feat: validate scenario deployment zones and objectives

src/Domain/ScenarioValidator.php

@@ -0,0 +1,82 @@
+<?php
+
+declare(strict_types=1);
+
+namespace BattleForge\Domain;
+
+final class ScenarioValidator
+{
+    /**
+     * @return list<string>
+     */
+    public static function validate(Scenario $scenario): array
+    {
+        $errors = [];
+
+        $occupied = [];
+
+        foreach ($scenario->deploymentZones as $teamId => $zone) {
+            foreach ($zone->positions as $position) {
+                if (!$scenario->battlefield->contains($position)) {
+                    $errors[] = "Deployment zone for {$teamId} includes a position outside the battlefield.";
+                    continue;
+                }
+                if ($scenario->battlefield->terrainAt($position)->movementCost() === null) {
+                    $errors[] = "Deployment zone for {$teamId} sits on impassable terrain at {$position->key()}.";
+                }
+                if (isset($occupied[$position->key()])) {
+                    $errors[] = "Deployment zones overlap at {$position->key()}.";
+                }
+                $occupied[$position->key()] = $teamId;
+            }
+        }
+
+        $reachableFromDeployment = self::reachableFromDeployment($scenario, $occupied);
+
+        foreach ($scenario->objectives as $objective) {
+            if (!$scenario->battlefield->contains($objective->position)) {
+                $errors[] = "Objective {$objective->id} is outside the battlefield.";
+                continue;
+            }
+            if ($scenario->battlefield->terrainAt($objective->position)->movementCost() === null) {
+                $errors[] = "Objective {$objective->id} sits on impassable terrain.";
+            }
+            if (!isset($reachableFromDeployment[$objective->position->key()])) {
+                $errors[] = "Objective {$objective->id} is unreachable from any deployment zone.";
+            }
+        }
+
+        return $errors;
+    }
+
+    /**
+     * @param array<string, string> $occupied
+     * @return array<string, true>
+     */
+    private static function reachableFromDeployment(Scenario $scenario, array $occupied): array
+    {
+        $merged = $scenario->units;
+        $allReachable = [];
+
+        foreach ($merged as $unit) {
+            $others = [];
+
+            foreach ($merged as $other) {
+                if ($other->id === $unit->id || $other->isDefeated()) {
+                    continue;
+                }
+                $others[] = $other->position;
+            }
+
+            $reachable = $scenario->battlefield->reachable($unit->position, $unit->speed, $others);
+
+            foreach ($reachable as $key => $_cost) {
+                if (!isset($occupied[$key])) {
+                    $allReachable[$key] = true;
+                }
+            }
+        }
+
+        return $allReachable;
+    }
+}