import React, { useMemo } from 'react'
import Head from 'next/head'
import { ApolloProvider } from '@apollo/react-hooks'
import { ApolloClient, InMemoryCache, HttpLink } from 'apollo-boost'
import fetch from 'isomorphic-unfetch'

const GRAPHQL_URL = process.env.BACKEND_URL || 'http://localhost:3005/graphql'

  let apolloClient = null

  /**
   * Creates and provides the apolloContext
   * to a next.js PageTree. Use it by wrapping
   * your PageComponent via HOC pattern.
   * @param {Function|Class} PageComponent
   * @param {Object} [config]
   * @param {Boolean} [config.ssr=true]
   */
  export function withApollo (PageComponent, { ssr = true } = {}) {
    const WithApollo = ({ apolloClient, apolloState, ...pageProps }) => {
      const client = useMemo(
        () => apolloClient || initApolloClient(apolloState),
        []
      )
      return (
        <ApolloProvider client={client}>
          <PageComponent {...pageProps} />
        </ApolloProvider>
      )
    }
  
    // Set the correct displayName in development
    if (process.env.NODE_ENV !== 'production') {
      const displayName =
        PageComponent.displayName || PageComponent.name || 'Component'
  
      if (displayName === 'App') {
        console.warn('This withApollo HOC only works with PageComponents.')
      }
  
      WithApollo.displayName = `withApollo(${displayName})`
    }
  
    // Allow Next.js to remove getInitialProps from the browser build
    if (typeof window === 'undefined') {
      if (ssr) {
        WithApollo.getInitialProps = async ctx => {
          const { AppTree } = ctx
  
          let pageProps = {}
          if (PageComponent.getInitialProps) {
            pageProps = await PageComponent.getInitialProps(ctx)
          }
  
          // Run all GraphQL queries in the component tree
          // and extract the resulting data
          const apolloClient = initApolloClient()
  
          try {
            // Run all GraphQL queries
            await require('@apollo/react-ssr').getDataFromTree(
              <AppTree
                pageProps={{
                  ...pageProps,
                  apolloClient
                }}
              />
            )
          } catch (error) {
            // Prevent Apollo Client GraphQL errors from crashing SSR.
            // Handle them in components via the data.error prop:
            // https://www.apollographql.com/docs/react/api/react-apollo.html#graphql-query-data-error
            console.error('Error while running `getDataFromTree`', error)
          }
  
          // getDataFromTree does not call componentWillUnmount
          // head side effect therefore need to be cleared manually
          Head.rewind()
  
          // Extract query data from the Apollo store
          const apolloState = apolloClient.cache.extract()
  
          return {
            ...pageProps,
            apolloState
          }
        }
      }
    }
  
    return WithApollo
  }
  
  /**
   * Always creates a new apollo client on the server
   * Creates or reuses apollo client in the browser.
   * @param  {Object} initialState
   */
  function initApolloClient (initialState) {
    // Make sure to create a new client for every server-side request so that data
    // isn't shared between connections (which would be bad)
    if (typeof window === 'undefined') {
      return createApolloClient(initialState)
    }
  
    // Reuse client on the client-side
    if (!apolloClient) {
      apolloClient = createApolloClient(initialState)
    }
  
    return apolloClient
  }
  
  /**
   * Creates and configures the ApolloClient
   * @param  {Object} [initialState={}]
   */
  function createApolloClient (initialState = {}) {
    // Check out https://github.com/zeit/next.js/pull/4611 if you want to use the AWSAppSyncClient
    const isBrowser = typeof window !== 'undefined'
    return new ApolloClient({
      connectToDevTools: isBrowser,
      ssrMode: !isBrowser, // Disables forceFetch on the server (so queries are only run once)
      link: new HttpLink({
        uri: GRAPHQL_URL, // Server URL (must be absolute)
        credentials: 'same-origin', // Additional fetch() options like `credentials` or `headers`
        // Use fetch() polyfill on the server
        fetch: !isBrowser && fetch
      }),
      cache: new InMemoryCache().restore(initialState)
    })
  }