Extremely generic swagger client

swagger.swift

import Foundation

typealias ApiCallback<Output> = Optional<(Result<Output, Error>) -> Void>

protocol EndpointClient {
    func execute<Output>(endpoint: Endpoint<Output>, onResult: ApiCallback<Output>)
}

struct RequestBuilder {
    var path: String = ""
    var headers: [String: String] = [:]
    var query: [String: Encodable] = [:]
    var body: Encodable?
    var tags: Set<String> = []
}

struct Endpoint<Output: Decodable> {
    let client: EndpointClient
    let request: RequestBuilder
    
    func execute(onResult: ApiCallback<Output>) {
        client.execute(endpoint: self, onResult: onResult)
    }
}

// MARK: - Code generated by Swagger

struct LoginResponse: Codable {
    var token: String
}

struct  GeneratedApi {
    let client: EndpointClient

    /// Generated documentation
    func login(name: String, password: String) -> Endpoint<LoginResponse> {
        var req = RequestBuilder()
        req.path = "/login"
        req.query["name"] = name
        req.query["password"] = password
        return Endpoint(client: client, request: req)
    }
}

// MARK: - Code that I will write myself according to my preferences.

extension URLSession: EndpointClient {
    func execute<T>(endpoint: Endpoint<T>, onResult: ApiCallback<T>) {
        /// TODO: run dataTask or something
    }

    var generated: GeneratedApi {
        return GeneratedApi(client: self)
    }
}

func loginExample() {
    let client = URLSession.shared
    client.generated.login(name: "login", password: "password").execute { result in
        print(result)
    }
}