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

#pragma once

// The rigid body's target evaluated on a GPU (CUDA builds only; the header itself needs no CUDA).
// It is the function RigidBodyTarget computes on the CPU - the same density, the same composition of
// Fcalc from one copy, the same bulk-solvent mask, scale fit, residuals and Jacobian - moved to the
// device so that a fit takes a fraction of a second instead of several seconds. The two agree to
// rounding, not bit for bit: float distances, cuFFT for FFTW. The GPU is deterministic on its own.

#include <condition_variable>
#include <map>
#include <memory>
#include <mutex>
#include <optional>
#include <stdexcept>
#include <string>
#include <vector>

#include "RigidBodyRefine.h"

class Logger;
class RigidBodyGPUEngine;
struct RigidBodyGPUZone;

// A CUDA failure inside the rigid body, or in model validation's structure factors and maps
// (ModelStructureFactorsGPU). Model validation catches it and reports the validation as failed.
class RigidBodyGPUFailure : public std::runtime_error {
public:
    explicit RigidBodyGPUFailure(const std::string &what) : std::runtime_error(what) {}
};

// A few engines, reserved once for a whole validation: each is a stream and the buffers for one fit at
// a time, sized for the finest zone of the ladder to d_min. The real fit and the null's replicates each
// take one for the length of their fit, and wait for one when all are taken. Engines are
// interchangeable and every kernel deterministic, so which replicate gets which engine does not change
// a number. A pool belongs to one model: what a zone needs of its atoms - their densities, radii and mask
// radii, which the placement does not change - is worked out once per zone and kept.
class RigidBodyGPUPool {
public:
    // Null where there is no GPU, where not even one engine fits the budget - a quarter of the card,
    // and never the last gigabyte of what is free, since the merge may be running beside it - or where
    // the cell is too small for the gather (an atom's box wider than the cell). Logged either way.
    // `max_observations`: the most working reflections any fit will be given in its finest zone.
    // `max_engines`: at most this many, however much memory there is.
    static std::unique_ptr<RigidBodyGPUPool> Create(const gemmi::Model &model, const gemmi::UnitCell &cell,
                                                    const gemmi::SpaceGroup &sg, double d_min,
                                                    size_t max_observations, size_t max_engines, Logger &logger);
    ~RigidBodyGPUPool();

    size_t Engines() const { return engines_.size(); }
    // The card the pool was made from, which its first engine is on and the others count on from.
    int Device() const { return device_; }
    // What max_engines engines take, however many fitted, and the memory of the card: the sizes a
    // caller decides by whether a second validation may run beside this one.
    size_t PlannedBytes() const { return planned_bytes_; }
    size_t CardBytes() const { return card_bytes_; }
    RigidBodyGPUEngine &Acquire();
    void Release(RigidBodyGPUEngine &engine);

    // The zone to d_min without its observations, for this pool's model.
    const RigidBodyGPUZone &Zone(const gemmi::Model &model, const gemmi::UnitCell &cell, const gemmi::SpaceGroup &sg,
                                 double d_min);
    // The zone with these observations and the composition of Fcalc at them. The null's replicates are all
    // fitted to the same reflections, so they share it.
    std::shared_ptr<const RigidBodyGPUZone> ObservedZone(const gemmi::Model &model, const gemmi::UnitCell &cell,
                                                         const gemmi::SpaceGroup &sg,
                                                         const gemmi::AsuData<gemmi::ValueSigma<float>> &fobs,
                                                         double d_min);

private:
    RigidBodyGPUPool() = default;
    int device_ = 0;
    size_t planned_bytes_ = 0;
    size_t card_bytes_ = 0;
    std::vector<std::unique_ptr<RigidBodyGPUEngine>> engines_;
    std::vector<RigidBodyGPUEngine *> idle_;
    std::mutex m_;
    std::condition_variable cv_;
    std::map<double, std::unique_ptr<RigidBodyGPUZone>> zones_;
    std::mutex zones_m_;
    struct ObservedEntry {
        double d_min;
        gemmi::AsuData<gemmi::ValueSigma<float>> fobs;
        std::shared_ptr<const RigidBodyGPUZone> zone;
    };
    std::vector<ObservedEntry> observed_;
    std::mutex observed_m_;
};

// An engine taken from a pool for as long as this lives.
class RigidBodyGPULease {
public:
    explicit RigidBodyGPULease(RigidBodyGPUPool &pool) : pool_(pool), engine_(pool.Acquire()) {}
    ~RigidBodyGPULease() { pool_.Release(engine_); }
    RigidBodyGPULease(const RigidBodyGPULease &) = delete;
    RigidBodyGPULease &operator=(const RigidBodyGPULease &) = delete;
    RigidBodyGPUEngine &Engine() { return engine_; }

private:
    RigidBodyGPUPool &pool_;
    RigidBodyGPUEngine &engine_;
};

class RigidBodyTargetGPU : public RigidBodyTargetBase {
public:
    // Takes an engine from `pool` for its lifetime. q = 0 is the placement `model` has now; unlike the
    // CPU target the model is never moved by an evaluation, only by Place().
    RigidBodyTargetGPU(RigidBodyGPUPool &pool, gemmi::Model &model, const gemmi::UnitCell &cell,
                       const gemmi::SpaceGroup &sg, size_t nthreads);
    ~RigidBodyTargetGPU() override;

    void SetZone(const gemmi::AsuData<gemmi::ValueSigma<float>> &fobs, double d_min) override;
    size_t NumObservations() const override;

    bool Residuals(const double q[6], double *residuals) override;
    bool Jacobian(const double q[6], double *jacobian) override;

private:
    // The placement at q as x -> R (x - centroid) + centroid + t.
    void Placement(const double q[6], double rotation[9], double translation[3]) const;
    void HostScale();

    RigidBodyGPUPool &pool_;
    RigidBodyGPULease lease_;
    RigidBodyGPUEngine &engine_;
    gemmi::Model &model_;
    const gemmi::UnitCell &cell_;
    const gemmi::SpaceGroup &sg_;
    size_t nthreads_;

    double d_min_ = 0;
    std::shared_ptr<const RigidBodyGPUZone> zone_;
    bool solvent_fitted_ = false;
    bool host_scale_ = false;             // the zone's scale is fitted on the host (HostScale)

    bool have_point_ = false;
    std::array<double, 6> q_{};
    double k_overall_ = 1;
    gemmi::SMat33<double> b_star_{0, 0, 0, 0, 0, 0};
};