Merge pull request #3 from lmirabal/account-operations

Account operations

Author: lmirabal

README.md

@@ -31,6 +31,13 @@ This example mainly focuses in the contract defining how the business behaves as
 approach, but the same strategy can be applied to any other port. For examples, if there were multiple ways to
 store/query accounts, a single test could be defined to test all of them.
 
+## How to run
+
+The full stack can be run in a single jvm for demonstration purposes using `Main.kt` in the `web` project:
+```shell
+./gradlew :web:run
+```
+
 ## Technology
 
 The intention is to have as simple as possible code so very few external dependencies are used. It's implemented in

domain/build.gradle

@@ -3,6 +3,8 @@ plugins {
 }
 
 dependencies {
+    api 'dev.forkhandles:result4k:1.6.0.0'
+
     testFixturesImplementation 'org.jetbrains.kotlin:kotlin-test-junit5'
     testFixturesImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.0'
     testFixturesImplementation 'com.natpryce:hamkrest:1.8.0.1'

domain/src/main/kotlin/lmirabal/bank/Bank.kt

@@ -1,8 +1,14 @@
 package lmirabal.bank
 
+import dev.forkhandles.result4k.Result
+import lmirabal.bank.model.Amount
 import lmirabal.bank.model.BankAccount
+import lmirabal.bank.model.BankAccountId
+import lmirabal.bank.model.NotEnoughFunds
 
 interface Bank {
     fun createAccount(): BankAccount
     fun listAccounts(): List<BankAccount>
+    fun deposit(id: BankAccountId, amount: Amount): BankAccount
+    fun withdraw(id: BankAccountId, amount: Amount): Result<BankAccount, NotEnoughFunds>
 }

domain/src/main/kotlin/lmirabal/bank/BankService.kt

@@ -1,9 +1,12 @@
 package lmirabal.bank
 
+import dev.forkhandles.result4k.Result
+import dev.forkhandles.result4k.peek
 import lmirabal.bank.data.BankAccountRepository
 import lmirabal.bank.model.Amount
 import lmirabal.bank.model.BankAccount
 import lmirabal.bank.model.BankAccountId
+import lmirabal.bank.model.NotEnoughFunds
 
 class BankService(
     private val accountRepository: BankAccountRepository,
@@ -15,4 +18,16 @@ class BankService(
     }
 
     override fun listAccounts(): List<BankAccount> = accountRepository.list()
+
+    override fun deposit(id: BankAccountId, amount: Amount): BankAccount {
+        val account = accountRepository.list().first { it.id == id }
+        return account.deposit(amount)
+            .also { updatedAccount -> accountRepository.update(updatedAccount) }
+    }
+
+    override fun withdraw(id: BankAccountId, amount: Amount): Result<BankAccount, NotEnoughFunds> {
+        val account = accountRepository.list().first { it.id == id }
+        return account.withdraw(amount)
+            .peek { updatedAccount -> accountRepository.update(updatedAccount) }
+    }
 }

domain/src/main/kotlin/lmirabal/bank/data/BankAccountRepository.kt

@@ -4,5 +4,6 @@ import lmirabal.bank.model.BankAccount
 
 interface BankAccountRepository {
     fun add(account: BankAccount)
+    fun update(account: BankAccount)
     fun list(): List<BankAccount>
 }

domain/src/main/kotlin/lmirabal/bank/data/InMemoryBankAccountRepository.kt

@@ -1,13 +1,18 @@
 package lmirabal.bank.data
 
 import lmirabal.bank.model.BankAccount
+import lmirabal.bank.model.BankAccountId
 
 class InMemoryBankAccountRepository : BankAccountRepository {
-    private val accounts: MutableList<BankAccount> = arrayListOf()
+    private val accounts = mutableMapOf<BankAccountId, BankAccount>()
 
     override fun add(account: BankAccount) {
-        accounts.add(account)
+        accounts[account.id] = account
     }
 
-    override fun list(): List<BankAccount> = accounts
+    override fun update(account: BankAccount) {
+        add(account)
+    }
+
+    override fun list(): List<BankAccount> = accounts.values.toList()
 }

domain/src/main/kotlin/lmirabal/bank/model/Amount.kt

@@ -1,6 +1,21 @@
 package lmirabal.bank.model
 
-data class Amount(val minorUnits: Long) {
+data class Amount(val minorUnits: Long) : Comparable<Amount> {
+    init {
+        require(minorUnits >= 0)
+    }
+
+    operator fun plus(other: Amount): Amount {
+        return Amount(minorUnits + other.minorUnits)
+    }
+
+    operator fun minus(other: Amount): Amount {
+        return Amount(minorUnits - other.minorUnits)
+    }
+
+    override fun compareTo(other: Amount): Int {
+        return minorUnits.compareTo(other.minorUnits)
+    }
 
     companion object {
         val ZERO = Amount(0)

domain/src/main/kotlin/lmirabal/bank/model/BankAccount.kt

@@ -1,12 +1,26 @@
 package lmirabal.bank.model
 
+import dev.forkhandles.result4k.Failure
+import dev.forkhandles.result4k.Result
+import dev.forkhandles.result4k.Success
 import java.util.UUID
 
-data class BankAccount(val id: BankAccountId, val balance: Amount)
+data class BankAccount(val id: BankAccountId, val balance: Amount) {
+    fun deposit(amount: Amount): BankAccount {
+        return copy(balance = balance + amount)
+    }
+
+    fun withdraw(amount: Amount): Result<BankAccount, NotEnoughFunds> {
+        return if (amount <= balance) Success(copy(balance = balance - amount))
+        else Failure(NotEnoughFunds(id, balance, amount - balance))
+    }
+}
 
 data class BankAccountId(val value: UUID) {
 
     companion object {
         fun random() = BankAccountId(UUID.randomUUID())
     }
 }
+
+data class NotEnoughFunds(val id: BankAccountId, val balance: Amount, val additionalFundsRequired: Amount)

domain/src/test/kotlin/lmirabal/bank/BankServiceTest.kt

@@ -9,14 +9,26 @@ import lmirabal.bank.model.BankAccountId
 import org.junit.jupiter.api.Test
 
 class BankServiceTest : BankTest() {
-    private val id = BankAccountId.random()
-    private val idFactory = { id }
+    private val idFactory = RecordingIdFactory()
     override val bank = BankService(InMemoryBankAccountRepository(), idFactory)
 
     @Test
     fun createsAnAccount() {
         val account = bank.createAccount()
 
+        val id = idFactory.last()
         assertThat(account, equalTo(BankAccount(id, Amount.ZERO)))
     }
+
+    class RecordingIdFactory : () -> BankAccountId {
+        private val values = mutableListOf<BankAccountId>()
+
+        override fun invoke(): BankAccountId {
+            return BankAccountId.random().also { values.add(it) }
+        }
+
+        fun last(): BankAccountId {
+            return values.last()
+        }
+    }
 }

domain/src/test/kotlin/lmirabal/bank/data/InMemoryBankAccountRepositoryTest.kt

@@ -11,12 +11,25 @@ class InMemoryBankAccountRepositoryTest {
     private val repository = InMemoryBankAccountRepository()
 
     @Test
-    fun persistsAccounts() {
+    fun `persists accounts`() {
         val account1 = BankAccount(BankAccountId.random(), Amount(10))
         repository.add(account1)
         val account2 = BankAccount(BankAccountId.random(), Amount(20))
         repository.add(account2)
 
         assertThat(repository.list(), equalTo(listOf(account1, account2)))
     }
+
+    @Test
+    fun `updates existing accounts`() {
+        val account1 = BankAccount(BankAccountId.random(), Amount(10))
+        repository.add(account1)
+        val account2 = BankAccount(BankAccountId.random(), Amount(20))
+        repository.add(account2)
+
+        val updatedAccount1 = BankAccount(account1.id, Amount(50))
+        repository.update(updatedAccount1)
+
+        assertThat(repository.list(), equalTo(listOf(updatedAccount1, account2)))
+    }
 }