/** @category Validation Rules */

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

import type {
  OperationTypeDefinitionNode,
  SchemaDefinitionNode,
  SchemaExtensionNode,
} from '../../language/ast.ts';
import type { ASTVisitor } from '../../language/visitor.ts';

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

/**
 * Unique operation types
 *
 * A GraphQL document is only valid if it has only one type per 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 } from 'graphql';
 * import { UniqueOperationTypesRule } from 'graphql/validation';
 *
 * const invalidSDL = `
 *   schema { query: Query query: Other } type Query { name: String } type Other { name: String }
 * `;
 *
 * UniqueOperationTypesRule.name; // => 'UniqueOperationTypesRule'
 * buildSchema(invalidSDL); // throws an error
 *
 * const validSDL = `
 *   schema { query: Query } type Query { name: String }
 * `;
 *
 * buildSchema(validSDL); // does not throw
 * ```
 */
export function UniqueOperationTypesRule(
  context: SDLValidationContext,
): ASTVisitor {
  const schema = context.getSchema();
  const definedOperationTypes = new Map<string, OperationTypeDefinitionNode>();
  const existingOperationTypes = schema
    ? {
        query: schema.getQueryType(),
        mutation: schema.getMutationType(),
        subscription: schema.getSubscriptionType(),
      }
    : {};

  return {
    SchemaDefinition: checkOperationTypes,
    SchemaExtension: checkOperationTypes,
  };

  function checkOperationTypes(
    node: SchemaDefinitionNode | SchemaExtensionNode,
  ) {
    const operationTypesNodes = node.operationTypes ?? [];

    for (const operationType of operationTypesNodes) {
      const operation = operationType.operation;
      const alreadyDefinedOperationType = definedOperationTypes.get(operation);

      if (existingOperationTypes[operation]) {
        context.reportError(
          new GraphQLError(
            `Type for ${operation} already defined in the schema. It cannot be redefined.`,
            { nodes: operationType },
          ),
        );
      } else if (alreadyDefinedOperationType) {
        context.reportError(
          new GraphQLError(
            `There can be only one ${operation} type in schema.`,
            { nodes: [alreadyDefinedOperationType, operationType] },
          ),
        );
      } else {
        definedOperationTypes.set(operation, operationType);
      }
    }

    return false;
  }
}