#
# Used by NotificationService to determine who should receive notification
#
class NotificationRecipientService
  attr_reader :project

  def initialize(project)
    @project = project
  end

  def build_recipients(target, current_user, action:, previous_assignee: nil, skip_current_user: true)
    custom_action = build_custom_key(action, target)

    recipients = participants(target, current_user)
    recipients = add_project_watchers(recipients)
    recipients = add_custom_notifications(recipients, custom_action)
    recipients = reject_mention_users(recipients)

    # Re-assign is considered as a mention of the new assignee so we add the
    # new assignee to the list of recipients after we rejected users with
    # the "on mention" notification level
    case custom_action
    when :reassign_merge_request
      recipients << previous_assignee if previous_assignee
      recipients << target.assignee
    when :reassign_issue
      previous_assignees = Array(previous_assignee)
      recipients.concat(previous_assignees)
      recipients.concat(target.assignees)
    end

    recipients = reject_muted_users(recipients)
    recipients = add_subscribed_users(recipients, target)

    if [:new_issue, :new_merge_request].include?(custom_action)
      recipients = add_labels_subscribers(recipients, target)
    end

    recipients = reject_unsubscribed_users(recipients, target)
    recipients = reject_users_without_access(recipients, target)

    recipients.delete(current_user) if skip_current_user && !current_user.notified_of_own_activity?

    recipients.uniq
  end

  def build_pipeline_recipients(target, current_user, action:)
    return [] unless current_user

    custom_action =
      case action.to_s
      when 'failed'
        :failed_pipeline
      when 'success'
        :success_pipeline
      end

    notification_setting = notification_setting_for_user_project(current_user, target.project)

    return [] if notification_setting.mention? || notification_setting.disabled?

    return [] if notification_setting.custom? && !notification_setting.event_enabled?(custom_action)

    return [] if (notification_setting.watch? || notification_setting.participating?) && NotificationSetting::EXCLUDED_WATCHER_EVENTS.include?(custom_action)

    reject_users_without_access([current_user], target)
  end

  def build_relabeled_recipients(target, current_user, labels:)
    recipients = add_labels_subscribers([], target, labels: labels)
    recipients = reject_unsubscribed_users(recipients, target)
    recipients = reject_users_without_access(recipients, target)
    recipients.delete(current_user) unless current_user.notified_of_own_activity?
    recipients.uniq
  end

  def build_new_note_recipients(note)
    target = note.noteable

    ability, subject = if note.for_personal_snippet?
                         [:read_personal_snippet, note.noteable]
                       else
                         [:read_project, note.project]
                       end

    mentioned_users = note.mentioned_users.select { |user| user.can?(ability, subject) }

    # Add all users participating in the thread (author, assignee, comment authors)
    recipients = participants(target, note.author) || mentioned_users

    unless note.for_personal_snippet?
      # Merge project watchers
      recipients = add_project_watchers(recipients)

      # Merge project with custom notification
      recipients = add_custom_notifications(recipients, :new_note)
    end

    # Reject users with Mention notification level, except those mentioned in _this_ note.
    recipients = reject_mention_users(recipients - mentioned_users)
    recipients = recipients + mentioned_users

    recipients = reject_muted_users(recipients)

    recipients = add_subscribed_users(recipients, note.noteable)
    recipients = reject_unsubscribed_users(recipients, note.noteable)
    recipients = reject_users_without_access(recipients, note.noteable)

    recipients.delete(note.author) unless note.author.notified_of_own_activity?
    recipients.uniq
  end

  # Remove users with disabled notifications from array
  # Also remove duplications and nil recipients
  def reject_muted_users(users)
    reject_users(users, :disabled)
  end

  protected

  # Ensure that if we modify this array, we aren't modifying the memoised
  # participants on the target.
  def participants(target, user)
    return unless target.respond_to?(:participants)

    target.participants(user).dup
  end

  # Get project/group users with CUSTOM notification level
  def add_custom_notifications(recipients, action)
    user_ids = []

    # Users with a notification setting on group or project
    user_ids += user_ids_notifiable_on(project, :custom, action)
    user_ids += user_ids_notifiable_on(project.group, :custom, action)

    # Users with global level custom
    user_ids_with_project_level_global = user_ids_notifiable_on(project, :global)
    user_ids_with_group_level_global   = user_ids_notifiable_on(project.group, :global)

    global_users_ids = user_ids_with_project_level_global.concat(user_ids_with_group_level_global)
    user_ids += user_ids_with_global_level_custom(global_users_ids, action)

    recipients.concat(User.find(user_ids))
  end

  def add_project_watchers(recipients)
    recipients.concat(project_watchers).compact
  end

  # Get project users with WATCH notification level
  def project_watchers
    project_members_ids = user_ids_notifiable_on(project)

    user_ids_with_project_global = user_ids_notifiable_on(project, :global)
    user_ids_with_group_global   = user_ids_notifiable_on(project.group, :global)

    user_ids = user_ids_with_global_level_watch((user_ids_with_project_global + user_ids_with_group_global).uniq)

    user_ids_with_project_setting = select_project_members_ids(project, user_ids_with_project_global, user_ids)
    user_ids_with_group_setting = select_group_members_ids(project.group, project_members_ids, user_ids_with_group_global, user_ids)

    User.where(id: user_ids_with_project_setting.concat(user_ids_with_group_setting).uniq).to_a
  end

  # Remove users with notification level 'Mentioned'
  def reject_mention_users(users)
    reject_users(users, :mention)
  end

  def add_subscribed_users(recipients, target)
    return recipients unless target.respond_to? :subscribers

    recipients + target.subscribers(project)
  end

  def user_ids_notifiable_on(resource, notification_level = nil, action = nil)
    return [] unless resource

    if notification_level
      settings = resource.notification_settings.where(level: NotificationSetting.levels[notification_level])
      settings = settings.select { |setting| setting.event_enabled?(action) } if action.present?
      settings.map(&:user_id)
    else
      resource.notification_settings.pluck(:user_id)
    end
  end

  # Build a list of user_ids based on project notification settings
  def select_project_members_ids(project, global_setting, user_ids_global_level_watch)
    user_ids = user_ids_notifiable_on(project, :watch)

    # If project setting is global, add to watch list if global setting is watch
    global_setting.each do |user_id|
      if user_ids_global_level_watch.include?(user_id)
        user_ids << user_id
      end
    end

    user_ids
  end

  # Build a list of user_ids based on group notification settings
  def select_group_members_ids(group, project_members, global_setting, user_ids_global_level_watch)
    uids = user_ids_notifiable_on(group, :watch)

    # Group setting is watch, add to user_ids list if user is not project member
    user_ids = []
    uids.each do |user_id|
      if project_members.exclude?(user_id)
        user_ids << user_id
      end
    end

    # Group setting is global, add to user_ids list if global setting is watch
    global_setting.each do |user_id|
      if project_members.exclude?(user_id) && user_ids_global_level_watch.include?(user_id)
        user_ids << user_id
      end
    end

    user_ids
  end

  def user_ids_with_global_level_watch(ids)
    settings_with_global_level_of(:watch, ids).pluck(:user_id)
  end

  def user_ids_with_global_level_custom(ids, action)
    settings = settings_with_global_level_of(:custom, ids)
    settings = settings.select { |setting| setting.event_enabled?(action) }
    settings.map(&:user_id)
  end

  def settings_with_global_level_of(level, ids)
    NotificationSetting.where(
      user_id: ids,
      source_type: nil,
      level: NotificationSetting.levels[level]
    )
  end

  # Reject users which has certain notification level
  #
  # Example:
  #   reject_users(users, :watch, project)
  #
  def reject_users(users, level)
    level = level.to_s

    unless NotificationSetting.levels.keys.include?(level)
      raise 'Invalid notification level'
    end

    users = users.to_a.compact.uniq
    users = users.select { |u| u.can?(:receive_notifications) }

    users.reject do |user|
      global_notification_setting = user.global_notification_setting

      next global_notification_setting.level == level unless project

      setting = user.notification_settings_for(project)

      if project.group && (setting.nil? || setting.global?)
        setting = user.notification_settings_for(project.group)
      end

      # reject users who globally set mention notification and has no setting per project/group
      next global_notification_setting.level == level unless setting

      # reject users who set mention notification in project
      next true if setting.level == level

      # reject users who have mention level in project and disabled in global settings
      setting.global? && global_notification_setting.level == level
    end
  end

  def reject_unsubscribed_users(recipients, target)
    return recipients unless target.respond_to? :subscriptions

    recipients.reject do |user|
      subscription = target.subscriptions.find_by_user_id(user.id)
      subscription && !subscription.subscribed
    end
  end

  def reject_users_without_access(recipients, target)
    ability = case target
              when Issuable
                :"read_#{target.to_ability_name}"
              when Ci::Pipeline
                :read_build # We have build trace in pipeline emails
              end

    return recipients unless ability

    recipients.select do |user|
      user.can?(ability, target)
    end
  end

  def add_labels_subscribers(recipients, target, labels: nil)
    return recipients unless target.respond_to? :labels

    (labels || target.labels).each do |label|
      recipients += label.subscribers(project)
    end

    recipients
  end

  # Build event key to search on custom notification level
  # Check NotificationSetting::EMAIL_EVENTS
  def build_custom_key(action, object)
    "#{action}_#{object.class.model_name.name.underscore}".to_sym
  end

  def notification_setting_for_user_project(user, project)
    project_setting = user.notification_settings_for(project)

    return project_setting unless project_setting.global?

    group_setting = user.notification_settings_for(project.group)

    return group_setting unless group_setting.global?

    user.global_notification_setting
  end
end
