rename scope to source

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

syft/source/scheme.go

@@ -0,0 +1,55 @@
+package source
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/anchore/stereoscope/pkg/image"
+	"github.com/mitchellh/go-homedir"
+	"github.com/spf13/afero"
+)
+
+type Scheme string
+
+const (
+	UnknownScheme   Scheme = "unknown-scheme"
+	DirectoryScheme Scheme = "directory-scheme"
+	ImageScheme     Scheme = "image-scheme"
+)
+
+func detectScheme(fs afero.Fs, imageDetector sourceDetector, userInput string) (Scheme, string, error) {
+	if strings.HasPrefix(userInput, "dir:") {
+		// blindly trust the user's scheme
+		dirLocation, err := homedir.Expand(strings.TrimPrefix(userInput, "dir:"))
+		if err != nil {
+			return UnknownScheme, "", fmt.Errorf("unable to expand directory path: %w", err)
+		}
+		return DirectoryScheme, dirLocation, nil
+	}
+
+	// we should attempt to let stereoscope determine what the source is first --just because the source is a valid directory
+	// doesn't mean we yet know if it is an OCI layout directory (to be treated as an image) or if it is a generic filesystem directory.
+	source, imageSpec, err := imageDetector(userInput)
+	if err != nil {
+		return UnknownScheme, "", fmt.Errorf("unable to detect the scheme from %q: %w", userInput, err)
+	}
+
+	if source == image.UnknownSource {
+		dirLocation, err := homedir.Expand(userInput)
+		if err != nil {
+			return UnknownScheme, "", fmt.Errorf("unable to expand potential directory path: %w", err)
+		}
+
+		fileMeta, err := fs.Stat(dirLocation)
+		if err != nil {
+			return UnknownScheme, "", nil
+		}
+
+		if fileMeta.IsDir() {
+			return DirectoryScheme, dirLocation, nil
+		}
+		return UnknownScheme, "", nil
+	}
+
+	return ImageScheme, imageSpec, nil
+}