import Foundation
import Observation

/// Verwaltet die Fahrzeugprofile, die darin eingerichteten Geräte und deren
/// Schlüssel.
@Observable
final class DeviceStore {

    private static let devicesKey = "configuredDevices"
    private static let profilesKey = "profiles"
    private static let activeProfileKey = "activeProfileID"

    /// Alle Geräte über alle Profile hinweg.
    private(set) var devices: [ConfiguredDevice] = []
    private(set) var profiles: [Profile] = []

    private(set) var activeProfileID: UUID = Profile.defaultID

    /// Zwischenspeicher, damit nicht bei jedem Advertisement die Keychain
    /// befragt wird – das passiert bis zu mehrmals pro Sekunde.
    @ObservationIgnored private var keyCache: [UUID: [UInt8]] = [:]

    init() {
        if DemoData.isEnabled {
            profiles = DemoData.profiles
            devices = DemoData.devices
            activeProfileID = DemoData.profiles[0].id
            return
        }
        load()
    }

    // MARK: - Profile

    var activeProfile: Profile? {
        profiles.first { $0.id == activeProfileID }
    }

    /// Die Geräte des gewählten Fahrzeugs.
    var activeDevices: [ConfiguredDevice] {
        devices.filter { $0.profileID == activeProfileID }
    }

    var hasMultipleProfiles: Bool { profiles.count > 1 }

    func selectProfile(_ profile: Profile) {
        guard profile.id != activeProfileID else { return }
        activeProfileID = profile.id
        save()
    }

    @discardableResult
    func addProfile(named name: String, symbol: String = "box.truck") -> Profile {
        let profile = Profile(name: name, symbol: symbol)
        profiles.append(profile)
        save()
        return profile
    }

    func update(_ profile: Profile) {
        guard let index = profiles.firstIndex(where: { $0.id == profile.id }) else { return }
        profiles[index] = profile
        save()
    }

    /// Entfernt ein Profil samt seiner Geräte und Schlüssel. Das letzte Profil
    /// bleibt bestehen – ohne Profil hätte die App keinen Ort für Geräte.
    func removeProfile(_ profile: Profile) {
        guard profiles.count > 1 else { return }
        for device in devices where device.profileID == profile.id {
            KeychainStore.setKey(nil, for: device.id)
            keyCache[device.id] = nil
        }
        devices.removeAll { $0.profileID == profile.id }
        profiles.removeAll { $0.id == profile.id }
        if activeProfileID == profile.id, let first = profiles.first {
            activeProfileID = first.id
        }
        save()
    }

    func deviceCount(in profile: Profile) -> Int {
        devices.count { $0.profileID == profile.id }
    }

    // MARK: - Geräte

    /// Legt ein Gerät im gerade gewählten Profil an.
    func add(_ device: ConfiguredDevice, victronKey: String? = nil) {
        devices.append(device)
        if let victronKey {
            setVictronKey(victronKey, for: device.id)
        }
        save()
    }

    func update(_ device: ConfiguredDevice) {
        guard let index = devices.firstIndex(where: { $0.id == device.id }) else { return }
        devices[index] = device
        save()
    }

    func remove(_ device: ConfiguredDevice) {
        devices.removeAll { $0.id == device.id }
        KeychainStore.setKey(nil, for: device.id)
        keyCache[device.id] = nil
        save()
    }

    /// Nur im aktiven Profil suchen: die Geräte des anderen Fahrzeugs sollen
    /// weder gelesen noch verbunden werden.
    func device(withPeripheralID id: UUID) -> ConfiguredDevice? {
        activeDevices.first { $0.peripheralID == id }
    }

    // MARK: - Victron-Schlüssel

    func victronKeyText(for deviceID: UUID) -> String? {
        KeychainStore.key(for: deviceID)
    }

    func setVictronKey(_ hex: String?, for deviceID: UUID) {
        let trimmed = hex?.trimmingCharacters(in: .whitespacesAndNewlines)
        let value = (trimmed?.isEmpty ?? true) ? nil : trimmed
        KeychainStore.setKey(value, for: deviceID)
        keyCache[deviceID] = value?.hexBytes
    }

    /// Der Schlüssel als Bytes, oder nil wenn keiner hinterlegt bzw. der
    /// hinterlegte keine 16 Byte lang ist.
    func victronKeyBytes(for deviceID: UUID) -> [UInt8]? {
        if let cached = keyCache[deviceID] { return cached }
        guard let bytes = KeychainStore.key(for: deviceID)?.hexBytes, bytes.count == 16 else {
            return nil
        }
        keyCache[deviceID] = bytes
        return bytes
    }

    // MARK: - Persistenz

    private func load() {
        let defaults = UserDefaults.standard

        if let data = defaults.data(forKey: Self.profilesKey),
           let decoded = try? JSONDecoder().decode([Profile].self, from: data),
           !decoded.isEmpty {
            profiles = decoded
        } else {
            // Erster Start oder Update von einer Version ohne Profile.
            profiles = [.initial]
        }

        if let data = defaults.data(forKey: Self.devicesKey),
           let decoded = try? JSONDecoder().decode([ConfiguredDevice].self, from: data) {
            devices = decoded
        }

        if let raw = defaults.string(forKey: Self.activeProfileKey),
           let id = UUID(uuidString: raw),
           profiles.contains(where: { $0.id == id }) {
            activeProfileID = id
        } else {
            activeProfileID = profiles[0].id
        }

        // Geräte, deren Profil nicht mehr existiert, wären sonst unerreichbar.
        let known = Set(profiles.map(\.id))
        for index in devices.indices where !known.contains(devices[index].profileID) {
            devices[index].profileID = profiles[0].id
        }
    }

    private func save() {
        let defaults = UserDefaults.standard
        if let data = try? JSONEncoder().encode(devices) {
            defaults.set(data, forKey: Self.devicesKey)
        }
        if let data = try? JSONEncoder().encode(profiles) {
            defaults.set(data, forKey: Self.profilesKey)
        }
        defaults.set(activeProfileID.uuidString, forKey: Self.activeProfileKey)
    }
}