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

///
/// # SecureIdentityStateManager
///
/// Manages the persistent storage and retrieval of identity mappings with
/// encryption at rest. This singleton service maintains the relationship between
/// ephemeral peer IDs, cryptographic fingerprints, and social identities.
///
/// ## Overview
/// The SecureIdentityStateManager provides a secure, privacy-preserving way to
/// maintain identity relationships across app launches. It implements:
/// - Encrypted storage of identity mappings
/// - In-memory caching for performance
/// - Thread-safe access patterns
/// - Automatic debounced persistence
///
/// ## Architecture
/// The manager operates at three levels:
/// 1. **In-Memory State**: Fast access to active identities
/// 2. **Encrypted Cache**: Persistent storage in Keychain
/// 3. **Privacy Controls**: User-configurable persistence settings
///
/// ## Security Features
///
/// ### Encryption at Rest
/// - Identity cache encrypted with AES-GCM
/// - Unique 256-bit encryption key per device
/// - Key stored separately in Keychain
/// - No plaintext identity data on disk
///
/// ### Privacy by Design
/// - Persistence is optional (user-controlled)
/// - Minimal data retention
/// - No cloud sync or backup
/// - Automatic cleanup of stale entries
///
/// ### Thread Safety
/// - Concurrent read access via GCD barriers
/// - Write operations serialized
/// - Atomic state updates
/// - No data races or corruption
///
/// ## Data Model
/// Manages three types of identity data:
/// 1. **Ephemeral Sessions**: Current peer connections
/// 2. **Cryptographic Identities**: Public keys and fingerprints
/// 3. **Social Identities**: User-assigned names and trust
///
/// ## Persistence Strategy
/// - Changes batched and debounced (2-second window)
/// - Automatic save on app termination
/// - Crash-resistant with atomic writes
/// - Migration support for schema changes
///
/// ## Usage Patterns
/// ```swift
/// // Register a new peer identity
/// manager.registerPeerIdentity(peerID, publicKey, fingerprint)
/// 
/// // Update social identity
/// manager.updateSocialIdentity(fingerprint, nickname, trustLevel)
/// 
/// // Query identity
/// let identity = manager.resolvePeerIdentity(peerID)
/// ```
///
/// ## Performance Optimizations
/// - In-memory cache eliminates Keychain roundtrips
/// - Debounced saves reduce I/O operations
/// - Efficient data structures for lookups
/// - Background queue for expensive operations
///
/// ## Privacy Considerations
/// - Users can disable all persistence
/// - Identity cache can be wiped instantly
/// - No analytics or telemetry
/// - Ephemeral mode for high-risk users
///
/// ## Future Enhancements
/// - Selective identity export
/// - Cross-device identity sync (optional)
/// - Identity attestation support
/// - Advanced conflict resolution
///

import Foundation
import CryptoKit

protocol SecureIdentityStateManagerProtocol {
    // MARK: Secure Loading/Saving
    func forceSave()
    
    // MARK: Social Identity Management
    func getSocialIdentity(for fingerprint: String) -> SocialIdentity?
    
    // MARK: Cryptographic Identities
    func upsertCryptographicIdentity(fingerprint: String, noisePublicKey: Data, signingPublicKey: Data?, claimedNickname: String?)
    func getCryptoIdentitiesByPeerIDPrefix(_ peerID: String) -> [CryptographicIdentity]
    func updateSocialIdentity(_ identity: SocialIdentity)
    
    // MARK: Favorites Management
    func getFavorites() -> Set<String>
    func setFavorite(_ fingerprint: String, isFavorite: Bool)
    func isFavorite(fingerprint: String) -> Bool
    
    // MARK: Blocked Users Management
    func isBlocked(fingerprint: String) -> Bool
    func setBlocked(_ fingerprint: String, isBlocked: Bool)
    
    // MARK: Geohash (Nostr) Blocking
    func isNostrBlocked(pubkeyHexLowercased: String) -> Bool
    func setNostrBlocked(_ pubkeyHexLowercased: String, isBlocked: Bool)
    func getBlockedNostrPubkeys() -> Set<String>
    
    // MARK: Ephemeral Session Management
    func registerEphemeralSession(peerID: String, handshakeState: HandshakeState)
    func updateHandshakeState(peerID: String, state: HandshakeState)
    
    // MARK: Cleanup
    func clearAllIdentityData()
    func removeEphemeralSession(peerID: String)
    
    // MARK: Verification
    func setVerified(fingerprint: String, verified: Bool)
    func isVerified(fingerprint: String) -> Bool
    func getVerifiedFingerprints() -> Set<String>
}

/// Singleton manager for secure identity state persistence and retrieval.
/// Provides thread-safe access to identity mappings with encryption at rest.
/// All identity data is stored encrypted in the device Keychain for security.
final class SecureIdentityStateManager: SecureIdentityStateManagerProtocol {
    private let keychain: KeychainManagerProtocol
    private let cacheKey = "bitchat.identityCache.v2"
    private let encryptionKeyName = "identityCacheEncryptionKey"
    
    // In-memory state
    private var ephemeralSessions: [String: EphemeralIdentity] = [:]
    private var cryptographicIdentities: [String: CryptographicIdentity] = [:]
    private var cache: IdentityCache = IdentityCache()
    
    // Thread safety
    private let queue = DispatchQueue(label: "bitchat.identity.state", attributes: .concurrent)
    
    // Debouncing for keychain saves
    private var saveTimer: Timer?
    private let saveDebounceInterval: TimeInterval = 2.0  // Save at most once every 2 seconds
    private var pendingSave = false
    
    // Encryption key
    private let encryptionKey: SymmetricKey
    
    init(_ keychain: KeychainManagerProtocol) {
        self.keychain = keychain
        
        // Generate or retrieve encryption key from keychain
        let loadedKey: SymmetricKey
        
        // Try to load from keychain
        if let keyData = keychain.getIdentityKey(forKey: encryptionKeyName) {
            loadedKey = SymmetricKey(data: keyData)
            SecureLogger.logKeyOperation(.load, keyType: "identity cache encryption key", success: true)
        }
        // Generate new key if needed
        else {
            loadedKey = SymmetricKey(size: .bits256)
            let keyData = loadedKey.withUnsafeBytes { Data($0) }
            // Save to keychain
            let saved = keychain.saveIdentityKey(keyData, forKey: encryptionKeyName)
            SecureLogger.logKeyOperation(.generate, keyType: "identity cache encryption key", success: saved)
        }
        
        self.encryptionKey = loadedKey
        
        // Load identity cache on init
        loadIdentityCache()
    }
    
    deinit {
        forceSave()
    }
    
    // MARK: - Secure Loading/Saving
    
    private func loadIdentityCache() {
        guard let encryptedData = keychain.getIdentityKey(forKey: cacheKey) else {
            // No existing cache, start fresh
            return
        }
        
        do {
            let sealedBox = try AES.GCM.SealedBox(combined: encryptedData)
            let decryptedData = try AES.GCM.open(sealedBox, using: encryptionKey)
            cache = try JSONDecoder().decode(IdentityCache.self, from: decryptedData)
        } catch {
            // Log error but continue with empty cache
            SecureLogger.error(error, context: "Failed to load identity cache", category: .security)
        }
    }
    
    private func saveIdentityCache() {
        // Mark that we need to save
        pendingSave = true
        
        // Cancel any existing timer
        saveTimer?.invalidate()
        
        // Schedule a new save after the debounce interval
        saveTimer = Timer.scheduledTimer(withTimeInterval: saveDebounceInterval, repeats: false) { [weak self] _ in
            self?.performSave()
        }
    }
    
    private func performSave() {
        guard pendingSave else { return }
        pendingSave = false
        
        do {
            let data = try JSONEncoder().encode(cache)
            let sealedBox = try AES.GCM.seal(data, using: encryptionKey)
            let saved = keychain.saveIdentityKey(sealedBox.combined!, forKey: cacheKey)
            if saved {
                SecureLogger.debug("Identity cache saved to keychain", category: .security)
            }
        } catch {
            SecureLogger.error(error, context: "Failed to save identity cache", category: .security)
        }
    }
    
    // Force immediate save (for app termination)
    func forceSave() {
        saveTimer?.invalidate()
        performSave()
    }
    
    // MARK: - Social Identity Management
    
    func getSocialIdentity(for fingerprint: String) -> SocialIdentity? {
        queue.sync {
            return cache.socialIdentities[fingerprint]
        }
    }

    // MARK: - Cryptographic Identities

    /// Insert or update a cryptographic identity and optionally persist its signing key and claimed nickname.
    /// - Parameters:
    ///   - fingerprint: SHA-256 hex of the Noise static public key
    ///   - noisePublicKey: Noise static public key data
    ///   - signingPublicKey: Optional Ed25519 signing public key for authenticating public messages
    ///   - claimedNickname: Optional latest claimed nickname to persist into social identity
    func upsertCryptographicIdentity(fingerprint: String, noisePublicKey: Data, signingPublicKey: Data?, claimedNickname: String? = nil) {
        queue.async(flags: .barrier) {
            let now = Date()
            if var existing = self.cryptographicIdentities[fingerprint] {
                // Update keys if changed
                if existing.publicKey != noisePublicKey {
                    existing = CryptographicIdentity(
                        fingerprint: fingerprint,
                        publicKey: noisePublicKey,
                        signingPublicKey: signingPublicKey ?? existing.signingPublicKey,
                        firstSeen: existing.firstSeen,
                        lastHandshake: now
                    )
                    self.cryptographicIdentities[fingerprint] = existing
                } else {
                    // Update signing key and lastHandshake
                    existing.signingPublicKey = signingPublicKey ?? existing.signingPublicKey
                    let updated = CryptographicIdentity(
                        fingerprint: existing.fingerprint,
                        publicKey: existing.publicKey,
                        signingPublicKey: existing.signingPublicKey,
                        firstSeen: existing.firstSeen,
                        lastHandshake: now
                    )
                    self.cryptographicIdentities[fingerprint] = updated
                }
                // Persist updated state (already assigned in branches above)
            } else {
                // New entry
                let entry = CryptographicIdentity(
                    fingerprint: fingerprint,
                    publicKey: noisePublicKey,
                    signingPublicKey: signingPublicKey,
                    firstSeen: now,
                    lastHandshake: now
                )
                self.cryptographicIdentities[fingerprint] = entry
            }

            // Optionally persist claimed nickname into social identity
            if let claimed = claimedNickname {
                var identity = self.cache.socialIdentities[fingerprint] ?? SocialIdentity(
                    fingerprint: fingerprint,
                    localPetname: nil,
                    claimedNickname: claimed,
                    trustLevel: .unknown,
                    isFavorite: false,
                    isBlocked: false,
                    notes: nil
                )
                // Update claimed nickname if changed
                if identity.claimedNickname != claimed {
                    identity.claimedNickname = claimed
                    self.cache.socialIdentities[fingerprint] = identity
                } else if self.cache.socialIdentities[fingerprint] == nil {
                    self.cache.socialIdentities[fingerprint] = identity
                }
            }

            self.saveIdentityCache()
        }
    }

    /// Find cryptographic identities whose fingerprint prefix matches a peerID (16-hex) short ID
    func getCryptoIdentitiesByPeerIDPrefix(_ peerID: String) -> [CryptographicIdentity] {
        queue.sync {
            // Defensive: ensure hex and correct length
            guard peerID.count == 16, peerID.allSatisfy({ $0.isHexDigit }) else { return [] }
            return cryptographicIdentities.values.filter { $0.fingerprint.hasPrefix(peerID) }
        }
    }
    
    func updateSocialIdentity(_ identity: SocialIdentity) {
        queue.async(flags: .barrier) {
            self.cache.socialIdentities[identity.fingerprint] = identity
            
            // Update nickname index
            if let existingIdentity = self.cache.socialIdentities[identity.fingerprint] {
                // Remove old nickname from index if changed
                if existingIdentity.claimedNickname != identity.claimedNickname {
                    self.cache.nicknameIndex[existingIdentity.claimedNickname]?.remove(identity.fingerprint)
                    if self.cache.nicknameIndex[existingIdentity.claimedNickname]?.isEmpty == true {
                        self.cache.nicknameIndex.removeValue(forKey: existingIdentity.claimedNickname)
                    }
                }
            }
            
            // Add new nickname to index
            if self.cache.nicknameIndex[identity.claimedNickname] == nil {
                self.cache.nicknameIndex[identity.claimedNickname] = Set<String>()
            }
            self.cache.nicknameIndex[identity.claimedNickname]?.insert(identity.fingerprint)
            
            // Save to keychain
            self.saveIdentityCache()
        }
    }
    
    // MARK: - Favorites Management
    
    func getFavorites() -> Set<String> {
        queue.sync {
            let favorites = cache.socialIdentities.values
                .filter { $0.isFavorite }
                .map { $0.fingerprint }
            return Set(favorites)
        }
    }
    
    func setFavorite(_ fingerprint: String, isFavorite: Bool) {
        queue.async(flags: .barrier) {
            if var identity = self.cache.socialIdentities[fingerprint] {
                identity.isFavorite = isFavorite
                self.cache.socialIdentities[fingerprint] = identity
            } else {
                // Create new social identity for this fingerprint
                let newIdentity = SocialIdentity(
                    fingerprint: fingerprint,
                    localPetname: nil,
                    claimedNickname: "Unknown",
                    trustLevel: .unknown,
                    isFavorite: isFavorite,
                    isBlocked: false,
                    notes: nil
                )
                self.cache.socialIdentities[fingerprint] = newIdentity
            }
            self.saveIdentityCache()
        }
    }
    
    func isFavorite(fingerprint: String) -> Bool {
        queue.sync {
            return cache.socialIdentities[fingerprint]?.isFavorite ?? false
        }
    }
    
    // MARK: - Blocked Users Management
    
    func isBlocked(fingerprint: String) -> Bool {
        queue.sync {
            return cache.socialIdentities[fingerprint]?.isBlocked ?? false
        }
    }
    
    func setBlocked(_ fingerprint: String, isBlocked: Bool) {
        SecureLogger.info("User \(isBlocked ? "blocked" : "unblocked"): \(fingerprint)", category: .security)
        
        queue.async(flags: .barrier) {
            if var identity = self.cache.socialIdentities[fingerprint] {
                identity.isBlocked = isBlocked
                if isBlocked {
                    identity.isFavorite = false  // Can't be both favorite and blocked
                }
                self.cache.socialIdentities[fingerprint] = identity
            } else {
                // Create new social identity for this fingerprint
                let newIdentity = SocialIdentity(
                    fingerprint: fingerprint,
                    localPetname: nil,
                    claimedNickname: "Unknown",
                    trustLevel: .unknown,
                    isFavorite: false,
                    isBlocked: isBlocked,
                    notes: nil
                )
                self.cache.socialIdentities[fingerprint] = newIdentity
            }
            self.saveIdentityCache()
        }
    }

    // MARK: - Geohash (Nostr) Blocking
    
    func isNostrBlocked(pubkeyHexLowercased: String) -> Bool {
        queue.sync {
            return cache.blockedNostrPubkeys.contains(pubkeyHexLowercased.lowercased())
        }
    }
    
    func setNostrBlocked(_ pubkeyHexLowercased: String, isBlocked: Bool) {
        let key = pubkeyHexLowercased.lowercased()
        queue.async(flags: .barrier) {
            if isBlocked {
                self.cache.blockedNostrPubkeys.insert(key)
            } else {
                self.cache.blockedNostrPubkeys.remove(key)
            }
            self.saveIdentityCache()
        }
    }
    
    func getBlockedNostrPubkeys() -> Set<String> {
        queue.sync { cache.blockedNostrPubkeys }
    }
    
    // MARK: - Ephemeral Session Management
    
    func registerEphemeralSession(peerID: String, handshakeState: HandshakeState = .none) {
        queue.async(flags: .barrier) {
            self.ephemeralSessions[peerID] = EphemeralIdentity(
                peerID: peerID,
                sessionStart: Date(),
                handshakeState: handshakeState
            )
        }
    }
    
    func updateHandshakeState(peerID: String, state: HandshakeState) {
        queue.async(flags: .barrier) {
            self.ephemeralSessions[peerID]?.handshakeState = state
            
            // If handshake completed, update last interaction
            if case .completed(let fingerprint) = state {
                self.cache.lastInteractions[fingerprint] = Date()
                self.saveIdentityCache()
            }
        }
    }
    
    // MARK: - Cleanup
    
    func clearAllIdentityData() {
        SecureLogger.warning("Clearing all identity data", category: .security)
        
        queue.async(flags: .barrier) {
            self.cache = IdentityCache()
            self.ephemeralSessions.removeAll()
            self.cryptographicIdentities.removeAll()
            
            // Delete from keychain
            let deleted = self.keychain.deleteIdentityKey(forKey: self.cacheKey)
            SecureLogger.logKeyOperation(.delete, keyType: "identity cache", success: deleted)
        }
    }
    
    func removeEphemeralSession(peerID: String) {
        queue.async(flags: .barrier) {
            self.ephemeralSessions.removeValue(forKey: peerID)
        }
    }
    
    // MARK: - Verification
    
    func setVerified(fingerprint: String, verified: Bool) {
        SecureLogger.info("Fingerprint \(verified ? "verified" : "unverified"): \(fingerprint)", category: .security)
        
        queue.async(flags: .barrier) {
            if verified {
                self.cache.verifiedFingerprints.insert(fingerprint)
            } else {
                self.cache.verifiedFingerprints.remove(fingerprint)
            }
            
            // Update trust level if social identity exists
            if var identity = self.cache.socialIdentities[fingerprint] {
                identity.trustLevel = verified ? .verified : .casual
                self.cache.socialIdentities[fingerprint] = identity
            }
            
            self.saveIdentityCache()
        }
    }
    
    func isVerified(fingerprint: String) -> Bool {
        queue.sync {
            return cache.verifiedFingerprints.contains(fingerprint)
        }
    }
    
    func getVerifiedFingerprints() -> Set<String> {
        queue.sync {
            return cache.verifiedFingerprints
        }
    }
}