/** @category Custom Rules */

import { GraphQLError } from '../../../error/GraphQLError';

import type { FieldNode } from '../../../language/ast';
import type { ASTVisitor } from '../../../language/visitor';

import { getNamedType } from '../../../type/definition';
import { isIntrospectionType } from '../../../type/introspection';

import type { ValidationContext } from '../../ValidationContext';

/**
 * Prohibit introspection queries
 *
 * A GraphQL document is only valid if all fields selected are not fields that
 * return an introspection type.
 *
 * Note: This rule is optional and is not part of the Validation section of the
 * GraphQL Specification. This rule effectively disables introspection, which
 * does not reflect best practices and should only be done if absolutely necessary.
 * @param context - The validation context used while checking the document.
 * @returns A visitor that reports validation errors for this rule.
 * @example
 * ```ts
 * import { buildSchema, parse, validate } from 'graphql';
 * import { NoSchemaIntrospectionCustomRule } from 'graphql/validation';
 *
 * const schema = buildSchema(`
 *   type Query {
 *     name: String
 *   }
 * `);
 *
 * const invalidDocument = parse(`
 *   { __schema { queryType { name } } }
 * `);
 * const invalidErrors = validate(schema, invalidDocument, [NoSchemaIntrospectionCustomRule]);
 *
 * invalidErrors.length; // => 1
 *
 * const validDocument = parse(`
 *   { name }
 * `);
 * const validErrors = validate(schema, validDocument, [NoSchemaIntrospectionCustomRule]);
 *
 * validErrors; // => []
 * ```
 */
export function NoSchemaIntrospectionCustomRule(
  context: ValidationContext,
): ASTVisitor {
  return {
    Field(node: FieldNode) {
      const type = getNamedType(context.getType());
      if (type && isIntrospectionType(type)) {
        context.reportError(
          new GraphQLError(
            `GraphQL introspection has been disabled, but the requested query contained the field "${node.name.value}".`,
            { nodes: node },
          ),
        );
      }
    },
  };
}