'use strict';

const { isEmpty, mergeWith, isArray } = require('lodash/fp');
const { execute, subscribe } = require('graphql');
const { SubscriptionServer } = require('subscriptions-transport-ws');
const { ApolloServer } = require('apollo-server-koa');
const {
  ApolloServerPluginLandingPageDisabled,
  ApolloServerPluginLandingPageGraphQLPlayground,
} = require('apollo-server-core');
const depthLimit = require('graphql-depth-limit');
const { graphqlUploadKoa } = require('graphql-upload');
const formatGraphqlError = require('./format-graphql-error');

const merge = mergeWith((a, b) => {
  if (isArray(a) && isArray(b)) {
    return a.concat(b);
  }
});

module.exports = async ({ strapi }) => {
  // Generate the GraphQL schema for the content API
  const schema = strapi
    .plugin('graphql')
    .service('content-api')
    .buildSchema();

  if (isEmpty(schema)) {
    strapi.log.warn('The GraphQL schema has not been generated because it is empty');

    return;
  }

  const { config } = strapi.plugin('graphql');

  const path = config('endpoint');

  const defaultServerConfig = {
    // Schema
    schema,

    // Initialize loaders for this request.
    context: ({ ctx }) => ({
      state: ctx.state,
      koaContext: ctx,
    }),

    // Validation
    validationRules: [depthLimit(config('depthLimit'))],

    // Errors
    formatError: formatGraphqlError,

    // Misc
    cors: false,
    uploads: false,
    bodyParserConfig: true,

    plugins: [
      process.env.NODE_ENV === 'production'
        ? ApolloServerPluginLandingPageDisabled()
        : ApolloServerPluginLandingPageGraphQLPlayground(),
    ],
  };

  const serverConfig = merge(defaultServerConfig, config('apolloServer'));

  // Handle subscriptions
  if (config('subscriptions')) {
    const subscriptionServer = SubscriptionServer.create(
      { schema, execute, subscribe },
      { server: strapi.server.httpServer, path }
    );

    serverConfig.plugins.push({
      async serverWillStart() {
        return {
          async drainServer() {
            subscriptionServer.close();
          },
        };
      },
    });
  }

  // Create a new Apollo server
  const server = new ApolloServer(serverConfig);

  // Register the upload middleware
  useUploadMiddleware(strapi, path);

  try {
    // Since Apollo-Server v3, server.start() must be called before using server.applyMiddleware()
    await server.start();
  } catch (e) {
    strapi.log.error('Failed to start the Apollo server', e.message);
  }

  // Link the Apollo server & the Strapi app
  strapi.server.routes([
    {
      method: 'ALL',
      path,
      handler: [
        (ctx, next) => {
          ctx.state.route = {
            info: {
              // Indicate it's a content API route
              type: 'content-api',
            },
          };

          return strapi.auth.authenticate(ctx, next);
        },

        // Apollo Server
        server.getMiddleware({ path }),
      ],
      config: {
        auth: false,
      },
    },
  ]);

  // Register destroy behavior
  // We're doing it here instead of exposing a destroy method to the strapi-server.js
  // file since we need to have access to the ApolloServer instance
  strapi.plugin('graphql').destroy = async () => {
    await server.stop();
  };
};

/**
 * Register the upload middleware powered by graphql-upload in Strapi
 * @param {object} strapi
 * @param {string} path
 */
const useUploadMiddleware = (strapi, path) => {
  const uploadMiddleware = graphqlUploadKoa();

  strapi.server.app.use((ctx, next) => {
    if (ctx.path === path) {
      return uploadMiddleware(ctx, next);
    }

    return next();
  });
};