add contain transform

lib/image_plug/param_parser.ex

@@ -5,6 +5,7 @@ defmodule ImagePlug.ParamParser do
           Transform.Crop
           | Transform.Focus
           | Transform.Scale
+          | Transform.Contain
           | Transform.Output
 
   @typedoc """
@@ -15,6 +16,7 @@ defmodule ImagePlug.ParamParser do
           {Transform.Crop, Transform.Crop.Parameters.t()}
           | {Transform.Focus, Transform.Focus.Parameters.t()}
           | {Transform.Scale, Transform.Scale.Parameters.t()}
+          | {Transform.Contain, Transform.Contain.Parameters.t()}
           | {Transform.Output, Transform.Output.Parameters.t()}
 
   @type transform_chain() :: list(transform_chain_item())

lib/image_plug/param_parser/twicpics.ex

@@ -7,13 +7,15 @@ defmodule ImagePlug.ParamParser.Twicpics do
     "crop" => ImagePlug.Transform.Crop,
     "resize" => ImagePlug.Transform.Scale,
     "focus" => ImagePlug.Transform.Focus,
+    "contain" => ImagePlug.Transform.Contain,
     "output" => ImagePlug.Transform.Output
   }
 
   @parsers %{
     ImagePlug.Transform.Crop => Twicpics.CropParser,
     ImagePlug.Transform.Scale => Twicpics.ScaleParser,
     ImagePlug.Transform.Focus => Twicpics.FocusParser,
+    ImagePlug.Transform.Contain => Twicpics.ContainParser,
     ImagePlug.Transform.Output => Twicpics.OutputParser
   }
 

lib/image_plug/param_parser/twicpics/contain_parser.ex

@@ -0,0 +1,40 @@
+defmodule ImagePlug.ParamParser.Twicpics.ContainParser do
+  import ImagePlug.ParamParser.Twicpics.Common
+
+  alias ImagePlug.Transform.Contain.ContainParams
+
+  @doc """
+  Parses a string into a `ImagePlug.Transform.Contain.ContainParams` struct.
+
+  Returns a `ImagePlug.Transform.Contain.ContainParams` struct.
+
+  ## Format
+
+  ```
+  <width>x<height>
+  ```
+
+  ## Units
+
+  Type      | Format
+  --------- | ------------
+  `pixel`   | `<int>`
+
+  ## Examples
+
+      iex> ImagePlug.ParamParser.Twicpics.ContainParser.parse("250x25.5")
+      {:ok, %ImagePlug.Transform.Contain.ContainParams{width: {:int, 250}, height: {:float, 25.5}}}
+  """
+  def parse(input) do
+    cond do
+      Regex.match?(~r/^(.+)x(.+)$/, input) ->
+        Regex.run(~r/^(.+)x(.+)$/, input, capture: :all_but_first)
+        |> with_parsed_units(fn [width, height] ->
+          {:ok, %ContainParams{width: width, height: height}}
+        end)
+
+      true ->
+        {:error, {:parameter_parse_error, input}}
+    end
+  end
+end

lib/image_plug/transform/contain.ex

@@ -0,0 +1,44 @@
+defmodule ImagePlug.Transform.Contain do
+  @behaviour ImagePlug.Transform
+
+  alias ImagePlug.Transform
+  alias ImagePlug.TransformState
+
+  defmodule ContainParams do
+    @doc """
+    The parsed parameters used by `ImagePlug.Transform.Contain`.
+    """
+    defstruct [:width, :height]
+
+    @type t :: %__MODULE__{width: ImagePlug.imgp_length(), height: ImagePlug.imgp_length()}
+  end
+
+  @impl ImagePlug.Transform
+  def execute(%TransformState{} = state, %ContainParams{width: width, height: height}) do
+    with {:ok, target_width} <- Transform.to_pixels(state, :width, width),
+         {:ok, target_height} <- Transform.to_pixels(state, :height, height),
+         {:ok, width_and_height} <-
+           fit_inside(state, %{width: target_width, height: target_height}),
+         {:ok, scaled_image} <- do_scale(state.image, width_and_height) do
+      # reset focus to :center on scale
+      %TransformState{state | image: scaled_image, focus: :center}
+    end
+  end
+
+  def fit_inside(%TransformState{image: image}, target) do
+    original_ar = Image.width(image) / Image.height(image)
+    target_ar = target.width / target.height
+
+    if original_ar > target_ar do
+      {:ok, %{width: target.width, height: round(target.width / original_ar)}}
+    else
+      {:ok, %{width: round(target.height * original_ar), height: target.height}}
+    end
+  end
+
+  def do_scale(image, %{width: width, height: height}) do
+    width_scale = width / Image.width(image)
+    height_scale = height / Image.height(image)
+    Image.resize(image, width_scale, vertical_scale: height_scale)
+  end
+end

test/param_parser/twicpics_parser_test.exs

@@ -5,11 +5,14 @@ defmodule ParamParser.TwicpicsParserTest do
   doctest ImagePlug.ParamParser.Twicpics.CropParser
   doctest ImagePlug.ParamParser.Twicpics.ScaleParser
   doctest ImagePlug.ParamParser.Twicpics.FocusParser
+  doctest ImagePlug.ParamParser.Twicpics.ContainParser
+  doctest ImagePlug.ParamParser.Twicpics.OutputParser
 
   alias ImagePlug.ParamParser.Twicpics
   alias ImagePlug.Transform.Crop
   alias ImagePlug.Transform.Scale
   alias ImagePlug.Transform.Focus
+  alias ImagePlug.Transform.Contain
 
   defp random_base_unit,
     do:
@@ -127,4 +130,13 @@ defmodule ParamParser.TwicpicsParserTest do
       assert parsed == expected
     end
   end
+
+  test "contain params parser" do
+    check all width <- random_root_unit(),
+              height <- random_root_unit() do
+                str_params = "#{unit_str(width)}x#{unit_str(height)}"
+      parsed = Twicpics.ContainParser.parse(str_params)
+      assert {:ok, %Contain.ContainParams{width: width, height: height}} == parsed
+    end
+  end
 end