feat: add treeviewer for output

chapi-ast-java/src/main/kotlin/chapi/ast/javaast/TreeViewer.kt

@@ -0,0 +1,51 @@
+package chapi.ast.javaast
+
+import org.antlr.v4.runtime.misc.Utils;
+import org.antlr.v4.runtime.tree.Tree;
+import org.antlr.v4.runtime.tree.Trees;
+
+class TreeViewer {
+
+    /** Platform dependent end-of-line marker  */
+    val Eol = System.lineSeparator()
+
+    /** The literal indent char(s) used for pretty-printing  */
+    val Indents = "  "
+    private var level = 0
+
+    /**
+     * Pretty print out a whole tree. [.getNodeText] is used on the node payloads to get the text
+     * for the nodes. (Derived from Trees.toStringTree(....))
+     */
+    fun toPrettyTree(t: Tree, ruleNames: List<String>): String {
+        level = 0
+        return process(t, ruleNames).replace("(?m)^\\s+$".toRegex(), "").replace("\\r?\\n\\r?\\n".toRegex(), Eol)
+    }
+
+    private fun process(t: Tree, ruleNames: List<String>): String {
+        if (t.childCount == 0) return Utils.escapeWhitespace(Trees.getNodeText(t, ruleNames), false)
+        val sb = StringBuilder()
+        sb.append(lead(level))
+        level++
+        val s: String = Utils.escapeWhitespace(Trees.getNodeText(t, ruleNames), false)
+        sb.append("$s ")
+        for (i in 0 until t.getChildCount()) {
+            sb.append(process(t.getChild(i), ruleNames))
+        }
+        level--
+        sb.append(lead(level))
+        return sb.toString()
+    }
+
+    private fun lead(level: Int): String {
+        val sb = StringBuilder()
+        if (level > 0) {
+            sb.append(Eol)
+            for (cnt in 0 until level) {
+                sb.append(Indents)
+            }
+        }
+
+        return sb.toString()
+    }
+}

chapi-ast-java/src/test/kotlin/chapi/ast/javaast/TreeViewerTest.kt

@@ -0,0 +1,13 @@
+package chapi.ast.javaast
+
+import org.junit.jupiter.api.Test
+
+internal class TreeViewerTest {
+    @Test
+    fun show() {
+        JavaAnalyser().parse("public class Test { }").let {
+            val ruleNamesList: List<String> = it.ruleNames.toList()
+            println(TreeViewer().toPrettyTree(it.compilationUnit(), ruleNamesList))
+        }
+    }
+}