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: "")
     }
 }

Sources/Generator/Generators/PageGenerator.swift

@@ -3,20 +3,13 @@ import Ink
 
 struct PageGenerator {
 
-    struct NavigationLink {
-
-        let link: String
-
-        let text: String
-    }
-
     private let factory: LocalizedSiteTemplate
 
     init(factory: LocalizedSiteTemplate) {
         self.factory = factory
     }
 
-    func generate(page: Element, language: String, nextPage: NavigationLink?, previousPage: NavigationLink?) {
+    func generate(page: Element, language: String, previousPage: Element?, nextPage: Element?) {
         guard !page.isExternalPage else {
             return
         }
@@ -35,10 +28,10 @@ struct PageGenerator {
 
         content[.header] = makeHeader(page: page, metadata: metadata, language: language)
         content[.content] = pageContent
-        content[.previousPageLinkText] = previousPage.unwrapped { factory.factory.html.makePrevText($0.text) }
-        content[.previousPageUrl] = previousPage?.link
-        content[.nextPageLinkText] = nextPage.unwrapped { factory.factory.html.makeNextText($0.text) }
-        content[.nextPageUrl] = nextPage?.link
+        content[.previousPageLinkText] = previousText(for: previousPage, language: language)
+        content[.previousPageUrl] = navLink(from: page, to: previousPage, language: language)
+        content[.nextPageLinkText] = nextText(for: nextPage, language: language)
+        content[.nextPageUrl] = navLink(from: page, to: nextPage, language: language)
         content[.footer] = page.customFooterContent()
 
         if pageIncludesCode {
@@ -58,6 +51,27 @@ struct PageGenerator {
         files.generated(page: path)
     }
 
+    private func navLink(from element: Element, to destination: Element?, language: String) -> String? {
+        guard let fullPath = destination?.fullPageUrl(for: language) else {
+            return nil
+        }
+        return element.relativePathToOtherSiteElement(file: fullPath)
+    }
+
+    private func previousText(for element: Element?, language: String) -> String? {
+        guard let text = element?.localized(for: language).navigationTextAsPreviousPage else {
+            return nil
+        }
+        return factory.factory.html.makePrevText(text)
+    }
+
+    private func nextText(for element: Element?, language: String) -> String? {
+        guard let text = element?.localized(for: language).navigationTextAsNextPage else {
+            return nil
+        }
+        return factory.factory.html.makeNextText(text)
+    }
+
     private func makeContent(page: Element, metadata: Element.LocalizedMetadata, language: String, path: String) -> (content: String, includesCode: Bool, isEmpty: Bool) {
         let create = configuration.createMdFilesIfMissing
         if let raw = files.contentOfOptionalFile(atPath: path, source: page.path, createEmptyFileIfMissing: create)?

Sources/Generator/Generators/SiteGenerator.swift

@@ -1,5 +1,7 @@
 import Foundation
 
+typealias LinkedElement = (previous: Element?, element: Element, next: Element?)
+
 struct SiteGenerator {
 
     let templates: TemplateFactory
@@ -26,22 +28,21 @@ struct SiteGenerator {
         let overviewGenerator = OverviewPageGenerator(factory: template)
         let pageGenerator = PageGenerator(factory: template)
         
-        var elementsToProcess: [Element] = [site]
-        while let element = elementsToProcess.popLast() {
+        var elementsToProcess: [LinkedElement] = [(nil, site, nil)]
+        while let (previous, element, next) = elementsToProcess.popLast() {
             // Move recursively down to all pages
-            elementsToProcess.append(contentsOf: element.elements)
+            elementsToProcess.append(contentsOf: element.linkedElements)
 
             processAllFiles(for: element)
 
             if !element.elements.isEmpty {
                 overviewGenerator.generate(section: element, language: language)
             } else {
-                #warning("Determine previous and next pages (with relative links)")
                 pageGenerator.generate(
                     page: element,
                     language: language,
-                    nextPage: nil,
-                    previousPage: nil)
+                    previousPage: previous,
+                    nextPage: next)
             }
         }
     }