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.

app/components/post_preview_component.rb

@@ -0,0 +1,116 @@
+# frozen_string_literal: true
+
+class PostPreviewComponent < ApplicationComponent
+  with_collection_parameter :post
+
+  attr_reader :post, :tags, :show_deleted, :show_cropped, :link_target, :pool, :pool_id, :favgroup_id, :similarity, :recommended, :compact, :size, :current_user, :options
+  delegate :external_link_to, :time_ago_in_words_tagged, to: :helpers
+
+  def initialize(post:, tags: "", show_deleted: false, show_cropped: true, link_target: post, pool: nil, pool_id: nil, favgroup_id: nil, similarity: nil, recommended: nil, compact: nil, size: nil, current_user: CurrentUser.user, **options)
+    @post = post
+    @tags = tags
+    @show_deleted = show_deleted
+    @show_cropped = show_cropped
+    @link_target = link_target
+    @pool = pool
+    @pool_id = pool_id
+    @favgroup_id = favgroup_id
+    @similarity = similarity.round(1) if similarity.present?
+    @recommended = recommended.round(1) if recommended.present?
+    @compact = compact
+    @size = post.file_size if size.present?
+    @current_user = current_user
+    @options = options
+  end
+
+  def render?
+    post.present? && post.visible?(current_user) && (!post.is_deleted? || show_deleted)
+  end
+
+  def article_attrs(classes = nil)
+    { class: [classes, *preview_class].compact.join(" "), **data_attributes }
+  end
+
+  def link_params
+    link_params = {}
+
+    link_params["q"] = tags if tags.present? && !current_user.is_anonymous?
+    link_params["pool_id"] = pool_id if pool_id
+    link_params["favgroup_id"] = favgroup_id if favgroup_id
+
+    link_params
+  end
+
+  def cropped_url
+    if show_cropped && post.has_cropped? && !current_user.disable_cropped_thumbnails?
+      post.crop_file_url
+    else
+      post.preview_file_url
+    end
+  end
+
+  def preview_dimensions
+    # XXX work around ancient bad posts with null or zero dimensions.
+    if post.image_width.to_i > 0 && post.image_height.to_i > 0
+      downscale_ratio = Danbooru.config.small_image_width.to_f / [post.image_width, post.image_height].max
+
+      {
+        width: [(downscale_ratio * post.image_width).floor, post.image_width].min,
+        height: [(downscale_ratio * post.image_height).floor, post.image_height].min
+      }
+    else
+      { width: 0, height: 0 }
+    end
+  end
+
+  def tooltip
+    "#{post.tag_string} rating:#{post.rating} score:#{post.score}"
+  end
+
+  def preview_class
+    klass = ["post-preview"]
+    klass << "captioned" if pool || size || similarity || recommended
+    klass << "post-status-pending" if post.is_pending?
+    klass << "post-status-flagged" if post.is_flagged?
+    klass << "post-status-deleted" if post.is_deleted?
+    klass << "post-status-has-parent" if post.parent_id
+    klass << "post-status-has-children" if post.has_visible_children?
+    klass << "post-preview-compact" if compact
+    klass
+  end
+
+  def data_attributes
+    attributes = {
+      "data-id" => post.id,
+      "data-has-sound" => post.has_tag?('video_with_sound|flash_with_sound'),
+      "data-tags" => post.tag_string,
+      "data-pools" => post.pool_string,
+      "data-approver-id" => post.approver_id,
+      "data-rating" => post.rating,
+      "data-large-width" => post.large_image_width,
+      "data-large-height" => post.large_image_height,
+      "data-width" => post.image_width,
+      "data-height" => post.image_height,
+      "data-flags" => post.status_flags,
+      "data-parent-id" => post.parent_id,
+      "data-has-children" => post.has_children?,
+      "data-score" => post.score,
+      "data-views" => post.view_count,
+      "data-fav-count" => post.fav_count,
+      "data-pixiv-id" => post.pixiv_id,
+      "data-file-ext" => post.file_ext,
+      "data-source" => post.source,
+      "data-uploader-id" => post.uploader_id,
+      "data-normalized-source" => post.normalized_source,
+    }
+
+    if post.visible?(current_user)
+      attributes["data-md5"] = post.md5
+      attributes["data-file-url"] = post.file_url
+      attributes["data-large-file-url"] = post.large_file_url
+      attributes["data-preview-file-url"] = post.preview_file_url
+    end
+
+    attributes
+  end
+end