feat: exclusion groups for additional services

src/Service/AdditionalServiceExclusionResolver.php

@@ -0,0 +1,91 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service;
+
+use App\Entity\Groups\AdditionalService;
+
+/**
+ * Resolves mutually exclusive additional services.
+ *
+ * Services sharing an exclusion group interact as soon as at least one of the two involved
+ * services is flagged as exclusive: selecting the exclusive one clears all other members of
+ * the group, selecting any other member clears the exclusive ones. Members that are not
+ * exclusive can be combined freely.
+ *
+ * Conflicts are resolved in favour of the newest selection, determined by diffing the
+ * submitted ids against the previously stored ones.
+ */
+class AdditionalServiceExclusionResolver
+{
+    /**
+     * @param AdditionalService[]   $availableServices
+     * @param array<array-key, int> $submittedIds      keys are preserved, grouped radios submit under their group name
+     * @param array<array-key, int> $previousIds
+     *
+     * @return array<array-key, int>
+     */
+    public function resolve(array $availableServices, array $submittedIds, array $previousIds): array
+    {
+        $rules = $this->buildRules($availableServices);
+
+        if ([] === $rules) {
+            return $submittedIds;
+        }
+
+        $added = array_values(array_diff($submittedIds, $previousIds));
+
+        foreach ($added as $addedId) {
+            if (!isset($rules[$addedId])) {
+                continue;
+            }
+
+            $submittedIds = array_filter(
+                $submittedIds,
+                fn(int $id) => !$this->conflicts($rules, $addedId, $id),
+            );
+        }
+
+        return $submittedIds;
+    }
+
+    /**
+     * @param array<int, array{group: string, exclusive: bool}> $rules
+     */
+    private function conflicts(array $rules, int $a, int $b): bool
+    {
+        if ($a === $b || !isset($rules[$b])) {
+            return false;
+        }
+
+        if ($rules[$a]['group'] !== $rules[$b]['group']) {
+            return false;
+        }
+
+        return $rules[$a]['exclusive'] || $rules[$b]['exclusive'];
+    }
+
+    /**
+     * @param AdditionalService[] $availableServices
+     *
+     * @return array<int, array{group: string, exclusive: bool}>
+     */
+    private function buildRules(array $availableServices): array
+    {
+        $rules = [];
+
+        foreach ($availableServices as $service) {
+            $group = $service->getExclusionGroup();
+            $id = $service->getId();
+
+            if (null === $id || null === $group || '' === $group) {
+                continue;
+            }
+
+            $rules[$id] = ['group' => $group, 'exclusive' => $service->isExclusive()];
+        }
+
+        return $rules;
+    }
+}