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

import type {
	Combatant,
	CreatureId,
	DifficultyTier,
	PlayerCharacter,
} from "@initiative/domain";
import { calculateEncounterDifficulty, crToXp } 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 interface BreakdownCombatant {
	readonly combatant: Combatant;
	readonly cr: string | null;
	readonly xp: number | null;
	readonly source: string | null;
	readonly editable: boolean;
}

interface DifficultyBreakdown {
	readonly tier: DifficultyTier;
	readonly totalMonsterXp: number;
	readonly partyBudget: {
		readonly low: number;
		readonly moderate: number;
		readonly high: number;
	};
	readonly pcCount: number;
	readonly combatants: readonly BreakdownCombatant[];
}

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

	return useMemo(() => {
		const partyLevels = derivePartyLevels(encounter.combatants, characters);
		const { entries, crs } = classifyCombatants(
			encounter.combatants,
			getCreature,
		);

		if (partyLevels.length === 0 || crs.length === 0) {
			return null;
		}

		const result = calculateEncounterDifficulty(partyLevels, crs);

		return {
			...result,
			pcCount: partyLevels.length,
			combatants: entries,
		};
	}, [encounter.combatants, characters, getCreature]);
}

function classifyBestiaryCombatant(
	c: Combatant,
	getCreature: (
		id: CreatureId,
	) => { cr: string; source: string; sourceDisplayName: string } | undefined,
): { entry: BreakdownCombatant; cr: string | null } {
	const creature = c.creatureId ? getCreature(c.creatureId) : undefined;
	if (creature) {
		return {
			entry: {
				combatant: c,
				cr: creature.cr,
				xp: crToXp(creature.cr),
				source: creature.sourceDisplayName ?? creature.source,
				editable: false,
			},
			cr: creature.cr,
		};
	}
	return {
		entry: {
			combatant: c,
			cr: null,
			xp: null,
			source: null,
			editable: false,
		},
		cr: null,
	};
}

function classifyCombatants(
	combatants: readonly Combatant[],
	getCreature: (
		id: CreatureId,
	) => { cr: string; source: string; sourceDisplayName: string } | undefined,
): { entries: BreakdownCombatant[]; crs: string[] } {
	const entries: BreakdownCombatant[] = [];
	const crs: string[] = [];

	for (const c of combatants) {
		if (c.playerCharacterId) continue;

		if (c.creatureId) {
			const { entry, cr } = classifyBestiaryCombatant(c, getCreature);
			entries.push(entry);
			if (cr) crs.push(cr);
		} else if (c.cr) {
			crs.push(c.cr);
			entries.push({
				combatant: c,
				cr: c.cr,
				xp: crToXp(c.cr),
				source: null,
				editable: true,
			});
		} else {
			entries.push({
				combatant: c,
				cr: null,
				xp: null,
				source: null,
				editable: true,
			});
		}
	}

	return { entries, crs };
}

function derivePartyLevels(
	combatants: readonly Combatant[],
	characters: readonly PlayerCharacter[],
): number[] {
	const levels: number[] = [];
	for (const c of combatants) {
		if (!c.playerCharacterId) continue;
		const pc = characters.find((p) => p.id === c.playerCharacterId);
		if (pc?.level !== undefined) levels.push(pc.level);
	}
	return levels;
}