diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
new file mode 100644
index 0000000..1c9df4c
--- /dev/null
+++ b/.github/workflows/main.yaml
@@ -0,0 +1,9 @@
+name: Main Workflow
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
+jobs:
diff --git a/.idea/gradle.xml b/.idea/gradle.xml
index f9163b4..ce1c62c 100644
--- a/.idea/gradle.xml
+++ b/.idea/gradle.xml
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
   <component name="GradleSettings">
     <option name="linkedExternalProjectsSettings">
       <GradleProjectSettings>
diff --git a/.idea/misc.xml b/.idea/misc.xml
index 590038f..4a4ab8c 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -4,7 +4,11 @@
   <component name="FrameworkDetectionExcludesConfiguration">
     <file type="web" url="file://$PROJECT_DIR$" />
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" project-jdk-name="corretto-19" project-jdk-type="JavaSDK">
+  <component name="PWA">
+    <option name="enabled" value="true" />
+    <option name="wasEnabledAtLeastOnce" value="true" />
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_17" project-jdk-name="openjdk-21" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/out" />
   </component>
 </project>
\ No newline at end of file
diff --git a/README.md b/README.md
index 2bf8db3..c3d3a0b 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,8 @@
 This is a small project to implement a subset of git's functionality in Kotlin and was created using the instructions
 below as part of my application to the JetBrains internship project "TeamCity support for Gitea".
 
+The package is named `tinyvm` for 'tiny version manager'.
+
 ## Assumptions
 
 Since this is an internship application project, I have assumed that a minimal usage of external libraries is preferred,
diff --git a/build.gradle.kts b/build.gradle.kts
index 58603c7..5f55b92 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -1,5 +1,6 @@
 plugins {
     kotlin("jvm") version "1.9.21"
+    id("org.jmailen.kotlinter") version "4.1.0"
 }
 
 group = "net.koval"
@@ -18,5 +19,5 @@ tasks.test {
 }
 
 kotlin {
-    jvmToolchain(8)
+    jvmToolchain(17)
 }
\ No newline at end of file
diff --git a/src/main/kotlin/tinyvm/Commit.kt b/src/main/kotlin/tinyvm/Commit.kt
new file mode 100644
index 0000000..9d9172a
--- /dev/null
+++ b/src/main/kotlin/tinyvm/Commit.kt
@@ -0,0 +1,33 @@
+package tinyvm
+
+import java.security.MessageDigest
+import java.time.Instant
+
+abstract class Object(
+    val type: String,
+) {
+    abstract val data: String
+    fun hash(): String = MessageDigest
+        .getInstance("SHA-1")
+        .digest("$type ${data.length}\u0000$data".toByteArray())
+        .toHex()
+}
+
+class Commit(
+    val tree: Tree,
+    val author: Author,
+    val message: String,
+    val timestamp: Instant
+) : Object("commit") {
+    // Use \n\n for end of header in-case additional metadata is implemented in the future.
+    override val data: String
+        get() = "tree ${tree.hash()}\nauthor $author\ntimestamp ${timestamp.epochSecond}\n\n$message"
+}
+
+data class Author(
+    val name: String,
+    val email: String
+) {
+    override fun toString(): String =
+        "$name <$email>"
+}
\ No newline at end of file
diff --git a/src/main/kotlin/tinyvm/Extensions.kt b/src/main/kotlin/tinyvm/Extensions.kt
new file mode 100644
index 0000000..b7cc489
--- /dev/null
+++ b/src/main/kotlin/tinyvm/Extensions.kt
@@ -0,0 +1,6 @@
+package tinyvm
+
+import java.util.HexFormat
+
+fun ByteArray.toHex(): String =
+     HexFormat.of().formatHex(this)
diff --git a/src/main/kotlin/tinyvm/Repository.kt b/src/main/kotlin/tinyvm/Repository.kt
new file mode 100644
index 0000000..df7f8a1
--- /dev/null
+++ b/src/main/kotlin/tinyvm/Repository.kt
@@ -0,0 +1,90 @@
+package tinyvm
+
+class HashCollisionException(hash: String) : Exception("Different object types with identical hash '$hash'")
+
+class CommitTimeComparator: Comparator<Commit> {
+    override fun compare(o1: Commit, o2: Commit): Int =
+        (o1.timestamp.epochSecond - o2.timestamp.epochSecond).toInt()
+}
+
+class Repository {
+    private val commits = sortedSetOf(CommitTimeComparator())
+
+    // Store all objects in one map like git does. This would simplify the data persistence implementation (if there was
+    // one) and allows for other objects to be added in the future without modifying the data persistence implementation
+    // at all.
+    private val objects = mutableMapOf<String, Object>()
+
+    /**
+     * (Deep) get or put a commit object into the repository.
+     * This will also get or put all child trees and blobs.
+     */
+    fun commit(commit: Commit): Commit {
+        val hash = commit.hash()
+        val obj = findObject<Commit>(hash)
+        if (obj != null) return obj
+        val newCommit = Commit(
+            tree = addTree(commit.tree),
+            author = commit.author,
+            message = commit.message,
+            timestamp = commit.timestamp
+        )
+        objects[hash] = newCommit
+        commits.add(newCommit)
+        return newCommit
+    }
+
+    /**
+     * Get a commit by its hash.
+     */
+    fun getCommit(hash: String): Commit? = findObject<Commit>(hash)
+
+    /**
+     * List all commits.
+     */
+    fun listCommits(): List<Commit> = commits.toList()
+
+    /**
+     * Find commit.
+     */
+    fun findCommit(predicate: (Commit) -> Boolean): Commit? =
+        commits.find(predicate)
+
+    /**
+     * Dump repository objects
+     */
+    fun dumpObjects(): Map<String, Object> = objects
+
+    /**
+     * (Deep) get or put a tree object into the repository.
+     * This will also get or put all child trees and blobs.
+     */
+    private fun addTree(tree: Tree): Tree {
+        val hash = tree.hash()
+        val obj = findObject<Tree>(hash)
+        if (obj != null) return obj
+        val newTree = Tree(
+            tree.nodes.map { (name, node) ->
+                when (node) {
+                    is Tree -> name to addTree(node)
+                    is Blob -> name to addObject(node)
+                }
+            }.toMap()
+        )
+        objects[hash] = newTree
+        return tree
+    }
+
+    /**
+     * (Shallow) get or put an object into the repository.
+     */
+    private inline fun <reified T : Object> addObject(obj: T): T =
+        objects.getOrPut(obj.hash()) { obj } as? T ?: throw HashCollisionException(obj.hash())
+
+    /**
+     * Find an object in the repository by its hash.
+     */
+    private inline fun <reified T : Object> findObject(hash: String): T? =
+        objects[hash]?.let { it as? T ?: throw HashCollisionException(hash) }
+
+}
\ No newline at end of file
diff --git a/src/main/kotlin/tinyvm/Tree.kt b/src/main/kotlin/tinyvm/Tree.kt
new file mode 100644
index 0000000..587f7de
--- /dev/null
+++ b/src/main/kotlin/tinyvm/Tree.kt
@@ -0,0 +1,13 @@
+package tinyvm
+
+sealed class Node(type: String): Object(type)
+
+class Tree(val nodes: Map<String, Node>) : Node("tree") {
+    // For simplicity just use the hex-formatted hash, not the actual value like git does.
+    override val data: String
+        get() = nodes.map { (name, node) ->
+            "${node.type} $name\u0000${node.hash()}"
+        }.sorted().joinToString()
+}
+
+class Blob(override val data: String) : Node("blob")
\ No newline at end of file
diff --git a/src/test/kotlin/tinyvm/RepositoryTest.kt b/src/test/kotlin/tinyvm/RepositoryTest.kt
new file mode 100644
index 0000000..8cef40b
--- /dev/null
+++ b/src/test/kotlin/tinyvm/RepositoryTest.kt
@@ -0,0 +1,111 @@
+package tinyvm
+
+import java.time.Instant
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+internal class RepositoryTest {
+    private val repository = Repository()
+    private val commits = listOf(
+        Commit(
+            tree = Tree(mapOf("test1.txt" to Blob("Hello World!"))),
+            author = Author("Gleb Koval", "gleb@koval.net"),
+            message = "Add test1.txt",
+            timestamp = Instant.ofEpochSecond(0)
+        ), Commit(
+            tree = Tree(
+                mapOf(
+                    "dir1" to Tree(
+                        mapOf(
+                            "test1.txt" to Blob("Hello World!")
+                        )
+                    ),
+                    "dir2" to Tree(
+                        mapOf(
+                            "test2.txt" to Blob("This is a second file")
+                        )
+                    )
+                )
+            ),
+            author = Author("Gleb Koval", "gleb@koval.net"),
+            message = "Move test1.txt and add dir2/test2.txt",
+            timestamp = Instant.ofEpochSecond(50)
+        ), Commit(
+            tree = Tree(
+                mapOf(
+                    "dir1" to Tree(
+                        mapOf(
+                            "test1.txt" to Blob("Hello World!")
+                        )
+                    ),
+                    "dir2" to Tree(
+                        mapOf(
+                            "test2.txt" to Blob("This is a second file")
+                        )
+                    ),
+                    "README.md" to Blob("# This is a test repo!")
+                )
+            ),
+            author = Author("Gleb Koval", "gleb@koval.net"),
+            message = "Add README.md",
+            timestamp = Instant.ofEpochSecond(100)
+        )
+    )
+
+    @Test
+    fun `can commit`() {
+        val committed = repository.commit(commits[0])
+        assertEquals(commits[0].hash(), committed.hash())
+        assertEquals(1, repository.listCommits().size)
+        assertEquals(3, repository.dumpObjects().size)
+    }
+
+    @Test
+    fun `can deduplicate commit`() {
+        repository.commit(commits[0])
+        assertEquals(1, repository.listCommits().size)
+        val committed = repository.commit(commits[0])
+        assertEquals(1, repository.listCommits().size)
+        assertEquals(3, repository.dumpObjects().size)
+        assertEquals(commits[0].hash(), committed.hash())
+    }
+
+    @Test
+    fun `can commit twice and deduplicate objects`() {
+        repository.commit(commits[0])
+        val committed = repository.commit(commits[1])
+        assertEquals(2, repository.listCommits().size)
+        assertEquals(7, repository.dumpObjects().size)
+        assertEquals(commits[1].hash(), committed.hash())
+        assertEquals(commits.take(2).map { it.hash() }, repository.listCommits().map { it.hash() })
+    }
+
+    @Test
+    fun `can commit in-between existing commits`() {
+        repository.commit(commits[0])
+        repository.commit(commits[2])
+        val committed = repository.commit(commits[1])
+        assertEquals(3, repository.listCommits().size)
+        assertEquals(10, repository.dumpObjects().size)
+        assertEquals(commits[1].hash(), committed.hash())
+        assertEquals(commits.map { it.hash() }, repository.listCommits().map { it.hash() })
+    }
+
+    @Test
+    fun `can get commit by hash`() {
+        repository.commit(commits[0])
+        val committed = repository.commit(commits[1])
+        repository.commit(commits[2])
+        assertEquals(committed, repository.getCommit(commits[1].hash()))
+        assertEquals(null, repository.getCommit("00000000000000000000"))
+    }
+
+    @Test
+    fun `can find commit by predicate`() {
+        repository.commit(commits[0])
+        val committed = repository.commit(commits[1])
+        repository.commit(commits[2])
+        assertEquals(committed, repository.findCommit { it.message.matches("Move.*".toRegex()) })
+        assertEquals(null, repository.getCommit("00000000000000000000"))
+    }
+}
\ No newline at end of file