From 15b6c636e28cd13aa49c7c5e0b1a271a3790e1a5 Mon Sep 17 00:00:00 2001
From: Yongwook Choi <flow@hrmm.xyz>
Date: Wed, 13 Mar 2024 23:34:15 +0900
Subject: [PATCH] Implement TargetSelector

---
 .../es/util/fuzzer/TargetSelector.scala       | 58 +++++++++++++++++++
 src/main/scala/esmeta/util/BaseUtils.scala    |  7 ++-
 2 files changed, 64 insertions(+), 1 deletion(-)
 create mode 100644 src/main/scala/esmeta/es/util/fuzzer/TargetSelector.scala

diff --git a/src/main/scala/esmeta/es/util/fuzzer/TargetSelector.scala b/src/main/scala/esmeta/es/util/fuzzer/TargetSelector.scala
new file mode 100644
index 0000000000..ef6eab7efc
--- /dev/null
+++ b/src/main/scala/esmeta/es/util/fuzzer/TargetSelector.scala
@@ -0,0 +1,58 @@
+package esmeta.es.util.fuzzer
+
+import esmeta.es.*
+import esmeta.es.util.*
+import esmeta.es.util.Coverage.*
+import esmeta.spec.Grammar
+import esmeta.util.*
+import esmeta.util.BaseUtils.*
+
+/** mutation target selector for fuzzer */
+trait TargetSelector {
+
+  /** target selection */
+  def apply(
+    pool: Iterable[Script],
+    cov: Coverage,
+  ): (String, Script, Option[CondView])
+
+  /** Possible names of underlying selectors */
+  val names: List[String]
+}
+
+/** weighted mutation target selector */
+class WeightedSelector(pairs: (TargetSelector, Int)*) extends TargetSelector {
+  def apply(
+    pool: Iterable[Script],
+    cov: Coverage,
+  ): (String, Script, Option[CondView]) = weightedChoose(pairs)(pool, cov)
+
+  val names = pairs.toList.flatMap(_._1.names)
+}
+
+/** branch coverage-based mutation target selector */
+object BranchSelector extends TargetSelector {
+  def apply(
+    pool: Iterable[Script],
+    cov: Coverage,
+  ): (String, Script, Option[CondView]) = if (!cov.targetCondViews.isEmpty) {
+    val cond = choose(cov.targetCondViews.keys)
+    val view = choose(cov.targetCondViews(cond))._1
+    val condView = CondView(cond, view)
+    cov.getScript(condView).fold(RandomSelector(pool, cov)) {
+      (names.head, _, Some(condView))
+    }
+  } else RandomSelector(pool, cov)
+
+  val names = List("BranchTarget")
+}
+
+/** random mutation target selector */
+object RandomSelector extends TargetSelector {
+  def apply(
+    pool: Iterable[Script],
+    cov: Coverage,
+  ): (String, Script, Option[CondView]) = (names.head, choose(pool), None)
+
+  val names = List("RandomTarget")
+}
diff --git a/src/main/scala/esmeta/util/BaseUtils.scala b/src/main/scala/esmeta/util/BaseUtils.scala
index 77cd4b0fb9..9255bb3b20 100644
--- a/src/main/scala/esmeta/util/BaseUtils.scala
+++ b/src/main/scala/esmeta/util/BaseUtils.scala
@@ -120,7 +120,9 @@ object BaseUtils {
   private def rand = Random()
 
   /** randomly choose an element in a list */
-  def choose[T](seq: Seq[T]): T = seq(rand.nextInt(seq.length))
+  def choose[T](vec: Vector[T]): T = vec(rand.nextInt(vec.length))
+  def choose[T](iter: Iterable[T]): T = choose(iter.toVector)
+  def choose[T](x: => T, y: => T): T = if randBool then x else y
 
   /** randomly choose an element in a list and return it with its index */
   def chooseWithIndex[T](seq: Seq[T]): (T, Int) =
@@ -133,6 +135,9 @@ object BaseUtils {
   def randInt(n: Int): Int = rand.nextInt(n)
 
   /** randomly choose an element in a list with different weights */
+  def weightedChoose[T](seq: (T, Int)*): T = weightedChoose(seq)
+  def weightedChoose[T](iter: Iterable[(T, Int)]): T =
+    weightedChoose(iter.toArray)
   def weightedChoose[T](arr: Array[(T, Int)]): T = {
     val _arr = arr.filter(_._2 != 0)
     val n = rand.nextInt(_arr.map(_._2).sum) + 1