Add extension normalization command

internal/extension/preview.go

@@ -0,0 +1,92 @@
+package extension
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"sort"
+	"strings"
+)
+
+// Preview generates a summary and planned operations for an extension normalization run.
+func Preview(ctx context.Context, req *ExtensionRequest, out io.Writer) (*ExtensionSummary, []PlannedRename, error) {
+	if req == nil {
+		return nil, nil, errors.New("extension request cannot be nil")
+	}
+
+	plan, err := BuildPlan(ctx, req)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	summary := plan.Summary
+
+	for _, dup := range req.DuplicateSources {
+		summary.AddWarning(fmt.Sprintf("duplicate source extension ignored: %s", dup))
+	}
+	for _, noop := range req.NoOpSources {
+		summary.AddWarning(fmt.Sprintf("source extension matches target and is skipped: %s", noop))
+	}
+
+	if summary.TotalCandidates == 0 {
+		summary.AddWarning("no candidates found for provided extensions")
+	}
+
+	if out != nil {
+		// Ensure deterministic ordering for preview output.
+		sort.SliceStable(summary.Entries, func(i, j int) bool {
+			if summary.Entries[i].OriginalPath == summary.Entries[j].OriginalPath {
+				return summary.Entries[i].ProposedPath < summary.Entries[j].ProposedPath
+			}
+			return summary.Entries[i].OriginalPath < summary.Entries[j].OriginalPath
+		})
+
+		conflictReasons := make(map[string]string, len(summary.Conflicts))
+		for _, conflict := range summary.Conflicts {
+			key := fmt.Sprintf("%s->%s", conflict.OriginalPath, conflict.ProposedPath)
+			conflictReasons[key] = conflict.Reason
+		}
+
+		for _, entry := range summary.Entries {
+			switch entry.Status {
+			case PreviewStatusChanged:
+				if entry.ProposedPath == entry.OriginalPath {
+					fmt.Fprintf(out, "%s (pending extension update)\n", entry.OriginalPath)
+				} else {
+					fmt.Fprintf(out, "%s -> %s\n", entry.OriginalPath, entry.ProposedPath)
+				}
+			case PreviewStatusNoChange:
+				fmt.Fprintf(out, "%s (no change)\n", entry.OriginalPath)
+			case PreviewStatusSkipped:
+				reason := conflictReasons[fmt.Sprintf("%s->%s", entry.OriginalPath, entry.ProposedPath)]
+				if reason == "" {
+					reason = "skipped"
+				}
+				fmt.Fprintf(out, "%s -> %s (skipped: %s)\n", entry.OriginalPath, entry.ProposedPath, reason)
+			default:
+				fmt.Fprintf(out, "%s (status: %s)\n", entry.OriginalPath, entry.Status)
+			}
+		}
+
+		if summary.TotalCandidates > 0 {
+			fmt.Fprintf(out, "\nSummary: %d candidates, %d will change, %d already target extension\n",
+				summary.TotalCandidates, summary.TotalChanged, summary.NoChange)
+		} else {
+			fmt.Fprintln(out, "No candidates found.")
+		}
+
+		if len(summary.Warnings) > 0 {
+			fmt.Fprintln(out)
+			for _, warning := range summary.Warnings {
+				if !strings.HasPrefix(strings.ToLower(warning), "warning:") {
+					fmt.Fprintf(out, "Warning: %s\n", warning)
+				} else {
+					fmt.Fprintln(out, warning)
+				}
+			}
+		}
+	}
+
+	return summary, plan.Operations, nil
+}