Swift Polymorphic Deserialization Challenge

Objective: You are given a JSON string representing a farm. The farm contains a list of animals. Your task is to deserialize this JSON into a Swift struct while maintaining a clean architecture.

Details:

1. Each animal in the list is recognized by the "type" field.
2. Each type of animal has unique fields associated with it.

The JSON structure is as follows:

{
    "farmName": "Green Acres",
    "animals": [
        {
            "type": "cow",
            "milkPerDay": 10,
            "grassRequirements": 20
        },
        {
            "type": "dog",
            "speed": 30,
            "name": "Buddy",
            "commandAbilities": ["sit", "fetch"]
        },
        {
            "type": "fish",
            "weight": 5,
            "swimmingSpeed": 15,
            "scaleColor": "blue"
        }
    ]
}

Expected structs:

struct Farm {
    let farmName: String
    let animals: [Animal]
}

protocol Animal {
    var type: String { get }
}

struct Cow: Animal {
    let type: String
    let milkPerDay: Int
    let grassRequirements: Int
}

struct Dog: Animal {
    let type: String
    let speed: Int
    let name: String
    let commandAbilities: [String]
}

struct Fish: Animal {
    let type: String
    let weight: Int
    let swimmingSpeed: Int
    let scaleColor: String
}

Requirements:

1. Use the native Swift libraries for JSON decoding (JSONDecoder).
2. You should create a custom Decodable implementation for the Farm struct to handle the polymorphic deserialization of the animals.
3. Proper error handling should be implemented. If an unknown animal type is encountered, your decoder should throw a meaningful error.
4. Write a simple main function to demonstrate the decoding of the given JSON string into the Farm struct.
5. Provide a way to print the deserialized farm and its animals.

Tips:

• Consider how the init(from decoder: Decoder) function for the Decodable protocol can be leveraged.
• Think about how you can switch on the "type" field to decode different animal structures.

Bonus: Write unit tests to validate your solution for the given JSON, potential edge cases, and error scenarios.