/** @category Validation Rules */

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

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

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

/**
 * No undefined variables
 *
 * A GraphQL operation is only valid if all variables encountered, both directly
 * and via fragment spreads, are defined by that operation.
 *
 * See https://spec.graphql.org/draft/#sec-All-Variable-Uses-Defined
 * @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 { NoUndefinedVariablesRule } from 'graphql/validation';
 *
 * const schema = buildSchema(`
 *   type Query {
 *     field(arg: ID): String
 *   }
 * `);
 *
 * const invalidDocument = parse(`
 *   query ($id: ID) { field(arg: $missing) }
 * `);
 * const invalidErrors = validate(schema, invalidDocument, [NoUndefinedVariablesRule]);
 *
 * invalidErrors.length; // => 1
 *
 * const validDocument = parse(`
 *   query ($id: ID) { field(arg: $id) }
 * `);
 * const validErrors = validate(schema, validDocument, [NoUndefinedVariablesRule]);
 *
 * validErrors; // => []
 * ```
 */
export function NoUndefinedVariablesRule(
  context: ValidationContext,
): ASTVisitor {
  let variableNameDefined = Object.create(null);

  return {
    OperationDefinition: {
      enter() {
        variableNameDefined = Object.create(null);
      },
      leave(operation) {
        const usages = context.getRecursiveVariableUsages(operation);

        for (const { node } of usages) {
          const varName = node.name.value;
          if (variableNameDefined[varName] !== true) {
            context.reportError(
              new GraphQLError(
                operation.name
                  ? `Variable "$${varName}" is not defined by operation "${operation.name.value}".`
                  : `Variable "$${varName}" is not defined.`,
                { nodes: [node, operation] },
              ),
            );
          }
        }
      },
    },
    VariableDefinition(node) {
      variableNameDefined[node.variable.name.value] = true;
    },
  };
}