// SPDX-FileCopyrightText: 2026 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
// SPDX-License-Identifier: GPL-3.0-only

#include <catch2/catch_all.hpp>

#include <cmath>
#include <random>

#include "../image_analysis/geom_refinement/BeamCenterFFT.h"

namespace {

// An isotropic scattered background about (cx, cy): a decaying continuum with a solvent-ring bump,
// the mean of ~60 frames' worth of counting noise on top, NAN outside the detector's usable area.
// A horizontal dead stripe stands in for a module gap.
std::vector<float> Synthesise(int64_t w, int64_t h, float cx, float cy, float shadow_sector) {
    std::vector<float> mean(static_cast<size_t>(w * h), NAN);
    std::mt19937 rng(20260912);
    std::normal_distribution<float> gauss(0.0f, 1.0f);
    for (int64_t y = 0; y < h; y++) {
        if (y >= 300 && y < 320)
            continue;   // module gap
        for (int64_t x = 0; x < w; x++) {
            const float r = std::hypot(static_cast<float>(x) - cx, static_cast<float>(y) - cy);
            const float t = (r - 260.0f) / 30.0f;
            float value = 120.0f * std::exp(-r / 220.0f) + 45.0f * std::exp(-0.5f * t * t) + 5.0f;
            const float phi = std::atan2(static_cast<float>(y) - cy, static_cast<float>(x) - cx);
            if (phi > 0.0f && phi < 1.0f)
                value *= shadow_sector;
            mean[static_cast<size_t>(y * w + x)] = value + gauss(rng) * std::sqrt(value / 60.0f);
        }
    }
    return mean;
}

} // namespace

TEST_CASE("BeamCenterFFT_SyntheticBackground", "[BeamCenter]") {
    // The centre is nowhere near the image middle - the score must not care.
    const int64_t w = 900, h = 700;
    const float cx = 297.25f, cy = 411.5f;

    SECTION("clean isotropic background") {
        const auto mean = Synthesise(w, h, cx, cy, 1.0f);
        const auto r = BeamCenterFFTScore(w, h, mean);

        REQUIRE(!r.point.empty());
        REQUIRE(!r.line_x.empty());
        REQUIRE(!r.line_y.empty());
        // Whole-detector capture: the strongest point-symmetry centre is the true one.
        CHECK(std::hypot(r.point[0].beam_x_pxl - cx, r.point[0].beam_y_pxl - cy) < 2.0f);
        CHECK(std::abs(r.line_x[0].beam_x_pxl - cx) < 2.0f);
        CHECK(std::abs(r.line_y[0].beam_y_pxl - cy) < 2.0f);
        // A clean unimodal surface separates its argmax from the runner-up by a wide margin.
        CHECK(r.margin_point > 0.05f);
    }

    SECTION("a shadowed sextant keeps the true centre in the shortlist") {
        const auto mean = Synthesise(w, h, cx, cy, 0.5f);
        const auto r = BeamCenterFFTScore(w, h, mean);

        REQUIRE(!r.point.empty());
        float best = 1e9f;
        for (const auto &c : r.point)
            best = std::min(best, std::hypot(c.beam_x_pxl - cx, c.beam_y_pxl - cy));
        // The argmax is pulled by the asymmetry (measured ~9 px here - the same shadow bias the
        // background estimator carries); the shortlist must still hold the answer within the
        // 12 px a re-indexing verifier accepts.
        CHECK(best < 12.0f);
    }
}