Google Play サブスクリプションオファーで解約を防ぎ収益を最大化する：Rork アプリ実践ガイド

// BillingManager.kt
import com.android.billingclient.api.*
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.suspendCancellableCoroutine
import kotlin.coroutines.resume
 
class BillingManager(private val activity: Activity) {
 
    private lateinit var billingClient: BillingClient
    
    private val _subscriptionOffers = MutableStateFlow<List<ProductDetails.SubscriptionOfferDetails>>(emptyList())
    val subscriptionOffers: StateFlow<List<ProductDetails.SubscriptionOfferDetails>> = _subscriptionOffers
 
    fun initialize() {
        billingClient = BillingClient.newBuilder(activity)
            .setListener { billingResult, purchases ->
                if (billingResult.responseCode == BillingClient.BillingResponseCode.OK) {
                    purchases?.forEach { handlePurchase(it) }
                }
            }
            .enablePendingPurchases()
            .build()
        
        billingClient.startConnection(object : BillingClientStateListener {
            override fun onBillingSetupFinished(result: BillingResult) {
                if (result.responseCode == BillingClient.BillingResponseCode.OK) {
                    loadSubscriptionOffers()
                }
            }
            override fun onBillingServiceDisconnected() {
                // 再接続ロジック
            }
        })
    }
 
    private fun loadSubscriptionOffers() {
        val queryParams = QueryProductDetailsParams.newBuilder()
            .setProductList(
                listOf(
                    QueryProductDetailsParams.Product.newBuilder()
                        .setProductId("premium_monthly")  // Play Consoleで設定したID
                        .setProductType(BillingClient.ProductType.SUBS)
                        .build()
                )
            )
            .build()
        
        billingClient.queryProductDetailsAsync(queryParams) { result, productDetailsList ->
            if (result.responseCode == BillingClient.BillingResponseCode.OK) {
                val product = productDetailsList.firstOrNull() ?: return@queryProductDetailsAsync
                val offers = product.subscriptionOfferDetails ?: emptyList()
                
                // オファーをログ出力（デバッグ用）
                offers.forEach { offer ->
                    println("Offer ID: ${offer.offerId}")
                    println("Tags: ${offer.offerTags}")
                    offer.pricingPhases.pricingPhaseList.forEach { phase ->
                        println("  Phase: ${phase.formattedPrice} for ${phase.billingCycleCount} cycles")
                    }
                }
                
                _subscriptionOffers.value = offers
            }
        }
    }
 
    fun getOfferForUser(
        offers: List<ProductDetails.SubscriptionOfferDetails>,
        isReturningUser: Boolean,
        hasUsedTrial: Boolean,
    ): ProductDetails.SubscriptionOfferDetails? {
        return when {
            // 過去の購読者 → ウィンバックオファーを優先
            isReturningUser -> offers.firstOrNull { offer ->
                offer.offerTags.contains("winback")
            }
            // 新規ユーザーでトライアル未使用 → 無料トライアル
            !hasUsedTrial -> offers.firstOrNull { offer ->
                offer.offerTags.contains("trial")
            }
            // トライアル使用済み → 入門価格
            else -> offers.firstOrNull { offer ->
                offer.offerTags.contains("introductory")
            }
        } ?: offers.firstOrNull()  // フォールバック: 通常価格
    }
 
    fun launchPurchaseFlow(
        productDetails: ProductDetails,
        selectedOffer: ProductDetails.SubscriptionOfferDetails,
    ) {
        val offerToken = selectedOffer.offerToken
        
        val productDetailsParamsList = listOf(
            BillingFlowParams.ProductDetailsParams.newBuilder()
                .setProductDetails(productDetails)
                .setOfferToken(offerToken)  // 選択したオファーのトークンを指定
                .build()
        )
        
        val billingFlowParams = BillingFlowParams.newBuilder()
            .setProductDetailsParamsList(productDetailsParamsList)
            .build()
        
        billingClient.launchBillingFlow(activity, billingFlowParams)
    }
 
    private fun handlePurchase(purchase: Purchase) {
        if (purchase.purchaseState == Purchase.PurchaseState.PURCHASED) {
            // 購入確認（Acknowledgement）— 3日以内に必須
            if (!purchase.isAcknowledged) {
                val acknowledgeParams = AcknowledgePurchaseParams.newBuilder()
                    .setPurchaseToken(purchase.purchaseToken)
                    .build()
                billingClient.acknowledgePurchase(acknowledgeParams) { result ->
                    if (result.responseCode == BillingClient.BillingResponseCode.OK) {
                        println("Purchase acknowledged: ${purchase.orderId}")
                    }
                }
            }
            // バックエンドに購入情報を送信して会員ステータスを更新
            updateSubscriptionStatus(purchase.purchaseToken)
        }
    }
 
    private fun updateSubscriptionStatus(purchaseToken: String) {
        // RevenueCatまたは自前バックエンドに通知
    }
}