INetworkSolver.hpp

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// SPDX-License-Identifier: Apache-2.0
//
// Copyright 2026 Caleb Buahin
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

 
#ifndef OPENSWMM_ENGINE_FV_I_NETWORK_SOLVER_HPP
#define OPENSWMM_ENGINE_FV_I_NETWORK_SOLVER_HPP
 
namespace openswmm::fv {
 
// Forward declarations — passed by reference, no definitions needed here.
struct NetworkMeshData;
struct NetworkStateData;
struct FvOptions;

struct FvStepForcing {
    const double* node_lateral = nullptr;

    const double* node_fixed_head = nullptr;

    const double* structure_flow = nullptr;

    const double* link_q_cap = nullptr;

    const double* conduit_loss = nullptr;

    void (*refresh)(void* user, double t_elapsed) = nullptr;
    void*  refresh_user = nullptr;
 
    int n_nodes = 0;
    int n_links = 0;
};

class INetworkSolver {
public:
    virtual ~INetworkSolver() = default;

    virtual void initialize(NetworkMeshData& mesh, NetworkStateData& state,
                            const FvOptions& opts) = 0;

    virtual double advance(double t_current, double t_target,
                           const FvStepForcing& forcing) = 0;

    virtual void reinitialize(double t0) = 0;

    virtual void finalize() = 0;

    virtual long last_num_steps() const noexcept = 0;

    virtual double last_step_size() const noexcept = 0;

    virtual double suggested_step() const noexcept = 0;

    struct RunStats {
        long   nsteps      = 0;    
        long   nflux       = 0;    
        double last_h      = 0.0;  
        double avg_h       = 0.0;  
        double min_h       = 0.0;  
 
        // Work-list compaction telemetry. Negative fractions mean "not
        // populated" (compaction disabled or never sampled).
        double active_frac_min  = -1.0;
        double active_frac_mean = -1.0;
        double active_frac_max  = -1.0;
 
        long   tier_cells[8] = {0}; 
        int    n_tiers       = 0;   
 
        // dt-argmin attribution (slot program R0): which regime owned the
        // binding CFL element, counted once per census (global path) or
        // re-tier (LTS path). Answers "who sets the step" without a trace.
        long   dt_argmin_pressurized = 0;  
        long   dt_argmin_band        = 0;  
        long   dt_argmin_free        = 0;  
        long   dt_argmin_node        = 0;  
    };

    virtual RunStats run_stats() const noexcept { return {}; }

    struct Divergence {
        int         link  = -1;       
        double      value = 0.0;      
        const char* what  = nullptr;  
    };

    virtual bool divergence(Divergence& d) const noexcept {
        (void)d;
        return false;
    }

    virtual bool is_initialized() const noexcept = 0;
};
 
} // namespace openswmm::fv
 
#endif // OPENSWMM_ENGINE_FV_I_NETWORK_SOLVER_HPP