From b2f6363e79c3406a3e330748b6bf2a2cd5c66176 Mon Sep 17 00:00:00 2001
From: Matt Enlow <enlow@adobe.com>
Date: Tue, 9 May 2023 16:02:01 -0600
Subject: [PATCH] Rewrite case true/false to if else
 (`Credo.Check.Refactor.CaseTrivialMatches`)

---
 lib/style/simple.ex        | 29 ++++++++++++++++
 test/style/simple_test.exs | 69 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+)

diff --git a/lib/style/simple.ex b/lib/style/simple.ex
index 7cfcc314..8618f7a2 100644
--- a/lib/style/simple.ex
+++ b/lib/style/simple.ex
@@ -55,8 +55,37 @@ defmodule Styler.Style.Simple do
     {:cont, Zipper.replace(zipper, {reverse, r_meta, [lhs, rhs]}), ctx}
   end
 
+  def run(
+        {{:case, _,
+          [
+            head,
+            [{_, [{:->, _, [[{:__block__, _, [true]}], true_body]}, {:->, _, [[{:__block__, _, [false]}], false_body]}]}]
+          ]}, _} = zipper,
+        ctx
+      ) do
+    {:cont, Zipper.replace(zipper, if_ast(head, true_body, false_body)), ctx}
+  end
+
+  def run(
+        {{:case, _,
+          [
+            head,
+            [{_, [{:->, _, [[{:__block__, _, [false]}], false_body]}, {:->, _, [[{:__block__, _, [true]}], true_body]}]}]
+          ]}, _} = zipper,
+        ctx
+      ) do
+    {:cont, Zipper.replace(zipper, if_ast(head, true_body, false_body)), ctx}
+  end
+
   def run(zipper, ctx), do: {:cont, zipper, ctx}
 
+  # don't write an else clause if it's `false -> nil`
+  defp if_ast(head, true_body, {:__block__, _, [nil]}),
+    do: {:if, [do: []], [head, [{{:__block__, [], [:do]}, true_body}]]}
+
+  defp if_ast(head, true_body, false_body),
+    do: {:if, [do: [], end: []], [head, [{{:__block__, [], [:do]}, true_body}, {{:__block__, [], [:else]}, false_body}]]}
+
   defp delimit(token), do: token |> String.to_charlist() |> remove_underscores([]) |> add_underscores([])
 
   defp remove_underscores([?_ | rest], acc), do: remove_underscores(rest, acc)
diff --git a/test/style/simple_test.exs b/test/style/simple_test.exs
index 273551fa..4114f53e 100644
--- a/test/style/simple_test.exs
+++ b/test/style/simple_test.exs
@@ -38,4 +38,73 @@ defmodule Styler.Style.SimpleTest do
       assert_style("Enum.reverse(foo, bar) ++ bar")
     end
   end
+
+  describe "case true false do" do
+    test "rewrites case true false to if else" do
+      assert_style(
+        """
+        case foo do
+          true -> :ok
+          false -> :error
+        end
+        """,
+        """
+        if foo do
+          :ok
+        else
+          :error
+        end
+        """
+      )
+
+      assert_style(
+        """
+        case foo do
+          false -> :error
+          true -> :ok
+        end
+        """,
+        """
+        if foo do
+          :ok
+        else
+          :error
+        end
+        """
+      )
+
+      assert_style(
+        """
+        case foo do
+          true -> :ok
+          false -> nil
+        end
+        """,
+        """
+        if foo do
+          :ok
+        end
+        """
+      )
+
+      assert_style(
+        """
+        case foo do
+          true -> :ok
+          false ->
+            Logger.warn("it's false")
+            nil
+        end
+        """,
+        """
+        if foo do
+          :ok
+        else
+          Logger.warn("it's false")
+          nil
+        end
+        """
+      )
+    end
+  end
 end