Branch support (#7)

Closes #6.

Implements branch support by _only extending_ the existing functionality. Note that the existing functionality DOES NOT implement a `parent` pointer for commits, and as a result branches are also implemented differently to how git implements them.

git branches are simply a named pointer to a commit object (which then has a pointer to its parent commit), here branches store the entire sequence of pointers to commit objects.

### Why different to git?
I made a mistake in the initial implementation by using a `TreeSet` instead of manually implementing a tree for commits. This allowed the ability to insert commits in-between other commits, which isn't normally possible in `git` _without rebasing which changes commits' hashes_.

The specification for this feature stated:
> All functionality that is implemented already should be preserved.

And so since I cannot remove this functionality any more, I have to build on top of it.

Reviewed-on: #7

.github/workflows/main.yaml

@@ -1,9 +0,0 @@
-name: Main Workflow
-on:
-  pull_request:
-    branches:
-      - main
-  push:
-    branches:
-      - main
-jobs:

.github/workflows/publish.yaml

@@ -0,0 +1,40 @@
+name: Publish Workflow
+on:
+  push:
+    tags:
+      - v*
+jobs:
+  publish:
+    name: Publish library
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Java
+        uses: actions/setup-java@v3
+        with:
+          distribution: adopt
+          java-version: 17
+
+      - name: Verify Gradle wrapper
+        uses: gradle/wrapper-validation-action@v1
+
+      - name: Setup Gradle
+        uses: gradle/gradle-build-action@v2
+
+      - name: Run checks
+        run: ./gradlew check
+
+      - name: Parse parameters
+        id: parse
+        run: |
+          export VERSION="$(echo ${{ github.ref_name }} | cut -c2-)"
+          echo "Parsed version: '$VERSION'"
+          echo "tinyvm_version=$VERSION" >> "$GITHUB_OUTPUT"
+
+      - name: Publish to Gitea package repository
+        env:
+          TINYVM_VERSION: ${{ steps.parse.outputs.tinyvm_version }}
+          GITEA_USERNAME: ${{ github.repository_owner }}
+          GITEA_TOKEN: ${{ secrets.deploy_token }}
+        run: ./gradlew publishAllPublicationsToGiteaRepository

.github/workflows/test.yaml

@@ -0,0 +1,29 @@
+name: Test Workflow
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
+jobs:
+  lint-and-test:
+    name: Lint and test library
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Java
+        uses: actions/setup-java@v3
+        with:
+          distribution: adopt
+          java-version: 17
+
+      - name: Verify Gradle wrapper
+        uses: gradle/wrapper-validation-action@v1
+
+      - name: Setup Gradle
+        uses: gradle/gradle-build-action@v2
+
+      - name: Run checks
+        run: ./gradlew check

.idea/gradle.xml

@@ -5,6 +5,7 @@
     <option name="linkedExternalProjectsSettings">
       <GradleProjectSettings>
         <option name="externalProjectPath" value="$PROJECT_DIR$" />
+        <option name="gradleJvm" value="corretto-19" />
         <option name="modules">
           <set>
             <option value="$PROJECT_DIR$" />

README.md

@@ -10,6 +10,26 @@ The package is named `tinyvm` for 'tiny version manager'.
 Since this is an internship application project, I have assumed that a minimal usage of external libraries is preferred,
 so that a greater technical understanding can be demonstrated.
 
+## Usage
+
+### Gradle
+```kotlin
+repositories {
+    // other repositories
+    maven { url "https://git.koval.net/api/packages/cyclane/maven" }
+}
+
+dependencies {
+    // other dependencies
+    implementation("net.koval.teamcity-gitea-test-task:tinyvm:0.1.1")
+}
+```
+
+### Documentation
+Use autocompletion and hover menus in your IDE, or download the
+[generated HTML documentation](https://git.koval.net/cyclane/teamcity-gitea-test-task/releases/download/v0.1.1/tinyvm-0.1.1-javadoc.zip)
+from the [latest release](https://git.koval.net/cyclane/teamcity-gitea-test-task/releases).
+
 ## Instructions
 
 Create a library that implements simple Git functionality. You need to implement at least three entities:

build.gradle.kts

@@ -1,10 +1,12 @@
 plugins {
     kotlin("jvm") version "1.9.21"
     id("org.jmailen.kotlinter") version "4.1.0"
+    id("org.jetbrains.dokka") version "1.9.10"
+    `maven-publish`
 }
 
-group = "net.koval"
-version = "1.0-SNAPSHOT"
+group = "net.koval.teamcity-gitea-test-task"
+version = System.getenv("TINYVM_VERSION")
 
 repositories {
     mavenCentral()
@@ -21,3 +23,46 @@ tasks.test {
 kotlin {
     jvmToolchain(17)
 }
+
+val dokkaHtml by tasks.getting(org.jetbrains.dokka.gradle.DokkaTask::class)
+val javadocJar: TaskProvider<Jar> by tasks.registering(Jar::class) {
+    dependsOn(dokkaHtml)
+    archiveClassifier.set("javadoc")
+    from(dokkaHtml.outputDirectory)
+}
+
+publishing {
+    publications.register<MavenPublication>("gpr") {
+        artifactId = "tinyvm"
+        from(components["java"])
+        artifact(javadocJar)
+        pom {
+            name.set("TeamCity support for Gitea - Test Task - tiny version manager")
+            description.set("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\".")
+            url.set("https://git.koval.net/cyclane/teamcity-gitea-test-task")
+            developers {
+                developer {
+                    id.set("cyclane")
+                    name.set("Gleb Koval")
+                    email.set("gleb@koval.net")
+                }
+            }
+            scm {
+                url.set("https://git.koval.net/cyclane/teamcity-gitea-test-task")
+            }
+        }
+    }
+
+    repositories {
+        maven {
+            name = "Gitea"
+            url = uri("https://git.koval.net/api/packages/cyclane/maven")
+            credentials {
+                username = System.getenv("GITEA_USERNAME")
+                password = System.getenv("GITEA_TOKEN")
+            }
+        }
+    }
+}

src/main/kotlin/tinyvm/Commit.kt

@@ -1,33 +1,25 @@
 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()
-}
-
+/**
+ * Commits are a pointer to a 'head' tree with some metadata.
+ */
 class Commit(
     val tree: Tree,
     val author: Author,
     val message: String,
-    val timestamp: Instant
+    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"
+
+    override fun toString(): String = "commit ${hash()}\n$data"
 }
 
 data class Author(
     val name: String,
-    val email: String
+    val email: String,
 ) {
-    override fun toString(): String =
-        "$name <$email>"
+    override fun toString(): String = "$name <$email>"
 }

src/main/kotlin/tinyvm/Extensions.kt

@@ -1,6 +0,0 @@
-package tinyvm
-
-import java.util.HexFormat
-
-fun ByteArray.toHex(): String =
-     HexFormat.of().formatHex(this)

src/main/kotlin/tinyvm/Object.kt

@@ -0,0 +1,17 @@
+package tinyvm
+
+import java.security.MessageDigest
+import java.util.HexFormat
+
+/**
+ * Represents an arbitrary version manager object.
+ */
+abstract class Object(val type: String) {
+    abstract val data: String
+
+    fun hash(): String =
+        HexFormat.of().formatHex(
+            MessageDigest.getInstance("SHA-1")
+                .digest("$type ${data.length}\u0000$data".toByteArray()),
+        )
+}

src/main/kotlin/tinyvm/Repository.kt

@@ -1,20 +1,59 @@
 package tinyvm
 
+import java.util.TreeSet
+
 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()
+private 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())
+private val commitTimeComparator = CommitTimeComparator()
+
+private class Branch(val name: String, val commits: TreeSet<Commit>)
+
+class Repository(initialBranch: String = "master") {
+    private var head = Branch(initialBranch, sortedSetOf(commitTimeComparator))
+    private val commits = mutableMapOf(initialBranch to head)
+
+    val branch: String
+        get() = head.name
+
+    val branches: Set<String>
+        get() = commits.keys
 
     // 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>()
 
+    /**
+     * Create a new branch as a copy of the current branch.
+     * @param name New branch name.
+     * @param use Whether to switch to this branch.
+     */
+    fun createBranch(
+        name: String,
+        use: Boolean = true,
+    ) {
+        commits[name] =
+            Branch(
+                name,
+                head.commits.clone() as? TreeSet<Commit> ?: throw Exception("TreeSet.clone() unexpected result"),
+            )
+        if (use) useBranch(name)
+    }
+
+    /**
+     * Use (switch to) a branch.
+     */
+    fun useBranch(name: String) {
+        head = commits[name] ?: throw BranchNotFoundException(name)
+    }
+
     /**
      * (Deep) get or put a commit object into the repository.
      * This will also get or put all child trees and blobs.
@@ -23,14 +62,15 @@ class Repository {
         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
-        )
+        val newCommit =
+            Commit(
+                tree = addTree(commit.tree),
+                author = commit.author,
+                message = commit.message,
+                timestamp = commit.timestamp,
+            )
         objects[hash] = newCommit
-        commits.add(newCommit)
+        head.commits.add(newCommit)
         return newCommit
     }
 
@@ -42,13 +82,12 @@ class Repository {
     /**
      * List all commits.
      */
-    fun listCommits(): List<Commit> = commits.toList()
+    fun listCommits(): List<Commit> = head.commits.toList()
 
     /**
      * Find commit.
      */
-    fun findCommit(predicate: (Commit) -> Boolean): Commit? =
-        commits.find(predicate)
+    fun findCommit(predicate: (Commit) -> Boolean): Commit? = head.commits.find(predicate)
 
     /**
      * Dump repository objects
@@ -63,14 +102,15 @@ class Repository {
         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()
-        )
+        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
     }
@@ -86,5 +126,6 @@ class Repository {
      */
     private inline fun <reified T : Object> findObject(hash: String): T? =
         objects[hash]?.let { it as? T ?: throw HashCollisionException(hash) }
-
 }
+
+class BranchNotFoundException(name: String) : Exception("Branch '$name' does not exist")

src/main/kotlin/tinyvm/Tree.kt

@@ -1,13 +1,36 @@
 package tinyvm
 
-sealed class Node(type: String): Object(type)
+/**
+ * Tree nodes are either trees or blobs, represented by this sealed class.
+ */
+sealed class Node(type: String) : Object(type)
 
+/**
+ * A tree is a set of named nodes.
+ */
 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()
+        get() =
+            nodes.map { (name, node) ->
+                "${node.type} $name\u0000${node.hash()}"
+            }.sorted().joinToString()
+
+    override fun toString(): String =
+        "tree ${hash()}\n" +
+            nodes.map { (name, node) ->
+                when (node) {
+                    is Tree -> "+$name/\n"
+                    is Blob -> "+$name\n"
+                } + node.toString().insertLeftMargin()
+            }.sorted().joinToString("\n")
 }
 
-class Blob(override val data: String) : Node("blob")
+/**
+ * A blob is a data container.
+ */
+class Blob(override val data: String) : Node("blob") {
+    override fun toString(): String = "blob ${hash()}\n${data.insertLeftMargin()}"
+}
+
+private fun String.insertLeftMargin(): String = split('\n').joinToString("\n") { "| $it" }

src/test/kotlin/tinyvm/RepositoryTest.kt

@@ -6,51 +6,60 @@ 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")
-                        )
-                    )
-                )
+    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),
             ),
-            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(
+            Commit(
+                tree =
+                    Tree(
                         mapOf(
-                            "test1.txt" to Blob("Hello World!")
-                        )
+                            "dir2" to
+                                Tree(
+                                    mapOf(
+                                        "test1.txt" to Blob("This is a second file"),
+                                    ),
+                                ),
+                            "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 = "Move test1.txt to dir1 and add dir2/test1.txt",
+                timestamp = Instant.ofEpochSecond(50),
+            ),
+            Commit(
+                tree =
+                    Tree(
+                        mapOf(
+                            "dir1" to
+                                Tree(
+                                    mapOf(
+                                        "test1.txt" to Blob("Hello World!"),
+                                    ),
+                                ),
+                            "dir2" to
+                                Tree(
+                                    mapOf(
+                                        "test1.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),
             ),
-            author = Author("Gleb Koval", "gleb@koval.net"),
-            message = "Add README.md",
-            timestamp = Instant.ofEpochSecond(100)
         )
-    )
 
     @Test
     fun `can commit`() {
@@ -108,4 +117,68 @@ internal class RepositoryTest {
         assertEquals(committed, repository.findCommit { it.message.matches("Move.*".toRegex()) })
         assertEquals(null, repository.getCommit("00000000000000000000"))
     }
+
+    @Test
+    fun `can create and use branch`() {
+        repository.commit(commits[0])
+        repository.commit(commits[1])
+        repository.commit(commits[2])
+        repository.createBranch("test-branch", use = false)
+        assertEquals("master", repository.branch)
+        repository.createBranch("test-branch-2")
+        assertEquals("test-branch-2", repository.branch)
+        assertEquals(setOf("master", "test-branch", "test-branch-2"), repository.branches)
+        assertEquals(commits.map { it.hash() }, repository.listCommits().map { it.hash() })
+        assertEquals(10, repository.dumpObjects().size)
+    }
+
+    @Test
+    fun `can commit to branch`() {
+        repository.commit(commits[0])
+        repository.createBranch("test-branch")
+        repository.commit(commits[1])
+        repository.createBranch("test-branch-2")
+        repository.commit(commits[2])
+
+        assertEquals(commits.map { it.hash() }, repository.listCommits().map { it.hash() })
+        repository.useBranch("test-branch")
+        assertEquals(commits.take(2).map { it.hash() }, repository.listCommits().map { it.hash() })
+        repository.useBranch("master")
+        assertEquals(commits.take(1).map { it.hash() }, repository.listCommits().map { it.hash() })
+    }
+
+    @Test
+    fun `can display commit`() {
+        assertEquals(
+            """
+            commit 804c6f0c66da0ea0eab8ac29f23a627e03a962b2
+            tree aaebbb258bce30749fc302cbd161b78462252a32
+            author Gleb Koval <gleb@koval.net>
+            timestamp 0
+            
+            Add test1.txt
+            """.trimIndent(),
+            commits[0].toString(),
+        )
+    }
+
+    @Test
+    fun `can display tree`() {
+        assertEquals(
+            """
+            tree 048b8e267dd7a6c5d4849d59f6ff82e6ae948f13
+            +dir1/
+            | tree aaebbb258bce30749fc302cbd161b78462252a32
+            | +test1.txt
+            | | blob c57eff55ebc0c54973903af5f72bac72762cf4f4
+            | | | Hello World!
+            +dir2/
+            | tree 0e14cbdba02924cd63a58c2492fc3dd05dc682bd
+            | +test1.txt
+            | | blob da3fcc31cbc16fcbb7526d68771f77e7e7f02fb1
+            | | | This is a second file
+            """.trimIndent(),
+            commits[1].tree.toString(),
+        )
+    }
 }