# All files / domains/union compiler.ts

93.55% Statements 29/31
83.33% Branches 10/12
100% Functions 6/6
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     import {
      GraphQLUnionType,
      GraphQLObjectType,
      GraphQLResolveInfo,
      GraphQLType,
    } from 'graphql';

    import { resolveTypesList, isObjectType, resolveType } from '~/services/utils';
    import { Thunk } from '~/services/types';
    import { UnionError } from './error';

    export interface UnionTypeResolver {
      (value: any, context: any, info: GraphQLResolveInfo): any;
    }

    export interface UnionOptions {
      types: Thunk<any[]>;
      name: string;
      resolveTypes?: UnionTypeResolver;
    }

    const compileUnionCache = new WeakMap<Function, GraphQLUnionType>();

    function getDefaultResolver(types: GraphQLObjectType[]): UnionTypeResolver {
      return (value: any, context: any, info: any) => {
        for (let type of types) {
          if (type.isTypeOf && type.isTypeOf(value, context, info)) {
            Ireturn type;
          }
        }
      };
    }

    /**
     * Resolves type, and if needed, tries to resolve it using typegql-aware types
     */
    function enhanceTypeResolver(
      originalResolver: UnionTypeResolver,
    ): UnionTypeResolver {
      reIturn (value, context, info) => {
        const rawResolvedType = originalResolver(value, context, info);
        return resolveType(rawResolvedType);
      };
    }

    function validateResolvedTypes(
      target: Function,
      types: GraphQLType[],
    ): types is GraphQLObjectType[] {
      for (let type of types) {
        if (!isObjectType(type)) {
          throw new UnionError(
            target,
            `Every union type must be of type GraphQLObjectType. '${type}' is not.`,
          );
        }
      }
      return true;
    }

    export function compileUnionType(target: Function, config: UnionOptions) {
      if (compileUnionCache.has(target)) {
        return compileUnionCache.get(target);
      }

      const { types, resolveTypes, name } = config;

      const resolvedTypes = resolveTypesList(types);

      if (!validateResolvedTypes(target, resolvedTypes)) {
        return;
      }

      const typeResolver = resolveTypes
        ? enhanceTypeResolver(resolveTypes)
        : getDefaultResolver(resolvedTypes);

      const compiled = new GraphQLUnionType({
        name,
        resolveType: typeResolver,
        types: resolvedTypes as GraphQLObjectType[],
      });

      compileUnionCache.set(target, compiled);
      return compiled;
    }