Encoder-Template.swift

import Foundation

struct EmojiUnkeyedEncodingContainer : UnkeyedEncodingContainer {
    // MARK: Properties
    private(set) public var codingPath: [CodingKey]
    
    private var encoder: EmojiEncoder;

    /// The number of elements encoded into the container.
    public var count: Int {
        return 0
    }

    // MARK: - Initialization
    init(referencing encoder: EmojiEncoder) {
        codingPath = []
        self.encoder = encoder
    }

    // MARK: - UnkeyedEncodingContainer Methods
    
    public mutating func encodeNil()             throws {  }
    public mutating func encode(_ value: Bool)   throws {  }
    public mutating func encode(_ value: Int)    throws {  }
    public mutating func encode(_ value: Int8)   throws {  }
    public mutating func encode(_ value: Int16)  throws {  }
    public mutating func encode(_ value: Int32)  throws {  }
    public mutating func encode(_ value: Int64)  throws {  }
    public mutating func encode(_ value: UInt)   throws {  }
    public mutating func encode(_ value: UInt8)  throws {  }
    public mutating func encode(_ value: UInt16) throws {  }
    public mutating func encode(_ value: UInt32) throws {  }
    public mutating func encode(_ value: UInt64) throws {  }
    public mutating func encode(_ value: String) throws { 
        encoder.storage += Array(value.utf8) 
    }

    public mutating func encode(_ value: Float)  throws {
    }

    public mutating func encode(_ value: Double) throws {
    }

    public mutating func encode<T : Encodable>(_ value: T) throws {
        try value.encode(to: superEncoder())
    }

    public mutating func nestedContainer<NestedKey>(keyedBy keyType: NestedKey.Type) -> KeyedEncodingContainer<NestedKey> {
        let container = EmojiEncodingContainer<NestedKey>(referencing: self.encoder)
        return KeyedEncodingContainer(container)
    }

    public mutating func nestedUnkeyedContainer() -> UnkeyedEncodingContainer {
        return EmojiUnkeyedEncodingContainer(referencing: self.encoder)
    }

    public mutating func superEncoder() -> Encoder {
        return EmojiEncoder()
    }
}


struct EmojiEncodingContainer<K : CodingKey> : KeyedEncodingContainerProtocol {
    typealias Key = K
    private(set) public var codingPath: [CodingKey]
    private var encoder: EmojiEncoder;

    init(referencing encoder: EmojiEncoder) {
        codingPath = []
        self.encoder = encoder
    }
    
    // MARK: - KeyedEncodingContainerProtocol Methods
    
    public mutating func encodeNil(forKey key: Key)               throws {  }
    public mutating func encode(_ value: Bool, forKey key: Key)   throws {  }
    public mutating func encode(_ value: Int, forKey key: Key)    throws {  }
    public mutating func encode(_ value: Int8, forKey key: Key)   throws {  }
    public mutating func encode(_ value: Int16, forKey key: Key)  throws {  }
    public mutating func encode(_ value: Int32, forKey key: Key)  throws {  }
    public mutating func encode(_ value: Int64, forKey key: Key)  throws {  }
    public mutating func encode(_ value: UInt, forKey key: Key)   throws {  }
    public mutating func encode(_ value: UInt8, forKey key: Key)  throws {  }
    public mutating func encode(_ value: UInt16, forKey key: Key) throws {  }
    public mutating func encode(_ value: UInt32, forKey key: Key) throws {  }
    public mutating func encode(_ value: UInt64, forKey key: Key) throws {  }
    public mutating func encode(_ value: String, forKey key: Key) throws { 
        encoder.storage += Array(value.utf8) 
    }

    public mutating func encode(_ value: Float, forKey key: Key)  throws {
    }

    public mutating func encode(_ value: Double, forKey key: Key) throws {
    }

    public mutating func encode<T : Encodable>(_ value: T, forKey key: Key) throws {
        try value.encode(to: superEncoder())
    }

    public mutating func nestedContainer<NestedKey>(keyedBy keyType: NestedKey.Type, forKey key: Key) -> KeyedEncodingContainer<NestedKey> {
        let container = EmojiEncodingContainer<NestedKey>(referencing: self.encoder)
        return KeyedEncodingContainer(container)
    }

    public mutating func nestedUnkeyedContainer(forKey key: Key) -> UnkeyedEncodingContainer {
        return EmojiUnkeyedEncodingContainer(referencing: self.encoder)
    }

    public mutating func superEncoder() -> Encoder {
        return EmojiEncoder()
    }

    public mutating func superEncoder(forKey key: Key) -> Encoder {
        return EmojiEncoder()
    }
}

public class EmojiEncoder: Encoder {
    public var codingPath: [CodingKey]
    public var userInfo: [CodingUserInfoKey : Any]
    fileprivate(set) var storage: [UInt8]
    
    public init() {
        codingPath = []
        userInfo = [:]
        storage = [UInt8]()
    }
    
    public func container<Key>(keyedBy: Key.Type) -> KeyedEncodingContainer<Key> {
        let container = EmojiEncodingContainer<Key>(referencing: self)
        return KeyedEncodingContainer(container)
    }
    
    public func singleValueContainer() -> SingleValueEncodingContainer {
        return self
    }
    
    public func unkeyedContainer() -> UnkeyedEncodingContainer {
        return EmojiUnkeyedEncodingContainer(referencing: self)
    }
    
    //
    
    public func data() -> Data {
        return Data(self.storage)
    }
}

extension EmojiEncoder : SingleValueEncodingContainer {

    public func encodeNil() throws {
    }

    public func encode(_ value: Bool) throws {
    }

    public func encode(_ value: Int) throws {
    }

    public func encode(_ value: Int8) throws {
    }

    public func encode(_ value: Int16) throws {
    }

    public func encode(_ value: Int32) throws {
    }

    public func encode(_ value: Int64) throws {
    }

    public func encode(_ value: UInt) throws {
    }

    public func encode(_ value: UInt8) throws {
    }

    public func encode(_ value: UInt16) throws {
    }

    public func encode(_ value: UInt32) throws {
    }

    public func encode(_ value: UInt64) throws {
    }

    public func encode(_ value: String) throws {
        storage += Array(value.utf8)
    }

    public func encode(_ value: Float) throws {
    }

    public func encode(_ value: Double) throws {
    }

    public func encode<T : Encodable>(_ value: T) throws {
        try value.encode(to: self)
    }
}


// Testing

struct Emoji: Encodable {
    private let value: String
    
    init(_ value: String) {
        self.value = value
    }
}

let encoder = EmojiEncoder()
try! encoder.encode(Emoji("🥟"))

print(Array(encoder.data()))