PathBuilder.swift

import UIKit

class PathBuilder {
    private var components: [String] = []
    private var pathBase: String
    
    init(pathBase: String) {
        self.pathBase = pathBase
    }
    
    func append(_ component: String) {
        components.append(component)
    }
    
    func build() -> String {
        defer { components.removeAll() }
        return pathBase + "/" + components.joined(separator: "/")
    }
}

class SubPathBase {
    let builder: PathBuilder
    
    init(builder: PathBuilder) {
        self.builder = builder
    }
}

class APIPathRoot: SubPathBase {
    
    func config() -> Config {
        builder.append("config")
        return Config(builder: builder)
    }
    
    func users(id: Int) -> Users {
        builder.append("users")
        builder.append("\(id)")
        return Users(builder: builder)
    }
    
    class Config: SubPathBase {
        
        func `default`() -> String {
            builder.append("default")
            return builder.build()
        }
        
    }

    class Users: SubPathBase {
        
        func messages() -> Messages {
            builder.append("messages")
            return Messages(builder: builder)
        }
        
        func settings() -> Settings {
            builder.append("settings")
            return Settings(builder: builder)
        }
        
        class Messages: SubPathBase {
            
            func `get`(id: Int) -> String {
                builder.append("\(id)")
                return builder.build()
            }
            
            func list() -> String {
                builder.append("list")
                return builder.build()
            }
            
        }
        
        class Settings: SubPathBase {
            
            func getPop() -> String {
                builder.append("pop")
                return builder.build()
            }
            
            func getImap() -> String {
                builder.append("imap")
                return builder.build()
            }
            
        }
    }
}


let builder = PathBuilder(pathBase: "root")
let root = APIPathRoot(builder: builder)
print(root.config().default())
print(root.users(id: 5).messages().list())
print(root.users(id: 6).messages().get(id: 1337))
print(root.users(id: 4).settings().getPop())
print(root.users(id: 4).settings().getImap())