Implementing In-App Purchases

<uses-permission android:name="com.android.vending.BILLING" />

implementation 'com.android.billingclient:billing-ktx:6.2.1'

import com.android.billingclient.api.BillingClient
import com.android.billingclient.api.BillingClientStateListener
import com.android.billingclient.api.BillingFlowParams

class BillingManager(private val context: Context) {
    private lateinit var billingClient: BillingClient

    fun initializeBillingClient() {
        billingClient = BillingClient.newBuilder(context)
            .setListener { billingResult, purchases -> handlePurchases(purchases) }
            .enablePendingPurchases()
            .build()
    }

    fun startConnection() {
        billingClient.startConnection(object : BillingClientStateListener {
            override fun onBillingSetupFinished(billingResult: BillingResult) {
                if (billingResult.responseCode == BillingClient.BillingResponse.OK) {
                    // The BillingClient is ready. You can query purchases here.
                }
            }

            override fun onBillingServiceDisconnected() {
                // Try to reconnect to the billing service.
            }
        })
    }

    private fun handlePurchases(purchases: List<Purchase>?) {
        // Handle purchases here
    }
}

val productIds = listOf("premium_upgrade", "subscription_monthly")
val queryProductDetails = QueryProductDetailsParams
    .Builder()
    .setProductIds(productIds)
    .build()

billingClient.queryProductDetailsAsync(queryProductDetails) { billingResult, productDetailsList ->
    if (billingResult.responseCode == BillingClient.BillingResponseCode.OK) {
        for (productDetails in productDetailsList) {
            Log.d("Product", "Title: " + productDetails.title)
            Log.d("Product", "Price: " + productDetails.price)
        }
    } else {
        Log.e("Billing", "Error: " + billingResult.responseCode)
    }
}

val billingClient = BillingClient.newBuilder(context)
    .setListener { _, _ -> }
    .enablePendingPurchases()
    .build()

billingClient.startConnection(object : BillingClientStateListener {
    override fun onBillingSetupFinished(billingResult: BillingResult) {
        if (billingResult.responseCode == BillingClient.BillingResponse.OK) {
            val skuDetails = SkuDetails("inapp:product1")
            val purchaseFlow = BillingFlowParams.newBuilder()
                .setSkuDetails(skuDetails)
                .build()

            billingClient.launchBillingFlow(activity, purchaseFlow)
        }
    }

    override fun onBillingServiceDisconnected() { }
})

class PurchaseHandler : PurchasesUpdatedListener {
    override fun onPurchasesUpdated(
        responseCode: Int,
        purchases: List<Purchase>?
    ) {
        if (responseCode == BillingClient.BillingResponse.OK && purchases != null) {
            for (purchase in purchases) {
                if (purchase.purchaseState == Purchase.PurchaseState.PURCHASED) {
                    // Process the purchase
                    val sku = purchase.sku
                    val token = purchase.purchaseToken
                }
            }
        }
    }
}

fun verifyPurchase(token: String, sku: String): Boolean {
    // Send token and SKU to your server for verification
    val verificationResult = sendToBackend(token, sku)
    return verificationResult.isValid
}

val purchase = purchasesResponse.purchasesList.firstOrNull()
if (purchase != null) {
    val acknowledgePurchaseRequest = AcknowledgePurchaseRequest(
        purchaseToken = purchase.purchaseToken,
        productId = purchase.productId
    )
    billingClient.acknowledgePurchase(acknowledgePurchaseRequest) { response ->
        if (response.responseCode == BillingClient.BillingResponseCode.OK) {
            // Purchase acknowledged successfully
        } else {
            // Handle error
        }
    }
}

val purchase = purchases.firstOrNull { it.productId == "consumable_item" }
if (purchase != null) {
    val purchaseToken = purchase.purchaseToken
    // Send to backend or consume directly on client
    consumePurchase(purchaseToken)
}

val query = QuerySkuDetailsParams
    .newBuilder()
    .setProductType(BillingClient.ProductType.SUBS)
    .setSkusList(listOf("monthly_subscription"))
    .build()

billingClient.querySkuDetailsAsync(query) { _, detailsList ->
    detailsList?.forEach { detail ->
        Log.d("Subscription", "Title: ${detail.title}, Price: ${detail.price}")
    }
}

val purchaseParams = BillingFlowParams
    .newBuilder()
    .setSkuDetails(skuDetails)
    .build()

billingClient.launchBillingFlow(activity, purchaseParams)

import com.android.billingclient.api.Purchase
import java.security.Signature
import java.security.PublicKey

fun verifyPurchase(purchase: Purchase, publicKey: PublicKey): Boolean {
    val signature = Signature.getInstance("SHA256withRSA")
    signature.initVerify(publicKey)
    signature.update(purchase.originalJson.toByteArray())
    return signature.verify(Base64.decode(purchase.signature, Base64.NO_WRAP))
}

val billingClient = BillingClient.newBuilder(context)
    .setListener { _, _ -> }
    .enablePendingPurchases()
    .build()

billingClient.startConnection(object : BillingClientStateListener {
    override fun onBillingSetupFinished(billingResult: BillingResult) {
        if (billingResult.responseCode == BillingClient.BillingResponse.OK) {
            val restoreRequest = BillingRequest.newBuilder()
                .setProductType(BillingClient.ProductType.IN_APP)
                .build()

            billingClient.acknowledgePurchase(
                AcknowledgePurchaseParams.newBuilder()
                    .setPurchaseToken("purchase_token")
                    .build()
            )
        }
    }

    override fun onBillingServiceDisconnected() {
        // Handle disconnection
    }
})