posts: refactor post previews to use ViewComponent.

Refactor the post preview html to use the ViewComponent framework. This
lets us encapsulate all the HTML, CSS, and helper methods for a UI
component in a single place.

See https://viewcomponent.org.

test/components/post_preview_component_test.rb

@@ -0,0 +1,115 @@
+require "test_helper"
+
+class PostPreviewComponentTest < ViewComponent::TestCase
+  include Rails.application.routes.url_helpers
+
+  def render_preview(post, **options)
+    render_inline(PostPreviewComponent.new(post: post, **options))
+  end
+
+  context "The PostPreviewComponent" do
+    context "for a post visible to the current user" do
+      should "render" do
+        @post = create(:post)
+        node = render_preview(@post, current_user: User.anonymous)
+
+        assert_equal(post_path(@post), node.css("article a").attr("href").value)
+        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+      end
+    end
+
+    context "for a post with restricted tags" do
+      setup do
+        Danbooru.config.stubs(:restricted_tags).returns(["touhou"])
+        @post = create(:post, tag_string: "touhou")
+      end
+
+      should "should be visible to Gold users" do
+        node = render_preview(@post, current_user: create(:gold_user))
+
+        assert_equal(post_path(@post), node.css("article a").attr("href").value)
+        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+      end
+
+      should "not be visible to Members" do
+        node = render_preview(@post, current_user: create(:user))
+        assert_equal("", node.to_s)
+      end
+    end
+
+    context "for a banned post" do
+      setup do
+        @post = create(:post, is_banned: true)
+      end
+
+      should "should be visible to Gold users" do
+        node = render_preview(@post, current_user: create(:gold_user))
+
+        assert_equal(post_path(@post), node.css("article a").attr("href").value)
+        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+      end
+
+      should "not be visible to Members" do
+        node = render_preview(@post, current_user: create(:user))
+        assert_equal("", node.to_s)
+      end
+    end
+
+    context "for a banned paid reward" do
+      setup do
+        @post = create(:post, tag_string: "paid_reward", is_banned: true)
+      end
+
+      should "should be visible to Approver users" do
+        node = render_preview(@post, current_user: create(:approver))
+
+        assert_equal(post_path(@post), node.css("article a").attr("href").value)
+        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+      end
+
+      should "not be visible to Gold users" do
+        node = render_preview(@post, current_user: create(:gold_user))
+        assert_equal("", node.to_s)
+      end
+    end
+
+    context "for a non-safe post" do
+      setup do
+        @post = create(:post, rating: "q")
+      end
+
+      should "should be visible to users with safe mode off" do
+        node = render_preview(@post, current_user: User.anonymous)
+
+        assert_equal(post_path(@post), node.css("article a").attr("href").value)
+        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+      end
+
+      should "not be visible to users with safe mode on" do
+        CurrentUser.stubs(:safe_mode?).returns(true)
+        node = render_preview(@post, current_user: User.anonymous)
+
+        assert_equal("", node.to_s)
+      end
+    end
+
+    context "for a deleted post" do
+      setup do
+        @post = create(:post, is_deleted: true)
+      end
+
+      should "should be visible when the show_deleted flag is set" do
+        node = render_preview(@post, current_user: User.anonymous, show_deleted: true)
+
+        assert_equal(post_path(@post), node.css("article a").attr("href").value)
+        assert_equal(@post.preview_file_url, node.css("article img").attr("src").value)
+      end
+
+      should "not be visible to users normally" do
+        node = render_preview(@post, current_user: User.anonymous)
+
+        assert_equal("", node.to_s)
+      end
+    end
+  end
+end