Gemini/GeminiProtocol/GeminiConnection.swift

//
//  GeminiConnection.swift
//  Gemini
//
//  Created by Shadowfacts on 7/12/20.
//

import Foundation
import Network

public protocol GeminiConnectionDelegate: class {
    func connectionReady(_ connection: GeminiConnection)
    func connection(_ connection: GeminiConnection, receivedData data: Data?, header: GeminiResponseHeader)
    func connection(_ connection: GeminiConnection, handleError error: GeminiConnection.Error)
    func connectionCompleted(_ connection: GeminiConnection)
}

public class GeminiConnection {
    
    public typealias Error = NWError
    
    public weak var delegate: GeminiConnectionDelegate?
    
    private let connection: NWConnection
    
    public init(endpoint: NWEndpoint, delegate: GeminiConnectionDelegate? = nil) {
        self.connection = NWConnection(to: endpoint, using: .gemini)
        self.delegate = delegate
    }
    
    public func startConnection() {
        connection.stateUpdateHandler = { (newState) in
            switch newState {
            case .ready:
                print("\(self.connection) established")
                self.delegate?.connectionReady(self)
            case let .failed(error):
                print("\(self.connection) failed: \(error)")
                self.connection.cancel()
            default:
                break
            }
        }
        
        // todo: should this be on a background queue?
        connection.start(queue: .main)
    }
    
    public func cancelConnection() {
        if connection.state != .cancelled {
            connection.cancel()
        }
    }
    
    public func sendRequest(_ request: GeminiRequest) {
        let message = NWProtocolFramer.Message(geminiRequest: request)
        let context = NWConnection.ContentContext(identifier: "GeminiRequest", metadata: [message])
        // todo: should this really always be idempotent?
        connection.send(content: nil, contentContext: context, isComplete: true, completion: .contentProcessed({ (_) in }))
        receiveNextMessage()
    }
    
    private func receiveNextMessage() {
        connection.receiveMessage { (data, context, isComplete, error) in
            if let error = error {
                self.delegate?.connection(self, handleError: error)
            } else if let message = context?.protocolMetadata(definition: GeminiProtocol.definition) as? NWProtocolFramer.Message,
               let header = message.geminiResponseHeader,
               let delegate = self.delegate {
                delegate.connection(self, receivedData: data, header: header)
            }
            
            guard isComplete else { fatalError("Connection should complete immediately") }
            self.delegate?.connectionCompleted(self)
            self.connection.cancel()
        }
    }
    
}