Introduce ControllersResourceWriter

Author: Soroosh Sarabadani

operator-framework/src/main/java/io/javaoperatorsdk/operator/processing/annotation/ControllersResourceWriter.java

@@ -0,0 +1,57 @@
+package io.javaoperatorsdk.operator.processing.annotation;
+
+import javax.annotation.processing.ProcessingEnvironment;
+import javax.tools.StandardLocation;
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.stream.Collectors;
+
+import static io.javaoperatorsdk.operator.ControllerUtils.CONTROLLERS_RESOURCE_PATH;
+
+public class ControllersResourceWriter {
+    private Map<String, String> mappings = new ConcurrentHashMap<>();
+    private final ProcessingEnvironment processingEnvironment;
+
+    public ControllersResourceWriter(ProcessingEnvironment processingEnvironment) {
+        this.processingEnvironment = processingEnvironment;
+    }
+
+    public ControllersResourceWriter loadExistingMappings() {
+        try {
+            final var readonlyResource = processingEnvironment
+                    .getFiler()
+                    .getResource(StandardLocation.CLASS_OUTPUT, "", CONTROLLERS_RESOURCE_PATH);
+
+            final var existingLines = new BufferedReader(new InputStreamReader(readonlyResource.openInputStream()))
+                    .lines()
+                    .map(l -> l.split(","))
+                    .collect(Collectors.toMap(parts -> parts[0], parts -> parts[1]));
+            mappings.putAll(existingLines);
+        } catch (IOException e) {
+        }
+        return this;
+    }
+
+    public ControllersResourceWriter add(String controllerClassName, String customResourceTypeName) {
+        this.mappings.put(controllerClassName, customResourceTypeName);
+        return this;
+    }
+
+    public void flush() {
+        try {
+            final var resource = processingEnvironment
+                    .getFiler()
+                    .createResource(StandardLocation.CLASS_OUTPUT, "", CONTROLLERS_RESOURCE_PATH);
+            final var printWriter = new PrintWriter(resource.openOutputStream());
+            for (Map.Entry<String, String> entry : mappings.entrySet()) {
+                printWriter.println(entry.getKey() + "," + entry.getValue());
+            }
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}