/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow strict
 */

import type ValidationContext from '../ValidationContext';
import { GraphQLError } from '../../error';
import type { ASTVisitor } from '../../language/visitor';
import { doTypesOverlap } from '../../utilities/typeComparators';
import { typeFromAST } from '../../utilities/typeFromAST';
import { isCompositeType } from '../../type/definition';
import type { GraphQLType } from '../../type/definition';

export function typeIncompatibleSpreadMessage(
  fragName: string,
  parentType: GraphQLType,
  fragType: GraphQLType,
): string {
  return (
    `Fragment "${fragName}" cannot be spread here as objects of ` +
    `type "${String(parentType)}" can never be of type "${String(fragType)}".`
  );
}

export function typeIncompatibleAnonSpreadMessage(
  parentType: GraphQLType,
  fragType: GraphQLType,
): string {
  return (
    'Fragment cannot be spread here as objects of ' +
    `type "${String(parentType)}" can never be of type "${String(fragType)}".`
  );
}

/**
 * Possible fragment spread
 *
 * A fragment spread is only valid if the type condition could ever possibly
 * be true: if there is a non-empty intersection of the possible parent types,
 * and possible types which pass the type condition.
 */
export function PossibleFragmentSpreads(
  context: ValidationContext,
): ASTVisitor {
  return {
    InlineFragment(node) {
      const fragType = context.getType();
      const parentType = context.getParentType();
      if (
        isCompositeType(fragType) &&
        isCompositeType(parentType) &&
        !doTypesOverlap(context.getSchema(), fragType, parentType)
      ) {
        context.reportError(
          new GraphQLError(
            typeIncompatibleAnonSpreadMessage(parentType, fragType),
            [node],
          ),
        );
      }
    },
    FragmentSpread(node) {
      const fragName = node.name.value;
      const fragType = getFragmentType(context, fragName);
      const parentType = context.getParentType();
      if (
        fragType &&
        parentType &&
        !doTypesOverlap(context.getSchema(), fragType, parentType)
      ) {
        context.reportError(
          new GraphQLError(
            typeIncompatibleSpreadMessage(fragName, parentType, fragType),
            [node],
          ),
        );
      }
    },
  };
}

function getFragmentType(context, name) {
  const frag = context.getFragment(name);
  if (frag) {
    const type = typeFromAST(context.getSchema(), frag.typeCondition);
    if (isCompositeType(type)) {
      return type;
    }
  }
}