Add trim selector parsing

2026-05-08 14:41:47 +00:00
parent d865bda4a9
commit 2c82f8bf5c
2 changed files with 283 additions and 0 deletions
--- a/internal/trim/selector.go
+++ b/internal/trim/selector.go
@@ -0,0 +1,156 @@
+package trim
+
+import (
+	"fmt"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+var selectorElementPattern = regexp.MustCompile(`^([+-]?\d+)(?:\s*-\s*([+-]?\d+))?$`)
+
+// Selector represents a normalized union of segment IDs.
+type Selector struct {
+	ranges []idRange
+}
+
+type idRange struct {
+	start int
+	end   int
+}
+
+// ParseSelector parses an inline segment selector expression.
+func ParseSelector(input string) (Selector, error) {
+	if strings.TrimSpace(input) == "" {
+		return Selector{}, fmt.Errorf("selector cannot be empty")
+	}
+
+	parts := strings.Split(input, ",")
+	ranges := make([]idRange, 0, len(parts))
+	for index, raw := range parts {
+		element := strings.TrimSpace(raw)
+		if element == "" {
+			return Selector{}, fmt.Errorf("selector element %d cannot be empty", index+1)
+		}
+
+		rangeValue, err := parseElement(element)
+		if err != nil {
+			return Selector{}, fmt.Errorf("selector element %d %q: %w", index+1, element, err)
+		}
+		ranges = append(ranges, rangeValue)
+	}
+
+	normalized := normalizeRanges(ranges)
+	if len(normalized) == 0 {
+		return Selector{}, fmt.Errorf("selector cannot be empty")
+	}
+	return Selector{ranges: normalized}, nil
+}
+
+// Contains returns true when id is included by this selector.
+func (s Selector) Contains(id int) bool {
+	if id <= 0 {
+		return false
+	}
+	index := sort.Search(len(s.ranges), func(i int) bool {
+		return s.ranges[i].end >= id
+	})
+	if index == len(s.ranges) {
+		return false
+	}
+	rangeValue := s.ranges[index]
+	return id >= rangeValue.start && id <= rangeValue.end
+}
+
+// IDs returns a deterministic ascending list of unique segment IDs.
+func (s Selector) IDs() []int {
+	total := 0
+	for _, rangeValue := range s.ranges {
+		total += rangeValue.end - rangeValue.start + 1
+	}
+
+	ids := make([]int, 0, total)
+	for _, rangeValue := range s.ranges {
+		for id := rangeValue.start; id <= rangeValue.end; id++ {
+			ids = append(ids, id)
+		}
+	}
+	return ids
+}
+
+func parseElement(element string) (idRange, error) {
+	matches := selectorElementPattern.FindStringSubmatch(element)
+	if matches == nil {
+		return idRange{}, fmt.Errorf("malformed element")
+	}
+
+	start, err := parseID(matches[1])
+	if err != nil {
+		return idRange{}, err
+	}
+
+	if matches[2] == "" {
+		return idRange{start: start, end: start}, nil
+	}
+
+	end, err := parseID(matches[2])
+	if err != nil {
+		return idRange{}, fmt.Errorf("invalid range end: %w", err)
+	}
+	if start > end {
+		return idRange{}, fmt.Errorf("descending range %d-%d is invalid", start, end)
+	}
+	return idRange{start: start, end: end}, nil
+}
+
+func parseID(value string) (int, error) {
+	value = strings.TrimSpace(value)
+	if value == "" {
+		return 0, fmt.Errorf("missing segment ID")
+	}
+
+	id, err := strconv.Atoi(value)
+	if err != nil {
+		return 0, fmt.Errorf("segment ID must be an integer")
+	}
+	if id <= 0 {
+		return 0, fmt.Errorf("segment ID must be positive")
+	}
+	return id, nil
+}
+
+func normalizeRanges(in []idRange) []idRange {
+	if len(in) == 0 {
+		return nil
+	}
+
+	sorted := make([]idRange, len(in))
+	copy(sorted, in)
+	sort.Slice(sorted, func(i, j int) bool {
+		if sorted[i].start == sorted[j].start {
+			return sorted[i].end < sorted[j].end
+		}
+		return sorted[i].start < sorted[j].start
+	})
+
+	merged := make([]idRange, 0, len(sorted))
+	for _, next := range sorted {
+		if len(merged) == 0 {
+			merged = append(merged, next)
+			continue
+		}
+
+		last := &merged[len(merged)-1]
+		if next.start <= last.end+1 {
+			if next.end > last.end {
+				last.end = next.end
+			}
+			continue
+		}
+
+		merged = append(merged, next)
+	}
+
+	return merged
+}