Rewrite import feature (#21054)

app/models/bulk_import.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+# == Schema Information
+#
+# Table name: bulk_imports
+#
+#  id                :bigint(8)        not null, primary key
+#  type              :integer          not null
+#  state             :integer          not null
+#  total_items       :integer          default(0), not null
+#  imported_items    :integer          default(0), not null
+#  processed_items   :integer          default(0), not null
+#  finished_at       :datetime
+#  overwrite         :boolean          default(FALSE), not null
+#  likely_mismatched :boolean          default(FALSE), not null
+#  original_filename :string           default(""), not null
+#  account_id        :bigint(8)        not null
+#  created_at        :datetime         not null
+#  updated_at        :datetime         not null
+#
+class BulkImport < ApplicationRecord
+  self.inheritance_column = false
+
+  belongs_to :account
+  has_many :rows, class_name: 'BulkImportRow', inverse_of: :bulk_import, dependent: :delete_all
+
+  enum type: {
+    following: 0,
+    blocking: 1,
+    muting: 2,
+    domain_blocking: 3,
+    bookmarks: 4,
+  }
+
+  enum state: {
+    unconfirmed: 0,
+    scheduled: 1,
+    in_progress: 2,
+    finished: 3,
+  }
+
+  validates :type, presence: true
+
+  def self.progress!(bulk_import_id, imported: false)
+    # Use `increment_counter` so that the incrementation is done atomically in the database
+    BulkImport.increment_counter(:processed_items, bulk_import_id) # rubocop:disable Rails/SkipsModelValidations
+    BulkImport.increment_counter(:imported_items, bulk_import_id) if imported # rubocop:disable Rails/SkipsModelValidations
+
+    # Since the incrementation has been done atomically, concurrent access to `bulk_import` is now bening
+    bulk_import = BulkImport.find(bulk_import_id)
+    bulk_import.update!(state: :finished, finished_at: Time.now.utc) if bulk_import.processed_items == bulk_import.total_items
+  end
+end