import { splitUint8Array, toUint8Array } from '../utils/bytes'
import { utf8ToBytes } from '../utils/hex'

/**
 * 按协议将 payload 拆成 A7 分包：
 * 第 1 字节固定包头 0xA7，第 2 字节高4位为总包数、低4位为包序号。
 */
export function buildA7Packets(payload, packetConfig = {}) {
  const {
    head = 0xA7,
    chunkSize = 18,
    maxChunk = 15
  } = packetConfig

  const bytes = typeof payload === 'string' ? utf8ToBytes(payload) : toUint8Array(payload)
  const chunks = splitUint8Array(bytes, chunkSize)

  if (chunks.length > maxChunk) {
    throw new Error(`分包数量超过上限: ${chunks.length} > ${maxChunk}`)
  }

  return chunks.map((chunk, index) => {
    const packetIndex = index + 1
    const lenByte = ((chunks.length & 0x0F) << 4) | (packetIndex & 0x0F)
    const packet = new Uint8Array(2 + chunk.length)

    packet[0] = head
    packet[1] = lenByte
    packet.set(chunk, 2)

    return packet
  })
}

/**
 * 合并多个 A7 分包数据体（去掉前两字节头信息后拼接）。
 */
export function concatA7PacketData(packets = []) {
  const sorted = [...packets].sort((a, b) => {
    const indexA = a[1] & 0x0F
    const indexB = b[1] & 0x0F
    return indexA - indexB
  })

  const totalLength = sorted.reduce((sum, packet) => sum + Math.max(packet.length - 2, 0), 0)
  const merged = new Uint8Array(totalLength)
  let offset = 0

  sorted.forEach((packet) => {
    const body = packet.slice(2)
    merged.set(body, offset)
    offset += body.length
  })

  return merged
}