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

import type {
	AnyCreature,
	Combatant,
	CreatureId,
	DifficultyThreshold,
	DifficultyTier,
	PlayerCharacter,
} from "@initiative/domain";
import {
	calculateEncounterDifficulty,
	crToXp,
	derivePartyLevel,
	pf2eCreatureXp,
} 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";
import { useRulesEditionContext } from "../contexts/rules-edition-context.js";
import { resolveSide } from "./use-difficulty.js";

export interface BreakdownCombatant {
	readonly combatant: Combatant;
	readonly cr: string | null;
	readonly xp: number | null;
	readonly source: string | null;
	readonly editable: boolean;
	readonly side: "party" | "enemy";
	readonly level: number | undefined;
	/** PF2e only: the creature's level from bestiary data. */
	readonly creatureLevel: number | undefined;
	/** PF2e only: creature level minus party level. */
	readonly levelDifference: number | undefined;
}

interface DifficultyBreakdown {
	readonly tier: DifficultyTier;
	readonly totalMonsterXp: number;
	readonly thresholds: readonly DifficultyThreshold[];
	readonly encounterMultiplier: number | undefined;
	readonly adjustedXp: number | undefined;
	readonly partySizeAdjusted: boolean | undefined;
	readonly partyLevel: number | undefined;
	readonly pcCount: number;
	readonly partyCombatants: readonly BreakdownCombatant[];
	readonly enemyCombatants: readonly BreakdownCombatant[];
}

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

	return useMemo(() => {
		const { partyCombatants, enemyCombatants, descriptors, pcCount } =
			classifyCombatants(encounter.combatants, characters, getCreature);

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

		if (edition === "pf2e") {
			const hasCreatureLevel = descriptors.some(
				(d) => d.creatureLevel !== undefined,
			);
			if (!hasPartyLevel || !hasCreatureLevel) return null;
		} else {
			const hasCr = descriptors.some((d) => d.cr !== undefined);
			if (!hasPartyLevel || !hasCr) return null;
		}

		const result = calculateEncounterDifficulty(descriptors, edition);

		return {
			...result,
			pcCount,
			partyCombatants,
			enemyCombatants,
		};
	}, [encounter.combatants, characters, getCreature, edition]);
}

type CreatureInfo = {
	cr?: string;
	creatureLevel?: number;
	source: string;
	sourceDisplayName: string;
};

function buildBreakdownEntry(
	c: Combatant,
	side: "party" | "enemy",
	level: number | undefined,
	creature: CreatureInfo | undefined,
	partyLevel: number | undefined,
): BreakdownCombatant {
	if (c.playerCharacterId) {
		return {
			combatant: c,
			cr: null,
			xp: null,
			source: null,
			editable: false,
			side,
			level,
			creatureLevel: undefined,
			levelDifference: undefined,
		};
	}
	if (creature && creature.creatureLevel !== undefined) {
		const levelDiff =
			partyLevel === undefined
				? undefined
				: creature.creatureLevel - partyLevel;
		const xp =
			partyLevel === undefined
				? null
				: pf2eCreatureXp(creature.creatureLevel, partyLevel);
		return {
			combatant: c,
			cr: null,
			xp,
			source: creature.sourceDisplayName ?? creature.source,
			editable: false,
			side,
			level: undefined,
			creatureLevel: creature.creatureLevel,
			levelDifference: levelDiff,
		};
	}
	if (creature) {
		const cr = creature.cr ?? null;
		return {
			combatant: c,
			cr,
			xp: cr ? crToXp(cr) : null,
			source: creature.sourceDisplayName ?? creature.source,
			editable: false,
			side,
			level: undefined,
			creatureLevel: undefined,
			levelDifference: undefined,
		};
	}
	if (c.cr) {
		return {
			combatant: c,
			cr: c.cr,
			xp: crToXp(c.cr),
			source: null,
			editable: true,
			side,
			level: undefined,
			creatureLevel: undefined,
			levelDifference: undefined,
		};
	}
	return {
		combatant: c,
		cr: null,
		xp: null,
		source: null,
		editable: !c.creatureId,
		side,
		level: undefined,
		creatureLevel: undefined,
		levelDifference: undefined,
	};
}

function resolveLevel(
	c: Combatant,
	characters: readonly PlayerCharacter[],
): number | undefined {
	if (!c.playerCharacterId) return undefined;
	return characters.find((p) => p.id === c.playerCharacterId)?.level;
}

function resolveCreatureInfo(
	c: Combatant,
	getCreature: (id: CreatureId) => AnyCreature | undefined,
): {
	cr: string | null;
	creatureLevel: number | undefined;
	creature: CreatureInfo | undefined;
} {
	const rawCreature = c.creatureId ? getCreature(c.creatureId) : undefined;
	if (!rawCreature) {
		return {
			cr: c.cr ?? null,
			creatureLevel: undefined,
			creature: undefined,
		};
	}
	if ("system" in rawCreature && rawCreature.system === "pf2e") {
		return {
			cr: null,
			creatureLevel: rawCreature.level,
			creature: {
				creatureLevel: rawCreature.level,
				source: rawCreature.source,
				sourceDisplayName: rawCreature.sourceDisplayName,
			},
		};
	}
	const cr = "cr" in rawCreature ? rawCreature.cr : undefined;
	return {
		cr: cr ?? c.cr ?? null,
		creatureLevel: undefined,
		creature: {
			cr,
			source: rawCreature.source,
			sourceDisplayName: rawCreature.sourceDisplayName,
		},
	};
}

function collectPartyLevel(
	combatants: readonly Combatant[],
	characters: readonly PlayerCharacter[],
): number | undefined {
	const partyLevels: number[] = [];
	for (const c of combatants) {
		if (resolveSide(c) !== "party") continue;
		const level = resolveLevel(c, characters);
		if (level !== undefined) partyLevels.push(level);
	}
	return partyLevels.length > 0 ? derivePartyLevel(partyLevels) : undefined;
}

function classifyCombatants(
	combatants: readonly Combatant[],
	characters: readonly PlayerCharacter[],
	getCreature: (id: CreatureId) => AnyCreature | undefined,
) {
	const partyCombatants: BreakdownCombatant[] = [];
	const enemyCombatants: BreakdownCombatant[] = [];
	const descriptors: {
		level?: number;
		cr?: string;
		creatureLevel?: number;
		side: "party" | "enemy";
	}[] = [];
	let pcCount = 0;
	const partyLevel = collectPartyLevel(combatants, characters);

	for (const c of combatants) {
		const side = resolveSide(c);
		const level = resolveLevel(c, characters);
		if (level !== undefined) pcCount++;

		const { cr, creatureLevel, creature } = resolveCreatureInfo(c, getCreature);

		if (level !== undefined || cr != null || creatureLevel !== undefined) {
			descriptors.push({
				level,
				cr: cr ?? undefined,
				creatureLevel,
				side,
			});
		}

		const entry = buildBreakdownEntry(c, side, level, creature, partyLevel);
		const target = side === "party" ? partyCombatants : enemyCombatants;
		target.push(entry);
	}

	return { partyCombatants, enemyCombatants, descriptors, pcCount };
}