Dynamic JSON full playground.swift

import UIKit

struct ComplexObject: Decodable {
    let timestamp: Int
    let identifier: String
}

extension ComplexObject {
    enum CodingKeys: String, CodingKey {
        case timestamp
        case identifier
    }
}

enum DecodingError: Error {
    case corruptedData
}

enum ValueType: Decodable {
    case number(Int)
    case string(String)
    case object(ComplexObject)
    
    init(from decoder: Decoder) throws {
        // 1
        do {
            let singleValueContainer = try decoder.singleValueContainer()
            let timestamp = try singleValueContainer.decode(Int.self)
            self = .number(timestamp)
            return
        } catch {}
        // 2
        do {
            let singleValueContainer = try decoder.singleValueContainer()
            let timestamp = try singleValueContainer.decode(String.self)
            self = .string(timestamp)
            return
        } catch {}
        // 3
        do {
            let keyedContainer = try decoder.container(keyedBy: ComplexObject.CodingKeys.self)
            let timestamp = try keyedContainer.decode(Int.self, forKey: .timestamp)
            let identifier = try keyedContainer.decode(String.self, forKey: .identifier)
            self = .object(ComplexObject(timestamp: timestamp, identifier: identifier))
            return
        } catch {}
        // 4
        throw DecodingError.corruptedData
    }
}

typealias Values = [String: ValueType]

// Test
let json = """
{
  "TjOnekTbvbh7XW7aTgEiyr2pccq1": 1565244404531,
  "Zu9ujNWUi0fSz3Y8pNFJ8PV4Phk1": "some string value",
  "AC5cZbp4XyPJfTu4zf9TfRQWRY02": {
    "timestamp": 1566474347575,
    "identifier": "Cu9BjNKU407Sz3Y8pNFJ8P64Phk1"
  }
}
"""

if let jsonData = json.data(using: .utf8) {    
    let events = try JSONDecoder().decode(Values.self, from: jsonData)
    for (key, eventData) in events {
        switch eventData {
        case ValueType.number(let timestamp):
            print("It's a number! \(timestamp)")
        case ValueType.string(let timestamp):
            print("It's a string! \(timestamp)")
        case ValueType.object(let timestamp):
            print("It's an object! \(timestamp)")
        }
    }
}