Add builder for file locator

Signed-off-by: Evan Lezar <elezar@nvidia.com>

internal/lookup/file.go

@@ -31,49 +31,55 @@ var ErrNotFound = errors.New("not found")
 // file can be used to locate file (or file-like elements) at a specified set of
 // prefixes. The validity of a file is determined by a filter function.
 type file struct {
-	logger     logger.Interface
-	root       string
-	prefixes   []string
-	filter     func(string) error
-	count      int
-	isOptional bool
+	builder
+	prefixes []string
 }
 
-// Option defines a function for passing options to the NewFileLocator() call
-type Option func(*file)
+// builder defines the builder for a file locator.
+type builder struct {
+	logger      logger.Interface
+	root        string
+	searchPaths []string
+	filter      func(string) error
+	count       int
+	isOptional  bool
+}
+
+// Option defines a function for passing builder to the NewFileLocator() call
+type Option func(*builder)
 
 // WithRoot sets the root for the file locator
 func WithRoot(root string) Option {
-	return func(f *file) {
+	return func(f *builder) {
 		f.root = root
 	}
 }
 
 // WithLogger sets the logger for the file locator
 func WithLogger(logger logger.Interface) Option {
-	return func(f *file) {
+	return func(f *builder) {
 		f.logger = logger
 	}
 }
 
 // WithSearchPaths sets the search paths for the file locator.
 func WithSearchPaths(paths ...string) Option {
-	return func(f *file) {
-		f.prefixes = paths
+	return func(f *builder) {
+		f.searchPaths = paths
 	}
 }
 
 // WithFilter sets the filter for the file locator
 // The filter is called for each candidate file and candidates that return nil are considered.
 func WithFilter(assert func(string) error) Option {
-	return func(f *file) {
+	return func(f *builder) {
 		f.filter = assert
 	}
 }
 
 // WithCount sets the maximum number of candidates to discover
 func WithCount(count int) Option {
-	return func(f *file) {
+	return func(f *builder) {
 		f.count = count
 	}
 }
@@ -81,32 +87,42 @@ func WithCount(count int) Option {
 // WithOptional sets the optional flag for the file locator
 // If the optional flag is set, the locator will not return an error if the file is not found.
 func WithOptional(optional bool) Option {
-	return func(f *file) {
+	return func(f *builder) {
 		f.isOptional = optional
 	}
 }
 
-// NewFileLocator creates a Locator that can be used to find files with the specified options.
+func newBuilder(opts ...Option) *builder {
+	o := &builder{}
+	for _, opt := range opts {
+		opt(o)
+	}
+	if o.logger == nil {
+		o.logger = logger.New()
+	}
+	if o.filter == nil {
+		o.filter = assertFile
+	}
+	return o
+}
+
+func (o builder) build() *file {
+	f := file{
+		builder: o,
+		// Since the `Locate` implementations rely on the root already being specified we update
+		// the prefixes to include the root.
+		prefixes: getSearchPrefixes(o.root, o.searchPaths...),
+	}
+	return &f
+}
+
+// NewFileLocator creates a Locator that can be used to find files with the specified builder.
 func NewFileLocator(opts ...Option) Locator {
 	return newFileLocator(opts...)
 }
 
 func newFileLocator(opts ...Option) *file {
-	f := &file{}
-	for _, opt := range opts {
-		opt(f)
-	}
-	if f.logger == nil {
-		f.logger = logger.New()
-	}
-	if f.filter == nil {
-		f.filter = assertFile
-	}
-	// Since the `Locate` implementations rely on the root already being specified we update
-	// the prefixes to include the root.
-	f.prefixes = getSearchPrefixes(f.root, f.prefixes...)
-
-	return f
+	return newBuilder(opts...).build()
 }
 
 // getSearchPrefixes generates a list of unique paths to be searched by a file locator.