requests.swift

import Foundation

infix operator >>- { associativity left precedence 150 }
public func >>-<T, U>(a: T?, f: T -> U?) -> U? {
    return a.flatMap(f)
}

extension Optional {
    func flatMap<U>(f: T -> U?) -> U? {
        switch self {
        case let .Some(x): return f(x)
        default: return .None
        }
    }
}

protocol RequestType { }

struct Request<T: RequestType> {
    let request: NSMutableURLRequest
}

struct GET: RequestType { }
struct POST: RequestType { }
struct Authenticated: RequestType { }
struct Payload: RequestType { }

func addPayload<T: RequestType>(json: AnyObject)(request: Request<T>) -> Request<Payload>? {
    let req = request.request
    req.setValue("application/json", forHTTPHeaderField: "Content-Type")
    req.HTTPBody = NSJSONSerialization.dataWithJSONObject(json, options: NSJSONWritingOptions(0), error: nil)
    return Request(request: req)
}

func postRequest(request: Request<GET>) -> Request<POST>? {
    let req = request.request
    req.HTTPMethod = "POST"
    return Request(request: req)
}

func authenticateRequest<T: RequestType>(request: Request<T>) -> Request<Authenticated>? {
    if let token = getToken() {
        let req = request.request
        req.setValue("Token token=\(token)", forHTTPHeaderField: "Authorization")
        return Request(request: req)
    }

    return .None
}

func getToken() -> String? {
    return "foo"
}


func mutableRequestForPath(path: String) -> Request<GET>? {
    let url = NSURL(string: path)

    if let request = url.map({ NSMutableURLRequest(URL: $0) }) {
        request.setValue("application/vnd.circus+json; version=foobar", forHTTPHeaderField: "Accept")
        request.setValue("gzip;q=1.0,compress;q=0.5", forHTTPHeaderField: "Accept-Encoding")
        return Request(request: request)
    }

    return .None
}

let request = mutableRequestForPath("foo") >>- postRequest >>- addPayload([]) >>- authenticateRequest