add TransactionService

src/main/kotlin/ltd/lulz/service/TransactionService.kt

@@ -0,0 +1,26 @@
+package ltd.lulz.service
+
+import io.github.oshai.kotlinlogging.KotlinLogging
+import java.math.BigDecimal
+import java.util.UUID
+import ltd.lulz.model.AccountEntity
+import org.springframework.stereotype.Service
+import org.springframework.transaction.annotation.Transactional
+import reactor.core.publisher.Mono
+
+private val log = KotlinLogging.logger {}
+
+@Service
+class TransactionService(
+    private val accountService: AccountService,
+) {
+
+    @Transactional
+    fun deposit(
+        id: UUID,
+        amount: BigDecimal,
+    ): Mono<AccountEntity> = accountService.getForUpdateById(id)
+        .map { it.copy(amount = it.amount + amount) }
+        .doOnNext { log.trace { "Deposited $amount to account ${it.id}" } }
+        .flatMap { accountService.save(it) }
+}