import { concat, hexlify, keccak256, toBeHex } from 'ethers'

import type { CCIPMessage, CCIPVersion } from '../types.ts'

/** Function type for computing the leaf hash of a CCIP message. */
export type LeafHasher<V extends CCIPVersion = CCIPVersion> = (message: CCIPMessage<V>) => string

const INTERNAL_DOMAIN_SEPARATOR = toBeHex(1, 32)
export const LEAF_DOMAIN_SEPARATOR = '0x00'
export const ZERO_HASH = hexlify(new Uint8Array(32).fill(0xff))

/**
 * Computes the Keccak-256 hash of the concatenation of two hash values.
 * @param a - The first hash as a Hash type.
 * @param b - The second hash as a Hash type.
 * @returns The Keccak-256 hash result as a Hash type.
 */
export function hashInternal(a: string, b: string): string {
  if (a > b) {
    ;[a, b] = [b, a]
  }
  const combinedData = concat([INTERNAL_DOMAIN_SEPARATOR, a, b])
  return keccak256(combinedData)
}