// The Death Creation Step: the one place minions leave play.
//
// Damage and destroy effects only mark a minion (0 or less Health, or pending
// destroy). It stays in play, and keeps triggering, until the outermost Phase
// ends. Then this step removes every marked minion at once.

import type { Event } from "./event";
import type { EntityId, World } from "./world";

/**
 * Remove every mortally wounded or pending-destroy minion from play, simultaneously.
 * Returns their Death Events in order of play; empty if nothing died.
 */
export function deathCreationStep(world: World): Event[] {
  const dying = world.minionsInPlay().filter((id) => world.isDoomed(id));
  // Every neighbour is read before anything moves: removal is simultaneous. Each Death
  // Event remembers where its minion stood as a handle, the minion that stays to its
  // right, not as a board index: an index goes stale as soon as a minion further left
  // leaves play in the same step (Module 1: hold handles, not indexes).
  const deaths = dying.map((id) => ({ type: "Destroyed" as const, id, before: survivorToTheRight(world, id) }));
  for (const { id, before } of deaths) world.kill(id, before);
  return deaths;
}

/** The nearest minion to the right of `id` on its board that is not leaving play in this step, if any. */
function survivorToTheRight(world: World, id: EntityId): EntityId | undefined {
  const board = world.zone(world.ownerOf(id), "board");
  return board.slice(board.indexOf(id) + 1).find((other) => !world.isDoomed(other));
}