Kotlin

package com.example.payment

import java.math.BigDecimal

// Cấu trúc kiểu kết quả sử dụng giao diện bị đóng
sealed interface PaymentResult {
    data class Success(val transactionId: String, val amount: BigDecimal) : PaymentResult
    data class Failure(val errorCode: String, val message: String) : PaymentResult
}

// Giao diện cho hành vi thanh toán
interface PaymentGateway {
    val providerName: String
    suspend fun processPayment(amount: BigDecimal, currency: String): PaymentResult
}

// Lớp cung cấp cơ sở trừu tượng
abstract class BaseGateway(override val providerName: String) : PaymentGateway {
    protected fun logTransaction(amount: BigDecimal) {
        println("[$providerName] Đang xử lý giao dịch của $amount")
    }
}

// Triển khai cụ thể cho Stripe
class StripeGateway(
    val apiKey: String,
    val merchantId: String
) : BaseGateway("Stripe") {

    override suspend fun processPayment(amount: BigDecimal, currency: String): PaymentResult {
        logTransaction(amount)
        return PaymentResult.Success(
            transactionId = "tx_stripe_${System.currentTimeMillis()}",
            amount = amount
        )
    }
}

package com.example.order

import java.math.BigDecimal

enum class OrderStatus {
    PENDING, PROCESSING, SHIPPED, DELIVERED, CANCELLED
}

data class LineItem(
    val sku: String,
    val price: BigDecimal,
    val quantity: Int
) {
    val total: BigDecimal get() = price.multiply(BigDecimal(quantity))
}

data class Customer(
    val id: String,
    val email: String,
    val isVip: Boolean = false
)

class Order(
    val orderId: String,
    val customer: Customer,
    val items: List
) {
    var status: OrderStatus = OrderStatus.PENDING
        private set

    val grandTotal: BigDecimal
        get() = items.fold(BigDecimal.ZERO) { acc, item -> acc.add(item.total) }

    fun markAsProcessing() {
        check(status == OrderStatus.PENDING) { "Đơn hàng phải ở trạng thái chờ để xử lý" }
        status = OrderStatus.PROCESSING
    }
}

package com.example.auth

enum class UserRole {
    GUEST, MEMBER, ADMIN
}

data class UserSession(
    val userId: String,
    val email: String,
    val role: UserRole,
    val authToken: String
) {
    val isAdmin: Boolean get() = role == UserRole.ADMIN
}

interface TokenProvider {
    fun generateToken(userId: String): String
    fun validateToken(token: String): Boolean
}

object JwtTokenProvider : TokenProvider {
    override fun generateToken(userId: String): String = "jwt_token_for_$userId"
    override fun validateToken(token: String): Boolean = token.startsWith("jwt_token_")
}

class AuthService(
    private val tokenProvider: TokenProvider
) {
    fun authenticate(user: UserSession, requiredRole: UserRole): Boolean {
        if (!tokenProvider.validateToken(user.authToken)) return false
        if (user.isAdmin) return true
        return user.role == requiredRole
    }
}