add ExposedContentAPI and test that it is correctly work with different connections

core/src/commonMain/kotlin/com/insanusmokrassar/postssystem/core/content/Content.kt

@@ -1,15 +1,76 @@
 package com.insanusmokrassar.postssystem.core.content
 
-import kotlinx.serialization.Serializable
+import kotlinx.serialization.*
+import kotlinx.serialization.internal.*
 
 typealias ContentId = String
 
 /**
  * Content which is planned to be registered in database
  */
-@Serializable
+@Serializable(ContentSerializer::class)
 sealed class Content
 
+@Serializer(Content::class)
+object ContentSerializer : KSerializer<Content> {
+    override val descriptor: SerialDescriptor = object : SerialClassDescImpl("com.insanusmokrassar.postssystem.core.content.Content") {
+        init {
+            addElement("type") // req will have index 0
+            addElement("data") // res will have index 1
+        }
+    }
+
+    override fun serialize(encoder: Encoder, obj: Content) {
+        encoder.beginCollection(
+            descriptor,
+            2
+        ).also {
+            when (obj) {
+                is SimpleSpecialContent -> {
+                    it.encodeStringElement(descriptor, 0, SimpleSpecialContent.serializer().descriptor.name)
+                    it.encodeSerializableElement(descriptor, 1, SimpleSpecialContent.serializer(), obj)
+                }
+                is SimpleTextContent -> {
+                    it.encodeStringElement(descriptor, 0, SimpleTextContent.serializer().descriptor.name)
+                    it.encodeSerializableElement(descriptor, 1, SimpleTextContent.serializer(), obj)
+                }
+            }
+        }
+    }
+
+    private fun <T> CompositeDecoder.deserialize(i: Int, deserializationStrategy: DeserializationStrategy<T>): T {
+        return decodeSerializableElement(
+            descriptor,
+            i,
+            deserializationStrategy
+        )
+    }
+
+    override fun deserialize(decoder: Decoder): Content {
+        lateinit var result: Content
+        decoder.beginStructure(descriptor).let {
+            var type: String? = null
+            deserializeLoop@while (true) {
+                when (val i = it.decodeElementIndex(descriptor)) {
+                    CompositeDecoder.READ_DONE -> break@deserializeLoop
+                    0 -> type = it.decodeStringElement(descriptor, i)
+                    1 -> result = when (type) {
+                        SimpleSpecialContent.serializer().descriptor.name -> it.deserialize(
+                            i, SimpleSpecialContent.serializer()
+                        )
+                        SimpleTextContent.serializer().descriptor.name -> it.deserialize(
+                            i, SimpleTextContent.serializer()
+                        )
+                        else -> throw UnsupportedOperationException("Can't decode object with type $type")
+                    }
+                    else -> throw SerializationException("Unknown index $i")
+                }
+            }
+        }
+        return result
+    }
+}
+
 @Serializable
 data class SimpleSpecialContent(
     val internalId: ContentId

core/src/commonMain/kotlin/com/insanusmokrassar/postssystem/core/utils/IdUtils.kt

@@ -6,5 +6,5 @@ import com.insanusmokrassar.postssystem.core.post.PostId
 
 private fun generateId() = uuid4().toString()
 
-internal fun generatePostId(): PostId = generateId()
-internal fun generateContentId(): ContentId = generateId()
+fun generatePostId(): PostId = generateId()
+fun generateContentId(): ContentId = generateId()

exposed/build.gradle

@@ -0,0 +1,38 @@
+project.version = "$project_public_version"
+project.group = "$project_public_group"
+
+buildscript {
+    repositories {
+        mavenLocal()
+        jcenter()
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+        classpath "org.jetbrains.kotlin:kotlin-serialization:$kotlin_version"
+        classpath "com.jfrog.bintray.gradle:gradle-bintray-plugin:$gradle_bintray_plugin_version"
+    }
+}
+
+apply plugin: 'kotlinx-serialization'
+apply plugin: 'kotlin'
+
+repositories {
+    mavenLocal()
+    jcenter()
+    mavenCentral()
+    maven { url "https://kotlin.bintray.com/kotlinx" }
+}
+
+dependencies {
+    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+    implementation project(":core")
+
+    api "org.jetbrains.exposed:exposed:$exposed_version"
+    testImplementation "org.xerial:sqlite-jdbc:$test_sqlite_version"
+    testImplementation "org.junit.jupiter:junit-jupiter-api:$test_junit_version"
+
+    api "com.soywiz.korlibs.klock:klock:$klockVersion"
+    api "com.benasher44:uuid:$uuidVersion"
+}

exposed/gradle.properties

@@ -0,0 +1,3 @@
+exposed_version=0.17.7
+test_sqlite_version=3.28.0
+test_junit_version=5.5.2

exposed/src/main/kotlin/com/insanusmokrassar/postssystem/core/exposed/ExposedContentAPI.kt

@@ -0,0 +1,83 @@
+package com.insanusmokrassar.postssystem.core.exposed
+
+import com.insanusmokrassar.postssystem.core.content.*
+import com.insanusmokrassar.postssystem.core.content.api.ContentAPI
+import com.insanusmokrassar.postssystem.core.utils.generateContentId
+import com.insanusmokrassar.postssystem.core.utils.pagination.*
+import kotlinx.coroutines.channels.BroadcastChannel
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.asFlow
+import kotlinx.serialization.json.Json
+import org.jetbrains.exposed.sql.*
+import org.jetbrains.exposed.sql.transactions.transaction
+
+private class ContentAPIDatabaseTable(
+    private val database: Database
+) : Table("ContentAPI"), ContentAPI {
+    internal val idColumn = text("_id")
+    internal val dataColumn = text("data")
+
+    private inline fun <T> transaction(noinline body: Transaction.() -> T): T = transaction(database, body)
+
+    init {
+        transaction {
+            SchemaUtils.createMissingTablesAndColumns(this@ContentAPIDatabaseTable)
+        }
+    }
+
+    private val contentCreatedBroadcastChannel = BroadcastChannel<RegisteredContent>(Channel.BUFFERED)
+    private val contentDeletedBroadcastChannel = BroadcastChannel<RegisteredContent>(Channel.BUFFERED)
+    override val contentCreatedFlow: Flow<RegisteredContent> = contentCreatedBroadcastChannel.asFlow()
+    override val contentDeletedFlow: Flow<RegisteredContent> = contentDeletedBroadcastChannel.asFlow()
+
+    override suspend fun createContent(content: Content): RegisteredContent? {
+        return transaction {
+            insert {
+                it[idColumn] = generateContentId()
+                it[dataColumn] = Json.plain.stringify(Content.serializer(), content)
+            }.getOrNull(idColumn) ?.let { id ->
+                RegisteredContent(
+                    id,
+                    content
+                )
+            }
+        } ?.also {
+            contentCreatedBroadcastChannel.send(it)
+        }
+    }
+    override suspend fun deleteContent(id: ContentId): Boolean {
+        val content = getContentById(id) ?: return false
+        return transaction {
+            deleteWhere {
+                idColumn.eq(id)
+            } > 0
+        }.also {
+            if (it) {
+                contentDeletedBroadcastChannel.send(content)
+            }
+        }
+    }
+
+    private fun ResultRow.asRegisteredContent(): RegisteredContent = RegisteredContent(
+        get(idColumn),
+        Json.plain.parse(Content.serializer(), get(dataColumn))
+    )
+
+    override suspend fun getContentById(id: ContentId): RegisteredContent? {
+        return transaction {
+            select { idColumn.eq(id) }.firstOrNull() ?.asRegisteredContent()
+        }
+    }
+    override suspend fun getContentByPagination(pagination: Pagination): PaginationResult<out RegisteredContent> {
+        return transaction {
+            selectAll().count() to selectAll().limit(n = pagination.size, offset = pagination.firstIndex).map { it.asRegisteredContent() }
+        }.let { (count, results) ->
+            pagination.createResult(count, results)
+        }
+    }
+}
+
+class ExposedContentAPI (
+    private val database: Database
+) : ContentAPI by ContentAPIDatabaseTable(database)

exposed/src/test/kotlin/com/insanusmokrassar/postssystem/core/exposed/ExposedContentAPICommonTests.kt

@@ -0,0 +1,50 @@
+package com.insanusmokrassar.postssystem.core.exposed
+
+import com.insanusmokrassar.postssystem.core.content.SimpleTextContent
+import kotlinx.coroutines.runBlocking
+import org.jetbrains.exposed.sql.Database
+import org.jetbrains.exposed.sql.transactions.transactionManager
+import org.junit.jupiter.api.Test
+import java.io.File
+import java.sql.Connection
+
+class ExposedContentAPICommonTests {
+    private val tempFolder = System.getProperty("java.io.tmpdir")!!
+
+    @Test
+    fun `Test that it is possible to use several different databases at one time`() {
+        val numberOfDatabases = 2
+
+        val databaseFiles = (0 until numberOfDatabases).map {
+            "$tempFolder/ExposedContentAPICommonTestsDB$it.db"
+        }
+
+        val apis = databaseFiles.map {
+            ExposedContentAPI(
+                Database.Companion.connect("jdbc:sqlite:$it", driver = "org.sqlite.JDBC").also {
+                    it.transactionManager.defaultIsolationLevel = Connection.TRANSACTION_SERIALIZABLE
+                }
+            )
+        }
+
+        val results = apis.mapIndexed { i, api ->
+            val content = runBlocking { api.createContent(SimpleTextContent(i.toString())) }
+            assert(content != null)
+            content!!
+        }
+
+        results.forEachIndexed { i, content ->
+            apis.forEachIndexed { j, api ->
+                assert(
+                    runBlocking {
+                        api.getContentById(content.id) == (if (i != j) null else content)
+                    }
+                )
+            }
+        }
+
+        databaseFiles.forEach {
+            File(it).delete()
+        }
+    }
+}

settings.gradle

@@ -16,3 +16,4 @@ include 'services:webservice'
 */
 
 include ':core'
+include ':exposed'