1 files changed, 250 insertions, 0 deletions
diff --git a/bin/when.y b/bin/when.y
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+/* Copyright (C) 2019  June 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 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 const struct tm Week = { .tm_mday = 7 };
+
+static struct tm normalize(struct tm date) {
+	time_t time = timegm(&date);
+	struct tm *norm = gmtime(&time);
+	if (!norm) err(EX_OSERR, "gmtime");
+	return *norm;
+}
+
+static struct tm today(void) {
+	time_t now = time(NULL);
+	struct tm *local = localtime(&now);
+	if (!local) err(EX_OSERR, "localtime");
+	struct tm date = {
+		.tm_year = local->tm_year,
+		.tm_mon = local->tm_mon,
+		.tm_mday = local->tm_mday,
+	};
+	return normalize(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 = today();
+	date.tm_mon = month;
+	date.tm_mday = day;
+	date.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,
+		.tm_mon = a.tm_mon - b.tm_mon,
+		.tm_mday = a.tm_mday - b.tm_mday,
+	};
+	if (a.tm_mon < b.tm_mon) {
+		diff.tm_year--;
+		diff.tm_mon += 12;
+	}
+	if (a.tm_mday < b.tm_mday) {
+		diff.tm_mon--;
+		diff.tm_mday = 0;
+		while (dateAdd(b, diff).tm_mday != a.tm_mday) diff.tm_mday++;
+	}
+	time_t atime = timegm(&a), btime = timegm(&b);
+	diff.tm_yday = (atime - btime) / 24 / 60 / 60;
+	return diff;
+}
+
+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 ", scalar.tm_mday);
+	} else if (scalar.tm_mday) {
+		printf("%dw ", scalar.tm_mday / 7);
+	}
+	if (scalar.tm_yday && scalar.tm_mon) printf("(%dd) ", scalar.tm_yday);
+	printf("\n");
+}
+
+%}
+
+%token Number Month Day
+%left '+' '-'
+%right '<' '>'
+
+%%
+
+expr:
+	date { printDate($1); }
+	| scalar { printScalar($1); }
+	;
+
+date:
+	dateLit
+	| '(' date ')' { $$ = $2; }
+	| '<' date { $$ = dateSub($2, Week); }
+	| '>' date { $$ = dateAdd($2, Week); }
+	| date '+' scalar { $$ = dateAdd($1, $3); }
+	| date '-' scalar { $$ = dateSub($1, $3); }
+	;
+
+scalar:
+	scalarLit
+	| '(' scalar ')' { $$ = $2; }
+	| scalar '+' scalar { $$ = scalarAdd($1, $3); }
+	| scalar '-' scalar { $$ = scalarSub($1, $3); }
+	| date '-' date { $$ = dateDiff($1, $3); }
+	;
+
+dateLit:
+	{ $$ = today(); }
+	| '.' { $$ = today(); }
+	| Month Number { $$ = 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); }
+	;
+
+scalarLit:
+	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(int argc, char *argv[]) {
+	if (argc > 1) {
+		input = argv[1];
+		return yyparse();
+	}
+
+	struct tm date = today();
+	printDate(date);
+	printf("\n");
+
+	char *line = NULL;
+	size_t cap = 0;
+	while (0 < getline(&line, &cap, stdin)) {
+		if (line[0] == '\n') continue;
+
+		if (today().tm_mday != date.tm_mday) {
+			warnx("the date has changed");
+			date = today();
+		}
+
+		input = line;
+		yyparse();
+		printf("\n");
+	}
+}