Category Archives: TUTORIALS

Detailed tutorials explaining how to build most common applications, in different languages.

Set up GraphQL with gqlgen and golang

The goal: setting up GraphQL server using Gqlgen library.
We are going to set up GraphQL server with Users, and create queries to retrieve the users by id or user name.

Schema-first approach – means that instead of using library apis (code-first approach) we are going to write our schema manually using the GraphQL schema definition language.

Setting up the project

  • Create project directory
    mkdir gqlgen-tutorial
  • Navigate to the folder
    cd gqlgen-tutorial
  • Initialize go project.
    go mod init gqlgen-tutorial
  • Create tools.go and add gqlgen  library
//go:build tools
// +build tools

package tools

import _ "github.com/99designs/gqlgen"
  • Add the library
    go mod tidy

Iinitializing Gqlgen with boilerplate schema and resolvers

gqlgen has handy command to Initialize gqlgen config and generate the models.

go run github.com/99designs/gqlgen init

This will create server.go the server starting point and ./graph directory with a couple of files including schema.graphqls and if you open it you will see that it comes with pre-defined example schema which we are going to remove later and start from scratch.

graph/model/model_gen.go – is auto generated file containing structure of defined by the schema file graph/schema.graphqls

graph/generated.go – this is a file with generated code that injects context and middleware for each query and mutation.

We should not modify these files since they will be modified by gqlgen as we update the schema. Instead, we should edit these files:

graph/schema.graphqls –  GraphQL schema file where types, queries, and mutations are defined.

graph/resolver.go – resolver functions for queries and mutations defined in schema.graphqls

At this point we could start the server and see the playground and the schema.

go run ./server.go

Defining queries

First let’s remove boilerplate schema from graph/schema.graphqls and add our new schema

graph/schema.graphqls

# GraphQL schema example
#
# https://gqlgen.com/getting-started/


type User {
  id: ID!
  name: String!
  userType: String!
}

type Query {
  getUser(id:ID!): User
}

input NewUser {
  userId: String!
  userName: String!
  userType: String!
}

type Mutation {
  createUser(input: NewUser!): User!
}

 

Generate code and running the API

We will now generate code, which will update the following files using the information we provided in the schema file:

  • schema.resolvers.go
  • model/models_gen.go
  • generated/generated.go

Delete the example code in schema.resolvers.go and then run the following command:

go run github.com/99designs/gqlgen generate

If we run the server we will run into an error because we didn’t define any resolver yet.

Defining the backend to fetch and store values

In resolver.go:

– import qlgen-tutorial/graph/model.  line: 3
– declare a Hash Map that we will use to store users. Line 10

package graph

import "gqlgen-tutorial/graph/model"

// This file will not be regenerated automatically.
//
// It serves as dependency injection for your app, add any dependencies you require here.

type Resolver struct{
    UsersStore map[string]model.User	
}

 

We defined UserStore of type map which essentially is a hash-map with keys of type string and values of type model.User.

In schema.resolvers.go, we are going to modify the boilerplate methods: CreateUser and GetUser

package graph

// This file will be automatically regenerated based on the schema, any resolver implementations
// will be copied through when generating and any unknown code will be moved to the end.
// Code generated by github.com/99designs/gqlgen version v0.17.24

import (
    "context"
    "fmt"
    "gqlgen-tutorial/graph/model"
)

// CreateUser is the resolver for the createUser field.
func (r *mutationResolver) CreateUser(ctx context.Context, input model.NewUser) (*model.User, error) {

    // create new user to be added in r.Resolver.UsersStore and returned
    var user model.User

    if len(r.Resolver.UsersStore) == 0 {
        // create new UserStore hash map if it does not exist
        r.Resolver.UsersStore = make(map[string]model.User)
    }
    // set up new user attributes
    user.ID = input.UserID
    user.Name = input.UserName
    user.UserType = input.UserType

    // adds newly created user into the resolver's UserStore
    r.Resolver.UsersStore[input.UserID] = user

    return &user, nil
}

// GetUser is the resolver for the getUser field.
func (r *queryResolver) GetUser(ctx context.Context, id string) (*model.User, error) {

    fmt.Println(r.Resolver.UsersStore)

    // retrieve user from  the store
    user, isOk := r.Resolver.UsersStore[id]
    if !isOk {
        return nil, fmt.Errorf("not found")
    }
    return &user, nil
}

// Mutation returns MutationResolver implementation.
func (r *Resolver) Mutation() MutationResolver { return &mutationResolver{r} }

// Query returns QueryResolver implementation.
func (r *Resolver) Query() QueryResolver { return &queryResolver{r} }

type mutationResolver struct{ *Resolver }
type queryResolver struct{ *Resolver }

GetUser is pretty straight forward: it gets user id and returns the user from the hash map store.

CreateUser first checks if UserStore is initialized. Line 19. If CreateUser length is 0 it initializes the hash-map. Line 21.
Then it gets the values for username, id and userType from the input parameter and sets up the new user, stores it into the UserStore, line 29, and returns it.

 

Testing

Creating user

Mutation:

mutation createUserMutation($input: NewUser!) {
  createUser(input: $input) {
    name
    id
  }
}

Variables:

{
  "input": {
    "userId": "1",
    "userName": "John",
    "userType": "admin",
    "userGender": "male"
  }
}

Query for user with id

Query:

query getUserQuery($nid: ID!) {
  getUser(id:$nid) {
    id
    name
    userType
    userGender
  }
}

Variables:

{
  "nid": "1"
}

 

Zigzag Conversion

Task

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P   A   H   N
A P L S I I G
Y   I   R

And then read line by line: "PAHNAPLSIIGYIR"

Write the code that will take a string and make this conversion given a number of rows:

string convert(string s, int numRows);

Example 1:

Input:

 s = "PAYPALISHIRING", numRows = 3

Output:

 "PAHNAPLSIIGYIR"

Example 2:

Input:

 s = "PAYPALISHIRING", numRows = 4

Output:

 "PINALSIGYAHRPI"

Explanation:

P     I    N
A   L S  I G
Y A   H R
P     I

Example 3:

Input:

 s = "A", numRows = 1

Output:

 "A"

 

This problem was taken from Leet code, ZigZag conversion

 

Solution

It’s take the first example string: “PAYPALISHIRING

An array representation of the string would be done by pushing each character into the array.

Then if we want to iterate through this array in zig zag pattern with 3 rows, it will look like this:

 

Then, we have to create 3 arrays representing the 3 rows as follows:

Dots represent empty strings which we have to ignore before concatenating all 3 rows, convert them to string and this is the answer to this problem.

But how to create the loop to traverse through the zig zag pattern (figure 1) ?

  • first we set up `headingDown` flag to determine if we are going down or up
  • each time when the row reaches numRows we are flipping the value of headingDown
  • when headingDown is false (meaning that we are heading up) we have to do it diagonally: row — , col ++
  • when row become 0 we are flipping again headingDown and it becomes true again: row ++ and we keep storing values of every character we traversed in the result array.
 /**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function(s, numRows) {

    // if we don't have any rows or there is an empty string just return back empty string
    if(s.length === 0 || numRows === 0) 
        return '';

    // if rows are numRows is just one, we return the same string
    if(numRows === 1) {
        return s;
    }
    
    var l = s.length;
    // put the string into single dimension array to iterate through
    var arr = s.split('');
    
    var rowsArray = [];
    var row = 0;
    var col = 0;
    var headingDown = true; // this determines if the cursor is heading down in the same column, or up leaping to the next column (dizgonal)

    // instantiate numRows arrays to store values of each row
    for(var i = 0; i < numRows; i ++) {
        rowsArray[i] = [];
    }

    // loop through each element in arr and fill rowsArray ()
    for(var i = 0; i < l; i ++) {
        rowsArray[row][col] = arr[i];
        if(headingDown) {
            row ++;
        }
        else {
            row --;
            col ++;
        }

        
        if(row == numRows -1) {
            headingDown = false;
        } else if(row == 0) {
            headingDown = true;
        }
        
    }

    // Read 2D array and assemble the string
    var result = [];
    for(var i = 0; i < numRows; i ++) {
        for(var j = 0; j < rowsArray[i].length; j ++) {
            if(typeof rowsArray[i][j] != 'undefined') {
                result.push(rowsArray[i][j]);
            }
        }
    }
    return result.join('');
};

convert('PAYPALISHIRING', 3);
convert('AB', 1);
//convert('ABC', 1);

 

How can we optimize this ?

the above example is good to read but not a good practical example. First we don’t need two dimensional array to store characters for each row. We could replace this with string array and just keep adding characters till we reached the end of the string. This way we also don’t need to keep track of cols

/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function(s, numRows) {

    // if we don't have any rows or there is an empty string just return back empty string
    if(s.length === 0 || numRows === 0) 
        return '';

    // if rows are numRows is just one, we return the same string
    if(numRows === 1) {
        return s;
    }
    
    var l = s.length;
    // put the string into single dimension array to iterate through
    var arr = s.split('');
    
    var left = 0;
    var arrStrings = [];
    var row = 0;
    var col = 0;
    var headingDown = true; // this determines if the cursor is heading down in the same column, or up leaping to the next column (dizgonal)

    // instantiate numRows arrays to store values of each row
    for(var i = 0; i < numRows; i ++) {
        arrStrings[i] = '';
    }

    
    // loop through each element in arr and fill arrStrings ()
    for(var i = 0; i < l; i ++) {
        //arrStrings[row][col] = arr[i];
        if(headingDown) {
            arrStrings[row] += arr[i];
            row ++;
        }
        else {
            arrStrings[row] += arr[i];
            row --;
            col ++;
        }

        
        if(row == numRows -1) {
            headingDown = false;
        } else if(row == 0) {
            headingDown = true;
        }
        
    }

    var result = '';
    // combine all strings and return as one 
    for(var i = 0; i < numRows; i ++) {
        result += arrStrings[i];
    }
        
    return result;
};

 

Log In With Apple using redirect pop-up

This tutorial demonstrates how to use oAuth to sign-in with Apple without using any library.We simply use HTTP GET request to their endpoint URL: appleid.apple.com/auth/authorize.

Just to space it up a bit, we are opening Sign-in popup in modal window using window.open but this could be done in the same window. The advantages of open it in modal window are that the user won’t be redirect to different screens and got confused of what’s going on.

Full example here

Main Web app

index.html

<html>
    <head>
      <style>

      </style>

    <script type = "text/javascript">

      var popUpObj;

      function showModalPopUp()    
      {
      popUpObj=window.open(
        "log-in-popup.html",
        "ModalPopUp",
        "toolbar=no," +
        "scrollbars=no," +
        "location=no," +
        "statusbar=no," +
        "menubar=no," +
        "resizable=0," +
        "width=500," +
        "height=640," +
        "left = 480," +
        "top=300"
      );

      popUpObj.focus();
      }   

      function receiveUserSignedInData(parsedToken) {
        console.dir(parsedToken, { depth: null });
      }

    </script>
    </head>
    <body>
    <h1>Welcome to oAuth example</h1>
    <input id="Button1" type="button" value="Log In" onclick="showModalPopUp()">
    </body>
</html>

The main app simply has a button that opens modal window with sign-in button. Line 39.

Log-In popup window

<html>
    <head>
        <style>
            #apple-auth-button {
                webkit-box-align: baseline;
                align-items: baseline;
                border-width: 0px;
                border-radius: 3px;
                box-sizing: border-box;
                display: inline-flex;
                font-size: inherit;
                font-style: normal;
                font-family: inherit;
                max-width: 100%;
                position: relative;
                text-align: center;
                text-decoration: none;
                transition: background 0.1s ease-out 0s, box-shadow 0.15s cubic-bezier(0.47, 0.03, 0.49, 1.38) 0s;
                white-space: nowrap;
                cursor: pointer;
                padding: 0px 10px;
                vertical-align: middle;
                width: 100%;
                -webkit-box-pack: center;
                justify-content: center;
                font-weight: bold;
                color: var(--ds-text,#42526E) !important;
                height: 40px !important;
                line-height: 40px !important;
                background: rgb(255, 255, 255) !important;
                box-shadow:  rgb(0 0 0 / 20%) 1px 1px 5px 0px !important           
            }
        </style>

    </head>
    <body>
        <a href="https://appleid.apple.com/auth/authorize?client_id=com.sign-in-with-apple-example-redirect-service&redirect_uri=https://www.toni-develops.com/external-files/examples/oauth-with-apple-with-redirect-step-by-step/callback.php&response_type=code id_token&state=123&scope=name email&response_mode=form_post">Sign In with Apple Simple A tag</a>

        <hr/>

        <div id="signInPanel">
            
            <form action="https://appleid.apple.com/auth/authorize?" method="get">
                <input type="hidden" id="client_id" name="client_id" value="com.sign-in-with-apple-example-redirect-service" />
                <input type="hidden" id="redirect_uri" name="redirect_uri" value="https://www.toni-develops.com/external-files/examples/oauth-with-apple-with-redirect-step-by-step/callback.php" />
                <input type="hidden" id="response_type" name="response_type" value="code id_token"/>
                <input type="hidden" id="scope" name="scope" value="name email" />
                <input type="hidden" id="response_mode" name="response_mode" value="form_post" />

                <button id="apple-auth-button" class="css-11s2kpt" type="submit" tabindex="0">
                <span class="css-1ujqpe8">
                    <img class="appleLogo" src="https://www.toni-develops.com/external-files/examples/assets/apple-logo.svg" alt="">
                </span>
                <span class="css-19r5em7"><span>Continue with Apple</span>
                </button> 
            </form>

          </div>        
    </body>
</html>

This window create two sign-in entities: one is simple A tag that demonstrates how we could start sign-in redirect process by simply redirect browser to authentication service, and the second one is a button, that does the same using form submit.

Callback function

callback.php

<html>
    <head>
      <style>

      </style>
      <script type = "text/javascript">
        var id_token = "<?php echo $_POST['id_token'] ?>";


        function parseJwt (token) {
          var base64Url = token.split('.')[1];
          var base64 = base64Url.replace(/-/g, '+').replace(/_/g, '/');
          var jsonPayload = decodeURIComponent(window.atob(base64).split('').map(function(c) {
              return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
          }).join(''));

          return JSON.parse(jsonPayload);
        }           

        function sendDataToMainApp() {
          var parsedToken = parseJwt(id_token);
          window.opener.receiveUserSignedInData(parsedToken);
          window.close();
        }
      </script>
    </head>
    <body onLoad="sendDataToMainApp()">

    
    
    </body>
</html>

what we just did:

Were, we get id_token from Apple authentication service, that passes this via the request type that we selected (post, fragment, get) decodes, id_token then passes it to the parent window and closes itself.

 

Full example here

 

Using Oauth2 to sign-in users with Apple using Java Script Library

Example project here

<html>
    <head>
      <style>
        h1 {
          text-align: center;
        }

        #welcomePanel {
          display: none;
          text-align: center;
        }

        #signInPanel h2 {
          text-align: center;
          border: 1px solid silver;
        }

        #google-auth-button {
          -webkit-box-align: baseline;
          align-items: baseline;
          border-width: 0px;
          border-radius: 3px;
          box-sizing: border-box;
          display: inline-flex;
          font-size: inherit;
          font-style: normal;
          font-family: inherit;
          max-width: 100%;
          position: relative;
          text-align: center;
          text-decoration: none;
          transition: background 0.1s ease-out 0s, box-shadow 0.15s cubic-bezier(0.47, 0.03, 0.49, 1.38) 0s;
          white-space: nowrap;
          cursor: pointer;
          padding: 0px 10px;
          vertical-align: middle;
          width: 100%;
          -webkit-box-pack: center;
          justify-content: center;
          font-weight: bold;
          color: var(--ds-text,#42526E) !important;
          height: 40px !important;
          line-height: 40px !important;
          background: rgb(255, 255, 255) !important;
          box-shadow: rgb(0 0 0 / 20%) 1px 1px 5px 0px !important;
        }
      </style>
      <!-- First we have to include Apple Sign-in script -->
      <script
        type="text/javascript"
        src="https://appleid.cdn-apple.com/appleauth/static/jsapi/appleid/1/en_US/appleid.auth.js"></script>
    </head>
    <body>
      <script>

        function parseJwt (token) {
            var base64Url = token.split('.')[1];
            var base64 = base64Url.replace(/-/g, '+').replace(/_/g, '/');
            var jsonPayload = decodeURIComponent(window.atob(base64).split('').map(function(c) {
                return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
            }).join(''));

            return JSON.parse(jsonPayload);
        }

        /**
         * This function will initialize the `AppleID.auth` object with parameter we pass in.
         */
       
        const initApple = () => {
          window.AppleID.auth.init({
            clientId: "com.toni-develops.sign-in-with-apple-identifier", // This is the service ID we created.
            scope: "name email", // To tell apple we want the user name and emails fields in the response it sends us.
            redirectURI: "https://www.toni-develops.com/external-files/examples/oauth-with-apple-using-js-library", // As registered along with our service ID
            state: "origin:web", // Any string of your choice that you may use for some logic. It's optional and you may omit it.
            usePopup: true, // Important if we want to capture the data apple sends on the client side.
          });
        };        
        
        
        /**
         * This function is where the magic happens.
         * This is a simple example, ideally you'll have catch block as well to handle authentication failure.
         */
        const singInApple = async () => {
          const response = await window.AppleID.auth.signIn();

          return response;
        };     
        
        initApple();


        function signInWithApple() {
          const userData = singInApple();

          userData.then( (data) => {
            console.dir(data, { depth: null });
            const result = parseJwt(data.authorization.id_token)
            console.dir(result, { depth: null });

            document.querySelector('#signInPanel').innerHTML = '<h2>Welcome ' + result.email + '</h2>';
          });
        }
      </script>
      <h1>Sign-In with Apple using Java Script library example</h1>
      <div id="signInPanel">
        <button id="google-auth-button" class="css-11s2kpt" type="button" tabindex="0" onclick="signInWithApple()">
          <span class="css-1ujqpe8">
            <img class="appleLogo" src="https://www.toni-develops.com/external-files/examples/assets/apple-logo.svg" alt="">
          </span>
          <span class="css-19r5em7"><span>Continue with Apple</span>
        </button> 
      </div>
    </body>
</html>

 

Sign-in with Apple prerequisite

In order to add Sign-In with Apple we have to do the following:

  1. Create an App ID.
  2. Create a Service ID.
  3. Register the domains for your website.

Create App ID

  • Select App and click continue

  • add description and Bundle ID following reverse domain recommendation by Apple

 

  • confirm and hit register

 

 

Register Service ID

  • Go back to https://developer.apple.com/account/resources/identifiers/add/bundleId
  • this time select “Service ID” and click continue

  • add description and identifier

  • select identifier that you just created

  • check the checkbox to configure the identifier and hit configure

  • add the domain and the Return URLs (Make a note of the return url since we have to add it into our Java Script code later)

.

 

Using oAuth2.0 to sign-in with Google using redirect method

No library required

In this example we have the main app (in this case my blogpost) with a Log-in button (Log in Example, above ), that redirects to the Log-In app, which on the other hand redirects to selected Log-In service (Google, Apple, Facebook, Github) passing app id an all necessary log in data.

After the user grant permissions to share requested data (email, username, real name, etc.) called scope, authentication service is calling back our app service, passing code which our service is using to make HTTP request to the provider and exchange it for JWT (Jason Web Token) containing requested user information.

Create Authorization credentials

  • Navigate to https://console.cloud.google.com/apis/credentials  and click on the + CREATE CREDENTIALS on the top left of the page.
  • on Authorized Java Script Origins add the domain from where the WEB app will be served. You could use http://localhost if you like.
  • on Authorized Redirect URIs add authentication service callback script that Google will call to pass code that could be exchanged for JWT (JSON Web Token) containing user’s information requested.

On the top right corner you will see ClientID and App secret. Write them down since we are going to need them in our authentication service later on.

Create main WEB app and authentication service

We will create main WEB app and authentication service that main app will use. This way same authentication service could be used for different WEB aps.

(Main web app) with Log In button, that redirects to the authentication app.

Let’s get started by creating simple WEB app that will have Log In button, that will simply redirect to our log in service. I already did that in the “Log In Example” above.

index.html

<html>
  <head>
    <style>
     ...
    </style>
  </head>

  <body>
    <!-- there is no Java script involved at all -->
    <div id="log_in_wrapper">
      <button class='continue_with_google'>
        <a href='https://log-in-service-app/index.html'>
          Log In
        </a>
      </button>
    </div>
  </body>
</html>

Nothing fancy happens here. We have button that simply redirects to our authentication service, which draws log-in with  buttons (with Google, Apple, Facebook, GitHub)

(Authentication app) that shows log-in with  buttons (with Google, Apple, Facebook, GitHub)

index.php

<html>
  <head>
    <style>
      ...
    </style>
  </head>

  <body>
    <!-- there is no Java script involved at all -->
    <div id="log_in_wrapper">
      <button class='continue_with_google'>
        <a href='step-1-auth-google-get-redirect.php'>
          <img src="some-google-logo"/>
          <span>Continue with Google</span>
        </a>
      </button>
    </div>
  </body>
</html>

This is just another Web app that shows log in buttons. We could skip this step and simply have this buttons in the main WEB app.

For simplicity I only added Log In With google.

This button redirects to step-1-auth-google-get-redirect.php the first part of our authentication service.

 

Creating config file

<?php

// Fill these out with the values you got from Google
$googleClientID = '989056576533-mtef8cl5is5ogjh3np580ireurns7l5k.apps.googleusercontent.com';
$googleClientSecret = 'xxxxxxxxxxxxxx';

// This is the URL we'll send the user to first to get their authorization
$authorizeURL = 'https://accounts.google.com/o/oauth2/v2/auth';

// This is Google's OpenID Connect token endpoint
$tokenURL = 'https://www.googleapis.com/oauth2/v4/token';

// The main application URL. Google will pass JWT token back to the main app
$baseURL = 'https://www.toni-develops.com/external-files/examples/oauth-with-google-with-redirect-step-by-step/step-2-auth-google-redirect.php';

$usserInfoURL = 'https://www.googleapis.com/oauth2/v3/userinfo';

// the initial app url
$initialAppURL = 'https://www.toni-develops.com/2023/01/05/using-oauth2-0-to-log-in-with-google-using-redirect/';

 

After selecting to log-in with desired authentication provider, call backend service to prepare all necessary parameters and call selected authentication service (Google, Apple, Facebook, GitHub)

step-1-auth-google-get-redirect.php

<?php
// add Google app config params
include 'google-config.php';

// Start a session so we have session id to make sure that the redicect is instantiated by this script
$sessionId = '123';

// ####################################################
// STEP 1: Start the login process by sending the user
// to Google's authorization page, 
// and passing app params
// ####################################################


  // Generate a random hash and store in the session to make sure that 
  //$_SESSION['state'] = bin2hex(random_bytes(16));

  $params = array(
    'response_type' => 'code',
    'client_id'     => $googleClientID,
    'redirect_uri'  => $baseURL,
    'scope'         => 'openid email profile',
    'state'         => $sessionId
  );

  // Redirect the user to Google's authorization page, passing the above parameters as a GET request
  header('Location: ' . $authorizeURL . '?' . http_build_query($params));

This simply redirects to the authentication service. In this case Google, passing these parameters:

  • response_type – we requesting code in the response which we are going to exchange it for JWT
  • client_id – is the app id that we registered
  • redirect_url – is our authentication service url, that Google will call passing code parameter. Here we are going to exchange it for JWT In this example this is step-2-auth-google-redirect.php` script below.
  • scope – is the requested scope. In our example we just need user name and email: openid email profile
  • state – this is unique string identifier, that we will check in the callback to make sure that this sign-in workflow is originated by our script

Everything that happens in the above file, could be achieved by simply passing this url in the browser. If you examine the url, it simply passes the same get parameters and query string params.

Next step: Google calls our callback script, passing code which our script exchange for JWT containing user info

step-2-auth-google-redirect.php

<?php
// add Google app config params
include 'google-config.php';

// ####################################################
// Step 2: When Google redirects the user back here, 
// there will be a "code" and "state"
// parameter in the query string
// Exchange the auth code for a JWT token,
// and extract requested user data from there
// ####################################################
if(isset($_GET['code'])) {
  
  // Verify the state matches our stored state
  if(!$_GET['state'] && $_GET['state'] !== '123') {    
    die('missing state!');
  }
  
  // Exchange the auth code for a token
  $ch = curl_init($tokenURL);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
  curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query([
    'grant_type' => 'authorization_code',
    'client_id' => $googleClientID,
    'client_secret' => $googleClientSecret,
    'redirect_uri' => $baseURL,
    'code' => $_GET['code']
  ]));

  $response = curl_exec($ch);

  // $data will contain 
  // access_token, 
  // expires_in, 
  // scope, 
  // token_type, 
  // id_token - which is JWT token, containing user data according to requested scope from the initial script.
  $data = json_decode($response, true);
  //echo '<pre>';print_r($data);die("</pre>");

  // Note: You'd probably want to use a real JWT library
  // but this will do in a pinch. This is only safe to do
  // because the ID token came from the https connection
  // from Google rather than an untrusted browser redirect

  // Split the JWT string into three parts
  $jwt = explode('.', $data['id_token']);

  // Extract the middle part, base64 decode it, then json_decode it
  $IDToken = json_decode(base64_decode($jwt[1]), true);
  
  // This step is required only if we want to get extra info
  /*
  $ch = curl_init($usserInfoURL);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
  curl_setopt($ch, CURLOPT_HTTPHEADER, [
    'Authorization: Bearer '.$data['access_token']
  ]);
  $userInfo = curl_exec($ch);
  */
  /*
  echo '<h1>Token ID</h1>';
  echo '<pre>';print_r($IDToken);echo '</pre>';
  echo '<h1>User info</h1>';
  echo '<pre>';print_r($userInfo);die('</pre>');
  */

  $params = array(
    'email'       => $IDToken['email'],
    'user_name'   => $IDToken['name'],
    'given_name'  => $IDToken['given_name'],
    'family_name'  => $IDToken['family_name']
  );

  // Redirect the user to the initial app passing user data as Query String parameters so the front end could use them.
  header('Location: ' . $initialAppURL . '?' . http_build_query($params));
}
else {
  echo 'Bad response. Missing `code` GET response';
}

line 19-30: we make curl request to Google service passing:

  • grant_type – authorization_code
  • client_id – App id
  • client_secret – App secret
  • redirect_uri – should be url registered in Authorized redirect URLs

  • code – this is the code returned by Google as GET parameter

Last step: We are redirecting back to the main app, passing parameters that front end needs (email, user name) as GET or POST params.

Additionally we could save the user into our database, or do some additional work before redirecting to the main app (line 76)

 

Using Oauth2 to sign-in users with Google using Google Java Script Library

Example project here:  Sign-in with Google using Google Java Script library

 

  • Main project
<head>
  <style>
    #signIn {
      width: 80%;
      height: 50%;
      display: none;
    }

    span {
      border: 1px solid silver;
      padding: 10px;
      cursor: pointer;
      font-size: 10px;
    }
  </style>
  <script>
    function userLoggedIn(userObject) {
      document.getElementById('signIn').style.display = 'none';
      document.getElementById('head').innerHTML = `Wellcome ${userObject.given_name} ${userObject.family_name} ! <hr/>email: ${userObject.email} `;
    }

    function showLogInPopup() {
      document.getElementById('signIn').style.display = 'block';
    }
  </script>  
</head>

<body>
  <h1 id="head">Integrating Google Sign-in for Websites with Google library. <span onclick="showLogInPopup()">Log In</span></h1>

  <iframe id="signIn" src="google-sign-in.html"></iframe>
</body>
  • create iFrame with the log in button
<head>
    <script src="https://accounts.google.com/gsi/client" async defer></script>
    <script>
        function userLoggedIn(credential) {
            document.getElementById('log-in-iframe').style.display = 'none';
            alert(credential);
        }
    </script>
</head>

<body>
    Log in with Google
    <div id="log-in-button">
        <div id="g_id_onload"
            data-client_id="989056576533-mtef8cl5is5ogjh3np580ireurns7l5k.apps.googleusercontent.com"
            data-context="signin"
            data-response-type="code"
            data-ux_mode="popup"
            data-login_uri="https://www.toni-develops.com/external-files/examples/oauth-with-google-with-popup/callback.php"
            data-itp_support="true"
            data-auto_prompt="false">
        </div>

        <div class="g_id_signin"
            data-type="standard"
            data-shape="rectangular"
            data-theme="filled_blue"
            data-text="signin_with"
            data-size="large"
            data-logo_alignment="left">
        </div>   
    </div>
</body>
  • create callback
<html>
<head>
</head>

<body>
  <pre>
  <?php
    $token = $_POST['credential'];
    $userObject = json_decode(base64_decode(str_replace('_', '/', str_replace('-','+',explode('.', $token)[1]))));
    print_r($userObject);
  ?>  
  </pre>
  <script>
  var userObject = {
    given_name : "<?php echo $userObject->given_name ?>",
    family_name : "<?php echo $userObject->family_name ?>",
    email : "<?php echo $userObject->email ?>"
  }

  function passUserObjectToParentDocument(userObject) {
    parent.userLoggedIn(userObject);
  }
  </script>
  <button onclick="passUserObjectToParentDocument(userObject)">continue</button>
</body>
</html>

 

Example project here:  Sign-in with Google using Google Java Script library

Longest Common Substring

Task

Given two strings text1 and text2, return the length of their longest common subsequenceIf there is no common subsequence, return 0.

subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters.

  • For example, "ace" is a subsequence of "abcde".

common subsequence of two strings is a subsequence that is common to both strings.

 

Example 1:

Input:

 text1 = "abcde", text2 = "ace" 

Output:

 3  

Explanation:

 The longest common subsequence is "ace" and its length is 3.

Example 2:

Input:

 text1 = "abc", text2 = "abc"

Output:

 3

Explanation:

 The longest common subsequence is "abc" and its length is 3.

Example 3:

Input:

 text1 = "abc", text2 = "def"

Output:

 0

Explanation:

 There is no such common subsequence, so the result is 0.

 

Constraints:

  • 1 <= text1.length, text2.length <= 1000
  • text1 and text2 consist of only lowercase English characters.

This problem was taken from Leetcode Longest Common Subsequence

 

Solution

Dynamic programming with memoization.

We create a matrix to store (memoize) the response from previous calculations so we won’t re-calculate them again.

We are starting from the first row comparing every character from column 1 with the first character from row one.

There are two cases:

  • either the character match, then we add 1 and add it with the value from the diagonal to the left of the cell where we are.

Longest Common Substring Step 1

  • the characters don’t match, then we get the MAX of the value above current cell  and the value to the left of the current cell.

Longest Common Substring Step 2

Here again c int the column (first string) matches c in the row (the second string)

so we get the value of last comparison (to the left and up diagonal of the current cell)  which is 1 and add 1 again since characters match.

Longest Common Substring 3

and keep going till we reach the end of both strings which is the answer.

 

Longest Common Substring 4

 

/**
 * @param {string} text1
 * @param {string} text2
 * @return {number}
 */
var longestCommonSubsequence = function(text1, text2) {
    var txt1 = text1.split('');
    var txt2 = text2.split('');

    txt1.unshift('0');
    txt2.unshift('1');

    var l1 = txt1.length;
    var l2 = txt2.length;

    var matrix = [];
    for(var i = 0; i < l2; i ++) {
        matrix[i] = new Array(l1).fill(0);
    }

    var maxCommon = 0;
    
    for(var row = 0; row < l2; row ++) {
        for(var col = 0; col < l1; col ++) {
            var last = 0;

            if(txt1[col] == txt2[row]) {
                var previousDiagonalRowVal = row == 0 || col == 0  ? 0 : matrix[row - 1][col - 1];
                last =  1 + previousDiagonalRowVal;
            }
            else {
                var prevUp = row == 0 ?  0 : matrix[row - 1][col];
                var prevLeft = col == 0 ? 0 : matrix[row][col - 1];               
                last = Math.max(prevUp, prevLeft);
            }
            matrix[row][col] = last;
            maxCommon = last > maxCommon ? last : maxCommon;
    
        }
    }    
    return maxCommon;
};

var text1 = "abcde", text2 = "ace";
var r = longestCommonSubsequence(text1, text2);
console.log(">>", r);

Copy List with Random Pointer

Task

 

A linked list of length n is given such that each node contains an additional random pointer, which could point to any node in the list, or null.

Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes, where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list.

For example, if there are two nodes X and Y in the original list, where X.random --> Y, then for the corresponding two nodes x and y in the copied list, x.random --> y.

Return the head of the copied linked list.

The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val, random_index] where:

  • val: an integer representing Node.val
  • random_index: the index of the node (range from 0 to n-1) that the random pointer points to, or null if it does not point to any node.

Your code will only be given the head of the original linked list.

 

Example 1:

Input:

 head = [[7,null],[13,0],[11,4],[10,2],[1,0]]

Output:

 [[7,null],[13,0],[11,4],[10,2],[1,0]]

Example 2:

Input:

 head = [[1,1],[2,1]]

Output:

 [[1,1],[2,1]]

Example 3:

Input:

 head = [[3,null],[3,0],[3,null]]

Output:

 [[3,null],[3,0],[3,null]]

 

Constraints:

  • 0 <= n <= 1000
  • -104 <= Node.val <= 104
  • Node.random is null or is pointing to some node in the linked list.

This problem was taken from https://leetcode.com/problems/copy-list-with-random-pointer/

Solution

 

Brute force using tree traversal

 

/**
 * // Definition for a Node.
 * function Node(val, next, random) {
 *    this.val = val;
 *    this.next = next;
 *    this.random = random;
 * };
 */

/**
 * @param {Node} head
 * @return {Node}
 */
var copyRandomList = function(head) {


    function dfsTraverse(node, visited={}) {
        if(!node) {
            return null;
        }
        
        // if a new node is created, return it. Otherwise you will fall into circular loops
        if(node?.clone) {
            return node?.clone;    
        }
        
        var newNode = new Node(node?.val, null, null);
        node.clone = newNode;
        var next = dfsTraverse(node?.next);
        var random = dfsTraverse(node?.random);

        newNode.next = next;
        newNode.random = random;
        return newNode;
    }

    var result = dfsTraverse(head);
    return result;
};

function Node(val, next, random) {
    this.val = val;
    this.next = next;
    this.random = random;
}
;// [1,null],[2,0],[3,1]

var nodes = {};
nodes['1'] = new Node(1,null,null);
nodes['2'] = new Node(2,null,null);
nodes['3'] = new Node(3,null,null);

nodes['1'].next = nodes['2'];
nodes['1'].random = null;

nodes['2'].next = nodes['3'];
nodes['2'].random = nodes['1'];

nodes['3'].next = null;
nodes['3'].random = nodes['2'];

//console.log("root");
//console.log(nodes['7']);
var result = copyRandomList(nodes['1']);
console.log(result);

 

 

More elegant solution

 

/**
 * // Definition for a Node.
 * function Node(val, next, random) {
 *    this.val = val;
 *    this.next = next;
 *    this.random = random;
 * };
 */

/**
 * @param {Node} head
 * @return {Node}
 */
var copyRandomList = function(head) {
  let cur = head;
  const copy = new Map();

  // add all new nodes and values for now
  while (cur) {
    copy.set(cur, new Node(cur.val));
    cur = cur.next;
  }
  
  cur = head;

  // iterate again and point curent node to the newly created nodes using the key 
  while (cur) {
    copy.get(cur).next = copy.get(cur.next) || null;
    copy.get(cur).random = copy.get(cur.random) || null;
    cur = cur.next;
  }
  
  return copy.get(head);
}


function Node(val, next, random) {
    this.val = val;
    this.next = next;
    this.random = random;
};


// [1,null],[2,0],[3,1]

var nodes = {};
nodes['1'] = new Node(1,null,null);
nodes['2'] = new Node(2,null,null);
nodes['3'] = new Node(3,null,null);

nodes['1'].next = nodes['2'];
nodes['1'].random = null;

nodes['2'].next = nodes['3'];
nodes['2'].random = nodes['1'];

nodes['3'].next = null;
nodes['3'].random = nodes['2'];


var result = copyRandomList(nodes['1']);
console.log(result);