visitFieldDefinitionWithDirectivedArguments.ts

import { GraphQLField, DirectiveNode, TypeNode, isNonNullType } from "graphql";

type FieldVisitorFn = (
  field: GraphQLField<any, any>,
  argumentDirectives: {
    directiveNode: DirectiveNode,
    targetNode: TypeNode,
    path: string
  }[]
) => GraphQLField<any, any> | void | null;


function visitFieldDefinitionWithDirectivedArguments(
  schema,
  directiveNames: string[],
  visitor: FieldVisitorFn
): void {};


// usage
visitFieldDefinitionWithDirectivedArguments(
  schema,
  ['isMax'],
  (field, argumentDirectives) => {
    field.resolve = (parent, variables, context, info) => {
      for (let { directiveNode, targetNode, path } of argumentDirectives) {
        const { max } = getArgumentValue(directiveNode);
        const value = getValue(variables, path);
  
        if (value > max) {
          if (isNonNullType(targetNode)) {
            throw new ApolloError(`Argument ${path} is not valid: it exceeds ${max}`);
          }
        } else {
          // silently repalced by null
          setValue(variables, path, null)
        }
      }
      return field.resolve(parent, variables, context, info);
    }
  }
);