Add blank commit/duplicate branch guards to Git CLI delegate

src/main/java/com/neo4j/sandbox/git/CommandIOException.java

@@ -0,0 +1,36 @@
+package com.neo4j.sandbox.git;
+
+import java.io.IOException;
+
+class CommandIOException extends IOException {
+
+    private final String stdout;
+    private final String stderr;
+
+    public CommandIOException(String faultyCommand, int status, String stdout, String stderr) {
+        super(String.format("Expected Git operation %s to succeed but got exit status %d. See error below%n%s",
+                faultyCommand, status, combinedOutputs(stdout, stderr)));
+
+        this.stdout = stdout;
+        this.stderr = stderr;
+    }
+
+    public boolean commandOutputContains(String msg) {
+        return this.stdout.contains(msg) || this.stderr.contains(msg);
+    }
+
+    private static String combinedOutputs(String stdout, String stderr) {
+        StringBuilder builder = new StringBuilder();
+        builder.append(String.format("=====%n"));
+        builder.append(String.format("Error stream%n"));
+        builder.append(String.format("=====%n"));
+        builder.append(stderr);
+        builder.append("\n");
+        builder.append(String.format("=====%n"));
+        builder.append(String.format("Output stream%n"));
+        builder.append(String.format("=====%n"));
+        builder.append(stdout);
+        builder.append("\n");
+        return builder.toString();
+    }
+}

src/main/java/com/neo4j/sandbox/git/GitCli.java

@@ -2,19 +2,21 @@
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-import org.springframework.stereotype.Service;
 
 import java.io.File;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.concurrent.TimeUnit;
 
 // @Service
 public class GitCli implements GitOperations {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(GitCli.class);
 
+    private static final String GIT_LOCALE = "en_US";
+
     @Override
     public void clone(Path cloneLocation, String repositoryUri, String token) throws IOException {
         File workingDirectory = cloneLocation.toFile();
@@ -25,6 +27,9 @@ public void clone(Path cloneLocation, String repositoryUri, String token) throws
 
     @Override
     public void checkoutNewBranch(Path cloneLocation, String branchName) throws IOException {
+        if (branchExists(cloneLocation, branchName)) {
+            throw new DuplicateBranchException();
+        }
         executeCommand(cloneLocation.toFile(), "git", "checkout", "-b", branchName);
     }
 
@@ -34,7 +39,10 @@ public void commitAll(Path cloneLocation, String message) throws IOException {
         executeCommand(workingDirectory, "git", "add", "--all");
         try {
             executeCommand(workingDirectory, "git", "commit", "-m", message);
-        } catch (IOException e) {
+        } catch (CommandIOException e) {
+            if (e.commandOutputContains("nothing to commit")) {
+                throw new BlankCommitException(e);
+            }
             throw new CommitException(e);
         }
     }
@@ -57,14 +65,22 @@ public String currentBranch(Path cloneLocation) throws IOException {
         return stdout.substring(stdout.lastIndexOf("/") + 1);
     }
 
-    private static void executeCommand(File workingDirectory, String... commands) throws IOException {
+    private boolean branchExists(Path cloneLocation, String branchName) throws IOException {
+        String remoteUrl = executeCommand(cloneLocation.toFile(), "git", "remote", "get-url", "origin");
+        String output = executeCommand(cloneLocation.toFile(), "git", "ls-remote", "--heads", remoteUrl.trim(), branchName);
+        return !output.isBlank();
+    }
+
+    private static String executeCommand(File workingDirectory, String... commands) throws IOException {
         Process process = runProcess(workingDirectory, commands);
         assertSuccessfulExitCode(process, commands);
+        return stdout(process);
     }
 
     private static Process runProcess(File workingDirectory, String... commands) throws IOException {
         String command = String.join(" ", commands);
         ProcessBuilder processBuilder = new ProcessBuilder(commands);
+        processBuilder.environment().put("LC_ALL", GIT_LOCALE);
         processBuilder.directory(workingDirectory);
         Process process = processBuilder.start();
         waitForProcess(command, process);
@@ -76,10 +92,7 @@ private static void assertSuccessfulExitCode(Process process, String[] commands)
         String command = String.join(" ", commands);
         LOGGER.trace("Git command {} exited with status code {}", command, exitStatus);
         if (exitStatus != 0) {
-            String error = combinedOutputs(process);
-            throw new IOException(
-                    String.format("Expected Git operation %s to succeed but got exit status %d. See error below%n%s",
-                            command, exitStatus, error));
+            throw new CommandIOException(command, exitStatus, stdout(process), stderr(process));
         }
     }
 
@@ -93,17 +106,6 @@ private static void waitForProcess(String command, Process process) throws IOExc
         }
     }
 
-    private static String combinedOutputs(Process process) throws IOException {
-        StringBuilder builder = new StringBuilder();
-        builder.append(String.format("Error stream%n"));
-        builder.append(stderr(process));
-        builder.append("\n");
-        builder.append(String.format("Output stream%n"));
-        builder.append(stdout(process));
-        builder.append("\n");
-        return builder.toString();
-    }
-
     private static String stdout(Process process) throws IOException {
         return new String(process.getInputStream().readAllBytes(), StandardCharsets.UTF_8);
     }