feat: add the booking domain layer

src/Entity/Booking.php

@@ -0,0 +1,77 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Entity;
+
+use App\Repository\BookingRepository;
+use Doctrine\ORM\Mapping as ORM;
+
+/**
+ * One person holding one resource for one whole day.
+ *
+ * The unique constraint is the actual guard against double-booking -- checking first and then
+ * inserting is racy, so callers insert and catch UniqueConstraintViolationException instead.
+ */
+#[ORM\Entity(repositoryClass: BookingRepository::class)]
+#[ORM\UniqueConstraint(name: 'uniq_booking_resource_date', columns: ['resource_id', 'date'])]
+class Booking
+{
+    #[ORM\Id]
+    #[ORM\GeneratedValue]
+    #[ORM\Column]
+    private ?int $id = null;
+
+    #[ORM\ManyToOne]
+    #[ORM\JoinColumn(nullable: false, onDelete: 'CASCADE')]
+    private User $user;
+
+    #[ORM\ManyToOne]
+    #[ORM\JoinColumn(nullable: false, onDelete: 'RESTRICT')]
+    private Resource $resource;
+
+    #[ORM\Column(type: 'date_immutable')]
+    private \DateTimeImmutable $date;
+
+    #[ORM\Column(type: 'datetime_immutable')]
+    private \DateTimeImmutable $createdAt;
+
+    public function __construct(User $user, Resource $resource, \DateTimeImmutable $date)
+    {
+        $this->user = $user;
+        $this->resource = $resource;
+        // Normalised to midnight so the unique constraint cannot be sidestepped by a time part.
+        $this->date = $date->setTime(0, 0);
+        $this->createdAt = new \DateTimeImmutable();
+    }
+
+    public function getId(): ?int
+    {
+        return $this->id;
+    }
+
+    public function getUser(): User
+    {
+        return $this->user;
+    }
+
+    public function getResource(): Resource
+    {
+        return $this->resource;
+    }
+
+    public function getDate(): \DateTimeImmutable
+    {
+        return $this->date;
+    }
+
+    public function getCreatedAt(): \DateTimeImmutable
+    {
+        return $this->createdAt;
+    }
+
+    public function belongsTo(User $user): bool
+    {
+        return $this->user->getId() === $user->getId();
+    }
+}