Merge pull request #12 from LiveUI/mapCodingStrategy

Added strategies for decoding and encoding maps.

Author: rafiki270

Sources/XMLCoding/Decoder/XMLDecoder.swift

@@ -115,6 +115,31 @@ open class XMLDecoder {
         case collapseListUsingItemTag(String)
     }
 
+    /// The strategy to use when decoding maps.
+    public enum MapDecodingStrategy {
+        /// Preserves the XML structure. Key and Value tags will be retained producing a
+        /// list of elements with these two attributes. This is the default strategy.
+        case preserveStructure
+        
+        /// Collapse the XML structure to avoid key and value tags. For example-
+        /// <Result>
+        ///   <Tag>
+        ///     <Key>QueueType</Key>
+        ///     <Value>Production</Value>
+        ///   </Tag>
+        ///   <Tag>
+        ///     <Key>Owner</Key>
+        ///     <Value>Developer123</Value>
+        ///   </Tag>
+        /// </Result>
+        ///
+        /// will be decoded into
+        /// struct Result {
+        ///     let tags: [String: String]
+        /// }
+        case collapseMapUsingTags(keyTag: String, valueTag: String)
+    }
+    
     /// The strategy to use in decoding dates. Defaults to `.secondsSince1970`.
     open var dateDecodingStrategy: DateDecodingStrategy = .secondsSince1970
 
@@ -127,6 +152,9 @@ open class XMLDecoder {
     /// The strategy to use in decoding lists. Defaults to `.preserveStructure`.
     open var listDecodingStrategy: ListDecodingStrategy = .preserveStructure
 
+    /// The strategy to use in decoding maps. Defaults to `.preserveStructure`.
+    open var mapDecodingStrategy: MapDecodingStrategy = .preserveStructure
+    
     /// Contextual user-provided information for use during decoding.
     open var userInfo: [CodingUserInfoKey : Any] = [:]
 
@@ -136,6 +164,7 @@ open class XMLDecoder {
         let dataDecodingStrategy: DataDecodingStrategy
         let nonConformingFloatDecodingStrategy: NonConformingFloatDecodingStrategy
         let listDecodingStrategy: ListDecodingStrategy
+        let mapDecodingStrategy: MapDecodingStrategy
         let userInfo: [CodingUserInfoKey : Any]
     }
 
@@ -145,6 +174,7 @@ open class XMLDecoder {
                         dataDecodingStrategy: dataDecodingStrategy,
                         nonConformingFloatDecodingStrategy: nonConformingFloatDecodingStrategy,
                         listDecodingStrategy: listDecodingStrategy,
+                        mapDecodingStrategy: mapDecodingStrategy,
                         userInfo: userInfo)
     }
 
@@ -209,14 +239,45 @@ internal class _XMLDecoder : Decoder {
 
     // MARK: - Decoder Methods
 
+    private func getMapFromListOfEntries(entryList: [Any], keyTag: String, valueTag: String) -> [String : Any] {
+        var newContainer: [String: Any] = [:]
+        
+        // construct a dictionary from each entry and the key and value tags
+        entryList.forEach { entry in
+            if let keyedContainer = entry as? [String : Any],
+                let key = keyedContainer[keyTag] as? String,
+                let value = keyedContainer[valueTag] {
+                newContainer[key] = value
+            }
+        }
+        
+        return newContainer
+    }
+    
     public func container<Key>(keyedBy type: Key.Type) throws -> KeyedDecodingContainer<Key> {
         guard !(self.storage.topContainer is NSNull) else {
             throw DecodingError.valueNotFound(KeyedDecodingContainer<Key>.self,
                                               DecodingError.Context(codingPath: self.codingPath,
                                                                     debugDescription: "Cannot get keyed decoding container -- found null value instead."))
         }
 
-        guard let topContainer = self.storage.topContainer as? [String : Any] else {
+        let topContainer: [String : Any]
+        // if this is a dictionary
+        if let currentContainer = self.storage.topContainer as? [String : Any] {
+            
+            // if we are combining collapsing lists and maps
+            if case let .collapseListUsingItemTag(itemTag) = options.listDecodingStrategy,
+                case let .collapseMapUsingTags(keyTag: keyTag, valueTag: valueTag) = options.mapDecodingStrategy,
+                let itemList = currentContainer[itemTag] as? [Any] {
+                topContainer = getMapFromListOfEntries(entryList: itemList, keyTag: keyTag, valueTag: valueTag)
+            } else {
+                topContainer = currentContainer
+            }
+        // if this is a list and the mapDecodingStrategy is collapseMapUsingTags
+        } else if let currentContainer = self.storage.topContainer as? [Any],
+            case let .collapseMapUsingTags(keyTag: keyTag, valueTag: valueTag) = options.mapDecodingStrategy {
+            topContainer = getMapFromListOfEntries(entryList: currentContainer, keyTag: keyTag, valueTag: valueTag)
+        } else {
             throw DecodingError._typeMismatch(at: self.codingPath, expectation: [String : Any].self, reality: self.storage.topContainer)
         }
 

Sources/XMLCoding/Encoder/XMLEncoder.swift

@@ -187,6 +187,31 @@ open class XMLEncoder {
         case expandListWithItemTag(String)
     }
 
+    /// The strategy to use when encoding maps.
+    public enum MapEncodingStrategy {
+        /// Preserves the XML structure. Key and Value tags will be retained producing a
+        /// list of elements with these two attributes. This is the default strategy.
+        case preserveStructure
+        
+        /// Expands the XML structure to avoid key and value tags. For example-
+        /// <Result>
+        ///   <Tag>
+        ///     <Key>QueueType</Key>
+        ///     <Value>Production</Value>
+        ///   </Tag>
+        ///   <Tag>
+        ///     <Key>Owner</Key>
+        ///     <Value>Developer123</Value>
+        ///   </Tag>
+        /// </Result>
+        ///
+        /// will be encoded from
+        /// struct Result {
+        ///     let tags: [String: String]
+        /// }
+        case expandMapUsingTags(keyTag: String, valueTag: String)
+    }
+    
     /// The output format to produce. Defaults to `[]`.
     open var outputFormatting: OutputFormatting = []
 
@@ -211,6 +236,9 @@ open class XMLEncoder {
     /// The strategy to use in encoding lists. Defaults to `.preserveStructure`.
     open var listEncodingStrategy: ListEncodingStrategy = .preserveStructure
 
+    /// The strategy to use in encoding map. Defaults to `.preserveStructure`.
+    open var mapEncodingStrategy: MapEncodingStrategy = .preserveStructure
+    
     /// Contextual user-provided information for use during encoding.
     open var userInfo: [CodingUserInfoKey : Any] = [:]
 
@@ -223,6 +251,7 @@ open class XMLEncoder {
         let attributeEncodingStrategy: AttributeEncodingStrategy
         let stringEncodingStrategy: StringEncodingStrategy
         let listEncodingStrategy: ListEncodingStrategy
+        let mapEncodingStrategy: MapEncodingStrategy
         let userInfo: [CodingUserInfoKey : Any]
     }
 
@@ -235,6 +264,7 @@ open class XMLEncoder {
                         attributeEncodingStrategy: attributeEncodingStrategy,
                         stringEncodingStrategy: stringEncodingStrategy,
                         listEncodingStrategy: listEncodingStrategy,
+                        mapEncodingStrategy: mapEncodingStrategy,
                         userInfo: userInfo)
     }
 
@@ -936,6 +966,9 @@ extension _XMLEncoder {
             return .uint64(UInt64(int))
         } else if let int = value as? UInt32 {
             return .uint64(UInt64(int))
+        } else if let boxableEncodable = value as? BoxableEncodable {
+            // this type knows how to box itself
+            return try boxableEncodable.box(forEncoder: self)
         }
 
         let depth = self.storage.count
@@ -950,3 +983,58 @@ extension _XMLEncoder {
     }
 }
 
+/// Protocol for a type that knows how to box itself
+protocol BoxableEncodable: Encodable {
+    func box(forEncoder encoder: _XMLEncoder) throws -> MutableContainer?
+}
+
+extension Dictionary: BoxableEncodable where Key == String, Value: Encodable {
+    /// function to box (and potentially expand
+    internal func box(forEncoder encoder: _XMLEncoder) throws -> MutableContainer? {
+        let depth = encoder.storage.count
+        // if we are expanding maps
+        if case let .expandMapUsingTags(keyTag: keyTag, valueTag: valueTag) = encoder.options.mapEncodingStrategy {
+            let outerMutableContainer: (MutableContainerDictionary, String)?
+            // if we are expanding lists, wrap everything in a dictionary with that item
+            if case let .expandListWithItemTag(itemTag) = encoder.options.listEncodingStrategy {
+                let newMutableContainerDictionary = MutableContainerDictionary()
+                encoder.storage.push(container: .dictionary(newMutableContainerDictionary))
+                outerMutableContainer = (newMutableContainerDictionary, itemTag)
+            } else {
+                outerMutableContainer = nil
+            }
+            
+            // create the expanded array
+            let mutableContainerArray = MutableContainerArray()
+            encoder.storage.push(container: .array(mutableContainerArray))
+            
+            try self.forEach { (key, value) in
+                // create the dictionary for the key and value entries
+                let mutableContainerDictionary = MutableContainerDictionary()
+                encoder.storage.push(container: .dictionary(mutableContainerDictionary))
+                mutableContainerDictionary[keyTag] = .string(key)
+                mutableContainerDictionary[valueTag] = try encoder.box(value)
+                
+                // add to the array
+                mutableContainerArray.append(encoder.storage.popContainer())
+            }
+            
+            // add to the outer container if it is needed
+            if let outerMutableContainer = outerMutableContainer {
+                outerMutableContainer.0[outerMutableContainer.1] = encoder.storage.popContainer()
+            }
+        } else {
+            // otherwise just encode this array as normal
+            try self.encode(to: encoder)
+        }
+        
+        // The top container should be a new container.
+        guard encoder.storage.count > depth else {
+            return nil
+        }
+        
+        // return what has been created
+        return encoder.storage.popContainer()
+    }
+}
+