// Copyright (c) Mysten Labs, Inc.
// SPDX-License-Identifier: Apache-2.0

// Helper utility: write number as an ULEB array.
// Original code is taken from: https://www.npmjs.com/package/uleb128 (no longer exists)
export function ulebEncode(num: number | bigint): number[] {
	let bigNum = BigInt(num);
	const arr: number[] = [];
	let len = 0;

	if (bigNum === 0n) {
		return [0];
	}

	while (bigNum > 0) {
		arr[len] = Number(bigNum & 0x7fn);
		bigNum >>= 7n;
		if (bigNum > 0n) {
			arr[len] |= 0x80;
		}
		len += 1;
	}

	return arr;
}

// Helper utility: decode ULEB as an array of numbers.
// Original code is taken from: https://www.npmjs.com/package/uleb128 (no longer exists)
export function ulebDecode(arr: number[] | Uint8Array): {
	value: number;
	length: number;
} {
	let total = 0n;
	let shift = 0n;
	let len = 0;

	while (true) {
		if (len >= arr.length) {
			throw new Error('ULEB decode error: buffer overflow');
		}

		const byte = arr[len];
		len += 1;
		total += BigInt(byte & 0x7f) << shift;
		if ((byte & 0x80) === 0) {
			break;
		}
		shift += 7n;
	}

	// TODO: return bigint in next major version
	if (total > BigInt(Number.MAX_SAFE_INTEGER)) {
		throw new Error('ULEB decode error: value exceeds MAX_SAFE_INTEGER');
	}

	return {
		value: Number(total),
		length: len,
	};
}