package com.example.medilightv2android.ble

object CRC16 {
    private const val POLYNOMIAL: Int = 0x1021
    private const val INITIAL_VALUE: Int = 0xFFFF

    fun calculate(data: ByteArray): Int {
        var crc = INITIAL_VALUE
        for (byte in data) {
            crc = crc xor ((byte.toInt() and 0xFF) shl 8)
            for (j in 0 until 8) {
                crc = if ((crc and 0x8000) != 0) {
                    (crc shl 1) xor POLYNOMIAL
                } else {
                    crc shl 1
                }
                crc = crc and 0xFFFF
            }
        }
        return crc
    }

    fun calculate(string: String): Int = calculate(string.toByteArray(Charsets.UTF_8))

    fun appendCRC(data: ByteArray): ByteArray {
        val crc = calculate(data)
        return data + byteArrayOf(
            (crc and 0xFF).toByte(),          // Low byte first (Little Endian)
            ((crc shr 8) and 0xFF).toByte()   // High byte
        )
    }

    fun appendCRC(string: String): ByteArray = appendCRC(string.toByteArray(Charsets.UTF_8))

    fun verify(data: ByteArray): Boolean {
        if (data.size < 2) return false
        val payload = data.copyOfRange(0, data.size - 2)
        val receivedCRC = (data[data.size - 2].toInt() and 0xFF) or
                ((data[data.size - 1].toInt() and 0xFF) shl 8)
        return calculate(payload) == receivedCRC
    }

    fun buildCommand(cmd: String, params: IntArray = intArrayOf()): ByteArray {
        val cmdBytes = "$cmd?".toByteArray(Charsets.UTF_8)
        val paramBytes = ByteArray(params.size * 2)
        for (i in params.indices) {
            paramBytes[i * 2] = (params[i] and 0xFF).toByte()       // Low byte
            paramBytes[i * 2 + 1] = ((params[i] shr 8) and 0xFF).toByte() // High byte
        }
        return appendCRC(cmdBytes + paramBytes)
    }

    fun buildCommandASCII(cmd: String, asciiParams: String = ""): ByteArray {
        return appendCRC("$cmd?$asciiParams".toByteArray(Charsets.UTF_8))
    }

    /** 파라미터를 16비트 Big Endian으로 추가 (펌웨어 테스터와 동일 포맷) */
    fun buildCommandBE(cmd: String, params: IntArray = intArrayOf()): ByteArray {
        val cmdBytes = "$cmd?".toByteArray(Charsets.UTF_8)
        val paramBytes = ByteArray(params.size * 2)
        for (i in params.indices) {
            paramBytes[i * 2] = ((params[i] shr 8) and 0xFF).toByte()  // High byte first
            paramBytes[i * 2 + 1] = (params[i] and 0xFF).toByte()      // Low byte
        }
        return appendCRC(cmdBytes + paramBytes)
    }

    fun buildSimpleCommand(cmd: String): ByteArray {
        return appendCRC(cmd.toByteArray(Charsets.UTF_8))
    }
}