After commit c018f5fd29 Fenrir is being switched over to go. If you do not want to be part of the testing process, please switch to master.

internal/datetime/datetime.go

@@ -0,0 +1,141 @@
+// Copyright (c) 2026 Storm Dragon
+// Author: Storm Dragon
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package datetime
+
+/*
+#include <locale.h>
+#include <stdlib.h>
+#include <time.h>
+*/
+import "C"
+
+import (
+	"time"
+	"unsafe"
+)
+
+type Option struct {
+	Value string
+	Label string
+}
+
+var timeFormats = []struct {
+	Value string
+	Spec  string
+}{
+	{"locale", "%X"},
+	{"12-hour", "%I:%M %p"},
+	{"12-hour-seconds", "%I:%M:%S %p"},
+	{"24-hour-seconds", "%H:%M:%S"},
+	{"24-hour-seconds-words", "%H hours, %M minutes and %S seconds"},
+	{"24-hour", "%H:%M"},
+	{"24-hour-words", "%H hours and %M minutes"},
+}
+
+var dateFormats = []struct {
+	Value string
+	Spec  string
+}{
+	{"locale", "%x"},
+	{"numbers-dm", "%d/%m"},
+	{"numbers-md", "%m/%d"},
+	{"numbers-dmy", "%d/%m/%Y"},
+	{"numbers-mdy", "%m/%d/%Y"},
+	{"numbers-ymd", "%Y/%m/%d"},
+	{"full-dm", "%A, %-d %B"},
+	{"full-md", "%A, %B %-d"},
+	{"full-dmy", "%A, %-d %B, %Y"},
+	{"full-mdy", "%A, %B %-d, %Y"},
+	{"full-ymd", "%Y. %B %-d, %A"},
+	{"abbreviated-dm", "%a, %-d %b"},
+	{"abbreviated-md", "%a, %b %-d"},
+	{"abbreviated-dmy", "%a, %-d %b, %Y"},
+	{"abbreviated-mdy", "%a, %b %-d, %Y"},
+	{"abbreviated-ymd", "%Y. %b %-d, %a"},
+}
+
+func init() {
+	locale := C.CString("")
+	defer C.free(unsafe.Pointer(locale))
+	C.setlocale(C.LC_TIME, locale)
+}
+
+func Time_options(now time.Time) []Option {
+	return options(timeFormats, now)
+}
+
+func Date_options(now time.Time) []Option {
+	return options(dateFormats, now)
+}
+
+func options(formats []struct {
+	Value string
+	Spec  string
+}, now time.Time) []Option {
+	result := make([]Option, 0, len(formats))
+	for _, item := range formats {
+		result = append(result, Option{Value: item.Value, Label: format(now, item.Spec)})
+	}
+	return result
+}
+
+func Format_time(value string, now time.Time) (string, bool) {
+	return format_value(timeFormats, value, now)
+}
+
+func Format_date(value string, now time.Time) (string, bool) {
+	return format_value(dateFormats, value, now)
+}
+
+func Valid_time(value string) bool {
+	return valid(timeFormats, value)
+}
+
+func Valid_date(value string) bool {
+	return valid(dateFormats, value)
+}
+
+func format_value(formats []struct {
+	Value string
+	Spec  string
+}, value string, now time.Time) (string, bool) {
+	for _, item := range formats {
+		if item.Value == value {
+			return format(now, item.Spec), true
+		}
+	}
+	return "", false
+}
+
+func valid(formats []struct {
+	Value string
+	Spec  string
+}, value string) bool {
+	for _, item := range formats {
+		if item.Value == value {
+			return true
+		}
+	}
+	return false
+}
+
+func format(now time.Time, spec string) string {
+	cSpec := C.CString(spec)
+	defer C.free(unsafe.Pointer(cSpec))
+	tm := C.struct_tm{
+		tm_year:  C.int(now.Year() - 1900),
+		tm_mon:   C.int(int(now.Month()) - 1),
+		tm_mday:  C.int(now.Day()),
+		tm_hour:  C.int(now.Hour()),
+		tm_min:   C.int(now.Minute()),
+		tm_sec:   C.int(now.Second()),
+		tm_wday:  C.int(int(now.Weekday())),
+		tm_yday:  C.int(now.YearDay() - 1),
+		tm_isdst: -1,
+	}
+	buffer := make([]C.char, 512)
+	length := C.strftime(&buffer[0], C.size_t(len(buffer)), cSpec, &tm)
+	return C.GoStringN(&buffer[0], C.int(length))
+}

internal/datetime/datetime_test.go

@@ -0,0 +1,53 @@
+// Copyright (c) 2026 Storm Dragon
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package datetime
+
+import (
+	"testing"
+	"time"
+)
+
+func TestFormatsAndExamples(t *testing.T) {
+	now := time.Date(2026, 10, 25, 14, 5, 9, 0, time.FixedZone("fixture", -4*3600))
+	for _, testCase := range []struct {
+		id, want string
+		date     bool
+	}{
+		{"24-hour", "14:05", false},
+		{"24-hour-seconds", "14:05:09", false},
+		{"24-hour-words", "14 hours and 05 minutes", false},
+		{"24-hour-seconds-words", "14 hours, 05 minutes and 09 seconds", false},
+		{"numbers-dm", "25/10", true},
+		{"numbers-md", "10/25", true},
+		{"numbers-dmy", "25/10/2026", true},
+		{"numbers-mdy", "10/25/2026", true},
+		{"numbers-ymd", "2026/10/25", true},
+	} {
+		format := Format_time
+		if testCase.date {
+			format = Format_date
+		}
+		if got, ok := format(testCase.id, now); !ok || got != testCase.want {
+			t.Fatal(testCase.id, got, ok)
+		}
+	}
+	for _, date := range []bool{false, true} {
+		options, format, valid := Time_options(now), Format_time, Valid_time
+		if date {
+			options, format, valid = Date_options(now), Format_date, Valid_date
+		}
+		for _, option := range options {
+			got, ok := format(option.Value, now)
+			if !ok || !valid(option.Value) || got == "" || got != option.Label {
+				t.Fatal(option, got, ok)
+			}
+		}
+		if got, ok := format("%arbitrary", now); ok || got != "" || valid("%arbitrary") {
+			t.Fatal("invalid preset accepted")
+		}
+	}
+	if got, _ := Format_time("24-hour-seconds", now.Add(10*time.Hour)); got != "00:05:09" {
+		t.Fatal(got)
+	}
+}