Moment.swift

import Foundation
import JavaScriptCore


/// Used to lookup our Bundle.
private class MomentBundleClass: NSObject {}


/// A wrapper around a moment.js object.
public struct Moment {
	/// A shared context that new instances are created from.
	public static let sharedContext: JSContext? = {
		guard let context = JSContext() else { return nil }
		
		guard let url = Bundle(for: MomentBundleClass.self).url(forResource: "moment", withExtension: "js") else { return nil }
		guard let javascript = try? String(contentsOf: url) else { return nil }
		
		_ = context.evaluateScript(javascript)
		
		return context
	}()
	
	
	/// The underlying JavaScript value.
	public let value: JSValue
	
	/// Create a new moment instance from a date
	///
	/// - Parameter date: The equivelant date to create the moment from.
	public init?(_ date: Date) {
		let timestamp = date.timeIntervalSince1970 * 1000
		
		// equivelant to `moment(timestamp);`
		guard let value = Moment.sharedContext?.objectForKeyedSubscript("moment").call(withArguments: [timestamp]) else { return nil }
		
		self.value = value
	}
	
	
	/// Generate a relative description from the current time
	///
	/// See [http://momentjs.com/docs/#/displaying/fromnow/](http://momentjs.com/docs/#/displaying/fromnow/).
	///
	/// - Returns: The description based on the amount of time from now.
	public func fromNow() -> String? {
		// `.fromNow();`
		return value.invokeMethod("fromNow", withArguments: []).toString()
	}
	
	
	public enum CalendarFormat: String {
		case sameDay
		case nextDay
		case nextWeek
		case lastDay
		case lastWeek
		case sameElse
	}
	
	public func calendar(formats: [CalendarFormat: String]? = nil) -> String? {
		let rawFormats = formats?.dictionaryMap({ ($0.rawValue, $1) })
		
		return value.invokeMethod("calendar", withArguments: [NSNull(), rawFormats.unwrapWithNSNull]).toString()
	}
}