From ab75a2f0c9558fe1313fa187a868963eb75a9b27 Mon Sep 17 00:00:00 2001
From: Graham <gpe@openrs2.dev>
Date: Fri, 31 Jan 2020 21:27:30 +0000
Subject: [PATCH] Add IdentityTransformer

---
 .../dev/openrs2/deob/ast/AstDeobfuscator.kt   |  2 +
 .../deob/ast/transform/IdentityTransformer.kt | 63 +++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 deob-ast/src/main/java/dev/openrs2/deob/ast/transform/IdentityTransformer.kt

diff --git a/deob-ast/src/main/java/dev/openrs2/deob/ast/AstDeobfuscator.kt b/deob-ast/src/main/java/dev/openrs2/deob/ast/AstDeobfuscator.kt
index b8d6b372..09b6c50c 100644
--- a/deob-ast/src/main/java/dev/openrs2/deob/ast/AstDeobfuscator.kt
+++ b/deob-ast/src/main/java/dev/openrs2/deob/ast/AstDeobfuscator.kt
@@ -15,6 +15,7 @@ import dev.openrs2.deob.ast.transform.BitMaskTransformer
 import dev.openrs2.deob.ast.transform.ComplementTransformer
 import dev.openrs2.deob.ast.transform.EncloseTransformer
 import dev.openrs2.deob.ast.transform.ForLoopConditionTransformer
+import dev.openrs2.deob.ast.transform.IdentityTransformer
 import dev.openrs2.deob.ast.transform.IfElseTransformer
 import dev.openrs2.deob.ast.transform.IncrementTransformer
 import dev.openrs2.deob.ast.transform.NegativeLiteralTransformer
@@ -86,6 +87,7 @@ class AstDeobfuscator(private val modules: List<Path>) {
             TernaryTransformer(),
             BinaryExprOrderTransformer(),
             AddSubTransformer(),
+            IdentityTransformer(),
             BitMaskTransformer(),
             ValueOfTransformer(),
             NewInstanceTransformer(),
diff --git a/deob-ast/src/main/java/dev/openrs2/deob/ast/transform/IdentityTransformer.kt b/deob-ast/src/main/java/dev/openrs2/deob/ast/transform/IdentityTransformer.kt
new file mode 100644
index 00000000..772ab54c
--- /dev/null
+++ b/deob-ast/src/main/java/dev/openrs2/deob/ast/transform/IdentityTransformer.kt
@@ -0,0 +1,63 @@
+package dev.openrs2.deob.ast.transform
+
+import com.github.javaparser.ast.CompilationUnit
+import com.github.javaparser.ast.Node
+import com.github.javaparser.ast.expr.BinaryExpr
+import com.github.javaparser.ast.expr.Expression
+import com.github.javaparser.ast.expr.UnaryExpr
+import dev.openrs2.deob.ast.util.walk
+
+class IdentityTransformer : Transformer() {
+    override fun transform(unit: CompilationUnit) {
+        unit.walk(Node.TreeTraversal.POSTORDER) { expr: BinaryExpr ->
+            @Suppress("NON_EXHAUSTIVE_WHEN")
+            when (expr.operator) {
+                BinaryExpr.Operator.PLUS -> {
+                    if (isZero(expr.left)) {
+                        // 0 + x => x
+                        expr.replace(expr.right)
+                    } else if (isZero(expr.right)) {
+                        // x + 0 => x
+                        expr.replace(expr.left)
+                    }
+                }
+                BinaryExpr.Operator.MINUS -> {
+                    if (isZero(expr.left)) {
+                        // 0 - x => -x
+                        expr.replace(UnaryExpr(expr.right, UnaryExpr.Operator.MINUS))
+                    } else if (isZero(expr.right)) {
+                        // x - 0 => x
+                        expr.replace(expr.left)
+                    }
+                }
+                BinaryExpr.Operator.MULTIPLY -> {
+                    if (isOne(expr.left)) {
+                        // 1 * x => x
+                        expr.replace(expr.right)
+                    } else if (isOne(expr.right)) {
+                        // x * 1 => x
+                        expr.replace(expr.left)
+                    }
+                }
+            }
+        }
+    }
+
+    companion object {
+        private fun isZero(expr: Expression): Boolean {
+            return when {
+                expr.isIntegerLiteralExpr -> expr.asIntegerLiteralExpr().asNumber() == 0
+                expr.isLongLiteralExpr -> expr.asLongLiteralExpr().asNumber() == 0L
+                else -> false
+            }
+        }
+
+        private fun isOne(expr: Expression): Boolean {
+            return when {
+                expr.isIntegerLiteralExpr -> expr.asIntegerLiteralExpr().asNumber() == 1
+                expr.isLongLiteralExpr -> expr.asLongLiteralExpr().asNumber() == 1L
+                else -> false
+            }
+        }
+    }
+}