A service for managing remote models fetched via a Django REST API.

NetworkService.swift

//  NetworkService.swift

import Alamofire
import AlamofireObjectMapper
import ObjectMapper

/*!
 * A service that abstracts the underlying network calls and stores data
 * to the data store, or returns them in the completion handler.
 */
struct NetworkService {
    
    static var endpoints: Dictionary<String, String>?
    
    init(apiRootUrl: String) {
        Alamofire.request(.GET, apiRootUrl, parameters: nil, encoding: .URL, headers: nil).responseJSON { (response: Response<AnyObject, NSError>) in
            if let data = response.data {
                do {
                    let json = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.AllowFragments)
                    NetworkService.endpoints = json as? Dictionary<String, String>
                } catch {
                    //Failed to fetch API endpoints.
                    fatalError("Failed to fetch intial endpoints.")
                }
            }
        }
    }
    
    // MARK: Private Methods
    
    /*!
     * Fetch a results list from the given API endpoint.
     */
    private static func getResults<T: RemoteResultProtocol>(url: String, params: Dictionary<String, String>?, headers: Dictionary<String, String>?,
                                   completionHandler: (results: [T]) -> ()) {
        let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
        let request = Alamofire.request(.GET, url, parameters: params, encoding: .URL, headers: headers)
        
        request.responseArray(queue: queue, keyPath: "results") { (results: Response<[T], NSError>) in
            if let value = results.result.value {
                completionHandler(results: value)
            }
        }
    }
    
    /*!
     * Fetch a single item from the given API endpoint.
     */
    private static func getObject<T: RemoteResultProtocol>(url: String, params: Dictionary<String, String>?, headers: Dictionary<String, String>?,
                                  completionHandler: (result: T) -> ()) {
        let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
        let request = Alamofire.request(.GET, url, parameters: params, encoding: .URL, headers: headers)

        request.responseObject(queue: queue, keyPath: "") { (result: Response<T, NSError>) in
            if let value = result.result.value {
                completionHandler(result: value)
            }
        }
    }
    
    
    /*!
     * Update a given item at the given API endpoint.
     */
    private static func putObject<T: RemoteResultProtocol>(object: T, url: String, params: Dictionary<String, String>?,
                                  headers: Dictionary<String, String>?, completionHandler: (response: Response<AnyObject, NSError>) -> ()) {
        let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
        let request = Alamofire.request(.PUT, url, parameters: params, encoding: .URLEncodedInURL, headers: headers)
        request.responseJSON(queue: queue, completionHandler: completionHandler)
    }
    
    
    /*!
     * Delete a given item from the given API endpoint.
     */
    private static func deleteObject<T: RemoteResultProtocol>(object: T, url: String, params: Dictionary<String, String>?,
                                     headers: Dictionary<String, String>?, completionHandler: (Response<AnyObject, NSError>) -> ()) {
        let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
        let request = Alamofire.request(.DELETE, url, parameters: params, encoding: .URLEncodedInURL, headers: headers)
        request.responseJSON(queue: queue, completionHandler: completionHandler)
    }
}

protocol RemoteResultProtocol: Mappable {
    static var serializedIdentifier: String { get set }
    var url: String { get set }
}

extension RemoteResultProtocol {
    
    /*!
     * Fetch a single object from the remote API.
     */
    static func getSingle<T: RemoteResultProtocol>(completionHandler: (_: T) -> ()) {
        let endpoint = NetworkService.endpoints![serializedIdentifier]
        NetworkService.getObject(endpoint!, params: nil, headers: nil, completionHandler: completionHandler)
    }
    
    /*!
     * Fetch a result set from the remote API.
     */
    static func getResultSet<T: RemoteResultProtocol>(completionHandler: (_: [T]) -> ()) {
        let endpoint = NetworkService.endpoints![serializedIdentifier]
        NetworkService.getResults(endpoint!, params: nil, headers: nil, completionHandler: completionHandler)
    }
    
    /*!
     * Search for a result set from the remote API.
     */
    static func search<T: RemoteResultProtocol>(params: Dictionary<String, String>?, completionHandler: (_: [T]) -> ()) {
        let endpoint = NetworkService.endpoints![serializedIdentifier]
        NetworkService.getResults(endpoint!, params: params, headers: nil, completionHandler: completionHandler)
    }
    
    /*! 
     * Given a model, persist it to the remote API.
     */
    func save(headers: Dictionary<String, String>?, completionHandler: (response: Response<AnyObject, NSError>) -> ()) {
        NetworkService.putObject(self, url: self.url, params: nil, headers: nil, completionHandler: completionHandler)
    }
    
    /*!
     * Deletes a given model from the remote API.
     */
    func delete(headers: Dictionary<String, String>?, completionHandler: (response: Response<AnyObject, NSError>) -> ()) {
        NetworkService.deleteObject(self, url: self.url, params: nil, headers: headers, completionHandler: completionHandler)
    }
}