/**
 * @file protocol.h
 * @brief AliceRC communication protocol definitions
 * 
 * Matches the AliceRX_STC receiver protocol:
 * - NRF24L01 32-byte payload
 * - Frame ID 0xA0 for channel data
 * - ACK payload 0xB0 for telemetry
 * - 16 SBUS channels packed as 11-bit little-endian bitstream
 */
#pragma once

#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif

/* Protocol constants */
#define FRAME_ID_CHANNELS      0xA0
#define FRAME_ID_TELEMETRY     0xB0
#define RF_PAYLOAD_SIZE        32
#define RF_ADDR_SIZE           5
#define SBUS_CHANNEL_COUNT     16
#define SBUS_CHANNEL_BITS      11

/* NRF24L01 TX payload (32 bytes) */
typedef struct __attribute__((packed)) {
    uint8_t frame_id;       /* 0xA0 = FRAME_ID_CHANNELS */
    uint8_t seq;            /* Sequence number, wraps around */
    uint8_t model_id;       /* Currently selected model ID */
    uint8_t flags;          /* Flags (reserved for future use) */
    uint8_t sbus_data[22];  /* 16 channels × 11 bit = 176 bit, little-endian */
    uint8_t reserved[6];    /* Reserved for future use */
} rf_tx_payload_t;

/* NRF24L01 ACK payload from receiver (32 bytes) */
typedef struct __attribute__((packed)) {
    uint8_t frame_id;       /* 0xB0 = FRAME_ID_TELEMETRY */
    uint8_t seq;            /* Sequence number */
    uint16_t battery_mv;    /* Battery voltage in mV (big-endian) */
    uint8_t reserved[28];   /* Reserved for future use */
} rf_rx_telemetry_t;

/* SBUS channel value range */
#define SBUS_MIN        200
#define SBUS_CENTER     1024
#define SBUS_MAX        1844

/* Function declarations */

/* Initialize protocol module */
void protocol_init(void);

/* Pack SBUS channels into 22-byte bitstream */
void protocol_pack_sbus(const uint16_t *channels, uint8_t *sbus_data);

/* Unpack SBUS channels from 22-byte bitstream */
void protocol_unpack_sbus(const uint8_t *sbus_data, uint16_t *channels);

/* Build TX payload from ADC channel values */
void protocol_build_tx_payload(rf_tx_payload_t *payload, 
                               const uint16_t *adc_channels, 
                               uint8_t model_id,
                               uint8_t seq);

/* Parse telemetry data from receiver */
void protocol_parse_telemetry(const rf_rx_telemetry_t *telemetry,
                              uint16_t *battery_mv);

/* Map ADC value (0-4095) to SBUS range (200-1844) */
uint16_t protocol_map_to_sbus(uint16_t adc_value);

#ifdef __cplusplus
}
#endif