initiative/packages/application/src/roll-all-initiative-use-case.ts

import {
	type Creature,
	type CreatureId,
	calculateInitiative,
	type DomainError,
	type DomainEvent,
	isDomainError,
	rollInitiative,
	setInitiative,
} from "@initiative/domain";
import type { EncounterStore } from "./ports.js";

export interface RollAllResult {
	events: DomainEvent[];
	skippedNoSource: number;
}

export function rollAllInitiativeUseCase(
	store: EncounterStore,
	rollDice: () => number,
	getCreature: (id: CreatureId) => Creature | undefined,
): RollAllResult | DomainError {
	let encounter = store.get();
	const allEvents: DomainEvent[] = [];
	let skippedNoSource = 0;

	for (const combatant of encounter.combatants) {
		if (!combatant.creatureId) continue;
		if (combatant.initiative !== undefined) continue;

		const creature = getCreature(combatant.creatureId);
		if (!creature) {
			skippedNoSource++;
			continue;
		}

		const { modifier } = calculateInitiative({
			dexScore: creature.abilities.dex,
			cr: creature.cr,
			initiativeProficiency: creature.initiativeProficiency,
		});
		const value = rollInitiative(rollDice(), modifier);

		if (isDomainError(value)) {
			return value;
		}

		const result = setInitiative(encounter, combatant.id, value);

		if (isDomainError(result)) {
			return result;
		}

		encounter = result.encounter;
		allEvents.push(...result.events);
	}

	store.save(encounter);
	return { events: allEvents, skippedNoSource };
}