/** @category Validation Rules */

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

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

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

/**
 * Executable definitions
 *
 * A GraphQL document is only valid for execution if all definitions are either
 * operation or fragment definitions.
 *
 * See https://spec.graphql.org/draft/#sec-Executable-Definitions
 * @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 { ExecutableDefinitionsRule } from 'graphql/validation';
 *
 * const schema = buildSchema(`
 *   type Query {
 *     name: String
 *   }
 * `);
 *
 * const invalidDocument = parse(`
 *   type Extra { field: String }
 * `);
 * const invalidErrors = validate(schema, invalidDocument, [ExecutableDefinitionsRule]);
 *
 * invalidErrors.length; // => 1
 *
 * const validDocument = parse(`
 *   { name }
 * `);
 * const validErrors = validate(schema, validDocument, [ExecutableDefinitionsRule]);
 *
 * validErrors; // => []
 * ```
 */
export function ExecutableDefinitionsRule(
  context: ASTValidationContext,
): ASTVisitor {
  return {
    Document(node) {
      for (const definition of node.definitions) {
        if (!isExecutableDefinitionNode(definition)) {
          const defName =
            definition.kind === Kind.SCHEMA_DEFINITION ||
            definition.kind === Kind.SCHEMA_EXTENSION
              ? 'schema'
              : '"' + definition.name.value + '"';
          context.reportError(
            new GraphQLError(`The ${defName} definition is not executable.`, {
              nodes: definition,
            }),
          );
        }
      }
      return false;
    },
  };
}