From e18ed69c5b53fa27455fff9a9f71cf1dc31a711a Mon Sep 17 00:00:00 2001
From: Fred Bricon <fbricon@gmail.com>
Date: Thu, 31 Aug 2023 17:39:11 +0200
Subject: [PATCH] feat: Mark observer methods as implicitly used

Signed-off-by: Fred Bricon <fbricon@gmail.com>
---
 .../psi/core/JavaEEImplicitUsageProvider.java | 51 +++++++++++++++++--
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/src/main/java/com/redhat/devtools/intellij/lsp4mp4ij/psi/core/JavaEEImplicitUsageProvider.java b/src/main/java/com/redhat/devtools/intellij/lsp4mp4ij/psi/core/JavaEEImplicitUsageProvider.java
index 094028891..13da9c734 100644
--- a/src/main/java/com/redhat/devtools/intellij/lsp4mp4ij/psi/core/JavaEEImplicitUsageProvider.java
+++ b/src/main/java/com/redhat/devtools/intellij/lsp4mp4ij/psi/core/JavaEEImplicitUsageProvider.java
@@ -14,18 +14,25 @@
 package com.redhat.devtools.intellij.lsp4mp4ij.psi.core;
 
 import com.intellij.codeInsight.daemon.ImplicitUsageProvider;
-import com.intellij.psi.PsiElement;
+import com.intellij.psi.*;
 import com.redhat.devtools.intellij.lsp4mp4ij.psi.core.jaxrs.JaxRsConstants;
 import com.redhat.devtools.intellij.lsp4mp4ij.psi.core.utils.AnnotationUtils;
 import com.redhat.devtools.intellij.lsp4mp4ij.psi.internal.restclient.MicroProfileRestClientConstants;
 import org.jetbrains.annotations.NotNull;
 
 /**
- * Automatically declares as used, methods annotated with jakarta.ws.rs.* or javax.ws.rs.* HTTP annotations,
- * or {@link org.eclipse.microprofile.rest.client.inject.RestClient}
+ * Automatically declares the following as used:
+ * <ul>
+ *     <li>methods annotated with jakarta.ws.rs.* or javax.ws.rs.* HTTP annotations, or {@link org.eclipse.microprofile.rest.client.inject.RestClient}</li>
+ *     <li>non-abstract public observer methods, i.e. with a parameter annotated with <code>@jakarta.enterprise.event.Observes</code> or <code>@javax.enterprise.event.Observes</code></li>
+ * </ul>
  */
 public class JavaEEImplicitUsageProvider implements ImplicitUsageProvider {
 
+    private static final String JAKARTA_OBSERVES = "jakarta.enterprise.event.Observes";
+    private static final String JAVAX_OBSERVES = "javax.enterprise.event.Observes";
+
+
     @Override
     public boolean isImplicitUsage(@NotNull PsiElement element) {
         return isImplicitRead(element) || isImplicitWrite(element);
@@ -33,6 +40,44 @@ public boolean isImplicitUsage(@NotNull PsiElement element) {
 
     @Override
     public boolean isImplicitRead(@NotNull PsiElement element) {
+        return isHttpOrRestClient(element) || isObserverMethod(element);
+    }
+
+    private boolean isObserverMethod(@NotNull PsiElement element) {
+        if (element instanceof PsiMethod) {
+            PsiMethod method = (PsiMethod) element;
+            return isPublicNonAbstract(method) && observesOneParameter(method);
+        }
+        return false;
+    }
+
+    private boolean observesOneParameter(PsiMethod method) {
+        //XXX ideally we might want to check if the parent class is a managed bean class or session bean class (or of an extension)
+        //But that might prove a bit complex, so let's skip this part for now.
+
+        PsiParameter[] parameters = method.getParameterList().getParameters();
+
+        int observesAnnotationCount = 0;
+
+        for (PsiParameter parameter : parameters) {
+            if (AnnotationUtils.hasAnyAnnotation(parameter, JAKARTA_OBSERVES, JAVAX_OBSERVES)) {
+                observesAnnotationCount++;
+                if (observesAnnotationCount > 1) {
+                    return false;
+                }
+            }
+        }
+
+        return observesAnnotationCount == 1;
+    }
+
+    private boolean isPublicNonAbstract(@NotNull PsiMethod method) {
+        return !method.isConstructor() &&
+                method.hasModifierProperty(PsiModifier.PUBLIC) &&
+                !method.hasModifierProperty(PsiModifier.ABSTRACT);
+    }
+
+    private boolean isHttpOrRestClient(@NotNull PsiElement element) {
         return AnnotationUtils.hasAnyAnnotation(element, JaxRsConstants.HTTP_METHOD_ANNOTATIONS) ||
                 AnnotationUtils.hasAnnotation(element, MicroProfileRestClientConstants.REST_CLIENT_ANNOTATION);
     }