import Foundation

@Observable
final class TokenManager {
    static let shared = TokenManager()

    private let keychain = KeychainHelper.shared
    let authService = FeishuAuthService()

    private let accessTokenKey = "feishu.access_token"
    private let refreshTokenKey = "feishu.refresh_token"
    private let tokenExpiryKey = "feishu.token_expiry"
    private let openIdKey = "feishu.open_id"

    enum State: Equatable {
        case unauthenticated
        case authenticating
        case authenticated
        case refreshing
        case error(String)
    }

    private(set) var state: State = .unauthenticated

    private init() {
        if keychain.read(accessTokenKey) != nil {
            state = .authenticated
        }
    }

    var isAuthenticated: Bool {
        if case .authenticated = state { return true }
        if keychain.read(accessTokenKey) != nil { return true }
        return false
    }

    var authorizeURL: URL? {
        guard authService.hasCredentials else { return nil }
        return authService.authorizeURL
    }

    /// The user's Feishu open_id, cached after the first OAuth callback or
    /// user-info fetch. Used for server-side filtering of Person-type fields
    /// on the Feishu search endpoint. Nil if the user hasn't authenticated.
    var cachedOpenId: String? {
        keychain.read(openIdKey)
    }

    func storeOpenId(_ openId: String) {
        guard !openId.isEmpty else { return }
        keychain.write(openId, forKey: openIdKey)
    }

    func getAccessToken() async throws -> String {
        if let token = keychain.read(accessTokenKey),
           let expiry = UserDefaults.standard.object(forKey: tokenExpiryKey) as? Date,
           expiry > Date().addingTimeInterval(60) {
            state = .authenticated
            return token
        }

        guard let refreshToken = keychain.read(refreshTokenKey),
              !refreshToken.isEmpty else {
            state = .unauthenticated
            throw TokenError.noRefreshToken
        }

        state = .refreshing
        do {
            let response = try await authService.refreshAccessToken(refreshToken)
            storeTokens(
                access: response.accessToken,
                refresh: response.refreshToken ?? refreshToken,
                expiresIn: response.expiresIn
            )
            state = .authenticated
            return response.accessToken
        } catch {
            state = .error(error.localizedDescription)
            throw error
        }
    }

    func storeTokens(access: String, refresh: String, expiresIn: Int) {
        keychain.write(access, forKey: accessTokenKey)
        if !refresh.isEmpty {
            keychain.write(refresh, forKey: refreshTokenKey)
        } else {
            keychain.delete(refreshTokenKey)
        }
        let expiry = Date().addingTimeInterval(TimeInterval(expiresIn))
        UserDefaults.standard.set(expiry, forKey: tokenExpiryKey)
        state = .authenticated
    }

    func clearTokens() {
        keychain.delete(accessTokenKey)
        keychain.delete(refreshTokenKey)
        keychain.delete(openIdKey)
        UserDefaults.standard.removeObject(forKey: tokenExpiryKey)
        state = .unauthenticated
    }

    func setError(_ message: String) {
        state = .error(message)
    }

    func handleCallback(code: String) async throws {
        guard !code.isEmpty else {
            BuggerLog.error("handleCallback: empty code")
            throw TokenError.invalidCallback
        }
        BuggerLog.info("handleCallback: exchanging code...")
        state = .authenticating
        let response = try await authService.exchangeCode(code)
        BuggerLog.info("handleCallback: got tokens, storing...")
        storeTokens(
            access: response.accessToken,
            refresh: response.refreshToken ?? "",
            expiresIn: response.expiresIn
        )
        // Fetch and cache the user's open_id for server-side record filtering.
        if let userInfo = try? await authService.fetchUserInfo(accessToken: response.accessToken),
           let openId = userInfo.openId {
            storeOpenId(openId)
        }
        state = .authenticated
        BuggerLog.info("handleCallback: done, authenticated ✓")
    }

    func resolveAssigneeName(config: AppConfig, accessToken: String) async throws -> String {
        if !config.assigneeName.isEmpty {
            return config.assigneeName
        }
        let userInfo = try await authService.fetchUserInfo(accessToken: accessToken)
        if let openId = userInfo.openId {
            storeOpenId(openId)
        }
        return userInfo.name ?? userInfo.enName ?? "Unknown"
    }

}

enum TokenError: Error, LocalizedError {
    case noRefreshToken
    case invalidCallback
    case refreshFailed

    var errorDescription: String? {
        switch self {
        case .noRefreshToken:
            return "No Feishu session found. Please connect Feishu."
        case .invalidCallback:
            return "Invalid OAuth callback URL."
        case .refreshFailed:
            return "Failed to refresh Feishu token."
        }
    }
}