consolidate tags, hide date

CHDataManagement/Model/Post.swift

@@ -17,6 +17,12 @@ final class Post: Item {
     @Published
     var endDate: Date
 
+    /**
+     The tags associated with the post
+
+     This list is only used if ``linkedPage`` is `nil`,
+     otherwise the tag list of the linked page is used.
+     */
     @Published
     var tags: [Tag]
 
@@ -52,6 +58,55 @@ final class Post: Item {
         super.init(content: content, id: id)
     }
 
+    // MARK: Tags
+
+    func usedTags() -> [Tag] {
+        linkedPage?.tags ?? tags
+    }
+
+    /**
+     Check if a tag is associated with this post.
+
+     If the post is linked to a page, then the tags of the page are checked.
+     */
+    func contains(_ tag: Tag) -> Bool {
+        guard let linkedPage else {
+            return tags.contains(tag)
+        }
+        return linkedPage.tags.contains(tag)
+    }
+
+    func toggle(_ tag: Tag) {
+        if let linkedPage {
+            linkedPage.toggle(tag)
+            return
+        }
+        guard let index = tags.firstIndex(of: tag) else {
+            tags.append(tag)
+            return
+        }
+        tags.remove(at: index)
+    }
+
+    func remove(_ tag: Tag) {
+        if let linkedPage {
+            linkedPage.remove(tag)
+            return
+        }
+        tags.remove(tag)
+    }
+
+    func associate(_ tag: Tag) {
+        if let linkedPage {
+            linkedPage.associate(tag)
+            return
+        }
+        guard !tags.contains(tag) else {
+            return
+        }
+        tags.append(tag)
+    }
+
     func localized(in language: ContentLanguage) -> LocalizedPost {
         switch language {
         case .english: return english