require "rack"

module Shamu
  module JsonApi
    module Rails

      # Add support for writing resources as well-formed JSON API.
      module Controller
        extend ActiveSupport::Concern

        # Pattern to identify request params that hold 'ids'
        ID_PATTERN = /\A(id|.+_id)\z/

        included do
          before_action do
            render json: json_error( "The 'include' parameter is not supported" ), status: :bad_request if params[:include] # rubocop:disable Metrics/LineLength
            request.formats = [ :json_api, :json ]
          end

          rescue_from Exception, with: :render_unhandled_exception unless ::Rails.env.test?
        end

        private

          # @!visibility public
          #
          # Builds a well-formed JSON API response for a single resource.
          #
          # @param [Object] resource to present as JSON.
          # @param [Class] presenter {Presenter} class to use when building the
          #     response for the given resource. If not given, attempts to find a
          #     presenter by calling {Context#find_presenter}.
          # @param (see #json_context)
          # @yield (response) write additional top-level links and meta
          #     information.
          # @yieldparam [JsonApi::Response] response
          # @return [JsonApi::Response] the presented JSON response.
          def json_resource( resource, presenter = nil, **context, &block )
            response = build_json_response( context )
            response.resource resource, presenter
            yield response if block_given?
            response.as_json
          end

          # @!visibility public
          #
          # Present the `resource` as json and render it adding appropriate
          # HTTP response codes and headers for standard JSON API actions.
          #
          # @param [Symbol,Number] status the HTTP status code.
          # @param (see #json_resource)
          def render_resource( resource, presenter: nil, status: nil, location: nil, **context, &block )
            json = json_resource( resource, presenter, **context, &block )

            # Include canonical url to resource if present
            if data = json[ "data" ]
              if links = data[ "links" ]
                location ||= links[ "self" ] if links[ "self" ]
              end
            end

            render json: json, status: status, location: location
          end

          # @!visibility public
          #
          # Renders a {Shamu::Services::Result} presenting either the
          # validation errors or the entity.
          #
          # @param [Shamu::Services::Result] result of a service call
          # @param (see #json_resource)
          def render_result( result, presenter: nil, status: nil, **context, &block )
            if result.valid?
              if result.entity
                status ||= case request.method
                           when 'POST'   then :created
                           when 'DELETE' then :no_content
                           else               :ok
                           end

                render_resource result.entity, presenter: presenter, status: status, **context, &block
              else
                head status || :no_content
              end
            else
              render json: json_validation_errors( result.errors, **context ), status: :unprocessable_entity
            end
          end

          # Builds a well-formed JSON API response for a collection of resources.
          #
          # @param [Enumerable<Object>] resources to present as a JSON array.
          # @param [Class] presenter {Presenter} class to use when building the
          #     response for each of the resources. If not given, attempts to find
          #     a presenter by calling {Context#find_presenter}
          # @param (see #json_context)
          # @yield (response) write additional top-level links and meta
          #     information.
          # @yieldparam [JsonApi::Response] response
          # @return [JsonApi::Response] the presented JSON response.
          def json_collection( resources, presenter = nil, pagination: :auto, **context, &block )
            response = build_json_response( context )
            response.collection resources, presenter
            json_paginate_resources response, resources, pagination
            yield response if block_given?
            response.as_json
          end

          # Present the resources as json and render it adding appropriate HTTP
          # response codes and headers.
          def render_collection( resources, presenter: nil, pagination: :auto, **context, &block )
            render json: json_collection( resources, presenter, pagination: pagination, **context, &block )
          end

          # Write all the validation errors from a record to the response.
          #
          # @param (see Shamu::JsonApi::Response#validation_errors)
          # @yield (builder, attr, message)
          # @yieldparam (see Shamu::JsonApi::Response#validation_errors)
          # @return [JsonApi::Response] the presented JSON response.
          def json_validation_errors( errors, **context, &block )
            response = build_json_response( context )
            response.validation_errors errors, &block

            response.as_json
          end

        private

          # @!visibility public
          #
          # Add page-based pagination links for the resources to the builder.
          #
          # @param [#current_page,#next_page,#previous_page] resources a collection that responds to `#current_page`
          # @param [JsonApi::BaseBuilder] builder to add links to.
          # @param [String] param the name of the key page parameter to adjust
          # @return [void]
          def json_paginate( resources, builder, param: :page )
            page = resources.current_page

            if resources.respond_to?( :next_page ) ? resources.next_page : true
              builder.link :next, url_for( json_page_parameter( param, :number, page + 1 ) )
            end

            if resources.respond_to?( :prev_page ) ? resources.prev_page : page > 1
              builder.link :prev, url_for( json_page_parameter( param, :number, page - 1 ) )
            end
          end

          def json_page_parameter( page_param_name, param, value )
            params = self.params
            params = params.to_unsafe_hash if params.respond_to?( :to_unsafe_hash )

            page_params = params.reverse_merge page_param_name => {}
            page_params[page_param_name][param] = value

            page_params
          end

          # @!visibility public
          #
          # Get the pagination request parameters.
          #
          # @param [Symbol] param the request parameter to read pagination
          #     options from.
          # @return [Pagination] the pagination state
          def json_pagination( param: :page )
            page_params = params[ param ] || {}

            Pagination.new( page_params.merge( param: param ) )
          end

          # @!visibility public
          #
          # Write an error response. See {Shamu::JsonApi::Response#error} for details.
          #
          # @param (see Shamu::JsonApi::Response#error)
          # @yield (builder)
          # @yieldparam [Shamu::JsonApi::ErrorBuilder] builder to customize the
          #     error response.
          # @return [JsonApi::Response] the presented JSON response.
          def json_error( error = nil, **context, &block )
            response = build_json_response( context )

            response.error error do |builder|
              builder.http_status json_http_status_code_from_error( error )
              annotate_json_error( error, builder )
              yield builder if block_given?
            end

            response.to_json
          end

          def render_unhandled_exception( exception )
            render json: json_error( exception ), status: :internal_server_error
          end

          # @!visibility public
          #
          # Annotate an exception that is being rendered to the browser - for
          # example to add current user or security information if available.
          def annotate_json_error( error, builder )
            if ::Rails.env.development?
              builder.meta :type, error.class.to_s
              builder.meta :backtrace, error.backtrace
            end
          end


          JSON_CONTEXT_KEYWORDS = [ :fields, :namespaces, :presenters ].freeze

          # @!visibility public
          #
          # Build a {JsonApi::Context} for the current request and controller.
          #
          # @param [Hash<Symbol,Array>] fields to include in the response. If not
          #     provided looks for a `fields` request argument and parses that.
          #     See {JsonApi::Context#initialize}.
          # @param [Array<String>] namespaces to look for {Presenter presenters}.
          #     If not provided automatically adds the controller name and it's
          #     namespace.
          #
          #     For example in the `Users::AccountController` it will add the
          #     `Users::Accounts` and `Users` namespaces.
          #
          #     See {JsonApi::Context#find_presenter}.
          # @param [Hash<Class,Class>] presenters a hash that maps resource classes
          #     to the presenter class to use when building responses. See
          #     {JsonApi::Context#find_presenter}.
          # @return [JsonApi::Context] the builder context honoring any filter
          #     parameters sent by the client.
          def json_context( fields: :not_set, namespaces: :not_set, presenters: :not_set )
            Shamu::JsonApi::Context.new fields: fields == :not_set ? json_context_fields : fields,
              namespaces: namespaces == :not_set ? json_context_namespaces : namespaces,
              presenters: presenters == :not_set ? json_context_presenters : presenters
          end


          # See (Shamu::Rails::Entity#request_params)
          def request_params( param_key )
            if relationships = json_request_payload[ :relationships ]
              return map_json_resource_payload( relationships[ param_key ][ :data ] ) if relationships.key?( param_key )
            end

            payload = map_json_resource_payload( json_request_payload )

            request.params.each do |key, value|
              if ID_PATTERN =~ key
                payload[ key.to_sym ] ||= value
              end
            end

            payload
          end

          def map_json_resource_payload( resource )
            payload = resource[ :attributes ] ? resource[ :attributes ].dup : {}
            payload[ :id ] = resource[ :id ] if resource.key?( :id )

            if relationships = resource[ :relationships ]
              relationships.each do |key, value|
                attr_key = "#{ key.to_s.singularize }_id"

                if value[ :data ].is_a?( Array )
                  attr_key += 's' if value[ :data ].is_a?( Array )

                  payload[ attr_key.to_sym ] = value[ :data ].map { |d| d[ :id ] }
                  payload[ key ] = value[ :data ].map { |d| map_json_resource_payload( d ) }
                else
                  payload[ attr_key.to_sym ] = value[ :data ][ :id ]
                  payload[ key ] = map_json_resource_payload( value[ :data ] )
                end
              end
            end

            payload
          end

          # @!visibility public
          #
          # Map a JSON body to a hash.
          # @return [Hash] the parsed JSON payload.
          def json_request_payload
            @json_request_payload ||=
              begin
                body = request.body.read || "{}"
                json = JSON.parse( body, symbolize_names: true )

                unless json.blank?
                  fail NoJsonBodyError unless json[ :data ]
                end

                json ? json[ :data ] : {}
              end
          end


          def json_context_fields
            params[:fields]
          end

          def json_context_namespaces
            name = self.class.name.sub( /Controller$/, "" )
            namespaces = [ name.pluralize ]
            loop do
              name = name.deconstantize
              break if name.blank?

              namespaces << name
            end

            namespaces
          end

          def json_context_presenters
          end

          def json_paginate_resources( response, resources, pagination )
            pagination = resources.respond_to?( :current_page ) if pagination == :auto
            return unless pagination

            json_paginate resources, response
          end

          def json_http_status_code_from_error( error )
            case error
            when ActiveRecord::RecordNotFound then :not_found
            when ActiveRecord::RecordInvalid  then :unprocessable_entity
            when /AccessDenied/               then :forbidden
            else
              if error.is_a?( Exception )
                ActionDispatch::ExceptionWrapper.status_code_for_exception( error )
              else
                :bad_request
              end
            end
          end

          def json_http_status_code_from_request
            case request.method
            when "POST"  then :created
            when "HEAD"  then :no_content
            else              :ok
            end
          end

          def build_json_response( context )
            Shamu::JsonApi::Response.new( json_context( **context.slice( *JSON_CONTEXT_KEYWORDS ) ) )
          end
      end
    end
  end
end