Add go/twelve-days

go/twelve-days/twelve-days.go

@@ -0,0 +1,72 @@
+// Package twelve outputs the lyrics to The Twelve Days of Christmas.
+package twelve
+
+import (
+	"fmt"
+)
+
+var ordinals = [13]string{
+	"zeroth",
+	"first",
+	"second",
+	"third",
+	"fourth",
+	"fifth",
+	"sixth",
+	"seventh",
+	"eighth",
+	"ninth",
+	"tenth",
+	"eleventh",
+	"twelfth",
+}
+
+var gifts = [13]string{
+	"a null pointer",
+	"a Partridge in a Pear Tree",
+	"two Turtle Doves",
+	"three French Hens",
+	"four Calling Birds",
+	"five Gold Rings",
+	"six Geese-a-Laying",
+	"seven Swans-a-Swimming",
+	"eight Maids-a-Milking",
+	"nine Ladies Dancing",
+	"ten Lords-a-Leaping",
+	"eleven Pipers Piping",
+	"twelve Drummers Drumming",
+}
+
+func giftsForDay(day int) string {
+	switch day {
+	case 0, 1:
+		return gifts[day]
+	case 2:
+		return fmt.Sprintf(
+			"%s, and %s",
+			gifts[day],
+			gifts[day-1],
+		)
+	default:
+		return fmt.Sprintf(
+			"%s, %s",
+			gifts[day],
+			giftsForDay(day-1),
+		)
+	}
+}
+
+func Verse(day int) string {
+	return fmt.Sprintf(
+		"On the %s day of Christmas my true love gave to me: %s.",
+		ordinals[day],
+		giftsForDay(day),
+	)
+}
+
+func Song() (song string) {
+	for day := 1; day <= 12; day++ {
+		song += fmt.Sprintf("%s\n", Verse(day))
+	}
+	return
+}