=encoding utf8

=head1 NAME

Mojolicious::Guides::Growing - Growing Mojolicious applications

=head1 OVERVIEW

This document explains the process of starting a L<Mojolicious::Lite> prototype from scratch and growing it into a
well-structured L<Mojolicious> application. The final result of this guide is also available as an
L<example application|https://github.com/mojolicious/mojo/tree/main/examples/login>.

=head1 CONCEPTS

Essentials every L<Mojolicious> developer should know.

=head2 Model View Controller

MVC is a software architectural pattern for graphical user interface programming originating in Smalltalk-80, that
separates application logic, presentation and input.

           +------------+    +-------+    +------+
  Input -> | Controller | -> | Model | -> | View | -> Output
           +------------+    +-------+    +------+

A slightly modified version of the pattern moving some application logic into the I<controller> is the foundation of
pretty much every web framework these days, including L<Mojolicious>.

              +----------------+     +-------+
  Request  -> |                | <-> | Model |
              |                |     +-------+
              |   Controller   |
              |                |     +-------+
  Response <- |                | <-> | View  |
              +----------------+     +-------+

The I<controller> receives a request from a user, passes incoming data to the I<model> and retrieves data from it,
which then gets turned into an actual response by the I<view>. But note that this pattern is just a guideline that most
of the time results in cleaner more maintainable code, not a rule that should be followed at all costs.

=head2 REpresentational State Transfer

REST is a software architectural style for distributed hypermedia systems such as the web. While it can be applied to
many protocols it is most commonly used with HTTP these days. In REST terms, when you are opening a URL like
C<http://mojolicious.org/foo> with your browser, you are basically asking the web server for the HTML I<representation>
of the C<http://mojolicious.org/foo> I<resource>.

  +--------+                                  +--------+
  |        | -> http://mojolicious.org/foo -> |        |
  | Client |                                  | Server |
  |        | <-  <html>Mojo rocks!</html>  <- |        |
  +--------+                                  +--------+

The fundamental idea here is that all resources are uniquely addressable with URLs and every resource can have
different representations such as HTML, RSS or JSON. User interface concerns are separated from data storage concerns
and all session state is kept client-side.

  +---------+                        +------------+
  |         | ->    PUT /foo      -> |            |
  |         | ->    Hello World!  -> |            |
  |         |                        |            |
  |         | <-    201 CREATED   <- |            |
  |         |                        |            |
  |         | ->    GET /foo      -> |            |
  | Browser |                        | Web Server |
  |         | <-    200 OK        <- |            |
  |         | <-    Hello World!  <- |            |
  |         |                        |            |
  |         | ->    DELETE /foo   -> |            |
  |         |                        |            |
  |         | <-    200 OK        <- |            |
  +---------+                        +------------+

While HTTP methods such as C<PUT>, C<GET> and C<DELETE> are not directly part of REST they go well with it and are
commonly used to manipulate I<resources>.

=head2 Sessions

HTTP was designed as a stateless protocol, web servers don't know anything about previous requests, which makes
user-friendly login systems tricky. Sessions solve this problem by allowing web applications to keep stateful
information across several HTTP requests.

  GET /login?user=sebastian&pass=s3cret HTTP/1.1
  Host: mojolicious.org

  HTTP/1.1 200 OK
  Set-Cookie: sessionid=987654321
  Content-Length: 10
  Hello sebastian.

  GET /protected HTTP/1.1
  Host: mojolicious.org
  Cookie: sessionid=987654321

  HTTP/1.1 200 OK
  Set-Cookie: sessionid=987654321
  Content-Length: 16
  Hello again sebastian.

Traditionally all session data was stored on the server-side and only session IDs were exchanged between browser and
web server in the form of cookies.

  Set-Cookie: session=hmac-sha256(base64(json($session)))

In L<Mojolicious> however we are taking this concept one step further by storing everything JSON serialized and Base64
encoded in HMAC-SHA256 signed cookies, which is more compatible with the REST philosophy and reduces infrastructure
requirements.

=head2 Test-Driven Development

TDD is a software development process where the developer starts writing failing test cases that define the desired
functionality and then moves on to producing code that passes these tests. There are many advantages such as always
having good test coverage and code being designed for testability, which will in turn often prevent future changes from
breaking old code. Much of L<Mojolicious> was developed using TDD.

=head1 PROTOTYPE

One of the main differences between L<Mojolicious> and other web frameworks is that it also includes
L<Mojolicious::Lite>, a micro web framework optimized for rapid prototyping.

=head2 Differences

You likely know the feeling, you've got a really cool idea and want to try it as quickly as possible, that's exactly
why L<Mojolicious::Lite> applications don't need more than a single file.

  myapp.pl   # Templates and even static files can be inlined

Full L<Mojolicious> applications on the other hand are much closer to a well organized CPAN distribution to maximize
maintainability.

  myapp                      # Application directory
  |- script                  # Script directory
  |  +- my_app               # Application script
  |- lib                     # Library directory
  |  |- MyApp.pm             # Application class
  |  +- MyApp                # Application namespace
  |     +- Controller        # Controller namespace
  |        +- Example.pm     # Controller class
  |- my_app.yml              # Configuration file
  |- t                       # Test directory
  |  +- basic.t              # Random test
  |- log                     # Log directory
  |  +- development.log      # Development mode log file
  |- public                  # Static file directory (served automatically)
  |  +- index.html           # Static HTML file
  +- templates               # Template directory
     |- layouts              # Template directory for layouts
     |  +- default.html.ep   # Layout template
     +- example              # Template directory for "Example" controller
        +- welcome.html.ep   # Template for "welcome" action

Both application skeletons can be automatically generated with the commands
L<Mojolicious::Command::Author::generate::lite_app> and L<Mojolicious::Command::Author::generate::app>.

  $ mojo generate lite-app myapp.pl
  $ mojo generate app MyApp

Feature-wise both are almost equal, the only real differences are organizational, so each one can be gradually
transformed into the other.

=head2 Foundation

We start our new application with a single executable Perl script.

  $ mkdir myapp
  $ cd myapp
  $ touch myapp.pl
  $ chmod 744 myapp.pl

This will be the foundation for our login manager example application.

  #!/usr/bin/env perl
  use Mojolicious::Lite -signatures;

  get '/' => sub ($c) {
    $c->render(text => 'Hello World!');
  };

  app->start;

The built-in development web server makes working on your application a lot of fun thanks to automatic reloading.

  $ morbo ./myapp.pl
  Web application available at http://127.0.0.1:3000

Just save your changes and they will be automatically in effect the next time you refresh your browser.

=head2 A bird's-eye view

It all starts with an HTTP request like this, sent by your browser.

  GET / HTTP/1.1
  Host: localhost:3000

Once the request has been received by the web server through the event loop, it will be passed on to L<Mojolicious>,
where it will be handled in a few simple steps.

=over 2

=item  1.

Check if a static file exists that would meet the requirements.

=item 2.

Try to find a route that would meet the requirements.

=item 3.

Dispatch the request to this route, usually reaching one or more actions.

=item 4.

Process the request, maybe generating a response with the renderer.

=item 5.

Return control to the web server, and if no response has been generated yet, wait for a non-blocking operation to do so
through the event loop.

=back

With our application the router would have found an action in step 2, and rendered some text in step 4, resulting in an
HTTP response like this being sent back to the browser.

  HTTP/1.1 200 OK
  Content-Length: 12
  Hello World!

=head2 Model

In L<Mojolicious> we consider web applications simple frontends for existing business logic. That means L<Mojolicious>
is by design entirely I<model> layer agnostic, and you just use whatever Perl modules you like most.

  $ mkdir -p lib/MyApp/Model
  $ touch lib/MyApp/Model/Users.pm
  $ chmod 644 lib/MyApp/Model/Users.pm

Our login manager will use a plain old Perl module abstracting away all logic related to matching usernames and
passwords. The name C<MyApp::Model::Users> is an arbitrary choice, and is simply used to make the separation of
concerns more visible.

  package MyApp::Model::Users;

  use strict;
  use warnings;
  use experimental qw(signatures);

  use Mojo::Util qw(secure_compare);

  my $USERS = {
    joel      => 'las3rs',
    marcus    => 'lulz',
    sebastian => 'secr3t'
  };

  sub new ($class) { bless {}, $class }

  sub check ($self, $user, $pass) {

    # Success
    return 1 if $USERS->{$user} && secure_compare $USERS->{$user}, $pass;

    # Fail
    return undef;
  }

  1;

A simple helper can be registered with the function L<Mojolicious::Lite/"helper"> to make our model available to all
actions and templates.

  #!/usr/bin/env perl
  use Mojolicious::Lite -signatures;

  use lib qw(lib);
  use MyApp::Model::Users;

  # Helper to lazy initialize and store our model object
  helper users => sub { state $users = MyApp::Model::Users->new };

  # /?user=sebastian&pass=secr3t
  any '/' => sub ($c) {

    # Query parameters
    my $user = $c->param('user') || '';
    my $pass = $c->param('pass') || '';

    # Check password
    return $c->render(text => "Welcome $user.") if $c->users->check($user, $pass);

    # Failed
    $c->render(text => 'Wrong username or password.');
  };

  app->start;

The method L<Mojolicious::Controller/"param"> is used to access query parameters, C<POST> parameters, file uploads and
route placeholders, all at once.

=head2 Testing

In L<Mojolicious> we take testing very seriously and try to make it a pleasant experience.

  $ mkdir t
  $ touch t/login.t
  $ chmod 644 t/login.t

L<Test::Mojo> is a scriptable HTTP user agent designed specifically for testing, with many fun state-of-the-art
features such as CSS selectors based on L<Mojo::DOM>.

  use Test::More;
  use Test::Mojo;

  # Include application
  use Mojo::File qw(curfile);
  require(curfile->dirname->sibling('myapp.pl'));

  # Allow 302 redirect responses
  my $t = Test::Mojo->new;
  $t->ua->max_redirects(1);

  # Test if the HTML login form exists
  $t->get_ok('/')
    ->status_is(200)
    ->element_exists('form input[name="user"]')
    ->element_exists('form input[name="pass"]')
    ->element_exists('form input[type="submit"]');

  # Test login with valid credentials
  $t->post_ok('/' => form => {user => 'sebastian', pass => 'secr3t'})
    ->status_is(200)
    ->text_like('html body' => qr/Welcome sebastian/);

  # Test accessing a protected page
  $t->get_ok('/protected')->status_is(200)->text_like('a' => qr/Logout/);

  # Test if HTML login form shows up again after logout
  $t->get_ok('/logout')
    ->status_is(200)
    ->element_exists('form input[name="user"]')
    ->element_exists('form input[name="pass"]')
    ->element_exists('form input[type="submit"]');

  done_testing();

Your application won't pass these tests, but from now on you can use them to check your progress.

  $ prove -l
  $ prove -l t/login.t
  $ prove -l -v t/login.t

Or perform quick requests right from the command line with L<Mojolicious::Command::get>.

  $ ./myapp.pl get /
  Wrong username or password.

  $ ./myapp.pl get -v '/?user=sebastian&pass=secr3t'
  GET /?user=sebastian&pass=secr3t HTTP/1.1
  User-Agent: Mojolicious (Perl)
  Accept-Encoding: gzip
  Content-Length: 0
  Host: localhost:59472

  HTTP/1.1 200 OK
  Date: Sun, 18 Jul 2010 13:09:58 GMT
  Server: Mojolicious (Perl)
  Content-Length: 12
  Content-Type: text/plain

  Welcome sebastian.

=head2 State keeping

Sessions in L<Mojolicious> pretty much just work out of the box once you start using the method
L<Mojolicious::Controller/"session">, there is no setup required, but we suggest setting a more secure passphrase with
L<Mojolicious/"secrets">.

  $app->secrets(['Mojolicious rocks']);

This passphrase is used by the HMAC-SHA256 algorithm to make signed cookies tamper resistant and can be changed at any
time to invalidate all existing sessions.

  $c->session(user => 'sebastian');
  my $user = $c->session('user');

By default all sessions expire after one hour, for more control you can use the C<expiration> session value to set an
expiration date in seconds from now.

  $c->session(expiration => 3600);

And the whole session can be deleted by using the C<expires> session value to set an absolute expiration date in the
past.

  $c->session(expires => 1);

For data that should only be visible on the next request, like a confirmation message after a C<302> redirect performed
with L<Mojolicious::Plugin::DefaultHelpers/"redirect_to">, you can use the flash, accessible through
L<Mojolicious::Plugin::DefaultHelpers/"flash">.

  $c->flash(message => 'Everything is fine.');
  $c->redirect_to('goodbye');

Just remember that all session data gets serialized with L<Mojo::JSON> and stored in HMAC-SHA256 signed cookies, which
usually have a C<4096> byte (4KiB) limit, depending on browser.

=head2 Final prototype

A final C<myapp.pl> prototype passing all of the tests above could look like this.

  #!/usr/bin/env perl
  use Mojolicious::Lite -signatures;

  use lib qw(lib);
  use MyApp::Model::Users;

  # Make signed cookies tamper resistant
  app->secrets(['Mojolicious rocks']);

  helper users => sub { state $users = MyApp::Model::Users->new };

  # Main login action
  any '/' => sub ($c) {

    # Query or POST parameters
    my $user = $c->param('user') || '';
    my $pass = $c->param('pass') || '';

    # Check password and render "index.html.ep" if necessary
    return $c->render unless $c->users->check($user, $pass);

    # Store username in session
    $c->session(user => $user);

    # Store a friendly message for the next page in flash
    $c->flash(message => 'Thanks for logging in.');

    # Redirect to protected page with a 302 response
    $c->redirect_to('protected');
  } => 'index';

  # Make sure user is logged in for actions in this group
  group {
    under sub ($c) {

      # Redirect to main page with a 302 response if user is not logged in
      return 1 if $c->session('user');
      $c->redirect_to('index');
      return undef;
    };

    # A protected page auto rendering "protected.html.ep"
    get '/protected';
  };

  # Logout action
  get '/logout' => sub ($c) {

    # Expire and in turn clear session automatically
    $c->session(expires => 1);

    # Redirect to main page with a 302 response
    $c->redirect_to('index');
  };

  app->start;
  __DATA__

  @@ index.html.ep
  % layout 'default';
  %= form_for index => begin
    % if (param 'user') {
      <b>Wrong name or password, please try again.</b><br>
    % }
    Name:<br>
    %= text_field 'user'
    <br>Password:<br>
    %= password_field 'pass'
    <br>
    %= submit_button 'Login'
  % end

  @@ protected.html.ep
  % layout 'default';
  % if (my $msg = flash 'message') {
    <b><%= $msg %></b><br>
  % }
  Welcome <%= session 'user' %>.<br>
  %= link_to Logout => 'logout'

  @@ layouts/default.html.ep
  <!DOCTYPE html>
  <html>
    <head><title>Login Manager</title></head>
    <body><%= content %></body>
  </html>

And the directory structure should be looking like this now.

  myapp
  |- myapp.pl
  |- lib
  |  +- MyApp
  |     +- Model
  |        +- Users.pm
  +- t
     +- login.t

Our templates are using quite a few features of the renderer, L<Mojolicious::Guides::Rendering> explains them all in
great detail.

=head1 WELL-STRUCTURED APPLICATION

Due to the flexibility of L<Mojolicious> there are many variations of the actual growing process, but this should give
you a good overview of the possibilities.

=head2 Inflating templates

All templates and static files inlined in the C<DATA> section can be automatically turned into separate files in the
C<templates> and C<public> directories with the command L<Mojolicious::Command::Author::inflate>.

  $ ./myapp.pl inflate

Those directories have a higher precedence, so inflating can also be a great way to allow your users to customize their
applications.

=head2 Simplified application class

This is the heart of every full L<Mojolicious> application and always gets instantiated during server startup.

  $ touch lib/MyApp.pm
  $ chmod 644 lib/MyApp.pm

We will start by extracting all actions from C<myapp.pl> and turn them into simplified hybrid routes in the
L<Mojolicious::Routes> router, none of the actual action code needs to be changed.

  package MyApp;
  use Mojo::Base 'Mojolicious', -signatures;

  use MyApp::Model::Users;

  sub startup ($self) {

    $self->secrets(['Mojolicious rocks']);
    $self->helper(users => sub { state $users = MyApp::Model::Users->new });

    my $r = $self->routes;

    $r->any('/' => sub ($c) {

      my $user = $c->param('user') || '';
      my $pass = $c->param('pass') || '';
      return $c->render unless $c->users->check($user, $pass);

      $c->session(user => $user);
      $c->flash(message => 'Thanks for logging in.');
      $c->redirect_to('protected');
    } => 'index');

    my $logged_in = $r->under(sub ($c) {
      return 1 if $c->session('user');
      $c->redirect_to('index');
      return undef;
    });
    $logged_in->get('/protected');

    $r->get('/logout' => sub ($c) {
      $c->session(expires => 1);
      $c->redirect_to('index');
    });
  }

  1;

The C<startup> method gets called right after instantiation and is the place where the whole application gets set up.
Since full L<Mojolicious> applications can use nested routes they have no need for C<group> blocks.

=head2 Simplified application script

C<myapp.pl> itself can now be turned into a simplified application script to allow running tests again.

  #!/usr/bin/env perl

  use Mojo::Base -strict;
  use lib qw(lib);
  use Mojolicious::Commands;

  # Start command line interface for application
  Mojolicious::Commands->start_app('MyApp');

And the directory structure of our hybrid application should be looking like this.

  myapp
  |- myapp.pl
  |- lib
  |  |- MyApp.pm
  |  +- MyApp
  |     +- Model
  |        +- Users.pm
  |- t
  |  +- login.t
  +- templates
     |- layouts
     |  +- default.html.ep
     |- index.html.ep
     +- protected.html.ep

=head2 Controller class

Hybrid routes are a nice intermediate step, but to maximize maintainability it makes sense to split our action code
from its routing information.

  $ mkdir lib/MyApp/Controller
  $ touch lib/MyApp/Controller/Login.pm
  $ chmod 644 lib/MyApp/Controller/Login.pm

Once again the actual action code does not need to change, we just rename C<$c> to C<$self> since the controller is now
the invocant.

  package MyApp::Controller::Login;
  use Mojo::Base 'Mojolicious::Controller', -signatures;

  sub index ($self) {
    my $user = $self->param('user') || '';
    my $pass = $self->param('pass') || '';
    return $self->render unless $self->users->check($user, $pass);

    $self->session(user => $user);
    $self->flash(message => 'Thanks for logging in.');
    $self->redirect_to('protected');
  }

  sub logged_in ($self) {
    return 1 if $self->session('user');
    $self->redirect_to('index');
    return undef;
  }

  sub logout ($self) {
    $self->session(expires => 1);
    $self->redirect_to('index');
  }

  1;

All L<Mojolicious::Controller> controllers are plain old Perl classes and get instantiated on demand.

=head2 Application class

The application class C<lib/MyApp.pm> can now be reduced to model and routing information.

  package MyApp;
  use Mojo::Base 'Mojolicious', -signatures;

  use MyApp::Model::Users;

  sub startup ($self) {

    $self->secrets(['Mojolicious rocks']);
    $self->helper(users => sub { state $users = MyApp::Model::Users->new });

    my $r = $self->routes;
    $r->any('/')->to('login#index')->name('index');

    my $logged_in = $r->under('/')->to('login#logged_in');
    $logged_in->get('/protected')->to('login#protected');

    $r->get('/logout')->to('login#logout');
  }

  1;

The router allows many different route variations, L<Mojolicious::Guides::Routing> explains them all in great detail.

=head2 Templates

Templates are our views, and usually bound to controllers, so they need to be moved into the appropriate directories.

  $ mkdir templates/login
  $ mv templates/index.html.ep templates/login/index.html.ep
  $ mv templates/protected.html.ep templates/login/protected.html.ep

=head2 Script

Finally C<myapp.pl> can be moved into a C<script> directory and renamed to C<my_app> to follow the CPAN standard.

  $ mkdir script
  $ mv myapp.pl script/my_app

Just a few small details change, instead of a relative path to L<lib> we now use L<Mojo::File> to get an absolute path,
allowing us to start the application from outside its home directory.

  #!/usr/bin/env perl

  use strict;
  use warnings;

  use Mojo::File qw(curfile);
  use lib curfile->dirname->sibling('lib')->to_string;
  use Mojolicious::Commands;

  # Start command line interface for application
  Mojolicious::Commands->start_app('MyApp');

=head2 Simplified tests

Full L<Mojolicious> applications are a little easier to test, so C<t/login.t> can be simplified.

  use Mojo::Base -strict;

  use Test::More;
  use Test::Mojo;

  my $t = Test::Mojo->new('MyApp');
  $t->ua->max_redirects(1);

  subtest 'Test login workflow' => sub {
    $t->get_ok('/')
      ->status_is(200)
      ->element_exists('form input[name="user"]')
      ->element_exists('form input[name="pass"]')
      ->element_exists('form input[type="submit"]');

    $t->post_ok('/' => form => {user => 'sebastian', pass => 'secr3t'})
      ->status_is(200)
      ->text_like('html body' => qr/Welcome sebastian/);

    $t->get_ok('/protected')->status_is(200)->text_like('a' => qr/Logout/);

    $t->get_ok('/logout')
      ->status_is(200)
      ->element_exists('form input[name="user"]')
      ->element_exists('form input[name="pass"]')
      ->element_exists('form input[type="submit"]');
  };

  done_testing();

And our final directory structure should be looking like this.

  myapp
  |- script
  |  +- my_app
  |- lib
  |  |- MyApp.pm
  |  +- MyApp
  |     |- Controller
  |     |  +- Login.pm
  |     +- Model
  |        +- Users.pm
  |- t
  |  +- login.t
  +- templates
     |- layouts
     |  +- default.html.ep
     +- login
        |- index.html.ep
        +- protected.html.ep

Test-driven development takes a little getting used to, but can be a very powerful tool.

=head1 MORE

You can continue with L<Mojolicious::Guides> now or take a look at the L<Mojolicious
wiki|https://github.com/mojolicious/mojo/wiki>, which contains a lot more documentation and examples by many different
authors.

=head1 SUPPORT

If you have any questions the documentation might not yet answer, don't hesitate to ask in the
L<Forum|https://forum.mojolicious.org>, on L<Matrix|https://matrix.to/#/#mojo:matrix.org>, or
L<IRC|https://web.libera.chat/#mojo>.

=cut