/*
 * Copyright 2017 Anton Khirnov <anton@khirnov.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef TEUKOLSKY_DATA_H
#define TEUKOLSKY_DATA_H

#include <stdarg.h>
#include <stddef.h>
#include <stdint.h>

/**
 * API usage:
 *
 * First, allocate the solver context with td_context_alloc(). All interaction
 * with the solver is done through this context.
 *
 * Fill any fields in the context that are described as settable by the caller.
 * Call td_solve() to solve the equation determined by the option values.
 *
 * The metric/extrinsic curvature can be evaluated with td_eval_metric()/td_eval_curv().
 *
 * Finally, free the solver context with td_context_free().
 */

typedef struct TDContext {
    /**
     *  Solver internals, not to be accessed by the caller
     */
    void *priv;

    /********************************
     *  options, set by the caller  *
     ********************************/

    /**
     * A callback that will be used to print diagnostic messages.
     *
     * Defaults to fprintf(stderr, ...)
     */
    void (*log_callback)(const struct TDContext *td, int level,
                         const char *fmt, va_list);

    /**
     * Arbitrary user data, e.g. to be used by the log callback.
     */
    void *opaque;

    /********************************
     *  initial data parameters     *
     ********************************/

    /**
     * The amplitude in the I function.
     * Defaults to 1.
     */
    double amplitude;

    /********************************
     *        solver options        *
     ********************************/

    /**
     * The number of basis functions in each direction.
     * [0] - radial, [1] - angular
     */
    unsigned int nb_coeffs[2];

    /**
     * The scaling factor used in the basis functions.
     * [0] - radial, [1] - angular
     */
    double basis_scale_factor[2];

    /**
     * Maximum number of Newton iterations.
     */
    unsigned int max_iter;

    /**
     * Absolute tolerance. The solver is deemed to have converged
     * after maximum difference between iterations is below this bound.
     */
    double atol;

    /**
     * Number of threads to use for parallelization. Set to 0 to automatically
     * detect according to the number of CPU cores.
     */
    unsigned int nb_threads;

    double *coeffs[3];

    unsigned int solution_branch;
} TDContext;

/**
 * Allocate and initialize the solver.
 */
TDContext *td_context_alloc(void);

/**
 * Free the solver and everything associated with it.
 */
void td_context_free(TDContext **td);

/**
 * Solve the equation for the conformal factor ψ and export the expansion coefficients in the
 * context.
 *
 * @return >= 0 on success, a negative error code on failure
 */
int td_solve(TDContext *td, double *coeffs_init[3]);

/**
 * Evaluate the 3-metric γ_ij at the specified rectangular grid (in cylindrical
 * coordinates { ρ, z, φ }).
 *
 * @param td the solver context
 * @param rho the array of ρ coordinates.
 * @param nb_coords_rho the number of elements in rho.
 * @param z   the array of z coordinates.
 * @param nb_coords_z the number of elements in z.
 * @param nb_comp number of needed components of the metric
 * @param comp a nb_comp-sized array specifying the components of the metric to evaluate
 * @param diff_order a nb_comp-sized array specifying the order of the derivatives of the
 *                   metric to evaluate. The first element specifies the derivative wrt ρ,
 *                   the second wrt z. I.e. diff_order[i] = { 0, 0 } evaluates the metric
 *                   itself, diff_order[i] = { 0, 1 } evaluates ∂γ/∂z etc.
 * @param out a nb_comp-sized array of pointers to the arrays into which the values of the
 *            metric will be written. Each requested component is evaluated on the grid
 *            formed by the outer product of the rho and z vectors. I.e.
 *            out[l][j * out_strides[l] + i] = γ_comp[l](rho[i], z[j]). The length of each
 *            array in out must be nb_coords_rho * nb_coords_z.
 * @param out_strides a nb_comp-sized array of distances (in double-sized elements), for each
 *                    array in out, between two elements corresponding to the same ρ but one
 *                    step in z. Each element in out_strides must be at least nb_coords_rho.
 *
 * @return >= 0 on success, a negative error code on failure.
 */
int td_eval_psi(const TDContext *td,
                size_t nb_coords, const double *r, const double *theta,
                const unsigned int diff_order[2],
                double *out);
int td_eval_krr(const TDContext *td,
                size_t nb_coords, const double *r, const double *theta,
                const unsigned int diff_order[2],
                double *out);
int td_eval_kpp(const TDContext *td,
                size_t nb_coords, const double *r, const double *theta,
                const unsigned int diff_order[2],
                double *out);

#endif /* TEUKOLSKY_DATA_H */