feat: Return location info and Hijri date from the prayer times endpoint

pkg/hijricalendar/calendar.go

@@ -0,0 +1,61 @@
+package hijricalendar
+
+import (
+	"fmt"
+	"math"
+	"time"
+)
+
+// JulianToIslamic converts a Julian calendar date to the Islamic (Hijri) calendar.
+// Algorithm from Jean Meeus, "Astronomical Algorithms", 2nd ed.
+func JulianToIslamic(year, month, day int) (iYear, iMonth, iDay int) {
+	jdn := julianToJDN(year, month, day)
+	return jdnToIslamic(jdn)
+}
+
+// GregorianToIslamic converts a Gregorian calendar date to the Islamic (Hijri)
+// calendar.
+func GregorianToIslamic(year, month, day int) (iYear, iMonth, iDay int) {
+	jdn := gregorianToJDN(year, month, day)
+	return jdnToIslamic(jdn)
+}
+
+// julianToJDN returns the Julian Day Number for a date on the Julian calendar.
+func julianToJDN(year, month, day int) int {
+	y, m := year, month
+	if m <= 2 {
+		y--
+		m += 12
+	}
+	return int(math.Floor(365.25*float64(y+4716))) +
+		int(math.Floor(30.6001*float64(m+1))) +
+		day - 1524
+}
+
+func gregorianToJDN(year, month, day int) int {
+	a := (14 - month) / 12
+	y := year + 4800 - a
+	m := month + 12*a - 3
+
+	return day + (153*m+2)/5 + 365*y + y/4 - y/100 + y/400 - 32045
+}
+
+// jdnToIslamic converts a Julian Day Number to an Islamic (Hijri) calendar date.
+// Source: F. de Moya, as cited in Meeus Ch. 9.
+func jdnToIslamic(jd int) (year, month, day int) {
+	l := jd - 1948440 + 10632
+	n := (l - 1) / 10631
+	l = l - 10631*n + 354
+	j := (10985-l)/5316*(50*l/17719) + (l/5670)*(43*l/15238)
+	l = l - (30-j)/15*(17719*j/50) - (j/16)*(15238*j/43) + 29
+	year = 30*n + j - 30
+	month = (24 * l) / 709
+	day = l - (709*month)/24
+	return
+}
+
+func ToISODate(t time.Time) string {
+	year, month, day := t.UTC().Date()
+	hYear, hMonth, hDay := GregorianToIslamic(year, int(month), day)
+	return fmt.Sprintf("%04d-%02d-%02d", hYear, hMonth, hDay)
+}

pkg/hijricalendar/calendar_test.go

@@ -0,0 +1,45 @@
+package hijricalendar
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestToISODate(t *testing.T) {
+	tests := []struct {
+		name string
+		date time.Time
+		want string
+	}{
+		{
+			name: "ramadan 3 1447",
+			date: time.Date(2026, 2, 20, 0, 0, 0, 0, time.UTC),
+			want: "1447-09-03",
+		},
+		{
+			name: "ramadan 1 1447",
+			date: time.Date(2026, 2, 18, 0, 0, 0, 0, time.UTC),
+			want: "1447-09-01",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ToISODate(tt.date)
+			require.NotEmpty(t, got)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func TestGregorianToIslamicRange(t *testing.T) {
+	y, m, d := GregorianToIslamic(2026, 2, 20)
+	assert.Positive(t, y)
+	assert.GreaterOrEqual(t, m, 1)
+	assert.LessOrEqual(t, m, 12)
+	assert.GreaterOrEqual(t, d, 1)
+	assert.LessOrEqual(t, d, 30)
+}