Initial commit

game/occupancy.ts

@@ -0,0 +1,76 @@
+import type { FactionId } from './catalog';
+import { territory } from './board';
+import { fighterCount } from './advisors';
+import { presenceAt, type ForcePresence } from './force-presence';
+import { ecazOccupancyIdentity, ecazOccupancyRelation } from './ecaz-occupy';
+
+/** Public board information only: a concealed No-Field contributes presence,
+ * never its hidden denomination. Advisor groups do not fill strongholds. */
+export type OccupancySeat = ForcePresence & {
+  id: string;
+  faction: FactionId;
+  ally?: string | null;
+  advisors?: Readonly<Record<string, { lockedTurn?: number }>>;
+};
+
+/** Count the occupying factions after admitting a fighter from enteringId.
+ * Ecaz and its reciprocal ally share a faction for board occupancy. Physical
+ * forces and player ownership remain separate. This is not a combat side. */
+export function occupyingFactionCount(
+  players: readonly OccupancySeat[],
+  to: string,
+  enteringId?: string,
+) {
+  const where = { kind: 'territory' as const, id: to };
+  const sides = new Set(
+    players
+      .filter((p) => fighterCount(p, to) > 0)
+      .map((p) => ecazOccupancyIdentity(players, p.id, where).key),
+  );
+  if (enteringId)
+    sides.add(ecazOccupancyIdentity(players, enteringId, where).key);
+  return sides.size;
+}
+
+export function territoryEntryBlock(
+  players: readonly OccupancySeat[],
+  playerId: string,
+  to: string,
+  advisors = false,
+): string | null {
+  // Validate the complete identity roster even for an empty destination.
+  ecazOccupancyIdentity(players, playerId, { kind: 'territory', id: to });
+  if (advisors) return null;
+  const player = players.find((p) => p.id === playerId)!;
+  const ally = players.find((p) => p.id === player.ally);
+  if (
+    to !== 'polar_sink' &&
+    ally &&
+    presenceAt(ally, to) > 0 &&
+    ecazOccupancyRelation(players, playerId, ally.id, {
+      kind: 'territory',
+      id: to,
+    }) !== 'ecazAlliance'
+  )
+    return 'You cannot enter a territory occupied by your ally.';
+  if (
+    territory(to).type === 'stronghold' &&
+    occupyingFactionCount(players, to, playerId) > 2
+  )
+    return 'A stronghold cannot contain three occupying factions.';
+  return null;
+}
+
+/** Passing through a stronghold uses capacity, not allied destination rules. */
+export function strongholdPathBlocked(
+  players: readonly OccupancySeat[],
+  playerId: string,
+  to: string,
+  advisors = false,
+) {
+  return (
+    !advisors &&
+    territory(to).type === 'stronghold' &&
+    occupyingFactionCount(players, to, playerId) > 2
+  );
+}