From defe686f2af18ed741bf1a9a5fa89beb541551c9 Mon Sep 17 00:00:00 2001
From: Carlos Buenosvinos <carlos.buenosvinos@gmail.com>
Date: Tue, 22 Mar 2022 06:58:03 +0100
Subject: [PATCH] [Chapter 8] Improvements

---
 .../NotifyToAuthorAboutNewFollowerCommand.php | 43 +++++++++++++++++
 ...ToAuthorAboutNewFollowerCommandHandler.php | 36 ++++++++++++++
 .../Author/Command/WelcomeCommand.php         | 29 +++++++++++
 .../Author/Command/WelcomeCommandHandler.php  | 35 ++++++++++++++
 ...crementFollowersProjectionEventHandler.php | 28 +++++++++++
 ...orFollowedThenNotifyAuthorEventHandler.php | 29 +++++++++++
 .../Event/AuthorFollowedEventHandler.php      | 15 +++++-
 ...FollowersCounterProjectionEventHandler.php | 26 ++++++++++
 ...horSignedThenWelcomeAuthorEventHandler.php | 26 ++++++++++
 .../Event/NewAuthorSignedEventHandler.php     |  9 ++++
 .../IncrementCountFollowersProjection.php     | 31 ++++++++++++
 ...rementCountFollowersProjectionHandler.php} | 10 ++--
 .../DomainModel/Notifier/Notifier.php         | 12 +++++
 .../Event/AuthorFollowedEventHandler.php      | 48 +++++++++++++++++++
 14 files changed, 369 insertions(+), 8 deletions(-)
 create mode 100644 src/Cheeper/Chapter7/Application/Author/Command/NotifyToAuthorAboutNewFollowerCommand.php
 create mode 100644 src/Cheeper/Chapter7/Application/Author/Command/NotifyToAuthorAboutNewFollowerCommandHandler.php
 create mode 100644 src/Cheeper/Chapter7/Application/Author/Command/WelcomeCommand.php
 create mode 100644 src/Cheeper/Chapter7/Application/Author/Command/WelcomeCommandHandler.php
 create mode 100644 src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowed/WhenAuthorFollowedThenIncrementFollowersProjectionEventHandler.php
 create mode 100644 src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowed/WhenAuthorFollowedThenNotifyAuthorEventHandler.php
 create mode 100644 src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSigned/WhenNewAuthorSignedThenCreateEmptyFollowersCounterProjectionEventHandler.php
 create mode 100644 src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSigned/WhenNewAuthorSignedThenWelcomeAuthorEventHandler.php
 create mode 100644 src/Cheeper/Chapter7/Application/Author/Projection/IncrementCountFollowersProjection.php
 rename src/Cheeper/{Chapter8/Application/Author/Projection/CountFollowersProjectionHandler.php => Chapter7/Application/Author/Projection/IncrementCountFollowersProjectionHandler.php} (50%)
 create mode 100644 src/Cheeper/Chapter7/DomainModel/Notifier/Notifier.php
 create mode 100644 src/Cheeper/Chapter8/Application/Author/Event/AuthorFollowedEventHandler.php

diff --git a/src/Cheeper/Chapter7/Application/Author/Command/NotifyToAuthorAboutNewFollowerCommand.php b/src/Cheeper/Chapter7/Application/Author/Command/NotifyToAuthorAboutNewFollowerCommand.php
new file mode 100644
index 0000000..00c26e1
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Author/Command/NotifyToAuthorAboutNewFollowerCommand.php
@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Author\Command;
+
+use Cheeper\Chapter7\Application\Command;
+use Cheeper\Chapter7\Application\MessageTrait;
+
+final class NotifyToAuthorAboutNewFollowerCommand implements Command
+{
+    use MessageTrait;
+
+    private function __construct(
+        private string $fromAuthorId,
+        private string $toAuthorId
+    ) {
+        $this->stampAsNewMessage();
+    }
+
+    public function fromAuthorId(): string
+    {
+        return $this->fromAuthorId;
+    }
+
+    public function toAuthorId(): string
+    {
+        return $this->toAuthorId;
+    }
+
+    public function followId(): string
+    {
+        return $this->followId;
+    }
+
+    public static function fromArray(array $array): self
+    {
+        return new self(
+            $array['from_author_id'] ?? '',
+            $array['to_author_id'] ?? '',
+        );
+    }
+}
diff --git a/src/Cheeper/Chapter7/Application/Author/Command/NotifyToAuthorAboutNewFollowerCommandHandler.php b/src/Cheeper/Chapter7/Application/Author/Command/NotifyToAuthorAboutNewFollowerCommandHandler.php
new file mode 100644
index 0000000..6cd5102
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Author/Command/NotifyToAuthorAboutNewFollowerCommandHandler.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Author\Command;
+
+use Cheeper\AllChapters\DomainModel\Author\AuthorDoesNotExist;
+use Cheeper\AllChapters\DomainModel\Author\AuthorId;
+use Cheeper\Chapter7\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Author\AuthorRepository;
+use Cheeper\Chapter7\DomainModel\Notifier\Notifier;
+
+final class NotifyToAuthorAboutNewFollowerCommandHandler
+{
+    public function __construct(
+        private AuthorRepository $authors,
+        private Notifier         $notifier
+    ) {
+    }
+
+    public function __invoke(NotifyToAuthorAboutNewFollowerCommand $command): void
+    {
+        $authorId = AuthorId::fromString($command->toAuthorId());
+        $author = $this->authors->ofId($authorId);
+        $this->checkAuthorExist($author, $authorId);
+
+        $this->notifier->notify($author);
+    }
+
+    private function checkAuthorExist(?Author $author, AuthorId $authorId): void
+    {
+        if (null === $author) {
+            throw AuthorDoesNotExist::withAuthorIdOf($authorId);
+        }
+    }
+}
diff --git a/src/Cheeper/Chapter7/Application/Author/Command/WelcomeCommand.php b/src/Cheeper/Chapter7/Application/Author/Command/WelcomeCommand.php
new file mode 100644
index 0000000..d7039d8
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Author/Command/WelcomeCommand.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Author\Command;
+
+use Cheeper\Chapter7\Application\Command;
+use Cheeper\Chapter7\Application\MessageTrait;
+
+final class WelcomeCommand implements Command
+{
+    use MessageTrait;
+
+    private function __construct(
+        private string $authorId,
+    ) {
+        $this->stampAsNewMessage();
+    }
+
+    public static function ofAuthorId(string $authorId): self
+    {
+        return new self($authorId);
+    }
+
+    public function authorId(): string
+    {
+        return $this->authorId;
+    }
+}
diff --git a/src/Cheeper/Chapter7/Application/Author/Command/WelcomeCommandHandler.php b/src/Cheeper/Chapter7/Application/Author/Command/WelcomeCommandHandler.php
new file mode 100644
index 0000000..065a77e
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Author/Command/WelcomeCommandHandler.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Author\Command;
+
+use Cheeper\AllChapters\DomainModel\Author\AuthorDoesNotExist;
+use Cheeper\AllChapters\DomainModel\Author\AuthorId;
+use Cheeper\Chapter7\DomainModel\Author\Author;
+use Cheeper\Chapter7\DomainModel\Author\AuthorRepository;
+use Cheeper\Chapter7\DomainModel\Notifier\Notifier;
+
+final class WelcomeCommandHandler
+{
+    public function __construct(
+        private AuthorRepository $authors,
+        private Notifier         $notifier
+    ) {
+    }
+
+    public function __invoke(WelcomeCommand $command): void
+    {
+        $authorId = AuthorId::fromString($command->authorId());
+        $author = $this->authors->ofId($authorId);
+        $this->checkAuthorExist($author, $authorId);
+        $this->notifier->notify($author);
+    }
+
+    private function checkAuthorExist(?Author $author, AuthorId $authorId): void
+    {
+        if (null === $author) {
+            throw AuthorDoesNotExist::withAuthorIdOf($authorId);
+        }
+    }
+}
diff --git a/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowed/WhenAuthorFollowedThenIncrementFollowersProjectionEventHandler.php b/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowed/WhenAuthorFollowedThenIncrementFollowersProjectionEventHandler.php
new file mode 100644
index 0000000..bdb774c
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowed/WhenAuthorFollowedThenIncrementFollowersProjectionEventHandler.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Author\Event\AuthorFollowed;
+
+use Cheeper\Chapter7\Application\Author\Projection\IncrementCountFollowersProjection;
+use Cheeper\Chapter7\Application\ProjectionBus;
+use Cheeper\Chapter7\DomainModel\Follow\AuthorFollowed;
+
+//snippet snippet
+final class WhenAuthorFollowedThenIncrementFollowersProjectionEventHandler
+{
+    public function __construct(
+        private ProjectionBus $projectionBus
+    ) {
+    }
+
+    public function __invoke(AuthorFollowed $event): void
+    {
+        $this->projectionBus->project(
+            IncrementCountFollowersProjection::ofAuthor(
+                $event->toAuthorId()
+            )
+        );
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowed/WhenAuthorFollowedThenNotifyAuthorEventHandler.php b/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowed/WhenAuthorFollowedThenNotifyAuthorEventHandler.php
new file mode 100644
index 0000000..1209f5a
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowed/WhenAuthorFollowedThenNotifyAuthorEventHandler.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Author\Event\AuthorFollowed;
+
+use Cheeper\Chapter7\Application\Author\Command\NotifyToAuthorAboutNewFollowerCommand;
+use Cheeper\Chapter7\Application\CommandBus;
+use Cheeper\Chapter7\DomainModel\Follow\AuthorFollowed;
+
+//snippet snippet
+final class WhenAuthorFollowedThenNotifyAuthorEventHandler
+{
+    public function __construct(
+        private CommandBus $commandBus
+    ) {
+    }
+
+    public function __invoke(AuthorFollowed $event): void
+    {
+        $this->commandBus->handle(
+            NotifyToAuthorAboutNewFollowerCommand::fromArray([
+                'from_author_id' => $event->fromAuthorId(),
+                'to_author_id' => $event->toAuthorId(),
+            ])
+        );
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowedEventHandler.php b/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowedEventHandler.php
index bbdcfc5..1621050 100644
--- a/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowedEventHandler.php
+++ b/src/Cheeper/Chapter7/Application/Author/Event/AuthorFollowedEventHandler.php
@@ -19,8 +19,19 @@ final class AuthorFollowedEventHandler
     public function __invoke(AuthorFollowed $event): void
     {
         $this->projectionHandler->__invoke(
-            CountFollowersProjection::ofAuthor($event->toAuthorId())
+            CountFollowersProjection::ofAuthor(
+                $event->toAuthorId()
+            )
         );
+
+        // Other actions, like welcoming the new author,
+        // can be added here. Alternatively, a more
+        // scalable design is to create one Event Handler
+        // for each of the needed actions to happen in
+        // reaction. All of those listening to the same
+        // AuthorFollowed Domain Event.
+        // @see: WhenAuthorFollowedThenCreateFollowersCounterProjectionEventHandler
+        // @see: WhenAuthorFollowedThenWelcomeAuthorEventHandler
     }
 }
-//end-snippet
+//end-snippet
\ No newline at end of file
diff --git a/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSigned/WhenNewAuthorSignedThenCreateEmptyFollowersCounterProjectionEventHandler.php b/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSigned/WhenNewAuthorSignedThenCreateEmptyFollowersCounterProjectionEventHandler.php
new file mode 100644
index 0000000..d8ade4f
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSigned/WhenNewAuthorSignedThenCreateEmptyFollowersCounterProjectionEventHandler.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Author\Event\NewAuthorSigned;
+
+use Cheeper\Chapter7\Application\Author\Projection\CountFollowersProjection;
+use Cheeper\Chapter7\Application\Author\Projection\CountFollowersProjectionHandlerInterface;
+use Cheeper\Chapter7\DomainModel\Author\NewAuthorSigned;
+
+//snippet author-followed-event-handler
+final class WhenNewAuthorSignedThenCreateEmptyFollowersCounterProjectionEventHandler
+{
+    public function __construct(
+        private CountFollowersProjectionHandlerInterface $projectionHandler
+    ) {
+    }
+
+    public function __invoke(NewAuthorSigned $event): void
+    {
+        $this->projectionHandler->__invoke(
+            CountFollowersProjection::ofAuthor($event->authorId())
+        );
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSigned/WhenNewAuthorSignedThenWelcomeAuthorEventHandler.php b/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSigned/WhenNewAuthorSignedThenWelcomeAuthorEventHandler.php
new file mode 100644
index 0000000..8cc7813
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSigned/WhenNewAuthorSignedThenWelcomeAuthorEventHandler.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Author\Event\AuthorFollowed;
+
+use Cheeper\Chapter7\Application\Author\Command\WelcomeCommand;
+use Cheeper\Chapter7\Application\CommandBus;
+use Cheeper\Chapter7\DomainModel\Author\NewAuthorSigned;
+
+//snippet snippet
+final class WhenNewAuthorSignedThenWelcomeAuthorEventHandler
+{
+    public function __construct(
+        private CommandBus $commandBus
+    ) {
+    }
+
+    public function __invoke(NewAuthorSigned $event): void
+    {
+        $this->commandBus->handle(
+            WelcomeCommand::ofAuthorId($event->authorId())
+        );
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSignedEventHandler.php b/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSignedEventHandler.php
index 234d27e..5c83d87 100644
--- a/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSignedEventHandler.php
+++ b/src/Cheeper/Chapter7/Application/Author/Event/NewAuthorSignedEventHandler.php
@@ -24,6 +24,15 @@ final class NewAuthorSignedEventHandler
                 $event->authorUsername()
             )
         );
+
+        // Other actions, like welcoming the new author,
+        // can be added here. Alternatively, a more
+        // scalable design is to create one Event Handler
+        // for each of the needed actions to happen in
+        // reaction. All of those listening to the same
+        // NewAuthorSigned Domain Event.
+        // @see: WhenNewAuthorSignedThenCreateEmptyFollowersCounterProjectionEventHandler
+        // @see: WhenNewAuthorSignedThenWelcomeAuthorEventHandler
     }
 }
 //end-snippet
diff --git a/src/Cheeper/Chapter7/Application/Author/Projection/IncrementCountFollowersProjection.php b/src/Cheeper/Chapter7/Application/Author/Projection/IncrementCountFollowersProjection.php
new file mode 100644
index 0000000..21aa94d
--- /dev/null
+++ b/src/Cheeper/Chapter7/Application/Author/Projection/IncrementCountFollowersProjection.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Application\Author\Projection;
+
+use Cheeper\Chapter7\Application\MessageTrait;
+use Cheeper\Chapter7\Application\Projection;
+
+//snippet snippet
+final class IncrementCountFollowersProjection implements Projection
+{
+    use MessageTrait;
+
+    public static function ofAuthor(string $authorId): self
+    {
+        return new self($authorId);
+    }
+
+    private function __construct(
+        private string $authorId
+    ) {
+        $this->stampAsNewMessage();
+    }
+
+    public function authorId(): string
+    {
+        return $this->authorId;
+    }
+}
+//end-snippet
diff --git a/src/Cheeper/Chapter8/Application/Author/Projection/CountFollowersProjectionHandler.php b/src/Cheeper/Chapter7/Application/Author/Projection/IncrementCountFollowersProjectionHandler.php
similarity index 50%
rename from src/Cheeper/Chapter8/Application/Author/Projection/CountFollowersProjectionHandler.php
rename to src/Cheeper/Chapter7/Application/Author/Projection/IncrementCountFollowersProjectionHandler.php
index dfc9f57..d591557 100644
--- a/src/Cheeper/Chapter8/Application/Author/Projection/CountFollowersProjectionHandler.php
+++ b/src/Cheeper/Chapter7/Application/Author/Projection/IncrementCountFollowersProjectionHandler.php
@@ -2,21 +2,19 @@
 
 declare(strict_types=1);
 
-namespace Cheeper\Chapter8\Application\Author\Projection;
+namespace Cheeper\Chapter7\Application\Author\Projection;
 
-use Cheeper\Chapter7\Application\Author\Projection\CountFollowersProjection;
-use Cheeper\Chapter7\Application\Author\Projection\CreateFollowersCounterProjectionHandler;
 use Redis;
 
-//snippet projector-count-followers
-final class CountFollowersProjectionHandler
+//snippet snippet
+final class IncrementCountFollowersProjectionHandler
 {
     public function __construct(
         private Redis $redis
     ) {
     }
 
-    public function __invoke(CountFollowersProjection $projection): void
+    public function __invoke(IncrementCountFollowersProjection $projection): void
     {
         $this->redis->hIncrBy(
             sprintf(
diff --git a/src/Cheeper/Chapter7/DomainModel/Notifier/Notifier.php b/src/Cheeper/Chapter7/DomainModel/Notifier/Notifier.php
new file mode 100644
index 0000000..11bcab7
--- /dev/null
+++ b/src/Cheeper/Chapter7/DomainModel/Notifier/Notifier.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\DomainModel\Notifier;
+
+use Cheeper\Chapter7\DomainModel\Author\Author;
+
+interface Notifier
+{
+    public function notify(Author $author): void;
+}
diff --git a/src/Cheeper/Chapter8/Application/Author/Event/AuthorFollowedEventHandler.php b/src/Cheeper/Chapter8/Application/Author/Event/AuthorFollowedEventHandler.php
new file mode 100644
index 0000000..afa4046
--- /dev/null
+++ b/src/Cheeper/Chapter8/Application/Author/Event/AuthorFollowedEventHandler.php
@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter8\Application\Author\Event;
+
+use Cheeper\Chapter6\Application\ProjectionBus;
+use Cheeper\Chapter7\Application\Author\Command\NotifyToAuthorAboutNewFollowerCommand;
+use Cheeper\Chapter7\Application\Author\Projection\IncrementCountFollowersProjection;
+use Cheeper\Chapter7\Application\CommandBus;
+use Cheeper\Chapter7\DomainModel\Follow\AuthorFollowed;
+
+//snippet snippet
+final class AuthorFollowedEventHandler
+{
+    public function __construct(
+        private ProjectionBus $projectionBus,
+        private CommandBus $commandBus,
+    ) {
+    }
+
+    public function __invoke(AuthorFollowed $event): void
+    {
+        $this->projectionBus->project(
+            IncrementCountFollowersProjection::ofAuthor(
+                $event->toAuthorId()
+            )
+        );
+
+        // Other actions, like notifying the author
+        // about the new follower can be added here.
+        // Alternatively, a more scalable design is
+        // to create one Event Handler for each of
+        // the needed actions to happen in reaction.
+        // All of those listening to the same
+        // AuthorFollowed Domain Event.
+        // @see: WhenAuthorFollowedThenIncrementFollowersProjectionEventHandler
+        // @see: WhenAuthorFollowedThenWelcomeAuthorEventHandler
+
+        $this->commandBus->handle(
+            NotifyToAuthorAboutNewFollowerCommand::fromArray([
+                'from_author_id' => $event->fromAuthorId(),
+                'to_author_id' => $event->toAuthorId(),
+            ])
+        );
+    }
+}
+//end-snippet