add encoding capabilities to the library.

Sources/FatturaElettronica/CustomDecoder/PABool.swift

@@ -26,7 +26,13 @@ public struct PABool: Codable {
 
     public func encode(to encoder: Encoder) throws {
         var container = encoder.singleValueContainer()
-        try container.encode(self.wrappedValue)
+    /// https://www.fatturapa.gov.it/it/norme-e-regole/documentazione-fattura-elettronica/formato-fatturapa/
+    /// As of documentation this value if true must be encoded as "SI".
+    /// and in case of false the value is not encoded
+        if let bool = self.wrappedValue,
+           bool {
+            try container.encode("SI")
+        }
     }
 }
 
@@ -38,7 +44,7 @@ extension KeyedDecodingContainer {
 
 extension KeyedEncodingContainer {
     public mutating func encode(_ value: PABool, forKey key: Self.Key) throws {
-        if value.wrappedValue != nil {
+        if let bool = value.wrappedValue, bool {
             try value.encode(to: self.superEncoder(forKey: key))
         }
     }

Sources/FatturaElettronica/FileHandler/FileHandler.swift

@@ -35,6 +35,10 @@ extension XMLHandler{
     public func handle(_ xml: String) -> EventLoopFuture<FatturaElettronica> {
         return self.xmlToInvoice(xml)
     }
+
+    public func encode(_ invoice: FatturaElettronica) throws -> Data {
+        try self.invoiceToXML(invoice)
+    }
 
     private func handleXML(_ data: Data) -> EventLoopFuture<FatturaElettronica> {
         self.eventLoop.submit{

Sources/FatturaElettronica/FileHandler/XMLHandler.swift

@@ -23,6 +23,9 @@ extension Date{
 public class XMLHandler{
     let eventLoop: EventLoop
     let decoder = XMLDecoder()
+    let encoder = XMLEncoder()
+
+    private let defaultFormatter: DateFormatter = DateFormatter()
 
     public convenience init() {
         let loop = MultiThreadedEventLoopGroup(numberOfThreads: System.coreCount).next()
@@ -48,7 +51,8 @@ public class XMLHandler{
     public init(on loop: EventLoop){
         self.eventLoop = loop
         self.decoder.shouldProcessNamespaces = true
-
+        self.defaultFormatter.dateFormat = "yyyy-MM-dd"
+
         self.decoder.dateDecodingStrategy = .custom {
             let container = try $0.singleValueContainer()
             let string = try container.decode(String.self)
@@ -72,8 +76,21 @@ public class XMLHandler{
             let loweCasedKey = last.stringValue.lowercased()
             return XMLKey(stringValue: loweCasedKey)
         }
+        self.decoder.dataDecodingStrategy = .base64
+        self.encoder.dateEncodingStrategy = .custom { date, encoder in
+            var container = encoder.singleValueContainer()
+            try container.encode(self.defaultFormatter.string(from: date))
+        }
+        self.encoder.dataEncodingStrategy = .base64
+        self.encoder.outputFormatting = .prettyPrinted
+        self.encoder.prettyPrintIndentation = .spaces(4)
+        self.encoder.stringEncodingStrategy = .deferredToString
     }
 
+    func invoiceToXML(_ invoice: FatturaElettronica) throws -> Data {
+        try self.encoder.encode(invoice)
+    }
+
     func xmlToInvoice(_ xml: String) -> EventLoopFuture<FatturaElettronica>{
         let loop = self.eventLoop.next()