# frozen_string_literal: true

# This module takes care of updating cache columns for Markdown-containing
# fields. Use like this in the body of your class:
#
#     include CacheMarkdownField
#     cache_markdown_field :foo
#     cache_markdown_field :bar
#     cache_markdown_field :baz, pipeline: :single_line
#     cache_markdown_field :baz, whitelisted: true
#
# Corresponding foo_html, bar_html and baz_html fields should exist.
module CacheMarkdownField
  extend ActiveSupport::Concern

  # changes to these attributes cause the cache to be invalidates
  INVALIDATED_BY = %w[author project].freeze

  def skip_project_check?
    false
  end

  def can_cache_field?(field)
    true
  end

  # Returns the default Banzai render context for the cached markdown field.
  def banzai_render_context(field)
    raise ArgumentError.new("Unknown field: #{field.inspect}") unless
      cached_markdown_fields.markdown_fields.include?(field)

    # Always include a project key, or Banzai complains
    project = self.project if self.respond_to?(:project)
    group   = self.group if self.respond_to?(:group)
    context = cached_markdown_fields[field].merge(project: project, group: group)

    # Banzai is less strict about authors, so don't always have an author key
    context[:author] = self.author if self.respond_to?(:author)

    context[:markdown_engine] = :common_mark

    context
  end

  def rendered_field_content(markdown_field)
    return unless can_cache_field?(markdown_field)

    options = { skip_project_check: skip_project_check? }
    Banzai::Renderer.cacheless_render_field(self, markdown_field, options)
  end

  # Update every applicable column in a row if any one is invalidated, as we only store
  # one version per row
  def refresh_markdown_cache
    updates = cached_markdown_fields.markdown_fields.map do |markdown_field|
      [
        cached_markdown_fields.html_field(markdown_field),
        rendered_field_content(markdown_field)
      ]
    end.to_h

    updates['cached_markdown_version'] = latest_cached_markdown_version

    updates.each { |field, data| write_markdown_field(field, data) }
  end

  def refresh_markdown_cache!
    updates = refresh_markdown_cache

    save_markdown(updates)
  end

  def cached_html_up_to_date?(markdown_field)
    return false if cached_html_for(markdown_field).nil? && __send__(markdown_field).present? # rubocop:disable GitlabSecurity/PublicSend

    html_field = cached_markdown_fields.html_field(markdown_field)

    markdown_changed = markdown_field_changed?(markdown_field)
    html_changed = markdown_field_changed?(html_field)

    latest_cached_markdown_version == cached_markdown_version &&
      (html_changed || markdown_changed == html_changed)
  end

  def invalidated_markdown_cache?
    cached_markdown_fields.html_fields.any? {|html_field| attribute_invalidated?(html_field) }
  end

  def attribute_invalidated?(attr)
    __send__("#{attr}_invalidated?") # rubocop:disable GitlabSecurity/PublicSend
  end

  def cached_html_for(markdown_field)
    raise ArgumentError.new("Unknown field: #{markdown_field}") unless
      cached_markdown_fields.markdown_fields.include?(markdown_field)

    __send__(cached_markdown_fields.html_field(markdown_field)) # rubocop:disable GitlabSecurity/PublicSend
  end

  # Updates the markdown cache if necessary, then returns the field
  # Unlike `cached_html_for` it returns `nil` if the field does not exist
  def updated_cached_html_for(markdown_field)
    return unless cached_markdown_fields.markdown_fields.include?(markdown_field)

    refresh_markdown_cache! if attribute_invalidated?(cached_markdown_fields.html_field(markdown_field))

    cached_html_for(markdown_field)
  end

  def latest_cached_markdown_version
    @latest_cached_markdown_version ||= (Gitlab::MarkdownCache::CACHE_COMMONMARK_VERSION << 16) | local_version
  end

  def local_version
    # because local_markdown_version is stored in application_settings which
    # uses cached_markdown_version too, we check explicitly to avoid
    # endless loop
    return local_markdown_version if respond_to?(:has_attribute?) && has_attribute?(:local_markdown_version)

    settings = Gitlab::CurrentSettings.current_application_settings

    # Following migrations are not properly isolated and
    # use real models (by calling .ghost method), in these migrations
    # local_markdown_version attribute doesn't exist yet, so we
    # use a default value:
    # db/migrate/20170825104051_migrate_issues_to_ghost_user.rb
    # db/migrate/20171114150259_merge_requests_author_id_foreign_key.rb
    if settings.respond_to?(:local_markdown_version)
      settings.local_markdown_version
    else
      0
    end
  end

  included do
    cattr_reader :cached_markdown_fields do
      Gitlab::MarkdownCache::FieldData.new
    end

    if self < ActiveRecord::Base
      include Gitlab::MarkdownCache::ActiveRecord::Extension
    else
      prepend Gitlab::MarkdownCache::Redis::Extension
    end
  end

  class_methods do
    private

    # Specify that a field is markdown. Its rendered output will be cached in
    # a corresponding _html field. Any custom rendering options may be provided
    # as a context.
    def cache_markdown_field(markdown_field, context = {})
      cached_markdown_fields[markdown_field] = context

      html_field = cached_markdown_fields.html_field(markdown_field)
      invalidation_method = "#{html_field}_invalidated?".to_sym

      # The HTML becomes invalid if any dependent fields change. For now, assume
      # author and project invalidate the cache in all circumstances.
      define_method(invalidation_method) do
        changed_fields = changed_attributes.keys
        invalidations  = changed_fields & [markdown_field.to_s, *INVALIDATED_BY]
        !invalidations.empty? || !cached_html_up_to_date?(markdown_field)
      end
    end
  end
end
