#include <time.h>
#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <stdlib.h>

#define DATEFMT "%a %d %b %Y"
#define SEP " ~> "

typedef struct event {
	char *name;
	time_t time;
} event;

static bool cal = true;

static const char *days[] = {
	"Su",
	"Mo",
	"Tu",
	"We",
	"Th",
	"Fr",
	"Sa"
};

static const char *months[] = {
	"Jan",
	"Feb",
	"Mar",
	"Apr",
	"May",
	"Jun",
	"Jul",
	"Aug",
	"Sep",
	"Oct",
	"Nov",
	"Dec"
};

static const int daysinmonth[] = {
	31, 28, 31, 30,	31, 30, 31, 31, 30, 31, 30, 31
};

static bool
isleap(int year) {
	if ((year % 4) == 0 && (year % 100) != 0) 
		return true;
	else if ((year % 400) == 0)
		return true;
	return false;
}

static void
print_month(struct tm *t) {
	printf("      %s %d\n", months[t->tm_mon], t->tm_year + 1900);
}

static void 
print_days() {
	for (int i = 0; i < 7; i++)
		printf("%s ", days[i]);
	putchar('\n');
}

static void 
print_padded(int n, int l) {
	int i = 1;
loop:
	if ((n / i) > 0) {
		i *= 10;
		l--;
		goto loop;
	}

	if (l != 0)
		printf("%*s", l, " ");
	if (l < 0)
		return;

	printf("%d", n);
}

static void 
print_month_grid(struct tm *t) {
	int day = 1;
	int total = daysinmonth[t->tm_mon];
	if (t->tm_mon == 1 && isleap(t->tm_year + 1900))
		total += 1;

	int offset = (t->tm_yday % 7) - 1;
	for (int i = 0; i < offset; i++)
		printf("   ");

	for (; day < total + 1; day++) {
		if (day == t->tm_mday) {
			printf("\e[4;34m");	
			print_padded(day, 2);
			printf("\e[0m");	
		} else
			print_padded(day, 2);
		putchar(' ');
		if (((day + offset) % 7) == 0)
			putchar('\n');
	}
	putchar('\n');
}

static void 
print_cal(struct tm *t) {
	print_month(t);
	print_days();
	print_month_grid(t);
}

static event *
read_event(FILE *f) {
	event *e = malloc(sizeof(event));
	char buf[256] = {0};
	if (!fgets(buf, 256, f)) {
		free(e);
		return NULL;
	}
	char *time = buf;
	char *name = strchr(buf, '|');
	if (!name) {
		fprintf(stderr, "invalid event! %s\n", buf);
		exit(1);
	}
	*name = 0;
	name++;

	e->name = strdup(name);	
	e->time = atoll(time);
	return e;
}

static void 
print_event(event *e) {
	struct tm *t = localtime(&e->time);
	char buf[256];
	strftime(buf, 256, DATEFMT, t);
	printf("%s" SEP "%s", buf, e->name);
}

static void
free_event(event *e) {
	free(e->name);
	free(e);
}

int 
main(int argc, char **argv) {
	if (argc > 1)
		if (strcmp(argv[1], "-h") == 0)
			cal = false;

	time_t ulocal = time(NULL);
	struct tm *local = localtime(&ulocal);

	if (cal)
		print_cal(local);

	bool dirty = false;
	event *e;
	while (e = read_event(stdin)) {
		if (ulocal + (86400 * 30) > e->time) {
			print_event(e);
			dirty = true;
		}
		free_event(e);
	}
	if (!dirty)
		printf("You have nothing upcoming\n");

	return 0;
}