Astronomy Picture of the Day with ReactiveCocoa 4

APOD.swift

// APOD.swift
// Test with ReactiveCocoa 4
//
// Created by Chris Patrick Schreiner on 17-11-2015.

import ReactiveCocoa
import Result
import XCPlayground

XCPlaygroundPage.currentPage.needsIndefiniteExecution = true

// Get your own key at https://api.nasa.gov/index.html#apply-for-an-api-key/
let APOD_API_KEY: String? = nil //when nil, use DEMO_KEY

//:#### Misc stuff used by the astronomyPictureOfTheDay-consumer

func mapDate(date: NSDate) -> String {
    let formatter = NSDateFormatter()
    formatter.dateFormat = "yyyy-MM-dd"
    return formatter.stringFromDate(date)
}

extension Double {
    var days: NSTimeInterval {return 86400*self}
}

extension NSImageView {
    convenience init(image:NSImage) {
        self.init()
        self.image = image
        self.frame = NSMakeRect(0,0,image.size.width, image.size.height)
    }
}

func presentImage(image:NSImage) {
    XCPlaygroundPage.currentPage.liveView = NSImageView(image: image)
}

func printError<T>(e:T) {
    print("error: \(e)")
}

//:### Helper functions used by the astronomyPictureOfTheDay-producer

typealias JSONDict = [NSObject:AnyObject]

enum APODError: ErrorType {
    case ErrorInURL
    case ServerHappenstance(String)
    case JSONHappenstance(String)
    case ValidationHappenstance(String)
    case ImageHappenstance
    case NSError(String, Int, JSONDict?)
}

func makeUrl(date: NSDate, hd: String = "false", format: String = "JSON", apiKey: String, urlAPI: NSURL? = NSURL(string: "https://api.nasa.gov/planetary/apod")) -> NSURL? {
    if let urlAPI = urlAPI, components = NSURLComponents(URL: urlAPI, resolvingAgainstBaseURL: false) {
        components.queryItems = [
                "api_key": apiKey,
                "format": format,
                "hd": hd,
                "date": mapDate(date),
        ].map(NSURLQueryItem.init)
        return components.URL
    }
    return nil
}

func validateResponse(data: NSData, response: NSURLResponse) -> Result<(NSData, NSURLResponse), APODError> {
    guard let r = response as? NSHTTPURLResponse else {
        return .Failure(APODError.ValidationHappenstance("NSHTTPURLResponse cast failed"))
    }
    guard 200..<299 ~= r.statusCode else {
        return .Failure(.ValidationHappenstance("statuscode \(r.statusCode)"))
    }
    return .Success((data, response))
}

func jsonAdaptor(data: NSData, response: NSURLResponse) -> Result<JSONDict, APODError> {
    guard let json = try? NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions()) else {
        return .Failure(.JSONHappenstance("got thrown at for serializing"))
    }
    guard let dict = json as? JSONDict else {
        return .Failure(.JSONHappenstance("JSONDict cast failed \(json)"))
    }
    return .Success(dict)
}

func performRequest(request: NSURLRequest) -> SignalProducer<(NSData, NSURLResponse), APODError> {
    return NSURLSession.sharedSession()
        .rac_dataWithRequest(request)
        .mapError {
            error in .NSError(error.domain, error.code, error.userInfo)
        }
}

func extractUrl(dict: JSONDict) -> Result<NSURL, APODError> {
    guard let urlString = dict["url"] as? String, url = NSURL(string:urlString) else {
        if let error = dict["error"] as? String {
            return .Failure(.ServerHappenstance(error))
        }
        return .Failure(.JSONHappenstance("url-field not found"))
    }
    return .Success(url)
}

func imageFromData(data: NSData, response: NSURLResponse) -> Result<NSImage, APODError> {
    guard let image = NSImage(data: data) else {
        return .Failure(.ImageHappenstance)
    }
    return .Success(image)
}

//:### Core

func astronomyPictureOfTheDay(date date: NSDate = NSDate(), apiKey: String? = nil) -> SignalProducer<NSImage, APODError> {
    if let url = makeUrl(date, apiKey: apiKey ?? "DEMO_KEY") {
        return SignalProducer(value: url)
            .map(NSURLRequest.init)
            .flatMap(.Latest, transform: performRequest) //fetch some JSON
            .attemptMap(validateResponse) //make sure we get a 200
            .attemptMap(jsonAdaptor) //convert NSData to JSON
            .attemptMap(extractUrl) //extract from JSON a URL
            .map(NSURLRequest.init)
            .flatMap(.Latest, transform: performRequest) //fetch an NSImage
            .attemptMap(validateResponse) //make sure we get a 200
            .attemptMap(imageFromData) //convert NSData to NSImage
    } else {
        return SignalProducer(error: APODError.ErrorInURL)
    }
}

astronomyPictureOfTheDay(date:NSDate(timeIntervalSinceNow: 0.days), apiKey: APOD_API_KEY)
    .observeOn(QueueScheduler.mainQueueScheduler)
    .on(next: presentImage)
    .on(failed: printError)
    .start()