Add beginning of date calculator

1 files changed, 213 insertions, 0 deletions

diff --git a/bin/ddc.y b/bin/ddc.y
new file mode 100644
index 00000000..ffce22e0
--- /dev/null
+++ b/bin/ddc.y
@@ -0,0 +1,213 @@
+/* Copyright (C) 2019  C. McEnroe <june@causal.agency>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+%{
+
+#include <ctype.h>
+#include <err.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <strings.h>
+#include <sysexits.h>
+#include <time.h>
+
+static void yyerror(const char *str);
+static int yylex(void);
+
+#define YYSTYPE struct tm
+
+static struct tm normalize(struct tm date) {
+	time_t time = mktime(&date);
+	struct tm *norm = localtime(&time);
+	if (!norm) err(EX_OSERR, "localtime");
+	return *norm;
+}
+
+static struct tm today(void) {
+	time_t now = time(NULL);
+	struct tm *date = localtime(&now);
+	if (!date) err(EX_OSERR, "localtime");
+	date->tm_hour = date->tm_min = date->tm_sec = 0;
+	return *date;
+}
+
+static struct tm monthDay(int month, int day) {
+	struct tm date = today();
+	date.tm_mon = month;
+	date.tm_mday = day;
+	return normalize(date);
+}
+
+static struct tm monthDayYear(int month, int day, int year) {
+	struct tm date = {
+		.tm_mon = month,
+		.tm_mday = day,
+		.tm_year = year - 1900,
+	};
+	return normalize(date);
+}
+
+static struct tm weekDay(int day) {
+	struct tm date = today();
+	date.tm_mday += day - date.tm_wday;
+	return normalize(date);
+}
+
+static struct tm scalarAdd(struct tm a, struct tm b) {
+	a.tm_mday += b.tm_mday;
+	a.tm_mon += b.tm_mon;
+	a.tm_year += b.tm_year;
+	return a;
+}
+
+static struct tm scalarSub(struct tm a, struct tm b) {
+	a.tm_mday -= b.tm_mday;
+	a.tm_mon -= b.tm_mon;
+	a.tm_year -= b.tm_year;
+	return a;
+}
+
+static struct tm dateAdd(struct tm date, struct tm scalar) {
+	return normalize(scalarAdd(date, scalar));
+}
+
+static struct tm dateSub(struct tm date, struct tm scalar) {
+	return normalize(scalarSub(date, scalar));
+}
+
+static struct tm dateDiff(struct tm a, struct tm b) {
+	struct tm diff = { .tm_year = a.tm_year - b.tm_year };
+	if (a.tm_mday < b.tm_mday) {
+		diff.tm_mon = a.tm_mon - b.tm_mon - 1;
+		while (dateAdd(b, diff).tm_mday != a.tm_mday) diff.tm_mday++;
+	} else {
+		diff.tm_mon = a.tm_mon - b.tm_mon;
+		diff.tm_mday = a.tm_mday - b.tm_mday;
+	}
+	return diff;
+}
+
+static const char *Days[7] = {
+	"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat",
+};
+
+static const char *Months[12] = {
+	"Jan", "Feb", "Mar", "Apr", "May", "Jun",
+	"Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
+};
+
+static void printDate(struct tm date) {
+	printf(
+		"%s %s %d %d\n",
+		Days[date.tm_wday], Months[date.tm_mon],
+		date.tm_mday, 1900 + date.tm_year
+	);
+}
+
+static void printScalar(struct tm scalar) {
+	if (scalar.tm_year) printf("%dy ", scalar.tm_year);
+	if (scalar.tm_mon) printf("%dm ", scalar.tm_mon);
+	if (scalar.tm_mday % 7) {
+		printf("%dd\n", scalar.tm_mday);
+	} else {
+		printf("%dw\n", scalar.tm_mday / 7);
+	}
+}
+
+%}
+
+%token Number Month Day
+%left '+' '-'
+
+%%
+
+expr:
+	date { printDate($1); }
+	| scalar { printScalar($1); }
+	;
+
+date:
+	dateSpec
+	| date '+' scalar { $$ = dateAdd($1, $3); }
+	| date '-' scalar { $$ = dateSub($1, $3); }
+	;
+
+scalar:
+	scalarSpec
+	| scalar '+' scalar { $$ = scalarAdd($1, $3); }
+	| scalar '-' scalar { $$ = scalarSub($1, $3); }
+	| date '-' date { $$ = dateDiff($1, $3); }
+	;
+
+dateSpec:
+	'.' { $$ = today(); }
+	| Month Number { $$ = monthDay($1.tm_mon, $2.tm_sec); }
+	| Month Number Number { $$ = monthDayYear($1.tm_mon, $2.tm_sec, $3.tm_sec); }
+	| Day { $$ = weekDay($1.tm_wday); }
+	;
+
+scalarSpec:
+	Number 'd' { $$ = (struct tm) { .tm_mday = $1.tm_sec }; }
+	| Number 'w' { $$ = (struct tm) { .tm_mday = 7 * $1.tm_sec }; }
+	| Number 'm' { $$ = (struct tm) { .tm_mon = $1.tm_sec }; }
+	| Number 'y' { $$ = (struct tm) { .tm_year = $1.tm_sec }; }
+	;
+
+%%
+
+static void yyerror(const char *str) {
+	warnx("%s", str);
+}
+
+static const char *input;
+
+static int yylex(void) {
+	while (isspace(*input)) input++;
+	if (!*input) return EOF;
+
+	if (isdigit(*input)) {
+		char *rest;
+		yylval.tm_sec = strtol(input, &rest, 10);
+		input = rest;
+		return Number;
+	}
+
+	for (int i = 0; i < 7; ++i) {
+		if (strncasecmp(input, Days[i], 3)) continue;
+		while (isalpha(*input)) input++;
+		yylval.tm_wday = i;
+		return Day;
+	}
+
+	for (int i = 0; i < 12; ++i) {
+		if (strncasecmp(input, Months[i], 3)) continue;
+		while (isalpha(*input)) input++;
+		yylval.tm_mon = i;
+		return Month;
+	}
+
+	return *input++;
+}
+
+int main(void) {
+	char *buf = NULL;
+	size_t cap = 0;
+	while (0 < getline(&buf, &cap, stdin)) {
+		input = buf;
+		yyparse();
+		printf("\n");
+	}
+}