Fix color mixing for legacy snapshots (with rgb() color syntax)

lib/asciinema/colors.ex

@@ -1,15 +1,7 @@
 defmodule Asciinema.Colors do
-  def mix(
-        <<"#", r1::binary-size(2), g1::binary-size(2), b1::binary-size(2)>>,
-        <<"#", r2::binary-size(2), g2::binary-size(2), b2::binary-size(2)>>,
-        ratio
-      ) do
-    r1 = String.to_integer(r1, 16)
-    g1 = String.to_integer(g1, 16)
-    b1 = String.to_integer(b1, 16)
-    r2 = String.to_integer(r2, 16)
-    g2 = String.to_integer(g2, 16)
-    b2 = String.to_integer(b2, 16)
+  def mix(c1, c2, ratio) do
+    {r1, g1, b1} = parse_color(c1)
+    {r2, g2, b2} = parse_color(c2)
     r = hex(floor(r1 * ratio + r2 * (1 - ratio)))
     g = hex(floor(g1 * ratio + g2 * (1 - ratio)))
     b = hex(floor(b1 * ratio + b2 * (1 - ratio)))
@@ -24,5 +16,18 @@ defmodule Asciinema.Colors do
     int
     |> Integer.to_string(16)
     |> String.pad_leading(2, "0")
+    |> String.downcase()
+  end
+
+  defp parse_color(<<"#", r::binary-size(2), g::binary-size(2), b::binary-size(2)>>) do
+    {String.to_integer(r, 16), String.to_integer(g, 16), String.to_integer(b, 16)}
+  end
+
+  defp parse_color("rgb(" <> rest) do
+    rest
+    |> String.slice(0, String.length(rest) - 1)
+    |> String.split(",", parts: 3)
+    |> Enum.map(&String.to_integer(String.trim(&1)))
+    |> List.to_tuple()
   end
 end

test/asciinema/colors_test.exs

@@ -0,0 +1,15 @@
+defmodule Asciinema.ColorsTest do
+  use ExUnit.Case, async: true
+  alias Asciinema.Colors
+
+  describe "mix/3" do
+    test "blends two colors using given ratio" do
+      assert Colors.mix("#000000", "#222222", 0.5) == "#111111"
+      assert Colors.mix("#007fff", "#ff7f00", 0.5) == "#7f7f7f"
+      assert Colors.mix("#007fff", "#ff7f00", 0) == "#ff7f00"
+      assert Colors.mix("#007fff", "#ff7f00", 1) == "#007fff"
+      assert Colors.mix("#007fff", "rgb(255,127,0)", 0.5) == "#7f7f7f"
+      assert Colors.mix("rgb(0,127,255)", "#ff7f00", 0.5) == "#7f7f7f"
+    end
+  end
+end