/**
 * BluettiCRC - CRC-16/MODBUS helpers for the Bluetti BLE protocol
 *
 * Ported from the Bluetti_ESP32_Bridge project (crc16.h / utils.cpp).
 * Polynomial 0xA001 (reversed 0x8005), initial value 0xFFFF.
 *
 * Copyright (c) 2026 Scott Penrose
 * License: MIT
 */

#ifndef BLUETTI_CRC_H
#define BLUETTI_CRC_H

#include <stdint.h>
#include <stddef.h>

// Update a running CRC-16/MODBUS with one byte.
static inline uint16_t bluettiCrc16Update(uint16_t crc, uint8_t a) {
    crc ^= a;
    for (int i = 0; i < 8; ++i) {
        if (crc & 1)
            crc = (crc >> 1) ^ 0xA001;
        else
            crc = (crc >> 1);
    }
    return crc;
}

// CRC-16/MODBUS over a buffer (init 0xFFFF).
static inline uint16_t bluettiModbusCrc(const uint8_t* buf, size_t len) {
    uint16_t crc = 0xFFFF;
    for (size_t i = 0; i < len; i++) {
        crc = bluettiCrc16Update(crc, buf[i]);
    }
    return crc;
}

// Swap the two bytes of a 16-bit value (used to place write values big-endian).
static inline uint16_t bluettiSwapBytes(uint16_t v) {
    return (uint16_t)((v << 8) | (v >> 8));
}

#endif // BLUETTI_CRC_H