feat(plugin): add per-file transformation report output

Author: OrionTheProgrammer

bpj-maven-plugin/src/main/java/io/github/bpj/maven/BpjPrepareMojo.java

@@ -8,6 +8,8 @@
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.time.OffsetDateTime;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.stream.Stream;
 import org.apache.maven.plugin.AbstractMojo;
@@ -43,6 +45,12 @@ public class BpjPrepareMojo extends AbstractMojo {
     @Parameter(defaultValue = "false")
     private boolean verbose;
 
+    @Parameter(defaultValue = "false")
+    private boolean writeReport;
+
+    @Parameter(defaultValue = "${project.build.directory}/reports/bpj-transform-report.txt")
+    private File reportFile;
+
     @Override
     public void execute() throws MojoExecutionException {
         if (inputDirectory == null || !inputDirectory.exists()) {
@@ -56,6 +64,7 @@ public void execute() throws MojoExecutionException {
 
         int changedCalls = 0;
         int filesProcessed = 0;
+        List<FileTransformResult> transformedFiles = new ArrayList<>();
 
         try {
             List<Path> sources;
@@ -79,13 +88,18 @@ public void execute() throws MojoExecutionException {
                 String original = Files.readString(source, StandardCharsets.UTF_8);
                 TransformationResult result = transformer.transform(source, original, failOnUnresolved);
                 changedCalls += result.replacements();
+                transformedFiles.add(new FileTransformResult(relative.toString(), result.replacements()));
 
                 Files.writeString(target, result.source(), StandardCharsets.UTF_8);
                 if (verbose && result.replacements() > 0) {
                     getLog().info("BPJ transformed " + relative + " (" + result.replacements() + " call(s))");
                 }
             }
 
+            if (writeReport) {
+                writeTransformReport(filesProcessed, changedCalls, transformedFiles);
+            }
+
             configureCompileRoots();
             getLog().info(
                     "BPJ prepare completed. Processed " + filesProcessed
@@ -133,4 +147,39 @@ private String stackTrace(Exception exception) {
         }
         return sb.toString();
     }
+
+    private void writeTransformReport(
+            int filesProcessed,
+            int changedCalls,
+            List<FileTransformResult> transformedFiles
+    ) throws IOException {
+        if (reportFile == null) {
+            return;
+        }
+
+        Path reportPath = reportFile.toPath();
+        Path parent = reportPath.getParent();
+        if (parent != null) {
+            Files.createDirectories(parent);
+        }
+
+        List<String> lines = new ArrayList<>();
+        lines.add("BPJ Transformation Report");
+        lines.add("generatedAt: " + OffsetDateTime.now());
+        lines.add("project: " + project.getGroupId() + ":" + project.getArtifactId() + ":" + project.getVersion());
+        lines.add("filesProcessed: " + filesProcessed);
+        lines.add("callsTransformed: " + changedCalls);
+        lines.add("");
+        lines.add("files:");
+
+        for (FileTransformResult result : transformedFiles) {
+            lines.add(result.path() + " -> " + result.replacements() + " call(s)");
+        }
+
+        Files.write(reportPath, lines, StandardCharsets.UTF_8);
+        getLog().info("BPJ report written to " + reportPath);
+    }
+
+    private record FileTransformResult(String path, int replacements) {
+    }
 }

bpj-starter-smoke/pom.xml

@@ -25,4 +25,26 @@
       <scope>test</scope>
     </dependency>
   </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>io.github.oriontheprogrammer</groupId>
+        <artifactId>bpj-maven-plugin</artifactId>
+        <version>${project.version}</version>
+        <executions>
+          <execution>
+            <id>bpj-prepare</id>
+            <goals>
+              <goal>prepare</goal>
+            </goals>
+          </execution>
+        </executions>
+        <configuration>
+          <writeReport>true</writeReport>
+          <reportFile>${project.build.directory}/reports/bpj-transform-report.txt</reportFile>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
 </project>

bpj-starter-smoke/src/test/java/io/github/bpj/smoke/TransformationReportTest.java

@@ -0,0 +1,26 @@
+package io.github.bpj.smoke;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import org.junit.jupiter.api.Test;
+
+class TransformationReportTest {
+
+    @Test
+    void shouldGenerateTransformationReport() throws IOException {
+        Path report = Path.of("target", "reports", "bpj-transform-report.txt");
+        assertTrue(Files.exists(report), "Expected BPJ report to exist");
+
+        String content = Files.readString(report, StandardCharsets.UTF_8).replace('\\', '/');
+
+        assertTrue(content.contains("BPJ Transformation Report"));
+        assertTrue(content.contains("callsTransformed: 3"));
+        assertTrue(content.contains("io/github/bpj/smoke/GreetingService.java -> 1 call(s)"));
+        assertTrue(content.contains("io/github/bpj/smoke/CheckoutService.java -> 1 call(s)"));
+        assertTrue(content.contains("io/github/bpj/smoke/WelcomeNotifier.java -> 1 call(s)"));
+    }
+}

docs/MAVEN_PLUGIN.md

@@ -114,6 +114,18 @@ Default: `false`
 
 Logs transformed files and replacement counts.
 
+### `writeReport`
+
+Default: `false`
+
+When enabled, the plugin writes a per-file transformation report.
+
+### `reportFile`
+
+Default: `${project.build.directory}/reports/bpj-transform-report.txt`
+
+Destination file for the transformation report when `writeReport=true`.
+
 ## Configuration
 
 ```xml
@@ -133,6 +145,7 @@ Logs transformed files and replacement counts.
       <configuration>
         <verbose>true</verbose>
         <failOnUnresolved>true</failOnUnresolved>
+        <writeReport>true</writeReport>
       </configuration>
     </plugin>
   </plugins>