import Combine
import Foundation
import MultipeerConnectivity

struct OwnPeer {
  let peer: MCPeerID
}

struct Peer: Identifiable {
  enum ConnectionState {
    case available
    case joined
    case rejected
    case invitationPending
  }

  var id: String { mcPeer.displayName }
  let mcPeer: MCPeerID
  var state: ConnectionState
}

@Observable
final class NoteEditingSessionServer: NSObject {
  private let session: MCSession
  private let browser: MCNearbyServiceBrowser
  private(set) var ownPeer: OwnPeer

  var visiblePeers: [Peer] = []
  let noteChangesEmitter = PassthroughSubject<NoteMessage, Never>()

  init(peer: OwnPeer) {
    ownPeer = peer
    browser = .init(peer: peer.peer, serviceType: "peered")
    session = .init(peer: peer.peer, securityIdentity: nil, encryptionPreference: .required)
    super.init()
    browser.delegate = self
    session.delegate = self
  }

  func startServer() {
    browser.startBrowsingForPeers()
  }

  func stopServer() {
    browser.stopBrowsingForPeers()
    session.disconnect()
  }

  func invite(peer: Peer, to note: NoteInvitation.NoteContent) {
    guard peer.state == .available, let note = try? JSONEncoder().encode(note) else { return }
    browser.invitePeer(
      peer.mcPeer,
      to: session,
      withContext: note,
      timeout: 600
    )
    guard let idxToUpdate = visiblePeers.firstIndex(where: { $0.mcPeer == peer.mcPeer }) else {
      return
    }
    visiblePeers[idxToUpdate].state = .invitationPending
  }

  func send(note: String, to peers: [MCPeerID]) {
    let message = NoteMessage(senderID: ownPeer.peer.displayName, content: note)
    guard !peers.isEmpty, let data = try? JSONEncoder().encode(message) else { return }
    try? session.send(data, toPeers: peers, with: .reliable)
  }
}

extension NoteEditingSessionServer: MCNearbyServiceBrowserDelegate {
  func browser(
    _ browser: MCNearbyServiceBrowser,
    foundPeer peerID: MCPeerID,
    withDiscoveryInfo info: [String: String]?
  ) {
    guard
      !visiblePeers.contains(where: { $0.mcPeer == peerID })
        && peerID.displayName != ownPeer.peer.displayName
    else { return }
    DispatchQueue.main.async {
      self.visiblePeers.append(Peer(mcPeer: peerID, state: .available))
    }
  }

  func browser(_ browser: MCNearbyServiceBrowser, lostPeer peerID: MCPeerID) {
    DispatchQueue.main.async {
      guard let peerIdx = self.visiblePeers.firstIndex(where: { $0.mcPeer == peerID }) else {
        return
      }
      self.visiblePeers.remove(at: peerIdx)
    }
  }
}

extension NoteEditingSessionServer: MCSessionDelegate {
  func session(
    _ session: MCSession,
    peer peerID: MCPeerID,
    didChange state: MCSessionState
  ) {
    DispatchQueue.main.async {
      guard let idx = self.visiblePeers.firstIndex(where: { $0.mcPeer == peerID }) else { return }
      switch state {
      case .connected:
        self.visiblePeers[idx].state = .joined
      case .notConnected:
        let currentState = self.visiblePeers[idx].state
        if currentState == .invitationPending || currentState == .joined {
          self.visiblePeers[idx].state = .rejected
        }
      default:
        break
      }
    }
  }

  func session(_ session: MCSession, didReceive data: Data, fromPeer peerID: MCPeerID) {
    guard let message = try? JSONDecoder().decode(NoteMessage.self, from: data) else { return }

    let otherPeers = session.connectedPeers.filter { $0 != peerID }
    if !otherPeers.isEmpty {
      try? session.send(data, toPeers: otherPeers, with: .reliable)
    }

    DispatchQueue.main.async {
      self.noteChangesEmitter.send(message)
    }
  }

  func session(
    _ session: MCSession, didReceive stream: InputStream, withName streamName: String,
    fromPeer peerID: MCPeerID
  ) {}
  func session(
    _ session: MCSession, didStartReceivingResourceWithName resourceName: String,
    fromPeer peerID: MCPeerID, with progress: Progress
  ) {}
  func session(
    _ session: MCSession, didFinishReceivingResourceWithName resourceName: String,
    fromPeer peerID: MCPeerID, at localURL: URL?, withError error: (any Error)?
  ) {}
}