output: Move layout logic to the output package

output/layout.go

@@ -0,0 +1,85 @@
+// Copyright 2017-present 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 output
+
+import (
+	"fmt"
+	"path"
+	"strings"
+)
+
+type LayoutIdentifier interface {
+	PageType() string
+	PageSection() string // TODO(bep) name
+	PageKind() string
+	PageLayout() string
+}
+
+// Layout calculates the layout template to use to render a given output type.
+// TODO(bep) output improve names
+type Layout struct {
+}
+
+// TODO(bep) output theme layouts
+var (
+	layoutsHome        = "index.html _default/list.html"
+	layoutsSection     = "section/SECTION.html  SECTION/list.html _default/section.html _default/list.html indexes/SECTION.html _default/indexes.html"
+	layoutTaxonomy     = "taxonomy/SECTION.html indexes/SECTION.html _default/taxonomy.html _default/list.html"
+	layoutTaxonomyTerm = "taxonomy/SECTION.terms.html _default/terms.html indexes/indexes.html"
+)
+
+func (l *Layout) For(id LayoutIdentifier, tp Type) []string {
+	var layouts []string
+
+	switch id.PageKind() {
+	// TODO(bep) move the Kind constants some common place.
+	case "home":
+		layouts = strings.Fields(layoutsHome)
+	case "section":
+		layouts = strings.Fields(strings.Replace(layoutsSection, "SECTION", id.PageSection(), -1))
+	case "taxonomy":
+		layouts = strings.Fields(strings.Replace(layoutTaxonomy, "SECTION", id.PageSection(), -1))
+	case "taxonomyTerm":
+		layouts = strings.Fields(strings.Replace(layoutTaxonomyTerm, "SECTION", id.PageSection(), -1))
+	case "page":
+		layouts = regularPageLayouts(id.PageType(), id.PageLayout())
+	}
+
+	for _, l := range layouts {
+		layouts = append(layouts, "theme/"+l)
+	}
+
+	return layouts
+}
+
+func regularPageLayouts(types string, layout string) (layouts []string) {
+	if layout == "" {
+		layout = "single"
+	}
+
+	if types != "" {
+		t := strings.Split(types, "/")
+
+		// Add type/layout.html
+		for i := range t {
+			search := t[:len(t)-i]
+			layouts = append(layouts, fmt.Sprintf("%s/%s.html", strings.ToLower(path.Join(search...)), layout))
+		}
+	}
+
+	// Add _default/layout.html
+	layouts = append(layouts, fmt.Sprintf("_default/%s.html", layout))
+
+	return
+}