Decodable from specific key of json

test.json

{
    "applmusic":{
        "code":"AAPL",
        "quality":"good",
        "line":"She told me don't worry",
    },
    "spotify":{
        "differentcode":"SPOT",
        "music_quality":"good",
        "spotify_specific_code":"absent in apple"
    },
    "amazon":{
        "amzncode":"SPOT",
        "music_quality":"good",
        "stanley":"absent in apple"
    }
}

try_nested_decoder.swift

import UIKit


struct Applmusic: Decodable {
    let code: String
    let quality: String
    let line: String
}

struct Spotify: Decodable {
    let differentcode: String
    let music_quality: String
    let spotify_specific_code: String
}

struct Amazon: Decodable {
    let amzncode: String
    let music_quality: String
    let stanley: String
}


struct DecodingHelper {

    private struct Key: CodingKey {
        let stringValue: String
        init?(stringValue: String) {
            self.stringValue = stringValue
            self.intValue = nil
        }

        let intValue: Int?
        init?(intValue: Int) {
            return nil
        }
    }

    private struct ModelResponse<NestedModel: Decodable>: Decodable {
        let nested: NestedModel

        public init(from decoder: Decoder) throws {
            let key = Key(stringValue: decoder.userInfo[CodingUserInfoKey(rawValue: "my_model_key")!]! as! String)!
            let values = try decoder.container(keyedBy: Key.self)
            nested = try values.decode(NestedModel.self, forKey: key)
        }
    }

    static func decode<T: Decodable>(modelType: T.Type, fromKey key: String) throws -> T {
        // mock data, replace with network response
        let path = Bundle.main.path(forResource: "test", ofType: "json")!
        let data = try Data(contentsOf: URL(fileURLWithPath: path), options: .mappedIfSafe)

        let decoder = JSONDecoder()
        decoder.userInfo[CodingUserInfoKey(rawValue: "my_model_key")!] = key
        let model = try decoder.decode(ModelResponse<T>.self, from: data).nested
        return model
    }
}

do {
    let appl = try DecodingHelper.decode(modelType: Applmusic.self, fromKey: "applmusic")
    let amazon = try DecodingHelper.decode(modelType: Amazon.self, fromKey: "amazon")
    let spotify = try DecodingHelper.decode(modelType: Spotify.self, fromKey: "spotify")
    print(appl, amazon, spotify)
} catch let error {
    print(error.localizedDescription)
}