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Version 1 of Functional Wish Fulfillment
//
// Version 1 of pagesFromData from Functional Wish Fulfillment
// http://robnapier.net/functional-wish-fulfillment
//
import Foundation
func pagesFromData(data: NSData) -> PageListResult {
// 1. Parse the NSData into a JSON object
var error: NSError?
let json: JSON? = NSJSONSerialization.JSONObjectWithData(data,
options: NSJSONReadingOptions(0), error: &error)
if let json: JSON = json {
// 2. Make sure the JSON object is an array
if let array = json as? JSONArray {
// 3. Get the second element
if array.count < 2 {
// Failure leg for 3
return .Failure(NSError(localizedDescription:
"Could not get second element. Array too short: \(array.count)"))
}
let element: JSON = array[1]
// 4. Make sure the second element is a list of strings
if let titles = element as? [String] {
// 5. Convert those strings into pages
return .Success(titles.map { Page(title: $0) })
}
else {
// Failure leg for 4
return .Failure(NSError(localizedDescription: "Expected string list. Got: \(array[1])"))
}
}
else {
// Failure leg for 2
return .Failure(NSError(localizedDescription: "Expected array. Got: \(json)"))
}
}
else if let error = error {
// Failure leg for 1
return .Failure(error)
}
else {
fatalError("Received neither JSON nor an error")
return .Failure(NSError())
}
}
//
// Some basic types
//
typealias JSON = AnyObject
typealias JSONArray = [JSON]
struct Page {
let title: String
}
extension Page: Printable {
var description: String {
return title
}
}
enum PageListResult {
case Success([Page])
case Failure(NSError)
}
extension PageListResult: Printable {
var description: String {
switch self {
case .Success(let pages):
return "Success: " + join(", ", pages.map { "\"\($0.description)\""})
case .Failure(let error):
return "Failure: \(error.localizedDescription)"
}
}
}
//
// A little helper to make errors easier
//
extension NSError {
convenience init(localizedDescription: String) {
self.init(domain: "", code: 0, userInfo: [NSLocalizedDescriptionKey: localizedDescription])
}
}
//
// TESTS
//
// Helper function for tests below
func asJSONData(string: NSString) -> NSData {
return string.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)!
}
let goodPagesJson = asJSONData("[\"a\",[\"Animal\",\"Association football\",\"Arthropod\",\"Australia\",\"AllMusic\",\"African American (U.S. Census)\",\"Album\",\"Angiosperms\",\"Actor\",\"American football\",\"Austria\",\"Argentina\",\"American Civil War\",\"Administrative divisions of Iran\",\"Alternative rock\"]]")
pagesFromData(goodPagesJson).description
let corruptJson = asJSONData("a\",[\"Animal\",\"Association football\",\"Arthropod\",\"Australia\",\"AllMusic\",\"African American (U.S. Census)\",\"Album\",\"Angiosperms\",\"Actor\",\"American football\",\"Austria\",\"Argentina\",\"American Civil War\",\"Administrative divisions of Iran\",\"Alternative rock\"]]")
pagesFromData(corruptJson).description
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