import Foundation

private let BML_API_BASE    = "https://www.bankofmaldives.com.mv/internetbanking"
private let BML_API_UA      = "bml-mobile-banking/348 (Apple; iOS 17.0; iPhone)"
private let BML_API_VERSION = "2.1.44.348"

final class BmlTapToPayClient {

    private let urlSession: URLSession = {
        let cfg = URLSessionConfiguration.default
        cfg.timeoutIntervalForRequest = 30
        return URLSession(configuration: cfg)
    }()

    func fetchTokens(
        session: BmlSession,
        cardId: String,
        otp: String,
        quantity: Int = 3
    ) async throws -> [BmlWalletToken] {
        let url = "\(BML_API_BASE)/api/mobile/walletpayments/gettoken"

        // Step 1: initiate
        let base: [String: Any] = ["type": "track2", "cardid": cardId, "quantity": quantity]
        let step1 = try await post(session: session, url: url, body: base)
        if step1.code == 0 { return step1.tokens }
        if step1.code != 99 { throw BmlError.serverError(step1.message ?? "Token request failed") }

        // Step 2: request OTP channel
        var body2 = base
        body2["channel"] = "token"
        let step2 = try await post(session: session, url: url, body: body2)
        if step2.code != 22 { throw BmlError.serverError(step2.message ?? "OTP channel request failed") }

        // Step 3: submit TOTP
        var body3 = body2
        body3["otp"] = otp
        let step3 = try await post(session: session, url: url, body: body3)
        if step3.code != 0 { throw BmlError.serverError(step3.message ?? "Token fetch failed") }

        return step3.tokens
    }

    private func post(session: BmlSession, url: String, body: [String: Any]) async throws -> TokenResponse {
        var req = URLRequest(url: URL(string: url)!)
        req.httpMethod = "POST"
        req.setValue("Bearer \(session.accessToken)", forHTTPHeaderField: "Authorization")
        req.setValue(BML_API_UA, forHTTPHeaderField: "User-Agent")
        req.setValue(BML_API_VERSION, forHTTPHeaderField: "x-app-version")
        req.setValue("application/json", forHTTPHeaderField: "Content-Type")
        req.httpBody = try JSONSerialization.data(withJSONObject: body)

        let (data, response) = try await urlSession.data(for: req)
        let code = (response as? HTTPURLResponse)?.statusCode ?? 0
        if code == 401 || code == 419 { throw BmlError.sessionExpired }
        if code >= 500 { throw BmlError.networkError("Server error HTTP \(code)") }

        guard let root = try? JSONSerialization.jsonObject(with: data) as? [String: Any] else {
            throw BmlError.invalidResponse
        }

        let respCode = root["code"] as? Int ?? -1
        let message  = root["message"] as? String
        let payload  = root["payload"] as? [[String: Any]] ?? []

        let tokens: [BmlWalletToken] = payload.map { item in
            BmlWalletToken(
                token:       item["token"] as? String ?? "",
                expiry:      item["expiry"] as? String ?? "",
                appCode:     item["app_code"] as? String ?? "",
                serviceCode: item["service_code"] as? String ?? "",
                data:        item["data"] as? String ?? "",
                validUntil:  item["valid_until"] as? String ?? ""
            )
        }

        return TokenResponse(code: respCode, message: message, tokens: tokens)
    }

    private struct TokenResponse {
        let code: Int
        let message: String?
        let tokens: [BmlWalletToken]
    }
}