// JK BMS Web Gateway — minimal REST API console client.
//
// Fetches GET /api/realtime from the gateway and prints pack voltage,
// current, and state of charge. Demonstrates the smallest useful client:
// one HTTP GET, one JSON parse. See the full endpoint list and JSON field
// reference on the site's #api section.
//
// Build (Linux/macOS, needs libcurl + nlohmann/json):
//   g++ -std=c++17 jkbms_client_example.cpp -lcurl -o jkbms_client_example
// Run:
//   ./jkbms_client_example http://jkbms.local

#include <curl/curl.h>
#include <nlohmann/json.hpp>
#include <cstdio>
#include <cstdlib>
#include <string>

using nlohmann::json;

// libcurl calls this once per received chunk of the HTTP response body;
// appending to a std::string is the standard way to buffer a small response.
static size_t appendToBuffer(char *data, size_t size, size_t count, void *userData) {
    auto *buffer = static_cast<std::string *>(userData);
    buffer->append(data, size * count);
    return size * count;
}

// Performs one blocking HTTP GET and returns the response body.
// Throws std::runtime_error if the transfer itself fails (not on HTTP
// error status — the caller is expected to check the JSON's own "error" field).
static std::string httpGet(const std::string &url) {
    CURL *curl = curl_easy_init();
    if (!curl) {
        throw std::runtime_error("curl_easy_init failed");
    }

    std::string body;
    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, appendToBuffer);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &body);
    curl_easy_setopt(curl, CURLOPT_TIMEOUT, 5L);

    CURLcode result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);

    if (result != CURLE_OK) {
        throw std::runtime_error(curl_easy_strerror(result));
    }
    return body;
}

int main(int argc, char *argv[]) {
    // Default to the gateway's mDNS name; override with a bare IP if mDNS
    // isn't reachable on your network (e.g. "http://192.168.1.50").
    std::string baseUrl = (argc > 1) ? argv[1] : "http://jkbms.local";

    std::string body;
    try {
        body = httpGet(baseUrl + "/api/realtime");
    } catch (const std::exception &ex) {
        std::fprintf(stderr, "request failed: %s\n", ex.what());
        return 1;
    }

    json realtime = json::parse(body, /*cb*/ nullptr, /*allow_exceptions*/ false);
    if (realtime.is_discarded()) {
        std::fprintf(stderr, "invalid JSON response: %s\n", body.c_str());
        return 1;
    }
    if (realtime.contains("error")) {
        std::fprintf(stderr, "gateway error: %s\n", realtime["error"].get<std::string>().c_str());
        return 1;
    }

    std::printf("Pack voltage: %.2f V\n", realtime.value("totalVoltage", 0.0));
    std::printf("Current:      %.2f A\n", realtime.value("current", 0.0));
    std::printf("SOC:          %d %%\n", realtime.value("soc", 0));
    return 0;
}