Helper methods for working with Codable objects and JSON Data and dictionaries. Provides two initializers and two methods for creating a Codable object using a dictionary or a Data object. And two methods for retreiving a dictionary or Data from the Codable instance.

ExtraCodable.swift

//
//  ExtraCodable.swift
//
//  Created by Khan Winter on 3/16/21.
//  Copyright © 2021 WindChillMedia. All rights reserved.
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.

import Foundation

/// An extension providing helper methods for working with JSON data and dictionaries
protocol ExtraCodable: Codable {
    /// Initializes an ExtraCodable instance using a JSON dictionary, throws on parsing error
    /// - Parameter dict: JSON dictionary, can be an array
    init(_ dict: [String: Any]) throws
    /// Initializes an ExtraCodable instance using JSON Data, throws on parsing error
    /// - Parameter data: Raw JSON Data, can be an array
    init(_ data: Data) throws
    
    /// Serializes the ExtraCoable instance to a JSON Dictionary, throws on parsing error
    func getJSONDictionary() throws -> [String: Any]
    /// Serializes the ExtraCoable instance into JSON Data, throws on parsing error
    func getJSONData() throws -> Data
    
    /// Optional wrapper for the `getJSONDictionary()` method, nil on parsing error
    var jsonData: Data? { get }
    /// Optional wrapper for the `getJOSNData()` method, nil on parsing error
    var jsonDictionary: [String: Any]? { get }
}

extension ExtraCodable {
    //MARK: - Init
    
    init(_ dict: [String: Any]) throws {
        let jsonData = try JSONSerialization.data(withJSONObject: dict, options: [])
        let decoder = JSONDecoder()
        self = try decoder.decode(Self.self, from: jsonData)
    }
    
    init(_ data: Data) throws {
        let decoder = JSONDecoder()
        self = try decoder.decode(Self.self, from: data)
    }
    
    //MARK: - Data
    
    func getJSONDictionary() throws -> [String: Any] {
        let data = try getJSONData()
        guard let dictionary = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [String: Any] else {
            throw NSError()
        }
        return dictionary
    }
    
    func getJSONData() throws -> Data {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .secondsSince1970
        return try encoder.encode(self)
    }
    
    //MARK: - Properties
    
    var jsonData: Data? {
        get {
            return try? getJSONData()
        }
    }
    
    var jsonDictionary: [String: Any]? {
        get {
            return try? getJSONDictionary()
        }
    }
}

Sample usage:

struct MeetingNotes: ExtraCodable {
  var date: Date
  var message: String
}

let dataFromServer = Data()
do {
  /// Initialize from `Data`
  let note = try MeetingNotes(dataFromServer)

  note.date = Date()

  /// Grab a dictionary from the object
  let dataToReturn = try note.getJSONDictionary()

} catch {
  print(error)
}

Or a real-world example with Firebase's Firestore

Firestore.firestore().collection("MeetingNotes").getDocuments { (snapshot, error) in
    guard let snapshot = snapshot, error == nil else {
        return
    }
    var notes: [MeetingNote] = []
    for document in snapshot.documents {
        if let note = try? MeetingNote(document.data()) { // Get the object from the firestore `data()` preoperty
            notes.append(note)
        }
    }
    return notes
}

Also please note
The default implementation sets the JSON serializer to use dateEncodingStrategy = .secondsSince1970 which will convert Dates to Doubles. Simply comment out those lines and it'll do dates normally.