From 71bb51c729f94dc926c3b12a878932e653e06466 Mon Sep 17 00:00:00 2001
From: Paul Campbell <pcampbell@kemitix.net>
Date: Fri, 15 Jun 2018 18:34:10 +0100
Subject: [PATCH] When starting an anonymous transaction then original branch
 is unchanged

---
 src/main/java/net/kemitix/gitdb/GitDBBranch.java   |  7 +++++++
 .../net/kemitix/gitdb/impl/GitDBBranchImpl.java    |  5 +++++
 .../kemitix/gitdb/impl/GitDBTransactionImpl.java   |  5 +++++
 .../java/net/kemitix/gitdb/test/GitDBTest.java     | 14 ++++++++++++++
 4 files changed, 31 insertions(+)

diff --git a/src/main/java/net/kemitix/gitdb/GitDBBranch.java b/src/main/java/net/kemitix/gitdb/GitDBBranch.java
index 99d0618..f6bd3ba 100644
--- a/src/main/java/net/kemitix/gitdb/GitDBBranch.java
+++ b/src/main/java/net/kemitix/gitdb/GitDBBranch.java
@@ -92,4 +92,11 @@ public interface GitDBBranch {
      * @return the branch name
      */
     String name();
+
+    /**
+     * Gets the commit id for the head of the branch.
+     *
+     * @return an Object Id.
+     */
+    String getCommitId();
 }
diff --git a/src/main/java/net/kemitix/gitdb/impl/GitDBBranchImpl.java b/src/main/java/net/kemitix/gitdb/impl/GitDBBranchImpl.java
index ca2e451..1adecf9 100644
--- a/src/main/java/net/kemitix/gitdb/impl/GitDBBranchImpl.java
+++ b/src/main/java/net/kemitix/gitdb/impl/GitDBBranchImpl.java
@@ -126,6 +126,11 @@ class GitDBBranchImpl implements GitDBBranch {
         return name;
     }
 
+    @Override
+    public String getCommitId() {
+        return branchRef.getObjectId().name();
+    }
+
     private String commitMessageForAdd(final String key, final String value) {
         return String.format("Add key [%s] = [%s]", key, value);
     }
diff --git a/src/main/java/net/kemitix/gitdb/impl/GitDBTransactionImpl.java b/src/main/java/net/kemitix/gitdb/impl/GitDBTransactionImpl.java
index de6ecd2..0e1630c 100644
--- a/src/main/java/net/kemitix/gitdb/impl/GitDBTransactionImpl.java
+++ b/src/main/java/net/kemitix/gitdb/impl/GitDBTransactionImpl.java
@@ -76,4 +76,9 @@ class GitDBTransactionImpl implements GitDBTransaction {
     public String name() {
         return branch.name();
     }
+
+    @Override
+    public String getCommitId() {
+        return null;
+    }
 }
diff --git a/src/test/java/net/kemitix/gitdb/test/GitDBTest.java b/src/test/java/net/kemitix/gitdb/test/GitDBTest.java
index 4eeccb6..6cfd077 100644
--- a/src/test/java/net/kemitix/gitdb/test/GitDBTest.java
+++ b/src/test/java/net/kemitix/gitdb/test/GitDBTest.java
@@ -339,6 +339,20 @@ class GitDBTest implements WithAssertions {
         assertThat(transaction.name()).isNotNull();
     }
 
+    // When starting an anonymous transaction then original branch is unchanged
+    @Test
+    void startAnonymousTransaction_thenOriginalBranchUnchanged() throws IOException {
+        //given
+        final GitDB gitDB = gitDB(dirDoesNotExist());
+        final GitDBBranch gitDBBranch = gitDB.branch("master").get();
+        final String commitId = gitDBBranch.getCommitId();
+        //when
+        final GitDBTransaction transaction = gitDBBranch.transaction();
+        //then
+        assertThat(gitDBBranch.getCommitId()).isEqualTo(commitId);
+        assertThat(gitDB.branch("master").map(GitDBBranch::getCommitId)).contains(commitId);
+    }
+
     // Given a GitDbTransaction handle (i.e. a new branch)
     // When putting a new key/value pair then the original GitDbBranch can't find it
     @Test