// Ai-Thinker RD-03E driver — see rd03e.h for wiring and honesty notes.
//
// UNVERIFIED AGAINST REAL HARDWARE, and the frame format below is
// reconstructed from a third-party bring-up write-up (electroniclinic.com's
// RD-03E/ESP32 tutorial), not Ai-Thinker's own datasheet PDF (not available
// while writing this) — treat this as the least-certain protocol detail in
// this driver. What's cross-confirmed from multiple independent sources:
// UART is 256000 baud / 8N1, and the module also has a separate, more
// complex configuration-frame protocol (0xFD 0xFC 0xFB 0xFA header /
// 0x04 0x03 0x02 0x01 footer) for calibration and firmware queries — this
// driver does NOT implement that; it only reads the module's free-running
// "simple report" output frames, which need no configuration to start
// streaming after power-up.
//
// Simple report frame, as reconstructed (6 bytes total):
//   [0]     0xAA               frame header
//   [1]     gesture code       raw value, meaning not confirmed against an
//                               official datasheet — reported as-is in
//                               metadata rather than translated to a label
//                               that might be wrong
//   [2]     distance lo byte   distance_cm = lo | (hi << 8), little-endian
//   [3]     distance hi byte
//   [4..5]  0x55 0x55          frame footer
// Real bring-up should verify this against a logic analyzer capture before
// trusting field values, same as the LD2410 driver this replaced.

#include <string.h>
#include <stdbool.h>
#include "rd03e.h"
#include "driver/uart.h"
#include "esp_log.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"

static const char *TAG = "rd03e";

#define RD03E_RX_BUF_SIZE   512
#define RD03E_SCRATCH_SIZE  256
#define RD03E_FRAME_LEN     6

static const uint8_t FRAME_HEADER = 0xAA;
static const uint8_t FRAME_FOOTER[2] = { 0x55, 0x55 };

static bool s_ready = false;

typedef struct {
    uint8_t gesture;
    uint16_t distance_cm;
} rd03e_frame_t;

esp_err_t rd03e_init(void) {
    uart_config_t cfg = {
        .baud_rate = RD03E_UART_BAUD,
        .data_bits = UART_DATA_8_BITS,
        .parity = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE,
        .source_clk = UART_SCLK_DEFAULT,
    };

    esp_err_t err = uart_param_config(RD03E_UART_PORT, &cfg);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "uart_param_config failed: %s", esp_err_to_name(err));
        return err;
    }

    // uart_set_pin(port, tx_pin, rx_pin, rts_pin, cts_pin) -- our TX GPIO
    // wires to the module's RX (labeled "RX" on the module), and our RX
    // GPIO wires to the module's TX output (labeled "OT1" on the module).
    err = uart_set_pin(RD03E_UART_PORT, RD03E_UART_TX_GPIO, RD03E_UART_RX_GPIO,
                        UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "uart_set_pin failed: %s", esp_err_to_name(err));
        return err;
    }

    err = uart_driver_install(RD03E_UART_PORT, RD03E_RX_BUF_SIZE, 0, 0, NULL, 0);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "uart_driver_install failed: %s", esp_err_to_name(err));
        return err;
    }

    s_ready = true;
    ESP_LOGI(TAG, "RD-03E UART init ok on port %d (%d baud)", RD03E_UART_PORT, RD03E_UART_BAUD);
    return ESP_OK;
}

esp_err_t rd03e_read(sensor_reading_t *out, size_t max_out, size_t *out_count) {
    *out_count = 0;
    if (!s_ready) {
        return ESP_ERR_INVALID_STATE;
    }
    if (max_out < 1) {
        return ESP_ERR_NO_MEM;
    }

    uint8_t buf[RD03E_SCRATCH_SIZE];
    // The module free-runs its simple report frames, so a short read should
    // find at least one complete frame already queued in the RX ring buffer.
    int len = uart_read_bytes(RD03E_UART_PORT, buf, sizeof(buf), pdMS_TO_TICKS(200));
    if (len < 0) {
        ESP_LOGW(TAG, "uart_read_bytes error");
        return ESP_FAIL;
    }
    if (len == 0) {
        ESP_LOGD(TAG, "no UART data from RD-03E this cycle");
        return ESP_OK; // nothing new isn't a driver failure
    }

    bool parsed_any = false;
    rd03e_frame_t latest = {0};

    // Scan for the newest complete, validated frame in whatever arrived
    // this cycle; keep overwriting `latest` so we report the freshest one.
    for (int i = 0; i + RD03E_FRAME_LEN <= len; i++) {
        if (buf[i] != FRAME_HEADER) {
            continue;
        }
        if (memcmp(&buf[i + 4], FRAME_FOOTER, 2) != 0) {
            continue; // not a real header byte, or a corrupted frame
        }
        latest.gesture = buf[i + 1];
        latest.distance_cm = (uint16_t)buf[i + 2] | ((uint16_t)buf[i + 3] << 8);
        parsed_any = true;
        i += RD03E_FRAME_LEN - 1; // loop's i++ moves past this frame
    }

    if (!parsed_any) {
        ESP_LOGD(TAG, "no complete/valid RD-03E frame in this read window");
        return ESP_OK;
    }

    // Reported as a numeric distance (not a boolean "presence" flag, unlike
    // the LD2410 this replaced) — a handheld "sense a presence at a
    // distance" device wants magnitude, and it lets the backend's
    // statistical anomaly detector treat "something got suddenly close" as
    // the anomaly signal, the same way it already treats a temperature
    // spike, rather than only firing on a coarse absent/present transition.
    memset(&out[0], 0, sizeof(out[0]));
    strncpy(out[0].sensor_type, "presence", SENSOR_READING_TYPE_MAXLEN - 1);
    out[0].value = (double)latest.distance_cm;
    strncpy(out[0].unit, "cm", SENSOR_READING_UNIT_MAXLEN - 1);

    cJSON *meta = cJSON_CreateObject();
    if (meta != NULL) {
        // Raw code, not translated to a label -- see the honesty note above
        // about the gesture byte's exact meaning being unconfirmed.
        cJSON_AddNumberToObject(meta, "gesture_code", latest.gesture);
    }
    out[0].metadata = meta;

    *out_count = 1;
    return ESP_OK;
}