クラスの修正とそれに伴うテストの修正

app/controllers/articles_controller.rb

@@ -103,6 +103,9 @@ def notice_message(article)
   end
 
   def fit_to_size_for_ogp
-    Ogp::ImageProcessor.fit_to_size(@article.thumbnail) if @article.thumbnail.attached?
+    return unless @article.thumbnail.attached?
+
+    image_resizer = ImageResizer.new(@article.thumbnail)
+    image_resizer.fit_to!(*ImageResizer::OGP_SIZE)
   end
 end

app/models/image_resizer.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+class ImageResizer
+  OGP_SIZE = [1200, 630].freeze
+
+  def initialize(attached_one)
+    @attached_one = attached_one
+    @transformation = ImageResizerTransformation.new
+  end
+
+  def fit_to!(width, height)
+    return nil if just_fit_to_size?(width, height)
+
+    original_width, original_height = original_size
+
+    fitted = @attached_one.variant(**@transformation.fit_to(original_width, original_height, width, height))
+                          .processed
+                          .image.blob
+
+    # 変形前の画像関連データの削除にpurge、purge_laterは不要。
+    # データの削除はattachで担える
+    @attached_one.attach(fitted)
+  end
+
+  def just_fit_to_size?(width, height)
+    original_width, original_height = original_size
+    width == original_width && height == original_height
+  end
+
+  private
+
+  def original_size
+    blob = @attached_one.blob
+    blob.analyze unless blob.analyzed?
+    [blob.metadata[:width], blob.metadata[:height]]
+  end
+end

app/models/image_resizer_transformation.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+class ImageResizerTransformation
+  def fit_to(original_width, original_height, width, height)
+    # ハッシュを返すが処理順(リサイズ->切り抜き)にオプションを記述
+    {}.merge(resize(original_width, original_height, width, height),
+             center_crop(width, height))
+  end
+
+  # 縦横比を維持しながら、リサイズ後の縦をx、横をyとしたときに
+  # いずれかの条件を満たすようにリサイズする
+  # x = widht かつ y >= height
+  # x >= width かつ y = height
+  def resize(original_width, original_height, width, height)
+    ratio_w = width.to_f / original_width
+    ratio_h = height.to_f / original_height
+
+    if ratio_w > ratio_h
+      { resize: "#{width}x" }
+    else
+      { resize: "x#{height}" }
+    end
+  end
+
+  def center_crop(width, height)
+    { gravity: :center,
+      # 仮想キャンバスのメタデータをリセットするために!を末尾につける
+      # +repageは指定できないため、+repage相当の動作をする!を採用
+      crop: "#{width}x#{height}+0+0!" }
+  end
+end

test/models/image_resizer_test.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class ImageResizerTest < ActiveSupport::TestCase
+  test '.fit_to!' do
+    article = articles(:article4)
+
+    ImageResizer.new(article.thumbnail).fit_to!(*ImageResizer::OGP_SIZE)
+
+    article.thumbnail.blob.analyze unless article.thumbnail.blob.analyzed?
+    assert_equal({ width: 1200, height: 630 },
+                 article.thumbnail.blob.metadata.slice(:width, :height).symbolize_keys)
+  end
+
+  test '.just_fit_to_size?' do
+    article = articles(:article4)
+
+    image_resizer = ImageResizer.new(article.thumbnail)
+    width, height = ImageResizer::OGP_SIZE
+    image_resizer.fit_to!(width, height)
+
+    assert image_resizer.just_fit_to_size?(width, height)
+    assert_not image_resizer.just_fit_to_size?(width + 1, height)
+    assert_not image_resizer.just_fit_to_size?(width, height + 1)
+  end
+end

test/models/image_resizer_transformation_test.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class ImageResizerTransformationTest < ActiveSupport::TestCase
+  setup do
+    @image_resizer_transformation = ImageResizerTransformation.new
+    @width = 1200
+    @height = 630
+  end
+
+  test '.fit_to' do
+    assert_equal({ resize: "#{@width}x", gravity: :center, crop: "#{@width}x#{@height}+0+0!" },
+                 @image_resizer_transformation.fit_to(500, 500, @width, @height))
+  end
+
+  test '.resize return 1200x when width magnification is grater than height magnification' do
+    assert_equal({ resize: "#{@width}x" }, @image_resizer_transformation.resize(500, 500, @width, @height))
+    assert_equal({ resize: "#{@width}x" }, @image_resizer_transformation.resize(500, 630, @width, @height))
+    assert_equal({ resize: "#{@width}x" }, @image_resizer_transformation.resize(1500, 1500, @width, @height))
+  end
+
+  test '.resize return x630 when height magnification is grater than width magnification' do
+    assert_equal({ resize: "x#{@height}" }, @image_resizer_transformation.resize(1000, 500, @width, @height))
+    assert_equal({ resize: "x#{@height}" }, @image_resizer_transformation.resize(1200, 500, @width, @height))
+    assert_equal({ resize: "x#{@height}" }, @image_resizer_transformation.resize(1500, 700, @width, @height))
+  end
+
+  test '.center_crop' do
+    assert_equal({ gravity: :center, crop: "#{@width}x#{@height}+0+0!" },
+                 @image_resizer_transformation.center_crop(@width, @height))
+  end
+end