DrinksCodable.swift

//: Playground - noun: a place where people can play

import UIKit

var drinks = """
{
    "drinks": [
        {
            "type": "water",
            "description": "All natural"
        },
        {
            "type": "orange_juice",
            "description": "Best drank with breakfast"
        },
        {
            "type": "beer",
            "description": "An alcoholic beverage, best drunk on fridays after work",
            "alcohol_content": "5%"
        }
    ]
}
"""

class Drink: Decodable {
    var type: String
    var description: String

    private enum CodingKeys: String, CodingKey {
        case type
        case description
    }
}

class Beer: Drink {
    var alcohol_content: String

    private enum CodingKeys: String, CodingKey {
        case alcohol_content
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.alcohol_content = try container.decode(String.self, forKey: .alcohol_content)
        try super.init(from: decoder)
    }
}

struct Drinks: Decodable {
    let drinks: [Drink]

    enum DrinksKey: CodingKey {
        case drinks
    }

    enum DrinkTypeKey: CodingKey {
        case type
    }

    enum DrinkTypes: String, Decodable {
        case water = "water"
        case orangeJuice = "orange_juice"
        case beer = "beer"
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: DrinksKey.self)
        var drinksArrayForType = try container.nestedUnkeyedContainer(forKey: DrinksKey.drinks)
        var drinks = [Drink]()

        var drinksArray = drinksArrayForType
        while(!drinksArrayForType.isAtEnd)
        {
            let drink = try drinksArrayForType.nestedContainer(keyedBy: DrinkTypeKey.self)
            let type = try drink.decode(DrinkTypes.self, forKey: DrinkTypeKey.type)
            switch type {
            case .water, .orangeJuice:
                print("found drink")
                drinks.append(try drinksArray.decode(Drink.self))
            case .beer:
                print("found beer")
                drinks.append(try drinksArray.decode(Beer.self))
            }
        }
        self.drinks = drinks
    }
}

let jsonDecoder = JSONDecoder()
do {
    let results = try jsonDecoder.decode(Drinks.self, from:drinks.data(using: .utf8)!)
    for result in results.drinks {
        print(result.description)
        if let beer = result as? Beer {
            print(beer.alcohol_content)
        }
    }
} catch {
    print("caught: \(error)")
}