# frozen_string_literal: true

require_relative '../../core/utils/only_once'

module Datadog
  module Tracing
    module Contrib
      # Common behavior for patcher modules.
      #
      # `include`ing {Contrib::Patcher} into a new module is the recommend way to create a custom patcher.
      # The patcher can then be provided to a custom {Datadog::Tracing::Contrib::Integration} for instrumentation.
      module Patcher
        def self.included(base)
          base.singleton_class.prepend(CommonMethods)
          base.prepend(CommonMethods) if base.instance_of?(Class)
        end

        # Prepended instance methods for all patchers
        # @public_api
        module CommonMethods
          attr_accessor \
            :patch_error_result,
            :patch_successful

          def patch_name
            self.class != Class && self.class != Module ? self.class.name : name
          end

          def patched?
            patch_only_once.ran?
          end

          def patch
            return unless defined?(super)

            patch_only_once.run do
              begin
                super.tap do
                  # Emit a metric
                  Datadog.health_metrics.instrumentation_patched(1, tags: default_tags)
                  @patch_successful = true
                end
              rescue StandardError => e
                on_patch_error(e)
              end
            end
          end

          # Processes patching errors. This default implementation logs the error and reports relevant metrics.
          # @param e [Exception]
          def on_patch_error(e)
            # Log the error
            Datadog.logger.error("Failed to apply #{patch_name} patch. Cause: #{e} Location: #{Array(e.backtrace).first}")

            @patch_error_result = {
              type: e.class.name,
              message: e.message,
              line: Array(e.backtrace).first
            }

            # Emit a metric
            tags = default_tags
            tags << "error:#{e.class.name}"

            Datadog.health_metrics.error_instrumentation_patch(1, tags: tags)
          end

          def default_tags
            ["patcher:#{patch_name}"].tap do |tags|
              tags << "target_version:#{target_version}" if respond_to?(:target_version) && !target_version.nil?
              super.each { |t| tags << t } if defined?(super)
            end
          end

          private

          def patch_only_once
            # NOTE: This is not thread-safe
            @patch_only_once ||= Core::Utils::OnlyOnce.new
          end
        end
      end
    end
  end
end