initiative/apps/web/src/hooks/use-difficulty.ts

import type {
	Combatant,
	CombatantDescriptor,
	CreatureId,
	DifficultyResult,
	PlayerCharacter,
} from "@initiative/domain";
import { calculateEncounterDifficulty } from "@initiative/domain";
import { useMemo } from "react";
import { useBestiaryContext } from "../contexts/bestiary-context.js";
import { useEncounterContext } from "../contexts/encounter-context.js";
import { usePlayerCharactersContext } from "../contexts/player-characters-context.js";

export function resolveSide(c: Combatant): "party" | "enemy" {
	if (c.side) return c.side;
	return c.playerCharacterId ? "party" : "enemy";
}

function buildDescriptors(
	combatants: readonly Combatant[],
	characters: readonly PlayerCharacter[],
	getCreature: (id: CreatureId) => { cr: string } | undefined,
): CombatantDescriptor[] {
	const descriptors: CombatantDescriptor[] = [];
	for (const c of combatants) {
		const side = resolveSide(c);
		const level = c.playerCharacterId
			? characters.find((p) => p.id === c.playerCharacterId)?.level
			: undefined;
		const cr = c.creatureId
			? getCreature(c.creatureId)?.cr
			: (c.cr ?? undefined);

		if (level !== undefined || cr !== undefined) {
			descriptors.push({ level, cr, side });
		}
	}
	return descriptors;
}

export function useDifficulty(): DifficultyResult | null {
	const { encounter } = useEncounterContext();
	const { characters } = usePlayerCharactersContext();
	const { getCreature } = useBestiaryContext();

	return useMemo(() => {
		const descriptors = buildDescriptors(
			encounter.combatants,
			characters,
			getCreature,
		);

		const hasPartyLevel = descriptors.some(
			(d) => d.side === "party" && d.level !== undefined,
		);
		const hasCr = descriptors.some((d) => d.cr !== undefined);

		if (!hasPartyLevel || !hasCr) return null;

		return calculateEncounterDifficulty(descriptors);
	}, [encounter.combatants, characters, getCreature]);
}