Move code out of cmd

day2/range.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+type idRange struct {
+	from, to uint
+}
+
+func readRanges(r io.Reader) ([]idRange, error) {
+	sc := bufio.NewScanner(r)
+	sc.Split(scanSimpleCSV)
+
+	var ranges []idRange
+	for sc.Scan() {
+		before, after, ok := strings.Cut(sc.Text(), "-")
+		if !ok {
+			return nil, fmt.Errorf("range %q: missing dash", sc.Text())
+		}
+		from, err := strconv.ParseUint(before, 10, 0)
+		if err != nil {
+			return nil, fmt.Errorf("range %q: %w", sc.Text(), err)
+		}
+		to, err := strconv.ParseUint(after, 10, 0)
+		if err != nil {
+			return nil, fmt.Errorf("range %q: %w", sc.Text(), err)
+		}
+		if from > to {
+			return nil, fmt.Errorf("range %q: refers from higher to lower", sc.Text())
+		}
+		ranges = append(ranges, idRange{
+			from: uint(from),
+			to:   uint(to),
+		})
+	}
+	return ranges, sc.Err()
+}
+
+func scanSimpleCSV(data []byte, atEOF bool) (advance int, token []byte, err error) {
+	if atEOF && len(data) == 0 {
+		return 0, nil, nil
+	}
+	if i := bytes.IndexByte(data, ','); i >= 0 {
+		return i + 1, data[:i], nil
+	}
+	if atEOF {
+		if trimmed, ok := bytes.CutSuffix(data, []byte("\r\n")); ok {
+			return len(data), trimmed, nil
+		}
+		if trimmed, ok := bytes.CutSuffix(data, []byte{'\n'}); ok {
+			return len(data), trimmed, nil
+		}
+		return len(data), data, nil
+	}
+	return 0, nil, nil
+}