exit(EXIT_FAILURE);

	if ((chdir("/")) < 0)
		exit(EXIT_FAILURE);

	close(STDIN_FILENO);
	close(STDOUT_FILENO);
	close(STDERR_FILENO);

	while (1) {
		FILE *capfile;
		char cap[6];
		int icap;

		capfile = fopen(CAPACITY_FILE, "r");
		fgets(cap, 5, capfile);
		fclose(capfile);
		icap = atoi(cap);
		if (icap < LOWER_CHARGE)
			set_charge_mode(CHARGE_AUTO);
		else if (icap > limit)
			set_charge_mode(CHARGE_FORCE_DISCHARGE);
		else
			set_charge_mode(CHARGE_INHIBIT_CHARGE);

		sleep(30);
	}

	exit(EXIT_SUCCESS);
}