Add tag overview, improve assets

CHDataManagement/Storage/Storage.swift

@@ -306,6 +306,18 @@ final class Storage {
         try writeIfChanged(fileDescriptions, to: fileDescriptionFilename)
     }
 
+    // MARK: Tag overview
+
+    private let tagOverviewFileName = "tag-overview.json"
+
+    func loadTagOverview() throws -> TagOverviewFile? {
+        try read(at: tagOverviewFileName)
+    }
+
+    func save(tagOverview: TagOverviewFile?) throws {
+        try writeIfChanged(tagOverview, to: tagOverviewFileName)
+    }
+
     // MARK: Files
 
     private let filesFolderName = "files"
@@ -499,6 +511,19 @@ final class Storage {
         }
     }
 
+    /**
+     Write the data of an encodable value to a relative path in the content folder,
+     or delete the file if nil is passed.
+     - Note: This function requires a security scope for the content path
+     */
+    private func writeIfChanged<T>(_ value: T?, to relativePath: String) throws where T: Encodable {
+        guard let value else {
+            try deleteFile(at: relativePath)
+            return
+        }
+        return try writeIfChanged(value, to: relativePath)
+    }
+
     /**
      Write the data of an encodable value to a relative path in the content folder
      - Note: This function requires a security scope for the content path
@@ -547,6 +572,16 @@ final class Storage {
         }
     }
 
+    /**
+     Read an object from a file, if the file exists
+     */
+    private func read<T>(at relativePath: String) throws -> T? where T: Decodable {
+        guard let data = try readData(at: relativePath) else {
+            return nil
+        }
+        return try decoder.decode(T.self, from: data)
+    }
+
     /**
 
      - Note: This function requires a security scope for the content path
@@ -632,4 +667,13 @@ final class Storage {
             try fm.copyItem(at: file, to: destination)
         }
     }
+
+    private func deleteFile(at relativePath: String) throws {
+        try withScopedContent(file: relativePath) { destination in
+            guard fm.fileExists(atPath: destination.path()) else {
+                return
+            }
+            try fm.removeItem(at: destination)
+        }
+    }
 }