Add completion contributor for Bukkit event handlers

src/main/kotlin/platform/bukkit/completion/BukkitEventHandlerCompletionContributor.kt

@@ -0,0 +1,16 @@
+package com.demonwav.mcdev.platform.bukkit.completion
+
+import com.intellij.codeInsight.completion.CompletionContributor
+import com.intellij.codeInsight.completion.CompletionType
+import com.intellij.patterns.PlatformPatterns
+import com.intellij.psi.PsiClass
+
+class BukkitEventHandlerCompletionContributor : CompletionContributor() {
+    init {
+        extend(
+            CompletionType.BASIC,
+            PlatformPatterns.psiElement().inside(PsiClass::class.java),
+            BukkitEventHandlerCompletionProvider()
+        )
+    }
+}

src/main/kotlin/platform/bukkit/completion/BukkitEventHandlerCompletionProvider.kt

@@ -0,0 +1,80 @@
+package com.demonwav.mcdev.platform.bukkit.completion
+
+import com.intellij.codeInsight.completion.CompletionParameters
+import com.intellij.codeInsight.completion.CompletionProvider
+import com.intellij.codeInsight.completion.CompletionResultSet
+import com.intellij.codeInsight.completion.PrioritizedLookupElement
+import com.intellij.codeInsight.lookup.LookupElementBuilder
+import com.intellij.icons.AllIcons
+import com.intellij.openapi.project.Project
+import com.intellij.psi.PsiClass
+import com.intellij.psi.PsiMethod
+import com.intellij.psi.PsiModifier
+import com.intellij.psi.impl.JavaPsiFacadeEx
+import com.intellij.psi.search.GlobalSearchScope
+import com.intellij.psi.search.searches.ClassInheritorsSearch
+import com.intellij.psi.util.PsiTreeUtil
+import com.intellij.util.ProcessingContext
+import org.jetbrains.annotations.NotNull
+
+class BukkitEventHandlerCompletionProvider : CompletionProvider<CompletionParameters>() {
+    companion object {
+        const val EVENT_LISTENER = "org.bukkit.event.Listener"
+        private const val BUKKIT_EVENT_FQN = "org.bukkit.event.Event"
+    }
+
+    override fun addCompletions(
+        @NotNull completionParameters: CompletionParameters,
+        @NotNull processingContext: ProcessingContext,
+        @NotNull completionResultSet: CompletionResultSet
+    ) {
+        val prefix = completionResultSet.prefixMatcher.prefix
+        if (!prefix.startsWith("on") || prefix.length == 2) return
+
+        val position = completionParameters.position
+        val containingClass = PsiTreeUtil.getParentOfType(position, PsiClass::class.java) ?: return
+        val project: Project = position.project
+        val facade = JavaPsiFacadeEx.getInstanceEx(project)
+
+        val eventListenerClass = facade.findClass(EVENT_LISTENER, GlobalSearchScope.allScope(project)) ?: return
+        if (!containingClass.isInheritor(eventListenerClass, true)) return
+        if (PsiTreeUtil.getParentOfType(position, PsiMethod::class.java) != null) return
+
+        val scope = GlobalSearchScope.allScope(project)
+        val eventBaseClass = facade.findClass(BUKKIT_EVENT_FQN, scope) ?: return
+
+        val eventNameFilter = prefix.substring(2).lowercase()
+
+        ClassInheritorsSearch.search(eventBaseClass, scope, true)
+            .forEach { psiClass ->
+                if (psiClass.isInterface || psiClass.hasModifierProperty(PsiModifier.ABSTRACT)) {
+                    return@forEach
+                }
+
+                val eventSimpleName = psiClass.name ?: return@forEach
+                if (eventNameFilter.isNotEmpty() && !eventSimpleName.lowercase().startsWith(eventNameFilter)) {
+                    return@forEach
+                }
+
+                val lookupString = "on$eventSimpleName"
+                val methodName = lookupString.replace("Event", "")
+                val qualifiedName = psiClass.qualifiedName
+
+                val element = LookupElementBuilder
+                    .create(lookupString)
+                    .withPresentableText("$lookupString()")
+                    .withTailText(" - $qualifiedName", true)
+                    .withTypeText("@EventHandler")
+                    .withIcon(AllIcons.Nodes.Method)
+                    .withBaseLookupString(lookupString)
+                    .withBoldness(true)
+                    .withInsertHandler(BukkitEventHandlerInsertHandler(methodName, qualifiedName))
+
+                completionResultSet.addElement(
+                    PrioritizedLookupElement.withPriority(element, 100.0)
+                )
+            }
+
+        completionResultSet.stopHere()
+    }
+}

src/main/kotlin/platform/bukkit/completion/BukkitEventHandlerInsertHandler.kt

@@ -0,0 +1,45 @@
+package com.demonwav.mcdev.platform.bukkit.completion
+
+import com.intellij.codeInsight.completion.InsertHandler
+import com.intellij.codeInsight.completion.InsertionContext
+import com.intellij.codeInsight.lookup.LookupElement
+import com.intellij.codeInsight.template.TemplateManager
+import com.intellij.codeInsight.template.impl.TextExpression
+import com.intellij.openapi.util.NlsSafe
+import org.jetbrains.annotations.NotNull
+
+class BukkitEventHandlerInsertHandler(
+    private val methodName: String,
+    private val qualifiedName: @NlsSafe String?
+) : InsertHandler<LookupElement> {
+
+    companion object {
+        private const val EVENT_HANDLER_FQN = "org.bukkit.event.EventHandler"
+    }
+
+    override fun handleInsert(@NotNull insertionContext: InsertionContext, @NotNull lookupElement: LookupElement) {
+        val project = insertionContext.project
+        val editor = insertionContext.editor
+
+        val templateManager = TemplateManager.getInstance(project)
+        val template = templateManager.createTemplate("", "")
+        template.isToReformat = true
+
+        template.addTextSegment("@${EVENT_HANDLER_FQN}\n")
+        template.addTextSegment("public void ")
+        template.addVariable("METHOD_NAME", TextExpression(methodName), true)
+        template.addTextSegment("($qualifiedName ")
+        template.addVariable("EVENT_PARAM", TextExpression("event"), true)
+        template.addTextSegment(") { \n")
+        template.addEndVariable()
+        template.addTextSegment("\n}")
+
+        insertionContext.getDocument().deleteString(
+            insertionContext.getStartOffset(),
+            insertionContext.getTailOffset()
+        );
+
+        templateManager.startTemplate(editor, template)
+
+    }
+}

src/main/resources/META-INF/plugin.xml

@@ -532,6 +532,13 @@
         <library.presentationProvider
                 implementation="com.demonwav.mcdev.platform.bukkit.framework.ModernPaperPresentationProvider"/>
 
+        <!-- Bukkit Completion Contributor -->
+
+        <completion.contributor
+                language="JAVA"
+                implementationClass="com.demonwav.mcdev.platform.bukkit.completion.BukkitEventHandlerCompletionContributor"
+                order="first"/>
+
         <!--endregion-->
 
         <!--region SPONGE-->