DoorCounter/firmware/src/ble_scanner.cpp

// firmware/src/ble_scanner.cpp
#include "ble_scanner.h"
#include <NimBLEDevice.h>
#include <NimBLEScan.h>
#include <NimBLEAdvertisedDevice.h>
#include "mbedtls/md.h"
#include <map>
#include <mutex>

#define RSSI_NEAR -65
#define RSSI_MID  -80

static std::mutex s_mutex;

struct DeviceObs {
    int rssi_sum;
    int count;
};

static std::map<String, DeviceObs> s_seen;
static int s_max_concurrent = 0;

static String sha256_prefix(const String& input) {
    const mbedtls_md_info_t* info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
    if (!info) return String(); // SHA256 not available

    uint8_t hash[32] = {};
    mbedtls_md_context_t ctx;
    mbedtls_md_init(&ctx);
    if (mbedtls_md_setup(&ctx, info, 0) != 0) {
        mbedtls_md_free(&ctx);
        return String();
    }
    mbedtls_md_starts(&ctx);
    mbedtls_md_update(&ctx, (const uint8_t*)input.c_str(), input.length());
    mbedtls_md_finish(&ctx, hash);
    mbedtls_md_free(&ctx);

    String hex = "";
    char buf[3];
    for (int i = 0; i < 16; i++) { snprintf(buf, 3, "%02x", hash[i]); hex += buf; }
    return hex;
}

class ScanCallback : public NimBLEScanCallbacks {
    void onResult(const NimBLEAdvertisedDevice* dev) override {
        String mac  = String(dev->getAddress().toString().c_str());
        String hash = sha256_prefix(mac);
        int    rssi = dev->getRSSI();

        std::lock_guard<std::mutex> lock(s_mutex);
        auto it = s_seen.find(hash);
        if (it == s_seen.end()) {
            s_seen[hash] = {rssi, 1};
        } else {
            it->second.rssi_sum += rssi;
            it->second.count++;
        }
        int concurrent = (int)s_seen.size();
        if (concurrent > s_max_concurrent) s_max_concurrent = concurrent;
    }
};

static ScanCallback s_callback;
static NimBLEScan*  s_scan = nullptr;

void ble_scanner_start() {
    NimBLEDevice::init("");
    s_scan = NimBLEDevice::getScan();
    s_scan->setScanCallbacks(&s_callback, true); // true = allow duplicates
    s_scan->setActiveScan(false);   // passive
    s_scan->setInterval(100);
    s_scan->setWindow(99);
    s_scan->setMaxResults(0);       // don't store results — callback-only
    s_scan->start(0, false, false); // duration=0 (forever), isContinue=false, restart=false
}

void ble_scanner_pause()  { if (s_scan) s_scan->stop(); }
void ble_scanner_resume() { if (s_scan) s_scan->start(0, false, false); }

void ble_scanner_deinit() {
    if (s_scan) s_scan->stop();
    s_scan = nullptr;
    NimBLEDevice::deinit(true); // frees NimBLE heap (~25KB)
}

void ble_scanner_reinit() {
    ble_scanner_start(); // re-init stack and restart scan
}

BLEHourlyRecord ble_scanner_collect(uint32_t period_start, uint32_t period_end) {
    // Swap accumulators under lock — minimise time with lock held
    std::map<String, DeviceObs> local_seen;
    int local_max = 0;
    {
        std::lock_guard<std::mutex> lock(s_mutex);
        std::swap(local_seen, s_seen);
        local_max = s_max_concurrent;
        s_max_concurrent = 0;
    }

    // Process outside the lock — heap allocation safe here
    BLEHourlyRecord rec;
    rec.period_start    = period_start;
    rec.period_end      = period_end;
    rec.unique_devices  = (int)local_seen.size();
    rec.max_concurrent  = local_max;
    rec.near_count = 0; rec.mid_count = 0; rec.far_count = 0;

    for (auto& kv : local_seen) {
        float avg_rssi = kv.second.rssi_sum / (float)kv.second.count;
        if (avg_rssi > RSSI_NEAR)      rec.near_count++;
        else if (avg_rssi > RSSI_MID)  rec.mid_count++;
        else                           rec.far_count++;
        rec.device_hashes.push_back(kv.first);
    }
    return rec;
}