/**
 * @file protocol.c
 * @brief AliceRC communication protocol implementation
 */
#include <string.h>
#include "protocol.h"

void protocol_init(void)
{
    /* Nothing to initialize for now */
}

void protocol_pack_sbus(const uint16_t *channels, uint8_t *sbus_data)
{
    memset(sbus_data, 0, 22);
    
    /* Pack 16 × 11-bit channels into 22 bytes, little-endian bitstream */
    for (int i = 0; i < SBUS_CHANNEL_COUNT; i++) {
        uint16_t ch = channels[i] & 0x07FF;  /* Mask to 11 bits */
        int byte_idx = (i * SBUS_CHANNEL_BITS) / 8;
        int bit_off = (i * SBUS_CHANNEL_BITS) % 8;
        
        sbus_data[byte_idx] |= (ch << bit_off) & 0xFF;
        sbus_data[byte_idx + 1] |= (ch >> (8 - bit_off)) & 0xFF;
        if (bit_off > 5) {
            /* 11-bit crosses 3-byte boundary when bit_off >= 6 */
            sbus_data[byte_idx + 2] |= (ch >> (16 - bit_off)) & 0xFF;
        }
    }
}

void protocol_unpack_sbus(const uint8_t *sbus_data, uint16_t *channels)
{
    for (int i = 0; i < SBUS_CHANNEL_COUNT; i++) {
        int byte_idx = (i * SBUS_CHANNEL_BITS) / 8;
        int bit_off = (i * SBUS_CHANNEL_BITS) % 8;
        
        uint16_t ch = sbus_data[byte_idx] >> bit_off;
        ch |= (uint16_t)(sbus_data[byte_idx + 1]) << (8 - bit_off);
        if (bit_off > 5) {
            ch |= (uint16_t)(sbus_data[byte_idx + 2]) << (16 - bit_off);
        }
        
        channels[i] = ch & 0x07FF;
    }
}

void protocol_build_tx_payload(rf_tx_payload_t *payload,
                               const uint16_t *adc_channels,
                               uint8_t model_id,
                               uint8_t seq)
{
    uint16_t sbus_channels[SBUS_CHANNEL_COUNT];
    
    /* Convert 8 ADC channels to SBUS range, center the rest */
    for (int i = 0; i < 8; i++) {
        sbus_channels[i] = protocol_map_to_sbus(adc_channels[i]);
    }
    for (int i = 8; i < SBUS_CHANNEL_COUNT; i++) {
        sbus_channels[i] = SBUS_CENTER;
    }
    
    /* Build payload */
    memset(payload, 0, sizeof(rf_tx_payload_t));
    payload->frame_id = FRAME_ID_CHANNELS;
    payload->seq = seq;
    payload->model_id = model_id;
    payload->flags = 0;
    
    protocol_pack_sbus(sbus_channels, payload->sbus_data);
}

void protocol_parse_telemetry(const rf_rx_telemetry_t *telemetry,
                              uint16_t *battery_mv)
{
    if (telemetry->frame_id == FRAME_ID_TELEMETRY) {
        /* Battery voltage is big-endian */
        *battery_mv = (telemetry->battery_mv >> 8) | 
                       (telemetry->battery_mv << 8);
    }
}

uint16_t protocol_map_to_sbus(uint16_t adc_value)
{
    /* Map 12-bit ADC (0-4095) to SBUS range (200-1844) */
    uint32_t result = SBUS_MIN + ((uint32_t)adc_value * (SBUS_MAX - SBUS_MIN) / 4095);
    if (result > SBUS_MAX) result = SBUS_MAX;
    return (uint16_t)result;
}