Make the schema into a subgraph

resolvers.js

@@ -0,0 +1,117 @@
+import countriesList from 'countries-list';
+import provinces from 'provinces';
+import sift from 'sift';
+
+function filterToSift(filter = {}) {
+  return sift(
+    Object.entries(filter).reduce(
+      (acc, [key, operators]) => ({
+        ...acc,
+        [key]: operatorsToSift(operators)
+      }),
+      {}
+    )
+  );
+}
+
+function operatorsToSift(operators) {
+  return Object.entries(operators).reduce(
+    (acc, [operator, value]) => ({
+      ...acc,
+      ['$' + operator]: value
+    }),
+    {}
+  );
+}
+
+const {continents, countries, languages} = countriesList;
+
+export const resolvers = {
+  Country: {
+    capital: country => country.capital || null,
+    currency: country => country.currency || null,
+    continent: ({continent}) => ({
+      code: continent,
+      name: continents[continent]
+    }),
+    languages: country =>
+      country.languages.map(code => {
+        const language = languages[code];
+        return {
+          ...language,
+          code
+        };
+      }),
+    states: country =>
+      provinces.filter(province => province.country === country.code),
+    __resolveReference: country => countries[country.code]
+  },
+  State: {
+    code: state => state.short,
+    country: state => countries[state.country]
+  },
+  Continent: {
+    countries: continent =>
+      Object.entries(countries)
+        .filter(entry => entry[1].continent === continent.code)
+        .map(([code, country]) => ({
+          ...country,
+          code
+        })),
+    __resolveReference: continent => continents[continent.code]
+  },
+  Language: {
+    rtl: language => Boolean(language.rtl),
+    __resolveReference: language => languages[language.code]
+  },
+  Query: {
+    continent(parent, {code}) {
+      const name = continents[code];
+      return (
+        name && {
+          code,
+          name
+        }
+      );
+    },
+    continents: (parent, {filter}) =>
+      Object.entries(continents)
+        .map(([code, name]) => ({
+          code,
+          name
+        }))
+        .filter(filterToSift(filter)),
+    country(parent, {code}) {
+      const country = countries[code];
+      return (
+        country && {
+          ...country,
+          code
+        }
+      );
+    },
+    countries: (parent, {filter}) =>
+      Object.entries(countries)
+        .map(([code, country]) => ({
+          ...country,
+          code
+        }))
+        .filter(filterToSift(filter)),
+    language(parent, {code}) {
+      const language = languages[code];
+      return (
+        language && {
+          ...language,
+          code
+        }
+      );
+    },
+    languages: (parent, {filter}) =>
+      Object.entries(languages)
+        .map(([code, language]) => ({
+          ...language,
+          code
+        }))
+        .filter(filterToSift(filter))
+  }
+};