1 files changed, 85 insertions, 0 deletions
diff --git a/batwarn_daemon.c b/batwarn_daemon.c
new file mode 100644
index 0000000..1cd1d17
--- /dev/null
+++ b/batwarn_daemon.c
@@ -0,0 +1,85 @@
+// For nanosleep(), pread()
+#define _POSIX_C_SOURCE 200809L
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <time.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/wait.h>
+#include <assert.h>
+
+
+// Warning when battery percentage is <= this
+static const int WARN_PERC = 10;
+
+// Time to sleep between checks
+static const struct timespec SLEEP_SPEC = {60, 0};
+
+// Format string with percentage %d
+static const char *MESSAGE_FORMAT = "Battery at %d%%!";
+
+
+static inline void parse(const char *buffer, bool *discharging, int *charge, int *full) {
+	while (true) {
+		if (memcmp(buffer, "POWER_SUPPLY_STATUS", 19) == 0) {
+			*discharging = memcmp(buffer + 20, "Discharging", 11) == 0;
+		} else if (memcmp(buffer, "POWER_SUPPLY_CHARGE_NOW", 23) == 0) {
+			*charge = strtol(buffer + 24, NULL, 10);
+		} else if (memcmp(buffer, "POWER_SUPPLY_CHARGE_FULL_DESIGN", 31) == 0) {
+			*full = strtol(buffer + 32, NULL, 10);
+		}
+		buffer = strchr(buffer, '\n');
+		if (buffer != NULL) buffer++;
+		else break;
+	}
+}
+
+int main(void) {
+	int fd = open("/sys/class/power_supply/BAT1/uevent", O_RDONLY);
+	if (fd < 0) {
+		perror("open");
+		return 1;
+	}
+
+	char buffer[1024];
+
+	while (true) {
+		ssize_t nr = pread(fd, buffer, sizeof buffer, 0);
+		if (nr < 0) {
+			perror("pread");
+			break;
+		}
+
+		bool discharging = false;
+		int charge = 1, full = 1;
+		parse(buffer, &discharging, &charge, &full);
+
+		if (full > 0 && discharging && charge * 100 / full <= WARN_PERC) {
+			pid_t pid = fork();
+			if (pid < 0) perror("fork");
+			else if (pid == 0) {
+				char msg[strlen(MESSAGE_FORMAT) + 16];
+				snprintf(msg, sizeof msg, MESSAGE_FORMAT, charge * 100 / full);
+				char *argv[4] = {"i3-nagbar", "-m", msg, NULL};
+				execv("/usr/bin/i3-nagbar", argv);
+				perror("execv");
+				exit(255);
+			} else {
+				int status;
+				do if (waitpid(pid, &status, 0) < 0 && errno == ECHILD) break;
+				while (!WIFEXITED(status) && !WIFSIGNALED(status));
+			}
+		}
+
+		(void)nanosleep(&SLEEP_SPEC, NULL);
+	}
+
+	if (close(fd) < 0) {
+		perror("close");
+		return 1;
+	}
+}