Initial commit

.gitignore

@@ -0,0 +1,42 @@
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store

.idea/.gitignore

@@ -0,0 +1,8 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

.idea/gradle.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
+  <component name="GradleSettings">
+    <option name="linkedExternalProjectsSettings">
+      <GradleProjectSettings>
+        <option name="externalProjectPath" value="$PROJECT_DIR$" />
+        <option name="gradleHome" value="" />
+        <option name="modules">
+          <set>
+            <option value="$PROJECT_DIR$" />
+          </set>
+        </option>
+      </GradleProjectSettings>
+    </option>
+  </component>
+</project>

.idea/kotlinc.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="KotlinJpsPluginSettings">
+    <option name="version" value="2.0.0-RC2" />
+  </component>
+</project>

.idea/misc.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="FrameworkDetectionExcludesConfiguration">
+    <file type="web" url="file://$PROJECT_DIR$" />
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" default="true" project-jdk-name="1.8" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+  <component name="accountSettings">
+    <option name="activeRegion" value="us-east-1" />
+    <option name="recentlyUsedRegions">
+      <list>
+        <option value="us-east-1" />
+      </list>
+    </option>
+  </component>
+</project>

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>

build.gradle.kts

@@ -0,0 +1,21 @@
+plugins {
+    kotlin("jvm") version "2.0.0-RC2"
+}
+
+group = "nl.astraeus"
+version = "1.0-SNAPSHOT"
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testImplementation(kotlin("test"))
+}
+
+tasks.test {
+    useJUnitPlatform()
+}
+kotlin {
+    jvmToolchain(17)
+}

gradle.properties

@@ -0,0 +1 @@
+kotlin.code.style=official

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,6 @@
+#Thu May 02 19:45:24 CEST 2024
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.5-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradlew

@@ -0,0 +1,234 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+APP_NAME="Gradle"
+APP_BASE_NAME=${0##*/}
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,89 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

settings.gradle.kts

@@ -0,0 +1,5 @@
+plugins {
+  id("org.gradle.toolchains.foojay-resolver-convention") version "0.5.0"
+}
+rootProject.name = "simple-persistence-kotlin"
+

src/main/kotlin/Main.kt

@@ -0,0 +1,5 @@
+package nl.astraeus
+
+fun main() {
+  println("Hello World!")
+}

src/main/kotlin/nl/astraeus/persistence/Datastore.kt

@@ -0,0 +1,229 @@
+package nl.astraeus.nl.astraeus.persistence
+
+import java.io.File
+import java.io.ObjectInputStream
+import java.io.ObjectOutputStream
+import java.io.Serializable
+import java.text.DecimalFormat
+import java.util.*
+import java.util.concurrent.ConcurrentHashMap
+import kotlin.reflect.KClass
+
+enum class ActionType {
+  STORE,
+  DELETE
+}
+
+class TypeData(
+  var nextId: Long = 1L,
+  val data: MutableMap<Any, Persistable> = ConcurrentHashMap(),
+) : Serializable
+
+class Action(
+  val type: ActionType,
+  val obj: Persistable
+) : Serializable
+
+class Datastore(
+  private val directory: File,
+  indexes: Array<PersistableIndex> = arrayOf(),
+) {
+  private val fileManager = FileManager(directory)
+  private val transactionFormatter = DecimalFormat("#")
+  private var nextTransactionNumber = 1L
+  private val data: MutableMap<Class<*>, TypeData> = ConcurrentHashMap()
+  private val indexes: MutableMap<Class<*>, MutableMap<String, PersistableIndex>> = ConcurrentHashMap()
+
+  init {
+    if (!directory.exists()) {
+      directory.mkdirs()
+    }
+
+    for (index in indexes) {
+      this.indexes.getOrPut(index.cls) {
+        ConcurrentHashMap()
+      }[index.name] = index
+    }
+
+    loadTransactions()
+  }
+
+  private fun loadTransactions() {
+    synchronized(this) {
+      val snapshots: Array<File>? = directory.listFiles { _, name -> name.startsWith("transaction-") && name.endsWith(".snp") }
+      val files: Array<File>? = directory.listFiles { _, name -> name.startsWith("transaction-") && name.endsWith(".trn") }
+
+      var lastSnapshot: Long? = null
+      var lastSnapshotFile: File? = null
+
+      snapshots?.let {
+        it.forEach {
+          val trnx = getTrnx(it)
+          if (lastSnapshot == null || trnx > (lastSnapshot ?: 0L)) {
+            lastSnapshot = trnx
+            lastSnapshotFile = it
+          }
+        }
+      }
+
+      val lastSnapshotFile2 = fileManager.findLastSnapshot()
+
+      if (lastSnapshotFile != null) {
+        ObjectInputStream(lastSnapshotFile?.inputStream()).use { ois ->
+          readSnapshot(ois)
+        }
+      }
+
+      val trns = fileManager.findTransactionsAfter(lastSnapshot ?: 0L)
+
+      files?.also { snaphotFiles ->
+        Arrays.sort(snaphotFiles) { o1, o2 -> if (getTrnx(o1) > getTrnx(o2)) 1 else -1}
+
+        snaphotFiles.forEach { file ->
+          if (getTrnx(file) > (lastSnapshot ?: 0L)) {
+            ObjectInputStream(file.inputStream()).use { ois ->
+              val transactionNumber = ois.readLong()
+              nextTransactionNumber = transactionNumber + 1
+              val actions = ois.readObject() as MutableList<Action>
+              execute(actions)
+            }
+          }
+        }
+      }
+    }
+  }
+
+  private fun getTrnx(file: File): Long {
+    return file.name.substringAfterLast('/').substringAfter("transaction-").substringBefore(".").toLong()
+  }
+
+  fun execute(actions: MutableList<Action>) {
+    synchronized(this) {
+      for (action in actions) {
+        val typeData = data.getOrPut(action.obj::class.java) {
+          TypeData()
+        }
+
+        when (action.type) {
+          ActionType.STORE -> {
+            if (action.obj.id == 0L) {
+              action.obj.id = typeData.nextId++
+            }
+            typeData.data[action.obj.id] = action.obj
+
+            for (index in indexes[action.obj::class.java]?.values ?: listOf()) {
+              index.add(action.obj as Persistable)
+            }
+          }
+
+          ActionType.DELETE -> {
+            typeData.data.remove(action.obj.id)
+
+            for (index in indexes[action.obj::class.java]?.values ?: listOf()) {
+              index.remove(action.obj)
+            }
+          }
+        }
+      }
+    }
+  }
+
+  fun <T : Persistable> find(clazz: KClass<T>, id: Long): T? {
+    val typeData = data.getOrPut(clazz.java) {
+      TypeData()
+    }
+
+    val p: Persistable? = typeData.data[id]
+
+    return (p?.copy() as T?)
+  }
+
+  fun <T : Persistable> search(
+    clazz: KClass<T>,
+    search: (T) -> Boolean
+  ): List<T> {
+    val typeData = data.getOrPut(clazz.java) {
+      TypeData()
+    }
+
+    return typeData.data.values
+      .filter { search(it as T) }
+      .map { o -> o.copy() as T }
+  }
+
+  fun findIndex(
+    kClass: KClass<*>,
+    indexName: String
+  ): PersistableIndex? {
+    return indexes[kClass.java]?.get(indexName)
+  }
+
+  fun storeActions(actions: MutableList<Action>) {
+    if (actions.isNotEmpty()) {
+      synchronized(this) {
+        val number = transactionFormatter.format(nextTransactionNumber)
+        val file = File(directory, "transaction-$number.trn")
+        ObjectOutputStream(file.outputStream()).use { oos ->
+          oos.writeLong(nextTransactionNumber++)
+          oos.writeObject(actions)
+        }
+      }
+    }
+  }
+
+  fun snapshot() {
+    synchronized(this) {
+      val number = transactionFormatter.format(nextTransactionNumber)
+      val file = File(directory, "transaction-$number.snp")
+      ObjectOutputStream(file.outputStream()).use { oos ->
+        oos.writeLong(nextTransactionNumber++)
+        oos.writeObject(data)
+        oos.writeInt(indexes.size)
+        for ((cls, index) in indexes) {
+          oos.writeObject(cls)
+          oos.writeInt(index.size)
+          for ((name, idx) in index) {
+            oos.writeObject(name)
+            oos.writeObject(idx.index)
+          }
+        }
+      }
+    }
+  }
+
+  private fun readSnapshot(ois: ObjectInputStream) {
+    nextTransactionNumber = ois.readLong() + 1
+    data.clear()
+    data.putAll(ois.readObject() as MutableMap<Class<*>, TypeData>)
+
+    val foundIndexes = mutableMapOf<Class<*>, MutableList<String>>()
+    val numberOfClassesWithIndex = ois.readInt()
+    for (i in 0 until numberOfClassesWithIndex) {
+      val cls = ois.readObject() as Class<*>
+      val numberOfIndexesForClass = ois.readInt()
+      for (indexForClass in 0 until numberOfIndexesForClass) {
+        val name = ois.readObject() as String
+        val idx = ois.readObject() as MutableMap<Serializable, MutableSet<Long>>
+        foundIndexes.getOrPut(cls) { mutableListOf() }.add(name)
+
+        val index = indexes[cls]
+        if (index != null) {
+          index[name]?.index?.putAll(idx)
+        } // else ignore, index is removed
+      }
+    }
+
+    // any (new) index not serialized needs to be build now
+    for ((cls, indexes) in indexes) {
+      for ((name, index) in indexes) {
+        if (!foundIndexes.getOrDefault(cls, mutableListOf()).contains(name)) {
+          index.index.clear()
+          for (obj in data.getOrDefault(cls, TypeData()).data.values) {
+            index.add(obj)
+          }
+        }
+      }
+    }
+  }
+
+}

src/main/kotlin/nl/astraeus/persistence/Indexing.kt

@@ -0,0 +1,37 @@
+package nl.astraeus.nl.astraeus.persistence
+
+import java.io.Serializable
+import kotlin.reflect.KClass
+
+typealias PersistableIndex = Index<out Persistable>
+
+class Index<T : Persistable>(
+  kcls: KClass<T>,
+  val name: String,
+  val value: (Persistable) -> Serializable?,
+) : Serializable {
+  val cls: Class<T> = kcls.java
+  val index = mutableMapOf<Serializable, MutableSet<Long>>()
+
+  fun add(obj: Persistable) {
+    val key = value(obj)
+
+    key?.also {
+      index.getOrPut(it) { mutableSetOf() }.add(obj.id)
+    }
+  }
+
+  fun remove(obj: Persistable) {
+    val key = value(obj)
+
+    index[key]?.remove(obj.id)
+  }
+
+  fun find(key: Any): List<T> {
+    return index[key]?.mapNotNull { currentTransaction()?.find(cls.kotlin, it) } ?: emptyList()
+  }
+
+  fun matches(obj: Persistable, value: Any): Boolean {
+    return value(obj) == value
+  }
+}

src/main/kotlin/nl/astraeus/persistence/Persistable.kt

@@ -0,0 +1,25 @@
+package nl.astraeus.nl.astraeus.persistence
+
+import java.io.ByteArrayInputStream
+import java.io.ByteArrayOutputStream
+import java.io.ObjectInputStream
+import java.io.ObjectOutputStream
+import java.io.Serializable
+
+interface Persistable : Serializable, Cloneable {
+  var id: Long
+  var version: Long
+
+  fun copy(): Persistable {
+    ByteArrayOutputStream().use { baos ->
+      ObjectOutputStream(baos).use { oos ->
+        oos.writeObject(this)
+      }
+      ByteArrayInputStream(baos.toByteArray()).use { bais ->
+        ObjectInputStream(bais).use { ois ->
+          return ois.readObject() as Persistable
+        }
+      }
+    }
+  }
+}

src/main/kotlin/nl/astraeus/persistence/Persistent.kt

@@ -0,0 +1,38 @@
+package nl.astraeus.nl.astraeus.persistence
+
+import java.io.File
+
+private val transactions: ThreadLocal<Transaction> = ThreadLocal<Transaction>()
+
+fun currentTransaction(): Transaction? {
+  return transactions.get()
+}
+
+class Persistent(
+  directory: File,
+  indexes: Array<PersistableIndex> = arrayOf(),
+) {
+  val datastore: Datastore = Datastore(directory, indexes)
+
+  fun transaction(block: Transaction.() -> Unit) {
+    var cleanup = false
+    if (transactions.get() == null) {
+      transactions.set(Transaction(this))
+      cleanup = true
+    }
+
+    try {
+      block(transactions.get())
+
+      transactions.get().commit()
+    } finally {
+      if (cleanup) {
+        transactions.remove()
+      }
+    }
+  }
+
+  fun snapshot() {
+    datastore.snapshot()
+  }
+}

src/main/kotlin/nl/astraeus/persistence/Reference.kt

@@ -0,0 +1,133 @@
+package nl.astraeus.nl.astraeus.persistence
+
+import java.io.Serializable
+import kotlin.reflect.KProperty
+
+class Reference<S : Persistable, H : Persistable>(
+  val cls: Class<S>,
+) : Serializable {
+  companion object {
+    private const val serialVersionUID: Long = 1L
+  }
+
+  var id: Long = 0
+
+  operator fun getValue(thisRef: H, property: KProperty<*>): S {
+    return currentTransaction()?.find(cls.kotlin, id) ?: throw IllegalStateException("Reference not found")
+  }
+
+  operator fun setValue(thisRef: H, property: KProperty<*>, value: S) {
+    id = value.id
+    currentTransaction()?.store(value)
+  }
+
+}
+
+class ListReference<S : Persistable, H : Persistable>(
+  val cls: Class<S>,
+) : Serializable {
+  companion object {
+    private const val serialVersionUID: Long = 1L
+  }
+
+  var ids: ReferenceList<S> = ReferenceList(cls)
+
+  operator fun getValue(thisRef: H, property: KProperty<*>): ReferenceList<S> {
+    return ids
+  }
+
+  operator fun setValue(thisRef: H, property: KProperty<*>, value: List<S>) {
+    this.ids.clear()
+    this.ids.addAll(value)
+  }
+}
+
+class ReferenceList<T : Persistable>(
+  val cls: Class<T>,
+) : MutableList<T> {
+  val ids = ArrayList<Long>()
+
+  private fun checkElementIsPersisted(element: T) {
+    if (currentTransaction()?.find(cls.kotlin, element.id) == null) {
+      currentTransaction()?.store(element)
+    }
+  }
+
+  override val size: Int = ids.size
+  override fun clear() = ids.clear()
+
+  override fun addAll(elements: Collection<T>): Boolean {
+    TODO("Not yet implemented")
+  }
+
+  override fun addAll(index: Int, elements: Collection<T>): Boolean {
+    TODO("Not yet implemented")
+  }
+
+  override fun add(index: Int, element: T) {
+    ids.add(index, element.id)
+  }
+
+  override fun add(element: T): Boolean {
+    return ids.add(element.id)
+  }
+
+  override fun get(index: Int): T = currentTransaction()?.find(cls.kotlin, ids[index]) ?: throw IllegalStateException("Reference not found")
+
+  override fun isEmpty(): Boolean = ids.isEmpty()
+
+  override fun iterator(): MutableIterator<T> {
+    TODO("Not yet implemented")
+  }
+
+  override fun listIterator(): MutableListIterator<T> {
+    TODO("Not yet implemented")
+  }
+
+  override fun listIterator(index: Int): MutableListIterator<T> {
+    TODO("Not yet implemented")
+  }
+
+  override fun removeAt(index: Int): T {
+    val id = ids.removeAt(index)
+
+    return currentTransaction()?.find(cls.kotlin, id) ?: throw IllegalStateException("Reference not found")
+  }
+
+  override fun set(index: Int, element: T): T {
+    TODO("Not yet implemented")
+  }
+
+  override fun retainAll(elements: Collection<T>): Boolean {
+    TODO("Not yet implemented")
+  }
+
+  override fun removeAll(elements: Collection<T>): Boolean {
+    TODO("Not yet implemented")
+  }
+
+  override fun remove(element: T): Boolean {
+    TODO("Not yet implemented")
+  }
+
+  override fun subList(fromIndex: Int, toIndex: Int): MutableList<T> {
+    TODO("Not yet implemented")
+  }
+
+  override fun lastIndexOf(element: T): Int {
+    TODO("Not yet implemented")
+  }
+
+  override fun indexOf(element: T): Int {
+    TODO("Not yet implemented")
+  }
+
+  override fun containsAll(elements: Collection<T>): Boolean {
+    TODO("Not yet implemented")
+  }
+
+  override fun contains(element: T): Boolean {
+    TODO("Not yet implemented")
+  }
+
+}

src/main/kotlin/nl/astraeus/persistence/Transaction.kt

@@ -0,0 +1,100 @@
+package nl.astraeus.nl.astraeus.persistence
+
+import java.io.Serializable
+import kotlin.reflect.KClass
+
+class Transaction(
+  val persistent: Persistent,
+) : Serializable {
+  private val actions = mutableListOf<Action>()
+
+  fun store(obj: Persistable) {
+    actions.add(Action(ActionType.STORE, obj))
+  }
+
+  fun delete(obj: Persistable) {
+    actions.add(Action(ActionType.DELETE, obj))
+  }
+
+  fun <T : Persistable> find(clazz: KClass<T>, id: Long): T? {
+    var result: T? = persistent.datastore.find(clazz, id)
+
+    for (action in actions) {
+      if (action.obj::class == clazz && action.obj.id == id) {
+        result = when {
+          action.type == ActionType.DELETE -> {
+            null
+          }
+
+          action.type == ActionType.STORE -> {
+            action.obj as? T
+          }
+
+          else -> {
+            result
+          }
+        }
+      }
+    }
+
+    return result
+  }
+
+  fun <T : Persistable> search(clazz: KClass<T>, search: (T) -> Boolean): List<T> {
+    val fromDatastore: List<T> = persistent.datastore.search(clazz, search)
+    val result = mutableListOf<T>()
+    result.addAll(fromDatastore)
+
+    for (obj in result) {
+      for (action in actions) {
+        if (action.obj.id == obj.id) {
+          if (action.type == ActionType.DELETE) {
+            result.remove(obj)
+          } else if (action.type == ActionType.STORE) {
+            result.remove(obj)
+            result.add(action.obj as T)
+          }
+        }
+      }
+    }
+
+    return result
+  }
+
+  fun commit() {
+    persistent.datastore.storeActions(actions)
+    persistent.datastore.execute(actions)
+    actions.clear()
+  }
+
+  fun <T : Persistable> findByIndex(
+    kClass: KClass<T>,
+    indexName: String,
+    search: Any
+  ): List<T> {
+    val result = mutableListOf<T>()
+    val index = persistent.datastore.findIndex(kClass, indexName) ?: throw IllegalArgumentException("Index not found")
+
+    index.find(search).forEach { id ->
+      result.add(id as T)
+    }
+
+    for (action in actions) {
+      if (action.obj::class == kClass) {
+        if (action.type == ActionType.DELETE) {
+          if (index.matches(action.obj, search)) {
+            result.remove(action.obj as T)
+          }
+        } else if (action.type == ActionType.STORE) {
+          if (index.matches(action.obj, search)) {
+            result.remove(action.obj)
+            result.add(action.obj as T)
+          }
+        }
+      }
+    }
+
+    return result
+  }
+
+}

src/test/kotlin/nl/astraeus/persistence/TestPersistence.kt

@@ -0,0 +1,152 @@
+package nl.astraeus.persistence
+
+import nl.astraeus.nl.astraeus.persistence.Index
+import nl.astraeus.nl.astraeus.persistence.Persistable
+import nl.astraeus.nl.astraeus.persistence.Persistent
+import nl.astraeus.nl.astraeus.persistence.Reference
+import java.io.File
+import kotlin.test.Test
+
+class TestPersistence {
+
+  class Company(
+    override var id: Long = 0,
+    override var version: Long = 0,
+    val name: String
+  ) : Persistable, Cloneable {
+    //var persons: MutableList<Person> by ListReference<Person, Company>(Person::class.java)
+
+    companion object {
+      private const val serialVersionUID: Long = 1L
+    }
+  }
+
+  class Person(
+    override var id: Long = 0,
+    override var version: Long = 0,
+    val name: String,
+    val age: Int,
+  ) : Persistable, Cloneable {
+    var company: Company by Reference<Company, Person>(Company::class.java)
+
+    companion object {
+      private const val serialVersionUID: Long = 1L
+    }
+  }
+
+  @Test
+  fun testPersistence() {
+    println("Test persistence")
+
+    val pst = Persistent(
+      directory = File("data"),
+      arrayOf(
+        Index(Person::class, "name") { p -> (p as? Person)?.name ?: "" },
+        Index(Person::class, "age") { p -> (p as? Person)?.age ?: -1 },
+        Index(Person::class, "ageGt20") { p -> ((p as? Person)?.age ?: 0) > 20 },
+        Index(Person::class, "ageGt23") { p -> ((p as? Person)?.age ?: 0) > 23 },
+        Index(Person::class, "ageOnlyGt20") { p ->
+          if (((p as? Person)?.age ?: 0) > 20) {
+            true
+          } else {
+            null
+          }
+        },
+        Index(Company::class, "name") { p -> (p as? Company)?.name ?: "" },
+      )
+    )
+
+    pst.transaction {
+      val person = find(Person::class, 1L) ?: Person(
+        id = 1L,
+        name = "John Doe",
+        age = 25
+      )
+
+      val company = find(Company::class, 1L) ?: Company(
+        id = 1L,
+        name = "ACME"
+      )
+
+      person.company = company
+      //company.persons.add(person)
+
+      store(person)
+      store(Person(
+        id = 2L,
+        name = "John Doe",
+        age = 23
+      ))
+      store(Person(
+        id = 3L,
+        name = "John Doe",
+        age = 18
+      ))
+
+      findByIndex(Person::class, "name", "John Doe").forEach { p ->
+        println("Found person by name: ${p.name} - ${p.age}")
+      }
+
+      findByIndex(Person::class, "age", 23).forEach { p ->
+        println("Found person by age: ${p.name} - ${p.age}")
+      }
+
+      findByIndex(Person::class, "ageGt20", true).forEach { p ->
+        println("Found person by age > 20: ${p.name} - ${p.age}")
+      }
+
+      findByIndex(Person::class, "ageGt23", true).forEach { p ->
+        println("Found person by age > 23: ${p.name} - ${p.age}")
+      }
+
+      findByIndex(Person::class, "ageGt20", false).forEach { p ->
+        println("Found person by age <= 20: ${p.name} - ${p.age}")
+      }
+
+      val p2 = find(Person::class, 1L)
+
+      assert(p2 != null)
+
+      val c2 = find(Company::class, 1L)
+
+      assert(c2 != null)
+    }
+
+    pst.transaction {
+      val person = find(Person::class, 1L)
+
+      delete(person!!)
+
+      val p2 = find(Person::class, 1L)
+
+      assert(p2 == null)
+    }
+
+    pst.transaction {
+      val persons = search(Person::class) { p -> p.name == "John Doe" }
+
+      if (persons.isNotEmpty()) {
+        delete(persons[0])
+      }
+    }
+
+    pst.snapshot()
+
+    pst.transaction {
+      store(
+        Person(
+          id = 10L,
+          name = "Pipo",
+          age = 23
+        )
+      )
+      store(
+        Person(
+          id = 11L,
+          name = "Clown",
+          age = 18
+        )
+      )
+    }
+  }
+}