Add regex command implementation

internal/regex/preview.go

@@ -0,0 +1,190 @@
+package regex
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// PlannedRename represents a proposed rename resulting from preview.
+type PlannedRename struct {
+	SourceRelative string
+	SourceAbsolute string
+	TargetRelative string
+	TargetAbsolute string
+	MatchGroups    []string
+	Depth          int
+}
+
+// Preview evaluates the regex rename request and returns a summary plus the planned operations.
+func Preview(ctx context.Context, req Request, out io.Writer) (Summary, []PlannedRename, error) {
+	reqCopy := req
+	if err := reqCopy.Validate(); err != nil {
+		return Summary{}, nil, err
+	}
+
+	engine, err := NewEngine(reqCopy.Pattern, reqCopy.Template)
+	if err != nil {
+		return Summary{}, nil, err
+	}
+
+	summary := Summary{
+		LedgerMetadata: map[string]any{
+			"pattern":  reqCopy.Pattern,
+			"template": reqCopy.Template,
+		},
+		Entries: make([]PreviewEntry, 0),
+	}
+
+	planned := make([]PlannedRename, 0)
+	plannedTargets := make(map[string]string)
+	plannedTargetsFold := make(map[string]string)
+
+	err = TraverseCandidates(ctx, &reqCopy, func(candidate Candidate) error {
+		summary.TotalCandidates++
+
+		rendered, groups, matched, err := engine.Apply(candidate.Stem)
+		if err != nil {
+			summary.Warnings = append(summary.Warnings, err.Error())
+			summary.Skipped++
+			summary.Entries = append(summary.Entries, PreviewEntry{
+				OriginalPath: candidate.RelativePath,
+				ProposedPath: candidate.RelativePath,
+				Status:       EntrySkipped,
+			})
+			return nil
+		}
+
+		if !matched {
+			summary.Skipped++
+			summary.Entries = append(summary.Entries, PreviewEntry{
+				OriginalPath: candidate.RelativePath,
+				ProposedPath: candidate.RelativePath,
+				Status:       EntrySkipped,
+			})
+			return nil
+		}
+
+		summary.Matched++
+
+		proposedName := rendered
+		if !candidate.IsDir && candidate.Extension != "" {
+			proposedName += candidate.Extension
+		}
+
+		dir := filepath.Dir(candidate.RelativePath)
+		if dir == "." {
+			dir = ""
+		}
+
+		var proposedRelative string
+		if dir != "" {
+			proposedRelative = filepath.ToSlash(filepath.Join(dir, proposedName))
+		} else {
+			proposedRelative = filepath.ToSlash(proposedName)
+		}
+
+		matchEntry := PreviewEntry{
+			OriginalPath: candidate.RelativePath,
+			ProposedPath: proposedRelative,
+			MatchGroups:  groups,
+		}
+
+		if proposedRelative == candidate.RelativePath {
+			summary.Entries = append(summary.Entries, PreviewEntry{
+				OriginalPath: candidate.RelativePath,
+				ProposedPath: candidate.RelativePath,
+				Status:       EntryNoChange,
+				MatchGroups:  groups,
+			})
+			return nil
+		}
+
+		if proposedName == "" || proposedRelative == "" {
+			summary.Conflicts = append(summary.Conflicts, Conflict{
+				OriginalPath: candidate.RelativePath,
+				ProposedPath: proposedRelative,
+				Reason:       ConflictInvalidTemplate,
+			})
+			summary.Skipped++
+			matchEntry.Status = EntrySkipped
+			summary.Entries = append(summary.Entries, matchEntry)
+			return nil
+		}
+
+		if existing, ok := plannedTargets[proposedRelative]; ok && existing != candidate.RelativePath {
+			summary.Conflicts = append(summary.Conflicts, Conflict{
+				OriginalPath: candidate.RelativePath,
+				ProposedPath: proposedRelative,
+				Reason:       ConflictDuplicateTarget,
+			})
+			summary.Skipped++
+			matchEntry.Status = EntrySkipped
+			summary.Entries = append(summary.Entries, matchEntry)
+			return nil
+		}
+
+		casefoldKey := strings.ToLower(proposedRelative)
+		if existing, ok := plannedTargetsFold[casefoldKey]; ok && existing != candidate.RelativePath {
+			summary.Conflicts = append(summary.Conflicts, Conflict{
+				OriginalPath: candidate.RelativePath,
+				ProposedPath: proposedRelative,
+				Reason:       ConflictDuplicateTarget,
+			})
+			summary.Skipped++
+			matchEntry.Status = EntrySkipped
+			summary.Entries = append(summary.Entries, matchEntry)
+			return nil
+		}
+
+		targetAbsolute := filepath.Join(reqCopy.WorkingDir, filepath.FromSlash(proposedRelative))
+		if info, statErr := os.Stat(targetAbsolute); statErr == nil {
+			origInfo, origErr := os.Stat(candidate.OriginalPath)
+			if origErr != nil || !os.SameFile(info, origInfo) {
+				reason := ConflictExistingFile
+				if info.IsDir() {
+					reason = ConflictExistingDir
+				}
+				summary.Conflicts = append(summary.Conflicts, Conflict{
+					OriginalPath: candidate.RelativePath,
+					ProposedPath: proposedRelative,
+					Reason:       reason,
+				})
+				summary.Skipped++
+				matchEntry.Status = EntrySkipped
+				summary.Entries = append(summary.Entries, matchEntry)
+				return nil
+			}
+		}
+
+		plannedTargets[proposedRelative] = candidate.RelativePath
+		plannedTargetsFold[casefoldKey] = candidate.RelativePath
+
+		matchEntry.Status = EntryChanged
+		summary.Entries = append(summary.Entries, matchEntry)
+		summary.Changed++
+
+		planned = append(planned, PlannedRename{
+			SourceRelative: candidate.RelativePath,
+			SourceAbsolute: candidate.OriginalPath,
+			TargetRelative: proposedRelative,
+			TargetAbsolute: targetAbsolute,
+			MatchGroups:    groups,
+			Depth:          candidate.Depth,
+		})
+
+		if out != nil {
+			fmt.Fprintf(out, "%s -> %s\n", candidate.RelativePath, proposedRelative)
+		}
+
+		return nil
+	})
+	if err != nil {
+		return Summary{}, nil, err
+	}
+
+	return summary, planned, nil
+}