Add an unified .Site.Config with a services section

Fixes #4751

config/services/servicesConfig.go

@@ -0,0 +1,61 @@
+// 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 services
+
+import (
+	"github.com/gohugoio/hugo/config"
+	"github.com/mitchellh/mapstructure"
+)
+
+const (
+	servicesConfigKey = "services"
+
+	disqusShortnameKey = "disqusshortname"
+	googleAnalyticsKey = "googleanalytics"
+)
+
+// Config is a privacy configuration for all the relevant services in Hugo.
+type Config struct {
+	Disqus          Disqus
+	GoogleAnalytics GoogleAnalytics
+}
+
+// Disqus holds the functional configuration settings related to the Disqus template.
+type Disqus struct {
+	// A Shortname is the unique identifier assigned to a Disqus site.
+	Shortname string
+}
+
+// GoogleAnalytics holds the functional configuration settings related to the Google Analytics template.
+type GoogleAnalytics struct {
+	// The GA tracking ID.
+	ID string
+}
+
+func DecodeConfig(cfg config.Provider) (c Config, err error) {
+	m := cfg.GetStringMap(servicesConfigKey)
+
+	err = mapstructure.WeakDecode(m, &c)
+
+	// Keep backwards compability.
+	if c.GoogleAnalytics.ID == "" {
+		// Try the global config
+		c.GoogleAnalytics.ID = cfg.GetString(googleAnalyticsKey)
+	}
+	if c.Disqus.Shortname == "" {
+		c.Disqus.Shortname = cfg.GetString(disqusShortnameKey)
+	}
+
+	return
+}