Add language endpoint to developer APIs (#41)

* Added languages endpoint and its tests

pages/api/graphql.ts

@@ -1,21 +1,31 @@
-import { ApolloServer, gql, IResolvers } from "apollo-server-micro";
+import { ApolloServer, gql, IResolvers, ApolloError, UserInputError } from "apollo-server-micro";
 import { NextApiHandler } from "next";
 import NextCors from "nextjs-cors";
 import { googleScrape, textToSpeechScrape } from "@utils/translate";
+import { retrieveFromType, getName } from "@utils/language";
 
 export const typeDefs = gql`
+    enum LangType {
+        SOURCE,
+        TARGET
+    }
     type Query {
         translation(source: String="auto" target: String="en" query: String!): Translation!
         audio(lang: String! query: String!): Entry!
+        languages(type: LangType): [Language]!
     }
     type Translation {
         source: Entry!
         target: Entry!
     }
     type Entry {
-        lang: String!
-        text: String
-        audio: [Int]
+        lang: Language!
+        text: String!
+        audio: [Int]!
+    }
+    type Language {
+        code: String!
+        name: String!
     }
 `;
 
@@ -25,35 +35,65 @@ export const resolvers: IResolvers = {
             const { source, target, query } = args;
             return {
                 source: {
-                    lang: source,
+                    lang: {
+                        code: source
+                    },
                     text: query
                 },
                 target: {
-                    lang: target
+                    lang: {
+                        code: target
+                    }
                 }
             };
         },
         audio(_, args) {
+            const { lang, query } = args;
             return {
-                lang: args.lang,
-                text: args.query
+                lang: {
+                    code: lang
+                },
+                text: query
             };
+        },
+        languages(_, args) {
+            const { type } = args;
+            const langEntries = retrieveFromType(type?.toLocaleLowerCase());
+            return langEntries.map(([code, name]) => ({ code, name }));
         }
     },
     Translation: {
         async target(parent) {
             const { source, target } = parent;
-            const { translationRes } = await googleScrape(source.lang, target.lang, source.text);
+            const textScrape = await googleScrape(source.lang.code, target.lang.code, source.text);
+
+            if ("errorMsg" in textScrape)
+                throw new ApolloError(textScrape.errorMsg);
             return {
                 lang: target.lang,
-                text: translationRes
+                text: textScrape.translationRes
             };
         }
     },
     Entry: {
         async audio(parent) {
             const { lang, text } = parent;
-            return await textToSpeechScrape(lang, text);
+            const audio = await textToSpeechScrape(lang.code, text);
+            if (!audio)
+                throw new ApolloError("An error occurred while retrieving the audio");
+            return audio;
+        }
+    },
+    Language: {
+        name(parent) {
+            const { code, name } = parent;
+            if (name)
+                return name;
+
+            const newName = getName(code);
+            if (!newName)
+                throw new UserInputError("Invalid language code");
+            return newName;
         }
     }
 };