import type {
	Pf2eCreature,
	TraitBlock,
	TraitSegment,
} from "./creature-types.js";

export type CreatureAdjustment = "weak" | "elite";

/** HP bracket delta by creature level (standard PF2e table). */
function hpBracketDelta(level: number): number {
	if (level <= 1) return 10;
	if (level <= 4) return 15;
	if (level <= 19) return 20;
	return 30;
}

/** Level shift: elite +1 (or +2 if level ≤ 0), weak −1 (or −2 if level is 1). */
export function adjustedLevel(
	baseLevel: number,
	adjustment: CreatureAdjustment,
): number {
	if (adjustment === "elite") {
		return baseLevel <= 0 ? baseLevel + 2 : baseLevel + 1;
	}
	return baseLevel === 1 ? baseLevel - 2 : baseLevel - 1;
}

/** Signed HP delta for a given base level and adjustment. */
export function hpDelta(
	baseLevel: number,
	adjustment: CreatureAdjustment,
): number {
	const delta = hpBracketDelta(baseLevel);
	return adjustment === "elite" ? delta : -delta;
}

/** AC delta: +2 for elite, −2 for weak. */
export function acDelta(adjustment: CreatureAdjustment): number {
	return adjustment === "elite" ? 2 : -2;
}

/** Generic ±2 modifier delta. Used for saves, Perception, attacks, damage. */
export function modDelta(adjustment: CreatureAdjustment): number {
	return adjustment === "elite" ? 2 : -2;
}

const ATTACK_BONUS_RE = /^([+-])(\d+)/;
const MAP_RE = /\[([+-]\d+)\/([+-]\d+)\]/g;
const DAMAGE_BONUS_RE = /(\d+d\d+)([+-])(\d+)/g;

/**
 * Adjust attack bonus in a formatted attack string.
 * "+15 (agile), 2d12+7 piercing plus Grab" → "+17 (agile), 2d12+9 piercing plus Grab"
 */
function adjustAttackText(text: string, delta: number): string {
	// Adjust leading attack bonus: "+15" → "+17"
	let result = text.replace(ATTACK_BONUS_RE, (_, sign, num) => {
		const adjusted = (sign === "+" ? 1 : -1) * Number(num) + delta;
		return adjusted >= 0 ? `+${adjusted}` : `${adjusted}`;
	});
	// Adjust MAP values in brackets: "[+10/+5]" → "[+12/+7]"
	result = result.replace(MAP_RE, (_, m1, m2) => {
		const a1 = Number(m1) + delta;
		const a2 = Number(m2) + delta;
		const f = (n: number) => (n >= 0 ? `+${n}` : `${n}`);
		return `[${f(a1)}/${f(a2)}]`;
	});
	// Adjust damage bonus in "NdN+N type" patterns
	result = result.replace(DAMAGE_BONUS_RE, (_, dice, sign, num) => {
		const current = (sign === "+" ? 1 : -1) * Number(num);
		const adjusted = current + delta;
		if (adjusted === 0) return dice as string;
		return adjusted > 0 ? `${dice}+${adjusted}` : `${dice}${adjusted}`;
	});
	return result;
}

function adjustTraitBlock(block: TraitBlock, delta: number): TraitBlock {
	return {
		...block,
		segments: block.segments.map(
			(seg): TraitSegment =>
				seg.type === "text"
					? { type: "text", value: adjustAttackText(seg.value, delta) }
					: seg,
		),
	};
}

/**
 * Apply a weak or elite adjustment to a full PF2e creature.
 * Returns a new Pf2eCreature with all numeric stats adjusted.
 */
export function applyPf2eAdjustment(
	creature: Pf2eCreature,
	adjustment: CreatureAdjustment,
): Pf2eCreature {
	const d = modDelta(adjustment);
	return {
		...creature,
		level: adjustedLevel(creature.level, adjustment),
		ac: creature.ac + d,
		hp: creature.hp + hpDelta(creature.level, adjustment),
		perception: creature.perception + d,
		saveFort: creature.saveFort + d,
		saveRef: creature.saveRef + d,
		saveWill: creature.saveWill + d,
		attacks: creature.attacks?.map((a) => adjustTraitBlock(a, d)),
	};
}