[java, completion] IJPL-207762 introduce JavaMethodCallInsertHandlerHelper

GitOrigin-RevId: b5e9ccc82536b85da0663a3e3b671c4af0e17e16

java/java-frontback-impl/src/com/intellij/codeInsight/completion/method/JavaMethodCallInsertHandlerHelper.kt

@@ -0,0 +1,55 @@
+// Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+package com.intellij.codeInsight.completion.method
+
+import com.intellij.codeInsight.completion.InsertionContext
+import com.intellij.codeInsight.completion.OffsetKey
+import com.intellij.codeInsight.completion.method.JavaMethodCallInsertHandlerHelper.findInsertedCall
+import com.intellij.codeInsight.lookup.LookupElement
+import com.intellij.openapi.util.Key
+import com.intellij.psi.PsiCallExpression
+import com.intellij.psi.PsiMethodCallExpression
+import com.intellij.psi.util.PsiTreeUtil
+
+
+object JavaMethodCallInsertHandlerHelper {
+  @JvmStatic
+  fun getReferenceStartOffset(context: InsertionContext, item: LookupElement): Int {
+    val refStartKey = requireNotNull(item.getUserData(refStartKey)) { "refStartKey must have been set" }
+    return context.offsetMap.getOffset(refStartKey)
+  }
+
+  @JvmStatic
+  fun findCallAtOffset(context: InsertionContext, offset: Int): PsiCallExpression? {
+    context.commitDocument()
+    return PsiTreeUtil.findElementOfClassAtOffset(context.file, offset, PsiCallExpression::class.java, false)
+  }
+
+  /**
+   * Use [findInsertedCall] to get PsiCallExpression representing the inserted code, or null if no code was inserted
+   * Can be called in [JavaMethodCallInsertHandler]'s afterHandler
+   */
+  @JvmStatic
+  fun findInsertedCall(element: LookupElement, context: InsertionContext): PsiCallExpression? {
+    return element.getUserData(callKey)
+  }
+
+  fun installRefStartKey(context: InsertionContext, item: LookupElement) {
+    val refStart = OffsetKey.create("refStart", true)
+    context.offsetMap.addOffset(refStart, context.startOffset)
+    item.putUserData(refStartKey, refStart)
+  }
+
+  fun installCall(context: InsertionContext, item: LookupElement) {
+    val methodCall = findCallAtOffset(context, getReferenceStartOffset(context, item)) ?: return
+
+    // make sure this is the method call we've just added, not the enclosing one
+    val completedElement = (methodCall as? PsiMethodCallExpression)?.methodExpression?.referenceNameElement
+    val completedElementRange = completedElement?.textRange ?: return
+    if (completedElementRange.startOffset != getReferenceStartOffset(context, item)) return
+
+    item.putUserData(callKey, methodCall)
+  }
+}
+
+private val callKey = Key.create<PsiCallExpression>("JavaMethodCallInsertHandler.call")
+private val refStartKey = Key.create<OffsetKey>("JavaMethodCallInsertHandler.refStart")