struct Post {
    let id: Int
    let title: String
    let body: String
}

extension Post {
    static let endPoint = URL(string: "https://jsonplaceholder.typicode.com/posts")!
    
    init?(json: JSONDictionary) {
        guard let id = json["id"] as? Int,
            let title = json["title"] as? String,
            let body = json["body"] as? String else { return nil }
        self.id = id
        self.title = title
        self.body = body
    }
}

let webservice = Webservice()

extension Post {
    static var postsResource: Resource<[Post]> {
        return Resource<[Post]>(url: Post.endPoint, parseJSON: { obj in
            guard let json = obj as? [JSONDictionary] else {
                return Result.failure(.invalidResponse)
            }
            let posts = json.compactMap(Post.init)
            return Result.success(posts)
        })
    }
}

webservice.load(Post.postsResource) { response in 
    switch response {
    case .failure(let error): // handle error
    case .success(let posts): // posts: [Post]
    }
}

extension Post {
    static func createResource(title: String, body: String) -> Resource<Post> {
        let data: JSONDictionary = ["title": title, "body": body]
        return Resource(url: Post.endPoint, jsonMethod: .post(data: data), parseJSON: { obj in
            guard let json = obj as? JSONDictionary,
                let post = Post(json: json) else {
                return Result.failure(.invalidResponse)
            }
            return Result.success(post)
        })
    }
}

let resource = Post.createResource(title: "xxx", body: "xxx")
webservice.load(resource) { response in 
    switch response {
    case .failure(let error): // handle error
    case .success(let post):  // post: Post
    }
}

extension Post {
    var updateResource: Resource<Post> {
        let url = Post.endPoint.appendingPathComponent("\(id)")
        let data: JSONDictionary = ["id": id, "title": title, "body": body]
        return Resource(url: url, jsonMethod: .put(data: data), parseJSON: { obj in
            guard let json = obj as? JSONDictionary,
                let post = Post(json: json) else {
                return Result.failure(.invalidResponse)
            }
            return Result.success(post)
        })
    }
}

let post = Post(id: xxx, title: "xxx", body: "xxx")
webservice.load(post.updateResource) { response in 
    switch response {
    case .failure(let error): // handle error
    case .success(let post):  // post: Post
    }
}

extension Post {
    var udpateTitleResource: Resource<Post> {
        let url = Post.endPoint.appendingPathComponent("\(id)")
        let data: JSONDictionary = ["title": title]
        return Resource(url: url, jsonMethod: .patch(data: data), parseJSON: { obj in
            guard let json = obj as? JSONDictionary,
                let post = Post(json: json) else {
                return Result.failure(.invalidResponse)
            }
            return Result.success(post)
        })
    }
}

let post = Post(id: xxx, title: "xxx", body: "xxx")
webservice.load(post.udpateTitleResource) { response in 
    switch response {
    case .failure(let error): // handle error
    case .success(let post):  // post: Post
    }
}

extension Post {
  var deleteResource: Resource<Bool> {
        let url = Post.endPoint.appendingPathComponent("\(id)")
        return Resource(url: url, method: .delete, parse: { _ in
            return Result.success(true)
        })
    }
}

let post = Post(id: xxx, title: "xxx", body: "xxx")
webservice.load(post.deleteResource) { response in 
    switch response {
    case .failure(let error): // handle error
    case .success(let flag):  // flag: Bool
    }
}