/**
 * PF2e Recall Knowledge DC calculation and type-to-skill mapping.
 *
 * DC is derived from creature level using the standard DC-by-level table
 * (Player Core / GM Core), adjusted for rarity.
 */

/** Standard DC-by-level table from PF2e GM Core. Index = level + 1 (level -1 → index 0). */
const DC_BY_LEVEL: readonly number[] = [
	13, // level -1
	14, // level 0
	15, // level 1
	16, // level 2
	18, // level 3
	19, // level 4
	20, // level 5
	22, // level 6
	23, // level 7
	24, // level 8
	26, // level 9
	27, // level 10
	28, // level 11
	30, // level 12
	31, // level 13
	32, // level 14
	34, // level 15
	35, // level 16
	36, // level 17
	38, // level 18
	39, // level 19
	40, // level 20
	42, // level 21
	44, // level 22
	46, // level 23
	48, // level 24
	50, // level 25
];

const RARITY_ADJUSTMENT: Readonly<Record<string, number>> = {
	uncommon: 2,
	rare: 5,
	unique: 10,
};

/**
 * Mapping from PF2e creature type traits to the skill(s) used for
 * Recall Knowledge. Types that map to multiple skills list all of them.
 */
const TYPE_TO_SKILLS: Readonly<Record<string, readonly string[]>> = {
	aberration: ["Occultism"],
	animal: ["Nature"],
	astral: ["Occultism"],
	beast: ["Arcana", "Nature"],
	celestial: ["Religion"],
	construct: ["Arcana", "Crafting"],
	dragon: ["Arcana"],
	dream: ["Occultism"],
	elemental: ["Arcana", "Nature"],
	ethereal: ["Occultism"],
	fey: ["Nature"],
	fiend: ["Religion"],
	fungus: ["Nature"],
	giant: ["Society"],
	humanoid: ["Society"],
	monitor: ["Religion"],
	ooze: ["Occultism"],
	plant: ["Nature"],
	undead: ["Religion"],
};

export interface RecallKnowledge {
	readonly dc: number;
	readonly type: string;
	readonly skills: readonly string[];
}

/**
 * Calculate Recall Knowledge DC, type, and skill(s) for a PF2e creature.
 *
 * Returns `null` when no recognized type trait is found in the creature's
 * traits array, indicating the Recall Knowledge line should be omitted.
 */
export function recallKnowledge(
	level: number,
	traits: readonly string[],
): RecallKnowledge | null {
	// Find the first type trait that maps to a skill
	let matchedType: string | undefined;
	let skills: readonly string[] | undefined;

	for (const trait of traits) {
		const lower = trait.toLowerCase();
		const mapped = TYPE_TO_SKILLS[lower];
		if (mapped) {
			matchedType = trait;
			skills = mapped;
			break;
		}
	}

	if (!matchedType || !skills) return null;

	// Calculate DC from level
	const clampedIndex = Math.max(0, Math.min(level + 1, DC_BY_LEVEL.length - 1));
	let dc = DC_BY_LEVEL[clampedIndex];

	// Apply rarity adjustment (rarity traits are included in the traits array
	// for non-common creatures by the normalization pipeline)
	for (const trait of traits) {
		const adjustment = RARITY_ADJUSTMENT[trait.toLowerCase()];
		if (adjustment) {
			dc += adjustment;
			break;
		}
	}

	return { dc, type: matchedType, skills };
}