Moved logic of collapsing songs into albums to model package

(it should really be called domain.... maybe will rename it later)

utils/slice/slice.go

@@ -0,0 +1,35 @@
+package slice
+
+func Group[T any, K comparable](s []T, keyFunc func(T) K) map[K][]T {
+	m := map[K][]T{}
+	for _, item := range s {
+		k := keyFunc(item)
+		m[k] = append(m[k], item)
+	}
+	return m
+}
+
+func MostFrequent[T comparable](list []T) T {
+	if len(list) == 0 {
+		var zero T
+		return zero
+	}
+	var topItem T
+	var topCount int
+	counters := map[T]int{}
+
+	if len(list) == 1 {
+		topItem = list[0]
+	} else {
+		for _, id := range list {
+			c := counters[id] + 1
+			counters[id] = c
+			if c > topCount {
+				topItem = id
+				topCount = c
+			}
+		}
+	}
+
+	return topItem
+}