Create LokiRSSFeedParser

SignalServiceKit/src/Loki/API/LokiRSSFeedParser.swift

@@ -0,0 +1,54 @@
+
+public final class LokiRSSFeedParser : NSObject, XMLParserDelegate {
+    private let url: URL
+    private var completion: (([Item]) -> Void)?
+    private var tag: Tag?
+    private var currentItem: Item?
+    private var items: [Item] = []
+    
+    private enum Tag : String {
+        case item, title, description, date = "pubDate"
+    }
+    
+    public struct Item {
+        public var title: String? = nil
+        public var description: String? = nil
+        public var dateAsString: String? = nil
+    }
+    
+    public init(url: URL) {
+        self.url = url
+        super.init()
+    }
+    
+    public func parse(completion: @escaping (([Item]) -> Void)) {
+        guard let parser = XMLParser(contentsOf: url) else { return }
+        self.completion = completion
+        parser.delegate = self
+        parser.parse()
+    }
+    
+    public func parser(_ parser: XMLParser, didStartElement elementAsString: String, namespaceURI: String?, qualifiedName: String?, attributes: [String:String] = [:]) {
+        if let element = Tag(rawValue: elementAsString) { self.tag = element }
+        if tag == .item { currentItem = Item() }
+    }
+    
+    public func parser(_ parser: XMLParser, foundCharacters string: String) {
+        guard let element = tag else { return }
+        switch element {
+        case .title: currentItem?.title = string
+        case .description: currentItem?.description = string
+        case .date: currentItem?.dateAsString = string
+        default: break
+        }
+    }
+    
+    public func parser(_ parser: XMLParser, didEndElement elementAsString: String, namespaceURI: String?, qualifiedName: String?) {
+        guard let element = Tag(rawValue: elementAsString) else { return }
+        if element == .item, let currentItem = self.currentItem { items.append(currentItem) }
+    }
+    
+    public func parserDidEndDocument(_ parser: XMLParser) {
+        completion?(items)
+    }
+}