Utilities for converting Lua tables into Elixir datastructures (#16)

lib/lua/table.ex

@@ -0,0 +1,76 @@
+defmodule Lua.Table do
+  @moduledoc """
+  In Lua, [tables](https://www.lua.org/pil/2.5.html) are the fundamental datastructure,
+  which are used both as associative arrays (maps), and arrays (lists).
+
+  `Lua.Table` provides some utilities for working with Lua tables when passed back to
+  Elixir.
+  """
+
+  @doc """
+  Converts a Lua table into a list. Assumes that the
+  table is correctly ordered.
+
+      iex> Lua.Table.as_list([{1, "a"}, {2, "b"}, {3, "c"}])
+      ["a", "b", "c"]
+
+  To ensure the list is ordered, you can pass the `:sort` option
+
+      iex> Lua.Table.as_list([{2, "b"}, {1, "a"}, {3, "c"}])
+      ["b", "a", "c"]
+
+      iex> Lua.Table.as_list([{2, "b"}, {1, "a"}, {3, "c"}], sort: true)
+      ["a", "b", "c"]
+
+  """
+  def as_list(values, opts \\ []) do
+    opts = Keyword.validate!(opts, sort: false)
+
+    sorter =
+      if Keyword.fetch!(opts, :sort) do
+        &List.keysort(&1, 0)
+      else
+        &Function.identity/1
+      end
+
+    values
+    |> sorter.()
+    |> Enum.map(fn {_, v} -> v end)
+  end
+
+  @doc """
+  Converts a Lua table into a map
+
+      iex> Lua.Table.as_map([{"a", 1}, {"b", 2}])
+      %{"a" => 1, "b" => 2}
+  """
+  def as_map(values) do
+    Map.new(values)
+  end
+
+  @doc """
+  Converts a Lua table into more "native" feeling lists and
+  maps, deeply traversing any sub-tables.
+
+  It uses the heuristic that maps with integer keys starting
+  as 1 will be auto-cast into lists
+
+      iex> Lua.Table.deep_cast([{"a", 1}, {"b", [{1, 3}, {2, 4}]}])
+      %{"a" => 1, "b" => [3, 4]}
+  """
+  def deep_cast(value) do
+    case value do
+      [{1, _val} | _rest] = list ->
+        Enum.map(list, fn
+          {_, v} when is_list(v) -> deep_cast(v)
+          {_, v} -> v
+        end)
+
+      map ->
+        Map.new(map, fn
+          {k, v} when is_list(v) -> {k, deep_cast(v)}
+          {k, v} -> {k, v}
+        end)
+    end
+  end
+end

test/lua/api_test.exs

@@ -1,5 +1,5 @@
 defmodule Lua.APITest do
-  use ExUnit.Case
+  use ExUnit.Case, async: true
 
   alias Lua
 

test/lua/table_test.exs

@@ -0,0 +1,5 @@
+defmodule Lua.TableTest do
+  use ExUnit.Case, async: true
+
+  doctest Lua.Table
+end

test/lua/util_test.exs

@@ -1,5 +1,5 @@
 defmodule Lua.UtilTest do
-  use ExUnit.Case
+  use ExUnit.Case, async: true
 
   doctest Lua.Util, import: true