feat: add folding builder

Author: xepozz

src/main/kotlin/com/github/xepozz/php_opcodes_language/language/PHPOpFoldingBuilder.kt

@@ -1,14 +1,28 @@
 package com.github.xepozz.php_opcodes_language.language
 
+import com.github.xepozz.php_opcodes_language.language.psi.PHPOpBlock
 import com.intellij.lang.ASTNode
 import com.intellij.lang.folding.FoldingBuilderEx
 import com.intellij.lang.folding.FoldingDescriptor
 import com.intellij.openapi.editor.Document
 import com.intellij.openapi.project.DumbAware
+import com.intellij.openapi.util.TextRange
 import com.intellij.psi.PsiElement
+import com.intellij.psi.util.PsiTreeUtil
 
 class PHPOpFoldingBuilder : FoldingBuilderEx(), DumbAware {
-    override fun buildFoldRegions(root: PsiElement, document: Document, quick: Boolean) = emptyArray<FoldingDescriptor>()
+    override fun buildFoldRegions(root: PsiElement, document: Document, quick: Boolean) =
+        collectFoldingBlocks(root).toTypedArray()
+
+    private fun collectFoldingBlocks(element: PsiElement) =
+        PsiTreeUtil
+            .findChildrenOfType(element, PHPOpBlock::class.java)
+            .map {
+                FoldingDescriptor(
+                    it.node,
+                    TextRange(it.blockName.textRange.endOffset + 1, it.textRange.endOffset)
+                )
+            }
 
     override fun getPlaceholderText(node: ASTNode) = "{ ... }"