import Foundation
import Observation

@MainActor
@Observable
final class TapToPayViewModel {

    let account: BankAccount

    var phase: Phase = .loading
    var token: BmlWalletToken?
    var errorMessage: String?
    var isReady = false

    enum Phase {
        case loading
        case ready
        case error
    }

    init(account: BankAccount) {
        self.account = account
    }

    func armToken() async {
        phase = .loading
        errorMessage = nil
        BmlContactlessUtil.clearToken()

        let loginId = account.loginTag.replacingOccurrences(of: "bml_", with: "")

        guard let otpSeed = CredentialStore.shared.load(
            forKey: CredentialStore.Keys.bmlOtpSeed(loginId)
        ) else {
            errorMessage = "OTP seed not found for \(loginId). Please log in again."
            phase = .error
            return
        }

        let profileId = account.profileId ?? ""

        guard let accessToken = CredentialStore.shared.load(
            forKey: CredentialStore.Keys.bmlAccessToken(profileId)
        ), !accessToken.isEmpty else {
            errorMessage = "Session not found. Please log in again."
            phase = .error
            return
        }

        let deviceId   = CredentialStore.shared.load(forKey: CredentialStore.Keys.bmlDeviceId(profileId)) ?? ""
        let refreshTok = CredentialStore.shared.load(forKey: CredentialStore.Keys.bmlRefreshToken(profileId)) ?? ""
        let expStr     = CredentialStore.shared.load(forKey: CredentialStore.Keys.bmlExpTime(profileId)) ?? "0"
        let expiresAt  = Int64(expStr) ?? 0
        let now        = Int64(Date().timeIntervalSince1970 * 1000)

        var session = BmlSession(
            accessToken: accessToken,
            deviceId: deviceId,
            refreshToken: refreshTok,
            expiresAt: expiresAt
        )

        // Refresh if expired or expiring within 60s
        if expiresAt > 0 && now >= expiresAt - 60_000 {
            do {
                let fresh = try await BmlLoginFlow().refreshSession(session)
                saveSession(fresh, profileId: profileId)
                session = fresh
            } catch {
                errorMessage = "Session expired. Please log in again. (\(error.localizedDescription))"
                phase = .error
                return
            }
        }

        let otp = Totp.generate(otpSeed)
        let internalId = account.internalId ?? ""

        do {
            let tokens = try await BmlTapToPayClient().fetchTokens(
                session: session,
                cardId: internalId,
                otp: otp
            )
            guard let firstToken = tokens.first else {
                errorMessage = "No payment tokens received from server."
                phase = .error
                return
            }
            token = firstToken
            BmlContactlessUtil.setToken(firstToken)
            phase = .ready
            isReady = true
        } catch {
            if error is CancellationError { return }
            errorMessage = error.localizedDescription
            phase = .error
        }
    }

    func cancel() {
        BmlContactlessUtil.clearToken()
    }

    private func saveSession(_ sess: BmlSession, profileId: String) {
        try? CredentialStore.shared.save(sess.accessToken, forKey: CredentialStore.Keys.bmlAccessToken(profileId))
        try? CredentialStore.shared.save(sess.deviceId, forKey: CredentialStore.Keys.bmlDeviceId(profileId))
        if !sess.refreshToken.isEmpty {
            try? CredentialStore.shared.save(sess.refreshToken, forKey: CredentialStore.Keys.bmlRefreshToken(profileId))
        }
        if sess.expiresAt > 0 {
            try? CredentialStore.shared.save(String(sess.expiresAt), forKey: CredentialStore.Keys.bmlExpTime(profileId))
        }
    }
}