Add configurable sequence numbering command

internal/sequence/options.go

@@ -0,0 +1,95 @@
+package sequence
+
+import (
+	"errors"
+	"fmt"
+	"path/filepath"
+	"strings"
+)
+
+// Placement controls where a sequence number is inserted.
+type Placement string
+
+const (
+	// PlacementSuffix appends the sequence number after the filename stem.
+	PlacementSuffix Placement = "suffix"
+	// PlacementPrefix inserts the sequence number before the filename stem.
+	PlacementPrefix Placement = "prefix"
+)
+
+// Options captures configuration for numbering operations.
+type Options struct {
+	WorkingDir         string
+	Start              int
+	Width              int
+	WidthSet           bool
+	NumberPrefix       string
+	NumberSuffix       string
+	Placement          Placement
+	Separator          string
+	IncludeHidden      bool
+	IncludeDirectories bool
+	Recursive          bool
+	Extensions         []string
+	DryRun             bool
+	AutoApply          bool
+}
+
+// DefaultOptions returns a copy of the default configuration.
+func DefaultOptions() Options {
+	return Options{
+		Start:     1,
+		Width:     3,
+		Placement: PlacementPrefix,
+		Separator: "_",
+	}
+}
+
+func validateOptions(opts *Options) error {
+	if opts == nil {
+		return errors.New("options cannot be nil")
+	}
+
+	if opts.WorkingDir == "" {
+		return errors.New("working directory must be provided")
+	}
+
+	abs, err := filepath.Abs(opts.WorkingDir)
+	if err != nil {
+		return fmt.Errorf("resolve working directory: %w", err)
+	}
+	opts.WorkingDir = abs
+
+	if opts.Start < 1 {
+		return errors.New("start must be >= 1")
+	}
+
+	if opts.Width < 0 {
+		return errors.New("width cannot be negative")
+	}
+	if opts.WidthSet && opts.Width < 1 {
+		return errors.New("width must be >= 1 when specified")
+	}
+
+	switch opts.Placement {
+	case PlacementPrefix, PlacementSuffix:
+		// ok
+	case "":
+		opts.Placement = PlacementSuffix
+	default:
+		return fmt.Errorf("unsupported placement %q", opts.Placement)
+	}
+
+	if strings.ContainsAny(opts.Separator, "/\\") {
+		return errors.New("separator cannot contain path separators")
+	}
+
+	if strings.ContainsAny(opts.NumberPrefix, "/\\") {
+		return errors.New("number prefix cannot contain path separators")
+	}
+	if strings.ContainsAny(opts.NumberSuffix, "/\\") {
+		return errors.New("number suffix cannot contain path separators")
+	}
+
+	return nil
+}