const DIGITS_ONLY = /^\d+$/;

function scanExisting(
	baseName: string,
	existingNames: readonly string[],
): { exactMatches: number[]; maxNumber: number } {
	const exactMatches: number[] = [];
	let maxNumber = 0;
	const prefix = `${baseName} `;

	for (let i = 0; i < existingNames.length; i++) {
		const name = existingNames[i];
		if (name === baseName) {
			exactMatches.push(i);
		} else if (name.startsWith(prefix)) {
			const suffix = name.slice(prefix.length);
			if (DIGITS_ONLY.test(suffix)) {
				const num = Number.parseInt(suffix, 10);
				if (num > maxNumber) maxNumber = num;
			}
		}
	}
	return { exactMatches, maxNumber };
}

/**
 * Resolves a creature name against existing combatant names,
 * handling auto-numbering for duplicates.
 *
 * - No conflict: returns name as-is, no renames.
 * - First conflict (one existing match): renames existing to "Name 1",
 *   new becomes "Name 2".
 * - Subsequent conflicts: new gets next number suffix.
 */
export function resolveCreatureName(
	baseName: string,
	existingNames: readonly string[],
): {
	newName: string;
	renames: ReadonlyArray<{ from: string; to: string }>;
} {
	const { exactMatches, maxNumber } = scanExisting(baseName, existingNames);

	// No conflict at all
	if (exactMatches.length === 0 && maxNumber === 0) {
		return { newName: baseName, renames: [] };
	}

	// First conflict: one exact match, no numbered ones yet
	if (exactMatches.length === 1 && maxNumber === 0) {
		return {
			newName: `${baseName} 2`,
			renames: [{ from: baseName, to: `${baseName} 1` }],
		};
	}

	// Subsequent conflicts: append next number
	const nextNumber = Math.max(maxNumber, exactMatches.length) + 1;
	return { newName: `${baseName} ${nextNumber}`, renames: [] };
}