/**
 * AWB Processor - OpenCV Gray World White Balance
 * Compiled to WASM via Emscripten (MAIN_MODULE, dynamic linking with .so)
 *
 * Reads:  /data/input.png  (MEMFS, injected by Node.js runner)
 * Writes: /data/output.png (MEMFS, read by Node.js runner)
 * Stdout: metadata string
 */
#include <stdio.h>
#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/imgcodecs.hpp>

int main() {
    const char* input = "/data/input.png";
    const char* output = "/data/output.png";

    cv::Mat img = cv::imread(input);
    if (img.empty()) {
        fprintf(stderr, "ERR:Failed to read: %s\n", input);
        return 1;
    }

    int h = img.rows, w = img.cols;

    // Convert to float for accuracy
    cv::Mat imgf;
    img.convertTo(imgf, CV_32FC3);

    // Split channels (BGR order in OpenCV)
    std::vector<cv::Mat> ch;
    cv::split(imgf, ch);

    // Compute channel means
    cv::Scalar m = cv::mean(imgf);

    // Gray World: average of all channels
    float avg = (m[0] + m[1] + m[2]) / 3.0f;

    // Scale each channel so its mean equals the global average
    if (m[0] > 0.01f) ch[0] *= (avg / m[0]);  // B
    if (m[1] > 0.01f) ch[1] *= (avg / m[1]);  // G
    if (m[2] > 0.01f) ch[2] *= (avg / m[2]);  // R

    // Merge and convert back
    cv::merge(ch, imgf);
    imgf.convertTo(img, CV_8UC3);

    // Write output
    cv::imwrite(output, img);

    // Metadata to stderr (runner reads pure base64 from stdout)
    fprintf(stderr, "OK:%dx%d:M=%.2f,%.2f,%.2f:S=%.4f,%.4f,%.4f\n",
            w, h,
            m[2], m[1], m[0],       // RGB means
            avg / m[2], avg / m[1], avg / m[0]); // RGB scales

    return 0;
}