# frozen_string_literal: true

# This service return notes grouped by discussion ID and paginated per discussion.
# System notes also have a discussion ID assigned including Synthetic system notes.
module Issuable
  class DiscussionsListService
    include RendersNotes
    include Gitlab::Utils::StrongMemoize

    attr_reader :current_user, :issuable, :params

    def initialize(current_user, issuable, params = {})
      @current_user = current_user
      @issuable = issuable
      @params = params.dup
    end

    def execute
      return Note.none unless can_read_issuable?

      notes = NotesFinder.new(current_user, params.merge({ target: issuable, project: issuable.project }))
                .execute.with_web_entity_associations.inc_relations_for_view.fresh

      if paginator
        paginated_discussions_by_type = paginator.records.group_by(&:table_name)

        notes = if paginated_discussions_by_type['notes'].present?
                  notes.with_discussion_ids(paginated_discussions_by_type['notes'].map(&:discussion_id))
                else
                  notes.none
                end
      end

      if params[:notes_filter] != UserPreference::NOTES_FILTERS[:only_comments]
        notes = ResourceEvents::MergeIntoNotesService.new(
          issuable, current_user, paginated_notes: paginated_discussions_by_type
        ).execute(notes)
      end

      notes = prepare_notes_for_rendering(notes)

      # TODO: optimize this permission check.
      # Given this loads notes on a single issuable and current permission system, we should not have to check
      # permission on every single note. We should be able to check permission on the given issuable or its container,
      # which should result in just one permission check. Perhaps that should also either be passed to NotesFinder or
      # should be done in NotesFinder, which would decide right away if it would need to return no notes
      # or if it should just filter out internal notes.
      notes = notes.select { |n| n.readable_by?(current_user) }

      Discussion.build_collection(notes, issuable)
    end

    def paginator
      return if params[:per_page].blank?
      return if issuable.instance_of?(MergeRequest) && Feature.disabled?(:paginated_mr_discussions, issuable.project)

      strong_memoize(:paginator) do
        issuable
          .discussion_root_note_ids(notes_filter: params[:notes_filter])
          .keyset_paginate(cursor: params[:cursor], per_page: params[:per_page].to_i)
      end
    end

    def can_read_issuable?
      return Ability.allowed?(current_user, :read_security_resource, issuable) if issuable.is_a?(Vulnerability)

      Ability.allowed?(current_user, :"read_#{issuable.to_ability_name}", issuable)
    end
  end
end