Create pkg/jsonnetfile to better encapsulate jsonnetfile things

pkg/jsonnetfile/jsonnetfile.go

@@ -0,0 +1,66 @@
+package jsonnetfile
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"os"
+	"path"
+
+	"github.com/jsonnet-bundler/jsonnet-bundler/spec"
+	"github.com/pkg/errors"
+)
+
+const File = "jsonnetfile.json"
+const LockFile = "jsonnetfile.lock.json"
+
+var ErrNoFile = errors.New("no jsonnetfile")
+
+func Choose(dir string) (string, bool, error) {
+	jsonnetfileLock := path.Join(dir, LockFile)
+	jsonnetfile := path.Join(dir, File)
+
+	lockExists, err := fileExists(jsonnetfileLock)
+	if err != nil {
+		return "", false, err
+	}
+	if lockExists {
+		return jsonnetfileLock, true, nil
+	}
+
+	fileExists, err := fileExists(jsonnetfile)
+	if err != nil {
+		return "", false, err
+	}
+	if fileExists {
+		return jsonnetfile, false, nil
+	}
+
+	return "", false, ErrNoFile
+}
+
+func Load(filepath string) (spec.JsonnetFile, error) {
+	m := spec.JsonnetFile{}
+
+	bytes, err := ioutil.ReadFile(filepath)
+	if err != nil {
+		return m, errors.Wrap(err, "failed to read file")
+	}
+
+	if err := json.Unmarshal(bytes, &m); err != nil {
+		return m, errors.Wrap(err, "failed to unmarshal file")
+	}
+
+	return m, nil
+}
+
+func fileExists(path string) (bool, error) {
+	_, err := os.Stat(path)
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	if err != nil {
+		return false, err
+	}
+
+	return true, nil
+}