add service layer with ProductService, add deleted_at and unique index to product table

src/main/kotlin/com/example/demo/exceptions/UnprocessableException.kt

@@ -0,0 +1,3 @@
+package com.example.demo.exceptions
+
+class UnprocessableException(override val message: String): RuntimeException(message)

src/main/kotlin/com/example/demo/models/Product.kt

@@ -27,6 +27,11 @@ data class Product(
     @Serializable(with = OffsetDateTimeSerialization::class)
     @Column(value = "updated_at")
     val updatedAt: OffsetDateTime?,
+    @Serializable(with = OffsetDateTimeSerialization::class)
+    @Column(value = "deleted_at")
+    val deletedAt: OffsetDateTime?,
 ) {
     fun getPriceDouble(): Double = (price.toDouble() / 100).roundTo(2)
+
+    fun isDeleted(): Boolean = deletedAt != null
 }

src/main/kotlin/com/example/demo/provider/ProductRepository.kt

@@ -1,13 +1,17 @@
 package com.example.demo.provider
 
 import com.example.demo.models.Product
-import org.springframework.data.jpa.repository.Query
+import org.springframework.data.jdbc.repository.query.Query
 import org.springframework.data.repository.CrudRepository
+import org.springframework.data.repository.query.Param
 import org.springframework.stereotype.Repository
+import java.time.OffsetDateTime
 import java.util.*
 
 @Repository
 interface ProductRepository: CrudRepository<Product, Long> {
-    @Query(value = "SELECT * FROM Product WHERE guid = :guid")
     fun findByGuid(guid: UUID): Product?
+
+    @Query(value = "UPDATE Product SET deleted_at = :deletedAt WHERE guid = :guid RETURNING *")
+    fun softDelete(@Param("guid") guid: UUID, @Param("deletedAt") deletedAt: OffsetDateTime): Product?
 }

src/main/kotlin/com/example/demo/services/ProductService.kt

@@ -0,0 +1,17 @@
+package com.example.demo.services
+
+import com.example.demo.exceptions.NotFoundException
+import com.example.demo.exceptions.UnprocessableException
+import com.example.demo.models.Product
+import org.springframework.stereotype.Service
+import java.util.*
+
+@Service
+interface ProductService {
+    fun findByGuid(guid: UUID): Product?
+
+    fun create(name: String, price: Long, description: String?): Product
+
+    @Throws(NotFoundException::class, UnprocessableException::class)
+    fun delete(guid: UUID): Product?
+}

src/main/kotlin/com/example/demo/services/ProductServiceImpl.kt

@@ -0,0 +1,48 @@
+package com.example.demo.services
+
+import com.example.demo.exceptions.NotFoundException
+import com.example.demo.exceptions.UnprocessableException
+import com.example.demo.models.Product
+import com.example.demo.provider.ProductRepository
+import java.time.OffsetDateTime
+import java.util.*
+
+class ProductServiceImpl(private val productRepository: ProductRepository): ProductService {
+    override fun findByGuid(guid: UUID): Product? = productRepository.findByGuid(guid)
+
+    override fun create(name: String, price: Long, description: String?): Product {
+        val product = Product(
+            id = null,
+            guid = UUID.randomUUID(),
+            name = name,
+            description = description,
+            price = price,
+            createdAt = OffsetDateTime.now(),
+            updatedAt = null,
+            deletedAt = null,
+        )
+
+        return productRepository.save(product)
+    }
+
+    override fun delete(guid: UUID): Product? {
+        val product = findByGuid(guid) ?: throw NotFoundException()
+
+        if (product.isDeleted()) {
+            throw UnprocessableException("product already deleted")
+        }
+
+        val deletedProduct = product.copy(
+            id = product.id!!,
+            guid = product.guid,
+            name = product.name,
+            description = product.description,
+            price = product.price,
+            createdAt = product.createdAt,
+            updatedAt = product.updatedAt,
+            deletedAt = OffsetDateTime.now(),
+        )
+
+        return productRepository.save(deletedProduct)
+    }
+}