Add new GraphQL types, schema (with fields) & base mutation

The current consul GraphQL API has two problems.

1) It uses some unnecessary complicated magic to automatically create
   the GraphQL types and querys using an `api.yml` file. This approach
   is over-engineered, complex and has no benefits. It's just harder to
   understand the code for people which are not familiar with the
   project (like me, lol).

2) It uses a deprecated DSL [1] that is soon going to be removed from
   `graphql-ruby` completely. We are already seeing deprecation warning
   because of this (see References).

There was one problem. I wanted to create the API so that it is fully
backwards compatible with the old one, BUT the old one uses field names
which are directly derived from the ruby code, which results in
snake_case field names - not the GraphQL way. When I'm using the
graphql-ruby Class-based syntax, it automatically creates the fields in
camelCase, which breaks backwards-compatibility.

So I've added deprecated snake_case field names to keep it
backwards-compatible.

[1] https://graphql-ruby.org/schema/class_based_api.html

app/controllers/graphql_controller.rb

@@ -6,52 +6,56 @@ class GraphqlController < ApplicationController
   skip_before_action :verify_authenticity_token
   skip_authorization_check
 
-  class QueryStringError < StandardError
-  end
+  class QueryStringError < StandardError; end
 
-  def query
+  def execute
     begin
-      if query_string.nil? then raise GraphqlController::QueryStringError end
+      raise GraphqlController::QueryStringError if query_string.nil?
 
-      response = consul_schema.execute query_string, variables: query_variables
-      render json: response, status: :ok
+      result = ConsulSchema.execute(query_string,
+        variables: prepare_variables,
+        context: {},
+        operation_name: params[:operationName]
+      )
+      render json: result
     rescue GraphqlController::QueryStringError
       render json: { message: "Query string not present" }, status: :bad_request
     rescue JSON::ParserError
       render json: { message: "Error parsing JSON" }, status: :bad_request
     rescue GraphQL::ParseError
       render json: { message: "Query string is not valid JSON" }, status: :bad_request
-    rescue
-      unless Rails.env.production? then raise end
+    rescue ArgumentError => e
+      render json: { message: e.message }, status: :bad_request
     end
   end
 
   private
 
-    def consul_schema
-      api_types  = GraphQL::ApiTypesCreator.create
-      query_type = GraphQL::QueryTypeCreator.create(api_types)
-
-      GraphQL::Schema.define do
-        query query_type
-        max_depth 8
-        max_complexity 2500
-      end
-    end
-
     def query_string
       if request.headers["CONTENT_TYPE"] == "application/graphql"
-        request.body.string # request.body.class => StringIO
+        request.body.string
       else
         params[:query]
       end
     end
 
-    def query_variables
-      if params[:variables].blank? || params[:variables] == "null"
+    # Handle variables in URL query string and JSON body
+    def prepare_variables
+      case variables_param = params[:variables]
+      # URL query string
+      when String
+        if variables_param.present?
+          JSON.parse(variables_param) || {}
+        else
+          {}
+        end
+      # JSON object in request body gets converted to ActionController::Parameters
+      when ActionController::Parameters
+        variables_param.to_unsafe_hash # GraphQL-Ruby will validate name and type of incoming variables.
+      when nil
         {}
       else
-        JSON.parse(params[:variables])
+        raise ArgumentError, "Unexpected parameter: #{variables_param}"
       end
     end
 end