refactor: clean up solution to part 1 on day 2

cmd/02/rnge/rnge.go

@@ -0,0 +1,67 @@
+// Package rnge provides a simple structure to represent a range with a start and end value.
+package rnge
+
+import (
+	"iter"
+	"strconv"
+	"strings"
+)
+
+const RangeSeparatorCharacter = "-"
+
+type Range interface {
+	InvalidIds() iter.Seq[int64]
+	Start() int64
+	End() int64
+}
+
+type rnge struct {
+	start int64
+	end   int64
+}
+
+func From(rngeStr string) Range {
+	parts := strings.Split(strings.TrimSpace(rngeStr), RangeSeparatorCharacter)
+	start, _ := strconv.ParseInt(parts[0], 10, 64)
+	end, _ := strconv.ParseInt(parts[1], 10, 64)
+
+	return rnge{
+		start: start,
+		end:   end,
+	}
+}
+
+func (r rnge) Start() int64 {
+	return r.start
+}
+
+func (r rnge) End() int64 {
+	return r.end
+}
+
+func (r rnge) InvalidIds() iter.Seq[int64] {
+	return func(yield func(int64) bool) {
+		for id := r.start; id <= r.end; id++ {
+			idStr := strconv.FormatInt(id, 10)
+			idLength := len(idStr)
+
+			if idLength%2 != 0 {
+				continue
+			}
+
+			midpoint := idLength / 2
+			firstHalf := idStr[:midpoint]
+			secondHalf := idStr[midpoint:]
+
+			if firstHalf != secondHalf {
+				continue
+			}
+
+			ok := yield(id)
+
+			if !ok {
+				return
+			}
+		}
+	}
+}