parser/metadecoders: Consolidate the metadata decoders

See #5324

parser/metadecoders/format.go

@@ -0,0 +1,66 @@
+// Copyright 2018 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metadecoders
+
+import (
+	"strings"
+
+	"github.com/gohugoio/hugo/parser/pageparser"
+)
+
+type Format string
+
+const (
+	// These are the supported metdata  formats in Hugo. Most of these are also
+	// supported as /data formats.
+	ORG  Format = "org"
+	JSON Format = "json"
+	TOML Format = "toml"
+	YAML Format = "yaml"
+)
+
+// FormatFromString turns formatStr, typically a file extension without any ".",
+// into a Format. It returns an empty string for unknown formats.
+func FormatFromString(formatStr string) Format {
+	formatStr = strings.ToLower(formatStr)
+	switch formatStr {
+	case "yaml", "yml":
+		return YAML
+	case "json":
+		return JSON
+	case "toml":
+		return TOML
+	case "org":
+		return ORG
+	}
+
+	return ""
+
+}
+
+// FormatFromFrontMatterType will return empty if not supported.
+func FormatFromFrontMatterType(typ pageparser.ItemType) Format {
+	switch typ {
+	case pageparser.TypeFrontMatterJSON:
+		return JSON
+	case pageparser.TypeFrontMatterORG:
+		return ORG
+	case pageparser.TypeFrontMatterTOML:
+		return TOML
+	case pageparser.TypeFrontMatterYAML:
+		return YAML
+	default:
+		return ""
+	}
+}