import MultipeerConnectivity
import Foundation
import Combine

struct OwnPeer {
	let peer: MCPeerID
	
	static var fallback: Self { Self(peer: .init(displayName: "fallback_user")) }
}

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 let ownPeer: OwnPeer
	
	var visiblePeers: [Peer] = []
	let noteChangesEmitter = PassthroughSubject<String, Never>()
	
	init(peer: OwnPeer) {
		ownPeer = peer
		browser = .init(peer: peer.peer, serviceType: "peered")
		session = .init(peer: peer.peer)
		super.init()
		browser.delegate = self
		session.delegate = self
	}
	
	func startServer() {
		browser.startBrowsingForPeers()
	}
	
	func stopServer() {
		browser.stopBrowsingForPeers()
	}
	
	func invite(peer: Peer, to note: NoteInvitation.NoteContent) {
		guard peer.state == .available else { return }
		browser.invitePeer(
			peer.mcPeer,
			to: session,
			withContext: try! JSONEncoder().encode(note),
			timeout: 5
		)
		
		let idxToUpdate = visiblePeers.firstIndex(where: { $0.mcPeer == peer.mcPeer })!
		visiblePeers[idxToUpdate].state = .invitationPending
	}
}

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 }
		let newPeer = Peer(mcPeer: peerID, state: .available)
		visiblePeers.append(newPeer)
	}
	
	func browser(_ browser: MCNearbyServiceBrowser, lostPeer peerID: MCPeerID) {
		guard let peerIdx = visiblePeers.firstIndex(where: { $0.mcPeer == peerID }) else { return }
		visiblePeers.remove(at: peerIdx)
	}
}

extension NoteEditingSessionServer: MCSessionDelegate {
	func session(
		_ session: MCSession,
		peer peerID: MCPeerID,
		didChange state: MCSessionState
	) {
		
	}
	
	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)?
	) {
		
	}
	
	func session(_ session: MCSession, didReceive data: Data, fromPeer peerID: MCPeerID) {
		guard let note = String(data: data, encoding: .utf8) else { fatalError() }
		noteChangesEmitter.send(note)
	}
}