Using Swift JSONSerialization along with JSONDecoder

test.swift

struct OccType: Codable {
    var id: Int = 0
    var type: String = ""
    var createdAt: String? = nil
    var updatedAt: String? = nil
    var image: String? = nil

    enum CodingKeys: String, CodingKey {
        case id, type
        case createdAt = "created_at"
        case updatedAt = "updated_at"
        case image
    }
}

struct Details: Codable {
    var id = 0, userID: Int = 0
    var occursOn = "", detailsDescription: String = ""
    var background: String? = nil
    var address = "", type = "", createdAt = "", updatedAt: String = ""
    var isDisabled = 0, isRepeated = 0, allowedGiftsDays: Int = 0
    var occType: OccType = OccType()

    enum CodingKeys: String, CodingKey {
        case id
        case userID = "user_id"
        case occursOn = "occurs_on"
        case detailsDescription = "description"
        case background, address, type
        case createdAt = "created_at"
        case updatedAt = "updated_at"
        case isDisabled = "is_disabled"
        case isRepeated = "is_repeated"
        case allowedGiftsDays = "allowed_gifts_days"
        case occType = "occ_type"
    }
}

struct Validator: Codable {
}

struct DataModel: Codable {
    var id: Int = 0
    var type: String = ""
    var image: String? = nil
    var remaining: String = ""
    var details: Details = Details()
}

struct Response: Codable {
    var success: Bool = false
    var data: [String: [DataModel]] = [:]
    var message: String = ""
    var validator: Validator = Validator()
}

var jsonStr = """
{
    "success": true,
    "data": {
        "Nov 2019": [
            {
                "id": 35,
                "type": "Birthday",
                "image": null,
                "remaining": "5 days ago",
                "details": {
                    "id": 35,
                    "user_id": 56,
                    "occurs_on": "2019-11-24 00:00:00",
                    "description": "مناسبة تفوقي",
                    "background": null,
                    "address": "عنوان منزلي قريبا",
                    "type": "1",
                    "created_at": "2019-11-26 16:32:35",
                    "updated_at": "2019-11-26 17:05:42",
                    "is_disabled": 0,
                    "is_repeated": 1,
                    "allowed_gifts_days": 5,
                    "occ_type": {
                        "id": 1,
                        "type": "Birthday",
                        "created_at": null,
                        "updated_at": null,
                        "image": null
                    }
                }
            }
        ],
        "Nov 2020": [
            {
                "id": 39,
                "type": "Engagment",
                "image": null,
                "remaining": "11 months from now",
                "details": {
                    "id": 39,
                    "user_id": 56,
                    "occurs_on": "2020-11-10 00:00:00",
                    "description": "Marraige",
                    "background": null,
                    "address": "Cairo",
                    "type": "2",
                    "created_at": "2019-11-29 12:17:12",
                    "updated_at": "2019-11-29 12:17:12",
                    "is_disabled": 0,
                    "is_repeated": 1,
                    "allowed_gifts_days": 10,
                    "occ_type": {
                        "id": 2,
                        "type": "Engagment",
                        "created_at": null,
                        "updated_at": null,
                        "image": null
                    }
                }
            },
            {
                "id": 40,
                "type": "Marriage",
                "image": null,
                "remaining": "11 months from now",
                "details": {
                    "id": 40,
                    "user_id": 56,
                    "occurs_on": "2020-11-10 00:00:00",
                    "description": "Engaged",
                    "background": null,
                    "address": "Cairo",
                    "type": "3",
                    "created_at": "2019-11-29 12:17:34",
                    "updated_at": "2019-11-29 12:17:34",
                    "is_disabled": 0,
                    "is_repeated": 1,
                    "allowed_gifts_days": 10,
                    "occ_type": {
                        "id": 3,
                        "type": "Marriage",
                        "created_at": null,
                        "updated_at": null,
                        "image": null
                    }
                }
            }
        ]
    },
    "message": "Operation done successfully!",
    "validator": {}
}
"""

func testJSON(jsonStr: String) -> Response? {
    var response: Response? = nil
    do {
        response = Response()
        if let jsonData = jsonStr.data(using: .utf8) {
            let JSON = try JSONSerialization.jsonObject(with: jsonData, options: .allowFragments) as! [String: Any]
            // Simple
            response!.message = JSON["message"] as? String ?? ""
            response!.success = JSON["success"] as? Bool ?? false
            response!.validator = JSON["validator"] as? Validator ?? Validator()
            // A little bit complicated
            // Get this JSON object as dictionary (key, value)
            let data = JSON["data"] as! [String: Any]
            // go through all the keys of the dictionary ex: (Nov 2019, Nov 2020)
            for key in data.keys {
                // print(data[key])
                // JSONDecoder needs Data data type so the following line turn it into data
                let dataData = try! JSONSerialization.data(withJSONObject: data[key]!)
                // Then we use our normal JSONDecoder to decode the array of models inside of it
                let decoder = JSONDecoder()
                let dateModels = try! decoder.decode([DataModel].self, from: dataData)
                // Finally we set the value in the response
                response!.data[key] = dateModels
            }
        } else {
            print("Failed: JSON String to Data failed")
        }
    } catch let parsingError {
        print("Error", parsingError)
    }
    return response
}

let response = testJSON(jsonStr: jsonStr)

print(response)