From b2305cb67db98bc658a4eaca7f3d97f5ecdcd2ed Mon Sep 17 00:00:00 2001
From: Kesse Jones <kjonesfc@outlook.com>
Date: Tue, 21 Apr 2020 20:17:16 -0300
Subject: [PATCH] LibJS: Add Array.prototype.lastIndexOf

---
 Libraries/LibJS/Runtime/ArrayPrototype.cpp    | 35 +++++++++++++++++++
 Libraries/LibJS/Runtime/ArrayPrototype.h      |  1 +
 .../Tests/Array.prototype.lastIndexOf.js      | 22 ++++++++++++
 3 files changed, 58 insertions(+)
 create mode 100644 Libraries/LibJS/Tests/Array.prototype.lastIndexOf.js

diff --git a/Libraries/LibJS/Runtime/ArrayPrototype.cpp b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
index c063085419..67a5630bca 100644
--- a/Libraries/LibJS/Runtime/ArrayPrototype.cpp
+++ b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
@@ -55,6 +55,7 @@ ArrayPrototype::ArrayPrototype()
     put_native_function("slice", slice, 2);
     put_native_function("indexOf", index_of, 1);
     put_native_function("reverse", reverse, 0);
+    put_native_function("lastIndexOf", last_index_of, 1);
     put("length", Value(0));
 }
 
@@ -365,4 +366,38 @@ Value ArrayPrototype::reverse(Interpreter& interpreter)
     return array;
 }
 
+Value ArrayPrototype::last_index_of(Interpreter& interpreter)
+{
+    auto* array = array_from(interpreter);
+    if (!array)
+        return {};
+
+    i32 array_size = static_cast<i32>(array->elements().size());
+    if (interpreter.argument_count() == 0 || array_size == 0)
+        return Value(-1);
+
+    i32 from_index = 0;
+    if (interpreter.argument_count() >= 2) {
+        from_index = interpreter.argument(1).to_number().to_i32();
+
+        if (from_index >= array_size)
+            return Value(-1);
+
+        auto negative_min_index = ((array_size - 1) * -1);
+        if (from_index < negative_min_index)
+            from_index = 0;
+        else if (from_index < 0)
+            from_index = array_size + from_index;
+    }
+
+    auto search_element = interpreter.argument(0);
+    for (i32 i = array_size - 1; i >= from_index; --i) {
+        auto& element = array->elements().at(i);
+        if (typed_eq(interpreter, element, search_element).as_bool())
+            return Value(i);
+    }
+
+    return Value(-1);
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/ArrayPrototype.h b/Libraries/LibJS/Runtime/ArrayPrototype.h
index 168827dcb5..e7c5dd833c 100644
--- a/Libraries/LibJS/Runtime/ArrayPrototype.h
+++ b/Libraries/LibJS/Runtime/ArrayPrototype.h
@@ -52,5 +52,6 @@ private:
     static Value slice(Interpreter&);
     static Value index_of(Interpreter&);
     static Value reverse(Interpreter&);
+    static Value last_index_of(Interpreter&);
 };
 }
diff --git a/Libraries/LibJS/Tests/Array.prototype.lastIndexOf.js b/Libraries/LibJS/Tests/Array.prototype.lastIndexOf.js
new file mode 100644
index 0000000000..642c897292
--- /dev/null
+++ b/Libraries/LibJS/Tests/Array.prototype.lastIndexOf.js
@@ -0,0 +1,22 @@
+load("test-common.js");
+
+try {
+    assert(Array.prototype.lastIndexOf.length === 1);
+
+    var array = [1, 2, 3, 1, "hello"];
+
+    assert(array.lastIndexOf("hello") === 4);
+    assert(array.lastIndexOf(1) === 3);
+    assert(array.lastIndexOf(1, -1) === -1);
+    assert(array.lastIndexOf(1, -2) === 3);
+    assert(array.lastIndexOf(2) === 1);
+    assert(array.lastIndexOf(2, -3) === -1);
+    assert(array.lastIndexOf(2, -4) === 1);
+    assert([].lastIndexOf('hello') === -1);
+    assert([].lastIndexOf('hello', 10) === -1);
+    assert([].lastIndexOf('hello', -10) === -1);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}