/** @category Validation Rules */

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

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

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

/**
 * Unique fragment names
 *
 * A GraphQL document is only valid if all defined fragments have unique names.
 *
 * See https://spec.graphql.org/draft/#sec-Fragment-Name-Uniqueness
 * @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 { UniqueFragmentNamesRule } from 'graphql/validation';
 *
 * const schema = buildSchema(`
 *   type Query {
 *     name: String
 *   }
 * `);
 *
 * const invalidDocument = parse(`
 *   fragment A on Query { name } fragment A on Query { name } query { ...A }
 * `);
 * const invalidErrors = validate(schema, invalidDocument, [
 *   UniqueFragmentNamesRule,
 * ]);
 *
 * invalidErrors.length; // => 1
 *
 * const validDocument = parse(`
 *   fragment A on Query { name } query { ...A }
 * `);
 * const validErrors = validate(schema, validDocument, [UniqueFragmentNamesRule]);
 *
 * validErrors; // => []
 * ```
 */
export function UniqueFragmentNamesRule(
  context: ASTValidationContext,
): ASTVisitor {
  const knownFragmentNames = new Map<string, NameNode>();
  return {
    OperationDefinition: () => false,
    FragmentDefinition(node) {
      const fragmentName = node.name.value;
      const knownFragmentName = knownFragmentNames.get(fragmentName);
      if (knownFragmentName != null) {
        context.reportError(
          new GraphQLError(
            `There can be only one fragment named "${fragmentName}".`,
            { nodes: [knownFragmentName, node.name] },
          ),
        );
      } else {
        knownFragmentNames.set(fragmentName, node.name);
      }
      return false;
    },
  };
}