Generate navigation links

Sources/Generator/Content/Element+LocalizedMetadata.swift

@@ -126,6 +126,20 @@ extension Element {
          This property is mandatory at root level, and is propagated to child elements.
          */
         let relatedContentText: String
+
+        /**
+         The text to display on the navigation element pointing to this element as the next page.
+
+         This property is mandatory at root level, and is propagated to child elements.
+         */
+        let navigationTextAsNextPage: String
+
+        /**
+         The text to display on a navigation element pointing to this element as the previous page.
+
+         This property is mandatory at root level, and is propagated to child elements.
+         */
+        let navigationTextAsPreviousPage: String
     }
 }
 
@@ -171,6 +185,10 @@ extension Element.LocalizedMetadata {
         self.externalUrl = log.unexpected(data.externalUrl, name: "externalUrl", source: source)
         self.relatedContentText = log
             .required(data.relatedContentText, name: "relatedContentText", source: source) ?? ""
+        self.navigationTextAsNextPage = log
+            .required(data.navigationTextAsNextPage, name: "navigationTextAsNextPage", source: source) ?? ""
+        self.navigationTextAsPreviousPage = log
+            .required(data.navigationTextAsPreviousPage, name: "navigationTextAsPreviousPage", source: source) ?? ""
 
         guard isComplete else {
             return nil
@@ -207,6 +225,8 @@ extension Element.LocalizedMetadata {
         self.cornerText = data.cornerText
         self.externalUrl = data.externalUrl
         self.relatedContentText = data.relatedContentText ?? parent.relatedContentText
+        self.navigationTextAsPreviousPage = data.navigationTextAsPreviousPage ?? parent.navigationTextAsPreviousPage
+        self.navigationTextAsNextPage = data.navigationTextAsNextPage ?? parent.navigationTextAsNextPage
 
         guard isComplete else {
             return nil

Sources/Generator/Content/Element.swift

@@ -310,6 +310,15 @@ extension Element {
         elements.filter { $0.state.isShownInOverview }
     }
 
+    var linkedElements: [LinkedElement] {
+        let items = sortedItems
+        return items.enumerated().map { i, element in
+            let previous = i+1 < items.count ? items[i+1] : nil
+            let next = i > 0 ? items[i-1] : nil
+            return (previous, element, next)
+        }
+    }
+
     /**
      The url of the top-level section of the element.
      */

Sources/Generator/Content/GenericMetadata+Localized.swift

@@ -119,6 +119,20 @@ extension GenericMetadata {
          This property is mandatory at root level, and is propagated to child elements.
          */
         let relatedContentText: String?
+
+        /**
+         The text to display on a navigation element pointing to this element as the previous page.
+
+         This property is mandatory at root level, and is propagated to child elements.
+         */
+        let navigationTextAsPreviousPage: String?
+
+        /**
+         The text to display on the navigation element pointing to this element as the next page.
+
+         This property is mandatory at root level, and is propagated to child elements.
+         */
+        let navigationTextAsNextPage: String?
     }
 }
 
@@ -142,6 +156,8 @@ extension GenericMetadata.LocalizedMetadata: Codable {
             .cornerText,
             .externalUrl,
             .relatedContentText,
+            .navigationTextAsPreviousPage,
+            .navigationTextAsNextPage,
         ]
     }
 
@@ -172,7 +188,9 @@ extension GenericMetadata.LocalizedMetadata {
             thumbnailSuffix: nil,
             cornerText: nil,
             externalUrl: nil,
-            relatedContentText: nil)
+            relatedContentText: nil,
+            navigationTextAsPreviousPage: nil,
+            navigationTextAsNextPage: nil)
     }
 
     /**
@@ -194,7 +212,9 @@ extension GenericMetadata.LocalizedMetadata {
               thumbnailSuffix: nil,
               cornerText: nil,
               externalUrl: nil,
-              relatedContentText: "")
+              relatedContentText: "",
+              navigationTextAsPreviousPage: "",
+              navigationTextAsNextPage: "")
     }
 
     static var full: GenericMetadata.LocalizedMetadata {
@@ -213,6 +233,8 @@ extension GenericMetadata.LocalizedMetadata {
               thumbnailSuffix: "",
               cornerText: "",
               externalUrl: "",
-              relatedContentText: "")
+              relatedContentText: "",
+              navigationTextAsPreviousPage: "",
+              navigationTextAsNextPage: "")
     }
 }