feat: add replace subcommand with multi-pattern support

internal/replace/summary.go

@@ -0,0 +1,80 @@
+package replace
+
+import "sort"
+
+// ConflictDetail describes a rename that could not be applied.
+type ConflictDetail struct {
+	OriginalPath string
+	ProposedPath string
+	Reason       string
+}
+
+// Summary aggregates metrics for previews, applies, and ledger entries.
+type Summary struct {
+	TotalCandidates  int
+	ChangedCount     int
+	PatternMatches   map[string]int
+	Conflicts        []ConflictDetail
+	Duplicates       []string
+	EmptyReplacement bool
+}
+
+// NewSummary constructs an initialized summary.
+func NewSummary() Summary {
+	return Summary{
+		PatternMatches: make(map[string]int),
+	}
+}
+
+// AddDuplicate records a duplicate pattern supplied by the user.
+func (s *Summary) AddDuplicate(pattern string) {
+	if pattern == "" {
+		return
+	}
+	s.Duplicates = append(s.Duplicates, pattern)
+}
+
+// AddResult incorporates an individual candidate replacement result.
+// RecordCandidate updates aggregate counts for a processed candidate and any matches.
+func (s *Summary) RecordCandidate(res Result) {
+	s.TotalCandidates++
+	if !res.Changed {
+		return
+	}
+	s.ChangedCount++
+	for pattern, count := range res.Matches {
+		s.PatternMatches[pattern] += count
+	}
+}
+
+// AddConflict appends a conflict detail to the summary.
+func (s *Summary) AddConflict(conflict ConflictDetail) {
+	s.Conflicts = append(s.Conflicts, conflict)
+}
+
+// SortedDuplicates returns de-duplicated duplicates list for reporting.
+func (s *Summary) SortedDuplicates() []string {
+	if len(s.Duplicates) == 0 {
+		return nil
+	}
+	copyList := make([]string, 0, len(s.Duplicates))
+	seen := make(map[string]struct{}, len(s.Duplicates))
+	for _, dup := range s.Duplicates {
+		if _, ok := seen[dup]; ok {
+			continue
+		}
+		seen[dup] = struct{}{}
+		copyList = append(copyList, dup)
+	}
+	sort.Strings(copyList)
+	return copyList
+}
+
+// ReplacementWasEmpty records whether the replacement string is empty and returns true.
+func (s *Summary) ReplacementWasEmpty(replacement string) bool {
+	if replacement == "" {
+		s.EmptyReplacement = true
+		return true
+	}
+	return false
+}