#399

backend/app/services/post_import_previewer.rb

@@ -0,0 +1,79 @@
+class PostImportPreviewer
+  FIELDS = %w[title thumbnail_base original_created_from original_created_before duration tags parent_post_ids].freeze
+
+  def initialize parsed:, url_column:, mappings: { }, existing: 'skip'
+    @parsed = parsed
+    @url_column = url_column.to_i
+    @mappings = mappings.to_h.stringify_keys
+    @existing = existing == 'error' ? 'error' : 'skip'
+  end
+
+  def preview
+    urls = { }
+    @parsed[:rows].map do |row|
+      values = row[:values]
+      attributes = FIELDS.to_h { |field| [field, mapped_value(field, values)] }
+      url = values[@url_column].to_s.strip
+      metadata, warnings = fetch_metadata(url)
+      attributes = metadata.merge(attributes) { |_key, automatic, input| input.presence || automatic }
+      post = Post.new(url:)
+      post.valid?
+      normal_url = post.url
+      errors = post.errors.to_hash.transform_values(&:dup)
+      errors[:url] = ['URL が重複しています．'] if normal_url.present? && urls.key?(normal_url)
+      urls[normal_url] = true if normal_url.present?
+      if normal_url.present? && Post.exists?(url: normal_url)
+        @existing == 'error' ? errors[:url] = ['既存投稿です．'] : warnings << '既存投稿のためスキップします．'
+      end
+      validate_preview_tags(attributes['tags'], errors)
+      validate_parents(attributes['parent_post_ids'], errors)
+      { source_row: row[:source_row], url: normal_url || url, attributes:, warnings:, errors:,
+        status: errors.present? ? 'error' : (warnings.present? ? 'warning' : 'ready'),
+        existing: normal_url.present? && Post.exists?(url: normal_url) }
+    end
+  end
+
+  private
+
+  def mapped_value field, values
+    mapping = @mappings[field]
+    return '' if mapping.blank?
+    return mapping['value'].to_s if mapping['kind'] == 'fixed'
+
+    Array(mapping['columns']).filter_map { |index| values[index.to_i].to_s.presence }.join(field == 'tags' ? ' ' : '')
+  end
+
+  def fetch_metadata url
+    return [{ }, ['URL が空です．']] if url.blank?
+
+    data = PostMetadataFetcher.fetch(url)
+    warnings = []
+    warnings << 'タイトルを取得できませんでした．' if data[:title].blank?
+    warnings << 'サムネールを取得できませんでした．' if data[:thumbnail_base].blank?
+    [data.compact, warnings]
+  rescue Preview::UrlSafety::UnsafeUrl, Preview::HttpFetcher::FetchFailed, Preview::HttpFetcher::ResponseTooLarge => e
+    [{ }, ["メタデータを取得できませんでした: #{ e.message }"]]
+  end
+
+  def validate_preview_tags raw, errors
+    names = raw.to_s.split
+    return if names.empty?
+    if names.any? { _1.downcase.start_with?('nico:') }
+      errors[:tags] = ['ニコニコ・タグは直接指定できません．']
+      return
+    end
+    canonical = names.map { TagName.canonicalise(_1.sub(/\[.*\]\z/, '')).first }
+    if Tag.joins(:tag_name).where(tag_names: { name: canonical }, deprecated_at: nil).count < canonical.uniq.length
+      errors[:tags] = ['存在しないタグ又は廃止済みタグがあります．']
+    end
+  rescue Tag::SectionLiteralParseError
+    errors[:tags] = ['タグ区間の記法が不正です．']
+  end
+
+  def validate_parents raw, errors
+    ids = raw.to_s.split.map { Integer(_1, exception: false) }
+    return if ids.compact.empty? && raw.to_s.blank?
+    errors[:parent_post_ids] = ['親投稿 Id. が不正です．'] and return if ids.any? { _1.nil? || _1 <= 0 }
+    errors[:parent_post_ids] = ['存在しない親投稿 Id. があります．'] if Post.where(id: ids).count != ids.uniq.length
+  end
+end