#define _POSIX_C_SOURCE 200809L

#include <sys/types.h>
#include <sys/stat.h>

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <dirent.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <time.h>
#include <limits.h>

		// TODO: handle multiple batteries
const char *CAPACITY_PATH = "/sys/class/power_supply/BAT1/capacity";
const char *STATUS_PATH = "/sys/class/power_supply/BAT1/status";
const char *POWER_PATH = "/sys/class/power_supply/BAT1/power_now";
int dead = 0;

void usage (void)
{
	printf("usage: bmon [-wuh] [-f file] [-t interval]\n"
	"-w\tDisplay power draw from battery\n"
	"-u\tPrint seconds as epoch\n"
	"-h\tPrint this message\n"
	"-f\tWrite output to file\n"
	"-t\tSet the update interval in seconds\n");
}

void int_handler (int signum)
{
	(void)signum;
        dead = 1;
}

int read_int (FILE *fp)
{
	int x;
	freopen(NULL, "r", fp);
	fscanf(fp, "%d", &x); 
	return x;
}

int main (int argc, char *argv[])
{
	/* Handle SIGINT */
	dead = 0;
	struct sigaction action;
	memset(&action, 0, sizeof(action));
	action.sa_handler = int_handler;
	sigaction(SIGINT, &action, NULL);

	int wflag = 0;
	int wait_time = 10;
	int fflag = 0;
	int uflag = 0;
	char ofile_path[256];

	int opc;
	while ((opc = getopt(argc, argv, "uhwf:t:")) != -1) {
		switch (opc) {
		case 'w':
			wflag = 1;
			break;
		case 'f':
			fflag = 1;
			strncpy(ofile_path, optarg, 255);
			break;
		case 't':
			wait_time = atoi(optarg);
			if (wait_time < 1) {
				usage();
				exit(1);
			}
			break;
		case 'u':
			uflag = 1;
			break;
		case 'h':
		default: /* '?' */
			usage();
			exit(1);
		break;
		}

	}

	FILE *capacity_fp = NULL, *status_fp = NULL, *power_fp = NULL;
	capacity_fp = fopen(CAPACITY_PATH, "r");
	if (capacity_fp == NULL) {
		fprintf(stderr, "Error opening %s: %s\n", CAPACITY_PATH, strerror(errno));
		exit(1);
	}

	if (wflag) {
		power_fp = fopen(POWER_PATH, "r");
		if (power_fp == NULL) {
			fprintf(stderr, "Error opening %s: %s\n", POWER_PATH, strerror(errno));
			exit(1);
		}
		status_fp = fopen(STATUS_PATH, "r");
		if (status_fp == NULL) {
			fprintf(stderr, "Error opening %s: %s\n", STATUS_PATH, strerror(errno));
			exit(1);
		}
	}


	FILE *output_fp = stdout;
	if (fflag) {
		if ((output_fp = fopen(ofile_path, "w")) == NULL) {
			fprintf(stderr, "Error opening %s: %s\n", ofile_path, strerror(errno));
			exit(1);
		}
	}

	long int elapsed_time = 0;
	fprintf(output_fp, "TIME\t");
	fprintf(output_fp, "CAP\t");
	if (wflag) fprintf(output_fp, "WATTS");
	fprintf(output_fp, "\n");
	while (!dead) {
		int capacity = read_int(capacity_fp);
		float power = 0;
		if (capacity < 0) {
			fprintf(stderr, "Error reading capacity: %s\n", strerror(errno));
			break;
		}
		if (wflag) {
			power = read_int(power_fp);
			if (power < 0) {
				fprintf(stderr, "Error reading power: %s\n", strerror(errno));
				break;
			}
			static char b[128] = {0};
			freopen(NULL, "r", status_fp);
			if (fgets(b, sizeof(b), status_fp) == NULL) {
				fprintf(stderr, "Error reading status: %s\n", strerror(errno));
			}
			if (strncmp(b, "Discharging\n", sizeof(b)) == 0) {
				power *= -1;
			}

			// power is in microwatts
			power /= 1e6;
		}

		fprintf(output_fp, "%ld\t", uflag ? time(NULL) : elapsed_time);
		fprintf(output_fp, "%d\t", capacity);
		if (wflag) fprintf(output_fp, "%.2f", power);
		fprintf(output_fp, "\n");

		sleep(wait_time);
		elapsed_time += wait_time;
	}

	if (fflag) {
		fclose(output_fp);
	}
	if (capacity_fp) {
		fclose(capacity_fp);
	}
	if (status_fp) {
		fclose(status_fp);
	}
	if (power_fp) {
		fclose(power_fp);
	}
	
	return 0;
}