//
// NoiseProtocolTests.swift
// bitchatTests
//
// This is free and unencumbered software released into the public domain.
// For more information, see <https://unlicense.org>
//

import XCTest
import CryptoKit
@testable import bitchat

final class NoiseProtocolTests: XCTestCase {
    
    var aliceKey: Curve25519.KeyAgreement.PrivateKey!
    var bobKey: Curve25519.KeyAgreement.PrivateKey!
    var aliceSession: NoiseSession!
    var bobSession: NoiseSession!
    
    override func setUp() {
        super.setUp()
        aliceKey = Curve25519.KeyAgreement.PrivateKey()
        bobKey = Curve25519.KeyAgreement.PrivateKey()
    }
    
    override func tearDown() {
        aliceSession = nil
        bobSession = nil
        super.tearDown()
    }
    
    // MARK: - Basic Handshake Tests
    
    func testXXPatternHandshake() throws {
        // Create sessions
        aliceSession = NoiseSession(
            peerID: TestConstants.testPeerID2,
            role: .initiator,
            localStaticKey: aliceKey
        )
        
        bobSession = NoiseSession(
            peerID: TestConstants.testPeerID1,
            role: .responder,
            localStaticKey: bobKey
        )
        
        // Alice starts handshake (message 1)
        let message1 = try aliceSession.startHandshake()
        XCTAssertFalse(message1.isEmpty)
        XCTAssertEqual(aliceSession.getState(), .handshaking)
        
        // Bob processes message 1 and creates message 2
        let message2 = try bobSession.processHandshakeMessage(message1)
        XCTAssertNotNil(message2)
        XCTAssertFalse(message2!.isEmpty)
        XCTAssertEqual(bobSession.getState(), .handshaking)
        
        // Alice processes message 2 and creates message 3
        let message3 = try aliceSession.processHandshakeMessage(message2!)
        XCTAssertNotNil(message3)
        XCTAssertFalse(message3!.isEmpty)
        XCTAssertEqual(aliceSession.getState(), .established)
        
        // Bob processes message 3 and completes handshake
        let finalMessage = try bobSession.processHandshakeMessage(message3!)
        XCTAssertNil(finalMessage) // No more messages needed
        XCTAssertEqual(bobSession.getState(), .established)
        
        // Verify both sessions are established
        XCTAssertTrue(aliceSession.isEstablished())
        XCTAssertTrue(bobSession.isEstablished())
        
        // Verify they have each other's static keys
        XCTAssertEqual(aliceSession.getRemoteStaticPublicKey()?.rawRepresentation, bobKey.publicKey.rawRepresentation)
        XCTAssertEqual(bobSession.getRemoteStaticPublicKey()?.rawRepresentation, aliceKey.publicKey.rawRepresentation)
    }
    
    func testHandshakeStateValidation() throws {
        aliceSession = NoiseSession(
            peerID: TestConstants.testPeerID2,
            role: .initiator,
            localStaticKey: aliceKey
        )
        
        // Cannot process message before starting handshake
        XCTAssertThrowsError(try aliceSession.processHandshakeMessage(Data()))
        
        // Start handshake
        _ = try aliceSession.startHandshake()
        
        // Cannot start handshake twice
        XCTAssertThrowsError(try aliceSession.startHandshake())
    }
    
    // MARK: - Encryption/Decryption Tests
    
    func testBasicEncryptionDecryption() throws {
        // Establish sessions
        try establishSessions()
        
        let plaintext = "Hello, Bob!".data(using: .utf8)!
        
        // Alice encrypts
        let ciphertext = try aliceSession.encrypt(plaintext)
        XCTAssertNotEqual(ciphertext, plaintext)
        XCTAssertGreaterThan(ciphertext.count, plaintext.count) // Should have overhead
        
        // Bob decrypts
        let decrypted = try bobSession.decrypt(ciphertext)
        XCTAssertEqual(decrypted, plaintext)
    }
    
    func testBidirectionalEncryption() throws {
        try establishSessions()
        
        // Alice -> Bob
        let aliceMessage = "Hello from Alice".data(using: .utf8)!
        let aliceCiphertext = try aliceSession.encrypt(aliceMessage)
        let bobReceived = try bobSession.decrypt(aliceCiphertext)
        XCTAssertEqual(bobReceived, aliceMessage)
        
        // Bob -> Alice
        let bobMessage = "Hello from Bob".data(using: .utf8)!
        let bobCiphertext = try bobSession.encrypt(bobMessage)
        let aliceReceived = try aliceSession.decrypt(bobCiphertext)
        XCTAssertEqual(aliceReceived, bobMessage)
    }
    
    func testLargeMessageEncryption() throws {
        try establishSessions()
        
        // Create a large message
        let largeMessage = TestHelpers.generateRandomData(length: 100_000)
        
        // Encrypt and decrypt
        let ciphertext = try aliceSession.encrypt(largeMessage)
        let decrypted = try bobSession.decrypt(ciphertext)
        
        XCTAssertEqual(decrypted, largeMessage)
    }
    
    func testEncryptionBeforeHandshake() {
        aliceSession = NoiseSession(
            peerID: TestConstants.testPeerID2,
            role: .initiator,
            localStaticKey: aliceKey
        )
        
        let plaintext = "test".data(using: .utf8)!
        
        // Should throw when not established
        XCTAssertThrowsError(try aliceSession.encrypt(plaintext))
        XCTAssertThrowsError(try aliceSession.decrypt(plaintext))
    }
    
    // MARK: - Session Manager Tests
    
    func testSessionManagerBasicOperations() throws {
        let manager = NoiseSessionManager(localStaticKey: aliceKey)
        
        // Create session
        let session = manager.createSession(for: TestConstants.testPeerID2, role: .initiator)
        XCTAssertNotNil(session)
        
        // Get session
        let retrieved = manager.getSession(for: TestConstants.testPeerID2)
        XCTAssertNotNil(retrieved)
        XCTAssertTrue(session === retrieved)
        
        // Remove session
        manager.removeSession(for: TestConstants.testPeerID2)
        XCTAssertNil(manager.getSession(for: TestConstants.testPeerID2))
    }
    
    func testSessionManagerHandshakeInitiation() throws {
        let manager = NoiseSessionManager(localStaticKey: aliceKey)
        
        // Initiate handshake
        let handshakeData = try manager.initiateHandshake(with: TestConstants.testPeerID2)
        XCTAssertFalse(handshakeData.isEmpty)
        
        // Session should exist
        let session = manager.getSession(for: TestConstants.testPeerID2)
        XCTAssertNotNil(session)
        XCTAssertEqual(session?.getState(), .handshaking)
    }
    
    func testSessionManagerIncomingHandshake() throws {
        let aliceManager = NoiseSessionManager(localStaticKey: aliceKey)
        let bobManager = NoiseSessionManager(localStaticKey: bobKey)
        
        // Alice initiates
        let message1 = try aliceManager.initiateHandshake(with: TestConstants.testPeerID2)
        
        // Bob responds
        let message2 = try bobManager.handleIncomingHandshake(from: TestConstants.testPeerID1, message: message1)
        XCTAssertNotNil(message2)
        
        // Continue handshake
        let message3 = try aliceManager.handleIncomingHandshake(from: TestConstants.testPeerID2, message: message2!)
        XCTAssertNotNil(message3)
        
        // Complete handshake
        let finalMessage = try bobManager.handleIncomingHandshake(from: TestConstants.testPeerID1, message: message3!)
        XCTAssertNil(finalMessage)
        
        // Both should have established sessions
        XCTAssertTrue(aliceManager.getSession(for: TestConstants.testPeerID2)?.isEstablished() ?? false)
        XCTAssertTrue(bobManager.getSession(for: TestConstants.testPeerID1)?.isEstablished() ?? false)
    }
    
    func testSessionManagerEncryptionDecryption() throws {
        let aliceManager = NoiseSessionManager(localStaticKey: aliceKey)
        let bobManager = NoiseSessionManager(localStaticKey: bobKey)
        
        // Establish sessions
        try establishManagerSessions(aliceManager: aliceManager, bobManager: bobManager)
        
        // Encrypt with manager
        let plaintext = "Test message".data(using: .utf8)!
        let ciphertext = try aliceManager.encrypt(plaintext, for: TestConstants.testPeerID2)
        
        // Decrypt with manager
        let decrypted = try bobManager.decrypt(ciphertext, from: TestConstants.testPeerID1)
        XCTAssertEqual(decrypted, plaintext)
    }
    
    // MARK: - Security Tests
    
    func testTamperedCiphertextDetection() throws {
        try establishSessions()
        
        let plaintext = "Secret message".data(using: .utf8)!
        var ciphertext = try aliceSession.encrypt(plaintext)
        
        // Tamper with ciphertext
        ciphertext[ciphertext.count / 2] ^= 0xFF
        
        // Decryption should fail
        XCTAssertThrowsError(try bobSession.decrypt(ciphertext))
    }
    
    func testReplayPrevention() throws {
        try establishSessions()
        
        let plaintext = "Test message".data(using: .utf8)!
        let ciphertext = try aliceSession.encrypt(plaintext)
        
        // First decryption should succeed
        _ = try bobSession.decrypt(ciphertext)
        
        // Replaying the same ciphertext should fail
        XCTAssertThrowsError(try bobSession.decrypt(ciphertext))
    }
    
    func testSessionIsolation() throws {
        // Create two separate session pairs
        let aliceSession1 = NoiseSession(peerID: "peer1", role: .initiator, localStaticKey: aliceKey)
        let bobSession1 = NoiseSession(peerID: "alice1", role: .responder, localStaticKey: bobKey)
        
        let aliceSession2 = NoiseSession(peerID: "peer2", role: .initiator, localStaticKey: aliceKey)
        let bobSession2 = NoiseSession(peerID: "alice2", role: .responder, localStaticKey: bobKey)
        
        // Establish both pairs
        try performHandshake(initiator: aliceSession1, responder: bobSession1)
        try performHandshake(initiator: aliceSession2, responder: bobSession2)
        
        // Encrypt with session 1
        let plaintext = "Secret".data(using: .utf8)!
        let ciphertext1 = try aliceSession1.encrypt(plaintext)
        
        // Should not be able to decrypt with session 2
        XCTAssertThrowsError(try bobSession2.decrypt(ciphertext1))
        
        // But should work with correct session
        let decrypted = try bobSession1.decrypt(ciphertext1)
        XCTAssertEqual(decrypted, plaintext)
    }
    
    // MARK: - Session Recovery Tests
    
    func testPeerRestartDetection() throws {
        // Establish initial sessions
        let aliceManager = NoiseSessionManager(localStaticKey: aliceKey)
        let bobManager = NoiseSessionManager(localStaticKey: bobKey)
        
        try establishManagerSessions(aliceManager: aliceManager, bobManager: bobManager)
        
        // Exchange some messages to establish nonce state
        let message1 = try aliceManager.encrypt("Hello".data(using: .utf8)!, for: TestConstants.testPeerID2)
        _ = try bobManager.decrypt(message1, from: TestConstants.testPeerID1)
        
        let message2 = try bobManager.encrypt("World".data(using: .utf8)!, for: TestConstants.testPeerID1)
        _ = try aliceManager.decrypt(message2, from: TestConstants.testPeerID2)
        
        // Simulate Bob restart by creating new manager with same key
        let bobManagerRestarted = NoiseSessionManager(localStaticKey: bobKey)
        
        // Bob initiates new handshake after restart
        let newHandshake1 = try bobManagerRestarted.initiateHandshake(with: TestConstants.testPeerID1)
        
        // Alice should accept the new handshake (clearing old session)
        let newHandshake2 = try aliceManager.handleIncomingHandshake(from: TestConstants.testPeerID2, message: newHandshake1)
        XCTAssertNotNil(newHandshake2)
        
        // Complete the new handshake
        let newHandshake3 = try bobManagerRestarted.handleIncomingHandshake(from: TestConstants.testPeerID1, message: newHandshake2!)
        XCTAssertNotNil(newHandshake3)
        _ = try aliceManager.handleIncomingHandshake(from: TestConstants.testPeerID2, message: newHandshake3!)
        
        // Should be able to exchange messages with new sessions
        let testMessage = "After restart".data(using: .utf8)!
        let encrypted = try bobManagerRestarted.encrypt(testMessage, for: TestConstants.testPeerID1)
        let decrypted = try aliceManager.decrypt(encrypted, from: TestConstants.testPeerID2)
        XCTAssertEqual(decrypted, testMessage)
    }
    
    func testNonceDesynchronizationRecovery() throws {
        // Create two sessions
        aliceSession = NoiseSession(peerID: TestConstants.testPeerID2, role: .initiator, localStaticKey: aliceKey)
        bobSession = NoiseSession(peerID: TestConstants.testPeerID1, role: .responder, localStaticKey: bobKey)
        
        // Establish sessions
        try performHandshake(initiator: aliceSession, responder: bobSession)
        
        // Exchange messages to advance nonces
        for i in 0..<5 {
            let msg = try aliceSession.encrypt("Message \(i)".data(using: .utf8)!)
            _ = try bobSession.decrypt(msg)
        }
        
        // Simulate desynchronization by encrypting but not decrypting
        for i in 0..<3 {
            _ = try aliceSession.encrypt("Lost message \(i)".data(using: .utf8)!)
        }
        
        // Next message from Alice should fail to decrypt (nonce mismatch)
        let desyncMessage = try aliceSession.encrypt("This will fail".data(using: .utf8)!)
        XCTAssertThrowsError(try bobSession.decrypt(desyncMessage))
    }
    
    func testConcurrentEncryption() throws {
        // Test thread safety of encryption operations
        let aliceManager = NoiseSessionManager(localStaticKey: aliceKey)
        let bobManager = NoiseSessionManager(localStaticKey: bobKey)
        
        try establishManagerSessions(aliceManager: aliceManager, bobManager: bobManager)
        
        let messageCount = 100
        let expectation = XCTestExpectation(description: "All messages encrypted and decrypted")
        expectation.expectedFulfillmentCount = messageCount * 2
        
        let group = DispatchGroup()
        var encryptedMessages: [Int: Data] = [:]
        let encryptionQueue = DispatchQueue(label: "test.encryption", attributes: .concurrent)
        let lock = NSLock()
        
        // Encrypt messages concurrently
        for i in 0..<messageCount {
            group.enter()
            DispatchQueue.global().async {
                do {
                    let plaintext = "Concurrent message \(i)".data(using: .utf8)!
                    let encrypted = try aliceManager.encrypt(plaintext, for: TestConstants.testPeerID2)
                    
                    lock.lock()
                    encryptedMessages[i] = encrypted
                    lock.unlock()
                    
                    expectation.fulfill()
                } catch {
                    XCTFail("Encryption failed: \(error)")
                }
                group.leave()
            }
        }
        
        // Wait for all encryptions to complete
        group.wait()
        
        // Decrypt messages in order
        for i in 0..<messageCount {
            encryptionQueue.async {
                do {
                    lock.lock()
                    guard let encrypted = encryptedMessages[i] else {
                        lock.unlock()
                        XCTFail("Missing encrypted message \(i)")
                        return
                    }
                    lock.unlock()
                    
                    let decrypted = try bobManager.decrypt(encrypted, from: TestConstants.testPeerID1)
                    let expected = "Concurrent message \(i)".data(using: .utf8)!
                    XCTAssertEqual(decrypted, expected)
                    expectation.fulfill()
                } catch {
                    XCTFail("Decryption failed for message \(i): \(error)")
                }
            }
        }
        
        wait(for: [expectation], timeout: 10.0)
    }
    
    func testSessionStaleDetection() throws {
        // Test that sessions are properly marked as stale
        let aliceManager = NoiseSessionManager(localStaticKey: aliceKey)
        let bobManager = NoiseSessionManager(localStaticKey: bobKey)
        
        try establishManagerSessions(aliceManager: aliceManager, bobManager: bobManager)
        
        // Get the session and check it needs renegotiation based on age
        let sessions = aliceManager.getSessionsNeedingRekey()
        
        // New session should not need rekey
        XCTAssertTrue(sessions.isEmpty || sessions.allSatisfy { !$0.needsRekey })
    }
    
    func testHandshakeAfterDecryptionFailure() throws {
        // Test that handshake is properly initiated after decryption failure
        let aliceManager = NoiseSessionManager(localStaticKey: aliceKey)
        let bobManager = NoiseSessionManager(localStaticKey: bobKey)
        
        // Establish sessions
        try establishManagerSessions(aliceManager: aliceManager, bobManager: bobManager)
        
        // Create a corrupted message
        var encrypted = try aliceManager.encrypt("Test".data(using: .utf8)!, for: TestConstants.testPeerID2)
        encrypted[10] ^= 0xFF // Corrupt the data
        
        // Decryption should fail
        XCTAssertThrowsError(try bobManager.decrypt(encrypted, from: TestConstants.testPeerID1))
        
        // Bob should still have the session (it's not removed on single failure)
        XCTAssertNotNil(bobManager.getSession(for: TestConstants.testPeerID1))
    }
    
    func testHandshakeAlwaysAcceptedWithExistingSession() throws {
        // Test that handshake is always accepted even with existing valid session
        let aliceManager = NoiseSessionManager(localStaticKey: aliceKey)
        let bobManager = NoiseSessionManager(localStaticKey: bobKey)
        
        // Establish sessions
        try establishManagerSessions(aliceManager: aliceManager, bobManager: bobManager)
        
        // Verify sessions are established
        XCTAssertTrue(aliceManager.getSession(for: TestConstants.testPeerID2)?.isEstablished() ?? false)
        XCTAssertTrue(bobManager.getSession(for: TestConstants.testPeerID1)?.isEstablished() ?? false)
        
        // Exchange messages to verify sessions work
        let testMessage = "Session works".data(using: .utf8)!
        let encrypted = try aliceManager.encrypt(testMessage, for: TestConstants.testPeerID2)
        let decrypted = try bobManager.decrypt(encrypted, from: TestConstants.testPeerID1)
        XCTAssertEqual(decrypted, testMessage)
        
        // Alice clears her session (simulating decryption failure)
        aliceManager.removeSession(for: TestConstants.testPeerID2)
        
        // Alice initiates new handshake despite Bob having valid session
        let newHandshake1 = try aliceManager.initiateHandshake(with: TestConstants.testPeerID2)
        
        // Bob should accept the new handshake even though he has a valid session
        let newHandshake2 = try bobManager.handleIncomingHandshake(from: TestConstants.testPeerID1, message: newHandshake1)
        XCTAssertNotNil(newHandshake2, "Bob should accept handshake despite having valid session")
        
        // Complete the handshake
        let newHandshake3 = try aliceManager.handleIncomingHandshake(from: TestConstants.testPeerID2, message: newHandshake2!)
        XCTAssertNotNil(newHandshake3)
        _ = try bobManager.handleIncomingHandshake(from: TestConstants.testPeerID1, message: newHandshake3!)
        
        // Verify new sessions work
        let testMessage2 = "New session works".data(using: .utf8)!
        let encrypted2 = try aliceManager.encrypt(testMessage2, for: TestConstants.testPeerID2)
        let decrypted2 = try bobManager.decrypt(encrypted2, from: TestConstants.testPeerID1)
        XCTAssertEqual(decrypted2, testMessage2)
    }
    
    func testNonceDesynchronizationCausesRehandshake() throws {
        // Test that nonce desynchronization leads to proper re-handshake
        let aliceManager = NoiseSessionManager(localStaticKey: aliceKey)
        let bobManager = NoiseSessionManager(localStaticKey: bobKey)
        
        // Establish sessions
        try establishManagerSessions(aliceManager: aliceManager, bobManager: bobManager)
        
        // Exchange messages normally
        for i in 0..<5 {
            let msg = try aliceManager.encrypt("Message \(i)".data(using: .utf8)!, for: TestConstants.testPeerID2)
            _ = try bobManager.decrypt(msg, from: TestConstants.testPeerID1)
        }
        
        // Simulate desynchronization - Alice sends messages that Bob doesn't receive
        for i in 0..<3 {
            _ = try aliceManager.encrypt("Lost message \(i)".data(using: .utf8)!, for: TestConstants.testPeerID2)
        }
        
        // Next message from Alice should fail to decrypt at Bob (nonce mismatch)
        let desyncMessage = try aliceManager.encrypt("This will fail".data(using: .utf8)!, for: TestConstants.testPeerID2)
        XCTAssertThrowsError(try bobManager.decrypt(desyncMessage, from: TestConstants.testPeerID1), "Should fail due to nonce mismatch")
        
        // Bob clears session and initiates new handshake
        bobManager.removeSession(for: TestConstants.testPeerID1)
        let rehandshake1 = try bobManager.initiateHandshake(with: TestConstants.testPeerID1)
        
        // Alice should accept despite having a "valid" (but desynced) session
        let rehandshake2 = try aliceManager.handleIncomingHandshake(from: TestConstants.testPeerID2, message: rehandshake1)
        XCTAssertNotNil(rehandshake2, "Alice should accept handshake to fix desync")
        
        // Complete handshake
        let rehandshake3 = try bobManager.handleIncomingHandshake(from: TestConstants.testPeerID1, message: rehandshake2!)
        XCTAssertNotNil(rehandshake3)
        _ = try aliceManager.handleIncomingHandshake(from: TestConstants.testPeerID2, message: rehandshake3!)
        
        // Verify communication works again
        let testResynced = "Resynced".data(using: .utf8)!
        let encryptedResync = try aliceManager.encrypt(testResynced, for: TestConstants.testPeerID2)
        let decryptedResync = try bobManager.decrypt(encryptedResync, from: TestConstants.testPeerID1)
        XCTAssertEqual(decryptedResync, testResynced)
    }
    
    // MARK: - Performance Tests
    
    func testHandshakePerformance() throws {
        measure {
            do {
                let alice = NoiseSession(peerID: "bob", role: .initiator, localStaticKey: aliceKey)
                let bob = NoiseSession(peerID: "alice", role: .responder, localStaticKey: bobKey)
                try performHandshake(initiator: alice, responder: bob)
            } catch {
                XCTFail("Handshake failed: \(error)")
            }
        }
    }
    
    func testEncryptionPerformance() throws {
        try establishSessions()
        let message = TestHelpers.generateRandomData(length: 1024)
        
        measure {
            do {
                for _ in 0..<100 {
                    let ciphertext = try aliceSession.encrypt(message)
                    _ = try bobSession.decrypt(ciphertext)
                }
            } catch {
                XCTFail("Encryption/decryption failed: \(error)")
            }
        }
    }
    
    // MARK: - Helper Methods
    
    private func establishSessions() throws {
        aliceSession = NoiseSession(
            peerID: TestConstants.testPeerID2,
            role: .initiator,
            localStaticKey: aliceKey
        )
        
        bobSession = NoiseSession(
            peerID: TestConstants.testPeerID1,
            role: .responder,
            localStaticKey: bobKey
        )
        
        try performHandshake(initiator: aliceSession, responder: bobSession)
    }
    
    private func performHandshake(initiator: NoiseSession, responder: NoiseSession) throws {
        let msg1 = try initiator.startHandshake()
        let msg2 = try responder.processHandshakeMessage(msg1)!
        let msg3 = try initiator.processHandshakeMessage(msg2)!
        _ = try responder.processHandshakeMessage(msg3)
    }
    
    private func establishManagerSessions(aliceManager: NoiseSessionManager, bobManager: NoiseSessionManager) throws {
        let msg1 = try aliceManager.initiateHandshake(with: TestConstants.testPeerID2)
        let msg2 = try bobManager.handleIncomingHandshake(from: TestConstants.testPeerID1, message: msg1)!
        let msg3 = try aliceManager.handleIncomingHandshake(from: TestConstants.testPeerID2, message: msg2)!
        _ = try bobManager.handleIncomingHandshake(from: TestConstants.testPeerID1, message: msg3)
    }
}