// SPDX-FileCopyrightText: 2025 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
// SPDX-License-Identifier: GPL-3.0-only

#include "Merge.h"

#include <algorithm>
#include <cmath>
#include <limits>
#include <random>
#include <unordered_map>

#include <spdlog/fmt/fmt.h>

#include <gemmi/reciproc.hpp>

#include "../../common/CorrelationCoefficient.h"
#include "../../common/ResolutionShells.h"
#include "HKLKey.h"

MergeOnTheFly::MergeOnTheFly(const DiffractionExperiment &x)
    : space_group_number(x.GetSpaceGroupNumber().value_or(1)),
      scaling_settings(x.GetScalingSettings()),
      indexing_settings(x.GetIndexingSettings()),
      high_resolution_limit(scaling_settings.GetHighResolutionLimit_A()),
      image_cc_limit(scaling_settings.GetMinCCForImage()),
      min_partiality(scaling_settings.GetMinPartiality()),
      generator(scaling_settings.GetMergeFriedel(), space_group_number) {
}

MergeOnTheFly &MergeOnTheFly::ReferenceCell(const std::optional<UnitCell> &cell) {
    reference_cell = cell;
    return *this;
}

void MergeOnTheFly::AddImage(const IntegrationOutcome &outcome, bool cc_mask) {
    std::unique_lock ul(merged_mutex);
    const int half = half_dist(rng);

    if (Mask(outcome, cc_mask))
        return;

    for (const auto &r: outcome.reflections) {
        if (generator.IsSystematicallyAbsent(r))
            continue;

        if (r.image_scale_corr <= 0.0 || !std::isfinite(r.image_scale_corr))
            continue;
        if (!AcceptReflection(r, high_resolution_limit))
            continue;
        if (r.partiality < min_partiality)
            continue;

        const float I_corr = r.I * r.image_scale_corr;
        const float sigma_corr = r.sigma * r.image_scale_corr;
        if (!std::isfinite(I_corr) || !std::isfinite(sigma_corr) || sigma_corr <= 0.0)
            continue;

        auto hkl = generator(r);
        auto hkl_key = hkl.pack();

        auto it = accumulator.find(hkl_key);
        if (it == accumulator.end())
            it = accumulator.emplace(hkl_key, MergeAccum{
                                 .h = hkl.plus ? hkl.h : -hkl.h,
                                 .k = hkl.plus ? hkl.k : -hkl.k,
                                 .l = hkl.plus ? hkl.l : -hkl.l,
                             }).first;

        const float w = 1.0f / (sigma_corr * sigma_corr);
        const float wI = w * I_corr;

        it->second.sum_wI += wI;
        it->second.sum_w += w;

        it->second.sum_wI_half[half] += wI;
        it->second.sum_w_half[half] += w;
        it->second.n_half[half]++;

        if (!std::isfinite(it->second.d) && std::isfinite(r.d) && r.d > 0.0f)
            it->second.d = r.d;
    }
}

bool MergeOnTheFly::Mask(const IntegrationOutcome &outcome, bool cc_mask) {
    if (reference_cell) {
        auto cell = outcome.latt.GetUnitCell();
        if (!cell.is_close(*reference_cell,
                          indexing_settings.GetUnitCellDistTolerance(),
                          indexing_settings.GetUnitCellAngleTolerance_deg()))
            return true;
    }

    if (cc_mask && image_cc_limit) {
        if (!outcome.image_scale_cc
            || std::isnan(outcome.image_scale_cc.value())
            || outcome.image_scale_cc.value() < image_cc_limit.value())
            return true;
    }
    return false;
}

std::vector<MergedReflection> MergeOnTheFly::ExportReflections() {
    std::unique_lock ul(merged_mutex);

    float d_min = std::numeric_limits<float>::max();
    float d_max = 0.0f;

    std::vector<MergedReflection> out;
    out.reserve(accumulator.size());
    for (const auto &accum: accumulator | std::views::values) {
        if (accum.sum_w <= 0.0)
            continue;

        MergedReflection mr{
            .h = accum.h,
            .k = accum.k,
            .l = accum.l,
            .I = static_cast<float>(accum.sum_wI / accum.sum_w),
            .sigma = 1.0f / std::sqrt(static_cast<float>(accum.sum_w)),
            .I_half = {NAN, NAN},
            .sigma_half = {NAN, NAN},
            .d = accum.d
        };

        if (accum.n_half[0] + accum.n_half[1] > 0 && accum.sum_w_half[0] > 0.0 && accum.sum_w_half[1] > 0.0) {
            for (int i = 0; i < 2; ++i) {
                mr.I_half[i] = static_cast<float>(accum.sum_wI_half[i] / accum.sum_w_half[i]);
                mr.sigma_half[i] = 1.0f / std::sqrt(static_cast<float>(accum.sum_w_half[i]));
            }
        }

        if (!std::isfinite(accum.d) || accum.d <= 0.0f)
            continue;

        d_min = std::min(d_min, accum.d);
        d_max = std::max(d_max, accum.d);

        out.emplace_back(mr);
    }

    const double rfree_fraction = scaling_settings.GetRfreeFraction();
    if (rfree_fraction > 0.0 && !out.empty()) {
        if (d_min < d_max && d_min > 0.0f) {
            constexpr int n_shells = 20;

            const float d_min_pad = d_min * 0.999f;
            const float d_max_pad = d_max * 1.001f;

            ResolutionShells shells(d_min_pad, d_max_pad, n_shells);
            std::vector<std::vector<size_t>> shell_groups(n_shells);

            for (size_t i = 0; i < out.size(); ++i) {
                const auto shell = shells.GetShell(out[i].d);
                if (!shell.has_value())
                    continue;

                const int s = *shell;
                if (s >= 0 && s < n_shells)
                    shell_groups[s].push_back(i);
            }

            std::mt19937 rfree_rng(12345u);
            std::bernoulli_distribution rfree_dist(rfree_fraction);

            for (const auto &group: shell_groups) {
                for (const size_t idx: group)
                    out[idx].rfree_flag = rfree_dist(rfree_rng);
            }
        }
    }
    return out;
}

std::vector<MergedReflection> MergeAll(const DiffractionExperiment &x,
                                       const std::vector<IntegrationOutcome> &integration_outcome,
                                       bool mask) {
    MergeOnTheFly merge(x);
    for (const auto &outcome: integration_outcome)
        merge.AddImage(outcome, mask);
    return merge.ExportReflections();
}

struct ShellAccum {
    int total_obs = 0;
    int unique = 0;
    int possible = 0;

    double sum_i_over_sigma = 0.0;
    int n_i_over_sigma = 0;

    CorrelationCoefficient cc_half;
    CorrelationCoefficient cc_ref;
};

void CalcPossibleReflections(int space_group_number ,
                             const UnitCell &cell,
                             double d_min,
                             double d_max,
                             const ResolutionShells &shells,
                             std::vector<ShellAccum> &acc) {
    gemmi::UnitCell gemmi_cell = cell;
    const gemmi::SpaceGroup *sg = gemmi::find_spacegroup_by_number(space_group_number);
    if (sg == nullptr)
        throw JFJochException(JFJochExceptionCategory::InputParameterInvalid,
            "Invalid space group number " + std::to_string(space_group_number));

    // Generate unique reflections
    std::vector<gemmi::Miller> possible_hkls = gemmi::make_miller_vector(gemmi_cell, sg, d_min, d_max, true);
    CrystalLattice lattice(cell);
    const auto astar = lattice.Astar();
    const auto bstar = lattice.Bstar();
    const auto cstar = lattice.Cstar();

    for (const auto &hkl: possible_hkls) {
        const auto q = hkl[0] * astar + hkl[1] * bstar + hkl[2] * cstar;
        const auto qlen = q.Length();
        if (qlen < 1e-6)
            continue;
        const auto d = 1.0 / qlen;
        const auto shell = shells.GetShell(d);
        if (!shell.has_value())
            continue;
        const int s = *shell;
        if (s >= 0 && s < acc.size())
            acc[s].possible++;
    }
}


MergeStatistics MergeOnTheFly::MergeStats(const std::vector<MergedReflection> &merged,
                           const std::vector<IntegrationOutcome > &integration_outcome,
                           const std::vector<MergedReflection> &reference) {

    constexpr int n_shells = 10;

    auto d_min_limit_A = scaling_settings.GetHighResolutionLimit_A();

    std::unordered_map<uint64_t, float> reference_intensities;
    if (!reference.empty()) {
        reference_intensities.reserve(reference.size());
        for (const auto &r: reference) {
            if (!std::isfinite(r.I))
                continue;

            const auto hkl = generator(r);
            reference_intensities[hkl.pack()] = r.I;
        }
    }

    float d_min = std::numeric_limits<float>::max();
    float d_max = 0.0f;

    for (const auto &m: merged) {
        if (!std::isfinite(m.d) || m.d <= 0.0f)
            continue;
        if (d_min_limit_A && m.d < d_min_limit_A)
            continue;

        d_min = std::min(d_min, m.d);
        d_max = std::max(d_max, m.d);
    }

    if (!(d_min < d_max && d_min > 0.0f))
        throw JFJochException(JFJochExceptionCategory::InputParameterInvalid,
            "MergeStats: Error in resolution calculation");

    const float d_min_pad = d_min * 0.999f;
    const float d_max_pad = d_max * 1.001f;

    ResolutionShells shells(d_min_pad, d_max_pad, n_shells);
    const auto shell_mean_1_d2 = shells.GetShellMeanOneOverResSq();
    const auto shell_min_res = shells.GetShellMinRes();

    std::vector<ShellAccum> acc(n_shells);

    if (reference_cell.has_value())
        CalcPossibleReflections(space_group_number, reference_cell.value(),
            d_min_pad, d_max_pad, shells, acc);

    CorrelationCoefficient cc_half_overall;
    CorrelationCoefficient cc_ref_overall;

    for (const auto &m: merged) {
        const auto shell = shells.GetShell(m.d);
        if (!shell.has_value())
            continue;

        const int s = *shell;
        if (s >= 0 && s < n_shells) {
            if (std::isfinite(m.I) && std::isfinite(m.sigma) && m.sigma > 0.0) {
                acc[s].unique++;
                acc[s].sum_i_over_sigma += m.I / m.sigma;
                ++acc[s].n_i_over_sigma;

                if (!reference_intensities.empty()) {
                    const auto hkl = generator(m);
                    const auto ref_it = reference_intensities.find(hkl.pack());
                    if (ref_it != reference_intensities.end() && std::isfinite(ref_it->second)) {
                        acc[s].cc_ref.Add(m.I, ref_it->second);
                        cc_ref_overall.Add(m.I, ref_it->second);
                    }
                }

                if (std::isfinite(m.I_half[0]) && std::isfinite(m.I_half[1])) {
                    acc[s].cc_half.Add(m.I_half[0], m.I_half[1]);
                    cc_half_overall.Add(m.I_half[0], m.I_half[1]);
                }

            }
        }
    }

    for (int i = 0; i < integration_outcome.size(); ++i) {
        if (Mask(integration_outcome[i], true))
            continue;

        for (const auto &r: integration_outcome[i].reflections) {
            if (generator.IsSystematicallyAbsent(r))
                continue;
            if (r.image_scale_corr <= 0.0 || !std::isfinite(r.image_scale_corr))
                continue;
            if (!AcceptReflection(r, d_min_limit_A))
                continue;
            if (r.partiality < min_partiality)
                continue;

            const float I_corr = r.I * r.image_scale_corr;
            const float sigma_corr = r.sigma * r.image_scale_corr;
            if (!std::isfinite(I_corr) || !std::isfinite(sigma_corr) || sigma_corr <= 0.0f)
                continue;

            const auto shell = shells.GetShell(r.d);
            if (!shell.has_value())
                continue;
            const int s = *shell;
            if (s >= 0 && s < n_shells)
                acc[s].total_obs++;
        }
    }

    MergeStatistics out;
    out.shells.resize(n_shells);

    for (int s = 0; s < n_shells; ++s) {
        const auto &sa = acc[s];
        auto &ss = out.shells[s];

        ss.mean_one_over_d2 = shell_mean_1_d2[s];
        ss.d_min = shell_min_res[s];
        ss.d_max = s == 0 ? d_max_pad : shell_min_res[s - 1];
        ss.total_observations = sa.total_obs;
        ss.unique_reflections = sa.unique;
        ss.possible_unique_reflections = sa.possible;
        ss.mean_i_over_sigma = sa.n_i_over_sigma > 0
                                   ? sa.sum_i_over_sigma / sa.n_i_over_sigma
                                   : 0.0;

        ss.cc_half = sa.cc_half.GetCC();
        ss.cc_ref = sa.cc_ref.GetCC();
    }

    auto &overall = out.overall;
    overall.d_min = d_min;
    overall.d_max = d_max;

    int all_possible = 0;
    int all_unique = 0;
    double sum_i_over_sigma = 0.0;
    int n_i_over_sigma = 0;


    for (const auto &sa: acc) {
        overall.total_observations += sa.total_obs;
        all_unique += sa.unique;
        all_possible += sa.possible;
        sum_i_over_sigma += sa.sum_i_over_sigma;
        n_i_over_sigma += sa.n_i_over_sigma;

    }

    overall.possible_unique_reflections = all_possible;
    overall.unique_reflections = all_unique;
    overall.mean_i_over_sigma = n_i_over_sigma > 0 ? sum_i_over_sigma / n_i_over_sigma : 0.0;
    overall.cc_half = cc_half_overall.GetCC();
    overall.cc_ref = cc_ref_overall.GetCC();

    return out;
}

std::ostream &operator<<(std::ostream &output, const MergeStatisticsShell &in) {
    double completeness = in.possible_unique_reflections > 0
        ? static_cast<double>(in.unique_reflections) / in.possible_unique_reflections * 100.0 : 0.0;

    output << fmt::format("{:8d} {:8d} {:8d} {:7.1f}% {:8.1f} {:7.1f}% {:7.1f}%",
                in.total_observations,
                in.unique_reflections,
                in.possible_unique_reflections,
                completeness,
                in.mean_i_over_sigma,
                in.cc_half*100.0,
                in.cc_ref*100.0);
    return output;
}

std::ostream &operator<<(std::ostream &output, const MergeStatistics &in) {
    output << std::endl;
    output << fmt::format("  {:>8s} {:>8s} {:>8s} {:>8s} {:>8s} {:>8s} {:>8s} {:>8s}",
        "d_min", "N_obs", "N_uniq", "N_possib", "Compl","<I/sig>", "CC1/2", "CCref")
    << std::endl;;
    output << fmt::format("  {:->8s} {:->8s} {:->8s} {:->8s} {:->8s} {:->8s} {:->8s} {:->8s}",
        "", "", "", "", "", "", "", "") << std::endl;
    for (const auto &sh: in.shells) {
        if (sh.unique_reflections == 0)
            continue;
        output << fmt::format("  {:8.2f} ", sh.d_min);
        output << sh;
        output << std::endl;
    }
    output << fmt::format("  {:->8s} {:->8s} {:->8s} {:->8s} {:->8s} {:->8s} {:->8s} {:->8s}",
        "", "", "", "", "", "", "", "") << std::endl;

    output << fmt::format("  {:>8s} ", "Overall");
    output << in.overall;
    output << std::endl;
    output << std::endl;
    return output;
}