/** @category Validation Rules */

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

import { Kind } from '../../language/kinds';
import type { ASTVisitor } from '../../language/visitor';

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

/**
 * Lone anonymous operation
 *
 * A GraphQL document is only valid if when it contains an anonymous operation
 * (the query short-hand) that it contains only that one operation definition.
 *
 * See https://spec.graphql.org/draft/#sec-Lone-Anonymous-Operation
 * @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 { LoneAnonymousOperationRule } from 'graphql/validation';
 *
 * const schema = buildSchema(`
 *   type Query {
 *     name: String
 *   }
 * `);
 *
 * const invalidDocument = parse(`
 *   query { name } query Other { name }
 * `);
 * const invalidErrors = validate(schema, invalidDocument, [LoneAnonymousOperationRule]);
 *
 * invalidErrors.length; // => 1
 *
 * const validDocument = parse(`
 *   { name }
 * `);
 * const validErrors = validate(schema, validDocument, [LoneAnonymousOperationRule]);
 *
 * validErrors; // => []
 * ```
 */
export function LoneAnonymousOperationRule(
  context: ASTValidationContext,
): ASTVisitor {
  let operationCount = 0;
  return {
    Document(node) {
      operationCount = node.definitions.filter(
        (definition) => definition.kind === Kind.OPERATION_DEFINITION,
      ).length;
    },
    OperationDefinition(node) {
      if (!node.name && operationCount > 1) {
        context.reportError(
          new GraphQLError(
            'This anonymous operation must be the only defined operation.',
            { nodes: node },
          ),
        );
      }
    },
  };
}