feat(cpp): add CppContextPrettify utility class and test case

This commit adds the `CppContextPrettify` utility class, which provides a method `extractStructureText` to extract the structure text from a given `OCStruct` object. It also includes a test case `CppContextPrettifyTest` to verify the functionality of the utility class.

Author: phodal

cpp/src/main/kotlin/cc/unitmesh/cpp/util/CppContextPrettify.kt

@@ -0,0 +1,59 @@
+package cc.unitmesh.cpp.util
+
+import com.intellij.psi.PsiComment
+import com.intellij.psi.PsiElement
+import com.intellij.psi.util.PsiTreeUtil
+import com.jetbrains.cidr.lang.psi.*
+
+object CppContextPrettify {
+    fun extractStructureText(struct: OCStruct): String {
+        val builder = StringBuilder()
+        findDeclAndExtractCommentWithTemplateLists(struct, builder)
+        builder.append("struct").append(' ').append(struct.name).append(" {\n")
+
+        struct.members.forEach { member ->
+            val declaration = member as? OCFunctionDeclaration ?: member
+            if (declaration is OCFunctionDeclaration) {
+                extractDeclCommentAndTemplateLists(declaration, builder)
+                val signature = declaration.symbol?.getSignature(struct.project)
+                builder.append("$signature;\n")
+            } else if (declaration != null) {
+                builder.append(declaration.text).append("\n")
+            }
+        }
+
+        builder.append("}")
+        return builder.toString()
+    }
+
+    private fun findDeclAndExtractCommentWithTemplateLists(
+        struct: OCStruct,
+        structTextBuilder: java.lang.StringBuilder
+    ) {
+        val parentPsiDecl = findParentOCDeclaration(struct as PsiElement)
+        if (parentPsiDecl != null) {
+            extractDeclCommentAndTemplateLists(parentPsiDecl, structTextBuilder)
+        }
+    }
+
+    private fun findParentOCDeclaration(globalContextElement: PsiElement): OCDeclaration? {
+        return PsiTreeUtil.findFirstParent(globalContextElement) { parentElement ->
+            parentElement is OCDeclaration
+        } as? OCDeclaration
+    }
+
+    private fun extractDeclCommentAndTemplateLists(parentPsiDecl: OCDeclaration, builder: StringBuilder) {
+        if (parentPsiDecl.firstChild is PsiComment) {
+            builder.append(parentPsiDecl.firstChild.text).append("\n")
+        }
+
+        parentPsiDecl.children.filterIsInstance<OCTemplateParameterList>().firstOrNull()?.let {
+            builder.append(it.text).append("\n")
+        }
+
+        parentPsiDecl.children.filterIsInstance<OCTemplateArgumentList>().firstOrNull()?.let {
+            builder.append(it.text).append("\n")
+        }
+    }
+
+}

cpp/src/test/kotlin/cc/unitmesh/cpp/util/CppContextPrettifyTest.kt

@@ -0,0 +1,52 @@
+package cc.unitmesh.cpp.util;
+
+import com.intellij.psi.PsiComment
+import com.intellij.psi.PsiElement
+import com.intellij.psi.util.PsiTreeUtil
+import com.intellij.testFramework.fixtures.BasePlatformTestCase
+import com.jetbrains.cidr.lang.psi.*
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class CppContextPrettifyTest : BasePlatformTestCase() {
+
+    fun testShouldExtractStructureText() {
+        // given
+        val psiElement = myFixture.configureByText(
+            "car.cpp", """
+            #include <iostream>
+            
+            class Car {
+            public:
+                // class data
+                std::string brand, model;
+                int mileage = 0;
+            
+                // class function
+                void drive(int distance) {
+                    mileage += distance;
+                }
+            };
+            """.trimIndent()
+        )
+
+        val decl = PsiTreeUtil.getChildrenOfTypeAsList(psiElement, OCDeclaration::class.java).first()
+        val type = PsiTreeUtil.getChildrenOfTypeAsList(decl, OCTypeElement::class.java).first()
+        val struct = PsiTreeUtil.getChildrenOfTypeAsList(type, OCStructLike::class.java).first()
+
+        // when
+        val result = CppContextPrettify.extractStructureText(struct as OCStruct)
+
+        // then
+        val expected = """
+        struct Car {
+        // class data
+            std::string brand, model;
+        int mileage = 0;
+        // class function
+        void drive(int distance);
+        }
+        """.trimIndent()
+        assertEquals(expected, result)
+    }
+}