Making progress on working CODE for all the application

src/Cheeper/Chapter7/Infrastructure/Persistence/InMemoryFollows.php

@@ -0,0 +1,68 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cheeper\Chapter7\Infrastructure\Persistence;
+
+use Cheeper\Chapter7\DomainModel\Follow\Follow;
+use Cheeper\Chapter7\DomainModel\Follow\Follows;
+use Cheeper\DomainModel\Author\AuthorId;
+use Cheeper\DomainModel\Follow\FollowId;
+use function Functional\head;
+use function Functional\reduce_left;
+use function Functional\select;
+
+final class InMemoryFollows implements Follows
+{
+    /** @var array<string, Follow> */
+    public array $collection = [];
+
+    public function ofId(FollowId $followId): ?Follow
+    {
+        $candidate = head(
+            select($this->collection, fn (Follow $u): bool => $u->followId()->equals($followId))
+        );
+
+        if (null === $candidate) {
+            return null;
+        }
+
+        return $candidate;
+    }
+
+    public function add(Follow $follow): void
+    {
+        $candidate = head(
+            select($this->collection, fn (Follow $u): bool => $u->fromAuthorId()->equals($follow->fromAuthorId()) && $u->toAuthorId()->equals($follow->toAuthorId()))
+        );
+
+        if ((null !== $candidate && $candidate != $follow) || null === $candidate) {
+            $this->collection[$follow->followId()->toString()] = $follow;
+        }
+    }
+
+    public function numberOfFollowersFor(AuthorId $authorId): int
+    {
+        return reduce_left(
+            $this->collection,
+            function(Follow $f, string $key, array $collection, int $initial) use($authorId): int {
+                return $initial + ($f->fromAuthorId()->equals($authorId) ? 1 : 0);
+            },
+            0
+        );
+    }
+
+    public function ofFromAuthorIdAndToAuthorId(AuthorId $fromAuthorId, AuthorId $toAuthorId): ?Follow
+    {
+        $candidate = head(
+            select($this->collection, fn (Follow $u): bool => $u->fromAuthorId()->equals($fromAuthorId) && $u->toAuthorId()->equals($toAuthorId))
+        );
+
+        return $candidate ?? null;
+    }
+
+    public function toAuthorId(AuthorId $authorId): array
+    {
+        return select($this->collection, fn (Follow $f): bool => $f->toAuthorId()->equals($authorId));
+    }
+}