Add date functionalities

date.c

@@ -0,0 +1,48 @@
+#include <time.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "date.h"
+#include "config.h"
+
+int
+get_day_diff(struct tm *date)
+{
+	time_t now;
+	time(&now);
+	double sec_diff = difftime(now, mktime(date));
+	int day_diff = sec_diff / 3600 / 24;
+	return day_diff;
+}
+
+struct tm
+parse_date(char *date_str)
+{
+	char year[4], month[3], day[3];
+	int i_year, i_mon, i_day;
+	sscanf(date_str, "%04s-%02s-%02s", year, month, day);
+	i_year = atoi(year) - 1900;
+	i_mon = atoi(month) - 1;
+	i_day = atoi(day);
+	struct tm date = {.tm_year=i_year, .tm_mon=i_mon, .tm_mday=i_day};
+	mktime(&date);
+	return date;
+}
+
+void
+print_days()
+{
+	char day[3];
+	time_t current_time;
+	current_time = time(NULL);
+	struct tm *local = localtime(&current_time);
+	for (int i = TRACK_LENGTH; i >0; --i) {
+		local->tm_mday -= i;
+		mktime(local);
+		strftime(day, sizeof day, DAY_REPR, local);
+		printf("%s ", day);
+		local->tm_mday += i;
+	}
+	printf("\n");
+}

date.h

@@ -0,0 +1,8 @@
+#ifndef DATE_H
+#define DATE_H
+
+int get_day_diff(struct tm *date);
+struct tm parse_date(char *date_str);
+void print_days();
+
+#endif

wochabit.c

@@ -19,9 +19,11 @@
 #include <errno.h>
 #include <stdio.h>
 #include <string.h>
+#include <time.h>
 
 #include "constants.h"
 #include "config.h"
+#include "date.h"
 
 void print_status(int status); // Print the status for a day of a habit
 void print_habit(int habit); // Print the habit stati during the tracked duration
@@ -69,6 +71,13 @@ main(int argc, char *argv[]){
 	print_habit(5);
 	print_habit(49);
 	print_habit(1 << TRACK_LENGTH - 2);
+	print_days();
+	struct tm date = parse_date("2020-11-19");
+	printf("%d\n", date.tm_year);
+	printf("%d\n", date.tm_mon);
+	printf("%d\n", date.tm_mday);
+	int diff = get_day_diff(&date);
+	printf("%d\n", diff);
 	printf("Bye\n");
 	return 0;
 }