Fix working with raw git diff

- Fix getting `baseSha` and `headSha`. Now I get `baseSha` from first commit, and `headSha` is got from the last commit. Need to sort commits by author date to be ordered chronologically
- Reverted `baseSha` and `headSha` when computing `git diff`
- Due to swapping `baseSha` and `headSha` also swapped additions and deletions in computation lambdas

Closes #250

Author: grine4ka

danger-kotlin-library/src/main/kotlin/systems/danger/kotlin/KtxGit.kt

@@ -1,6 +1,7 @@
 package systems.danger.kotlin
 
 import systems.danger.kotlin.models.git.Git
+import systems.danger.kotlin.models.git.GitCommit
 import systems.danger.kotlin.tools.shell.ShellExecutorFactory
 
 // extensions over [Git] object
@@ -12,16 +13,16 @@ val Git.changedLines: PullRequestChangedLines
     get() {
         if (headSha == null || baseSha == null) return PullRequestChangedLines(0, 0)
         val shellExecutor = ShellExecutorFactory.get()
-        val commandRawOutput = shellExecutor.execute("git diff --numstat $headSha $baseSha")
+        val commandRawOutput = shellExecutor.execute("git diff --numstat $baseSha $headSha")
         val additionDeletionPairs = commandRawOutput.lines()
             .filter { it.isNotEmpty() }
             .map { line ->
                 val parts = line.split("\\s+".toRegex())
                 (parts[0].toIntOrNull() ?: 0) to (parts[1].toIntOrNull() ?: 0)
             }
-        val additions = additionDeletionPairs.fold(0) { acc, (_, addition) -> acc + addition }
-        val deletions = additionDeletionPairs.fold(0) { acc, (deletion, _) -> acc + deletion }
-        val commandRawDiffOutput = shellExecutor.execute("git diff $headSha $baseSha")
+        val additions = additionDeletionPairs.fold(0) { acc, (addition, _) -> acc + addition }
+        val deletions = additionDeletionPairs.fold(0) { acc, (_, deletion) -> acc + deletion }
+        val commandRawDiffOutput = shellExecutor.execute("git diff $baseSha $headSha")
         return PullRequestChangedLines(additions, deletions, commandRawDiffOutput)
     }
 
@@ -47,13 +48,13 @@ val Git.deletions: Int
  * Reference to a SHA of head commit of this PR
  */
 val Git.headSha: String?
-    get() = commits.firstOrNull()?.sha
+    get() = commits.sortChronologically().lastOrNull()?.sha
 
 /**
  * Reference to a SHA of base commit of this PR
  */
 val Git.baseSha: String?
-    get() = commits.lastOrNull()?.sha?.let { "$it^1" }
+    get() = commits.sortChronologically().firstOrNull()?.sha?.let { "$it^1" }
 
 /**
  * Unified diff of this PR 
@@ -74,3 +75,7 @@ data class PullRequestChangedLines(
     val deletions: Int,
     val diff: String? = null
 )
+
+private fun List<GitCommit>.sortChronologically(): List<GitCommit> {
+    return sortedBy { it.author.date }
+}

danger-kotlin-library/src/test/kotlin/systems/danger/kotlin/KtxGitTest.kt

@@ -2,7 +2,7 @@ package systems.danger.kotlin
 
 import io.mockk.every
 import io.mockk.mockk
-import junit.framework.Assert.assertEquals
+import org.junit.Assert.assertEquals
 import org.junit.Before
 import org.junit.Test
 import systems.danger.kotlin.models.git.Git
@@ -32,16 +32,24 @@ internal class GitKtxTest {
         commits = listOf(
             GitCommit(
                 sha = "commit1",
-                author = GitCommitAuthor("John Doe", "[email protected]", "now"),
-                committer = GitCommitAuthor("John Doe", "[email protected]", "now"),
+                author = GitCommitAuthor("John Doe", "[email protected]", "2024-11-28T13:41:53Z"),
+                committer = GitCommitAuthor("John Doe", "[email protected]", "2024-12-04T09:15:23Z"),
+                message = "Random message",
+                parents = listOf(),
+                url = ""
+            ),
+            GitCommit(
+                sha = "commit2",
+                author = GitCommitAuthor("John Doe", "[email protected]", "2024-11-28T13:54:45Z"),
+                committer = GitCommitAuthor("John Doe", "[email protected]", "2024-12-04T09:15:23Z"),
                 message = "Random message",
                 parents = listOf(),
                 url = ""
             )
         )
     )
 
-    private val expectedResult = PullRequestChangedLines(22, 8, diffCommandOutput)
+    private val expectedResult = PullRequestChangedLines(8, 22, diffCommandOutput)
 
     @Before
     fun setup() {
@@ -75,4 +83,14 @@ internal class GitKtxTest {
         val gitWOCommits = basicGit.copy(commits = emptyList())
         assertEquals(PullRequestChangedLines(0, 0), gitWOCommits.changedLines)
     }
+
+    @Test
+    fun testBaseShaIsCorrect() {
+        assertEquals("commit1^1", basicGit.baseSha)
+    }
+
+    @Test
+    fun testHeadShaIsCorrect() {
+        assertEquals("commit2", basicGit.headSha)
+    }
 }