#include <errno.h>

#include <math.h>

#include "proj.h"

#include "proj_internal.h"

PROJ_HEAD(hammer, "Hammer & Eckert-Greifendorff")

"\n\tMisc Sph, \n\tW= M=";

#define EPS 1.0e-10

namespace { // anonymous namespace

struct pq_hammer {

    double w;

    double m, rm;

};

} // anonymous namespace

static PJ_XY hammer_s_forward(PJ_LP lp, PJ *P) { /* Spheroidal, forward */

    PJ_XY xy = {0.0, 0.0};

    struct pq_hammer *Q = static_cast<struct pq_hammer *>(P->opaque);

    double cosphi, d;

    cosphi = cos(lp.phi);

    lp.lam *= Q->w;

    double denom = 1. + cosphi * cos(lp.lam);

    if (denom == 0.0) {

        proj_errno_set(P, PROJ_ERR_COORD_TRANSFM_OUTSIDE_PROJECTION_DOMAIN);

        return proj_coord_error().xy;

    }

    d = sqrt(2. / denom);

    xy.x = Q->m * d * cosphi * sin(lp.lam);

    xy.y = Q->rm * d * sin(lp.phi);

    return xy;

}

static PJ_LP hammer_s_inverse(PJ_XY xy, PJ *P) { /* Spheroidal, inverse */

    PJ_LP lp = {0.0, 0.0};

    struct pq_hammer *Q = static_cast<struct pq_hammer *>(P->opaque);

    double z;

    z = sqrt(1. - 0.25 * Q->w * Q->w * xy.x * xy.x - 0.25 * xy.y * xy.y);

    if (fabs(2. * z * z - 1.) < EPS) {

        lp.lam = HUGE_VAL;

        lp.phi = HUGE_VAL;

        proj_errno_set(P, PROJ_ERR_COORD_TRANSFM_OUTSIDE_PROJECTION_DOMAIN);

    } else {

        lp.lam = aatan2(Q->w * xy.x * z, 2. * z * z - 1) / Q->w;

        lp.phi = aasin(P->ctx, z * xy.y);

    }

    return lp;

}

PJ *PJ_PROJECTION(hammer) {

    struct pq_hammer *Q =

        static_cast<struct pq_hammer *>(calloc(1, sizeof(struct pq_hammer)));

    if (nullptr == Q)

        return pj_default_destructor(P, PROJ_ERR_OTHER /*ENOMEM*/);

    P->opaque = Q;

    if (pj_param(P->ctx, P->params, "tW").i) {

        Q->w = fabs(pj_param(P->ctx, P->params, "dW").f);

        if (Q->w <= 0.) {

            proj_log_error(P, _("Invalid value for W: it should be > 0"));

            return pj_default_destructor(P,

                                         PROJ_ERR_INVALID_OP_ILLEGAL_ARG_VALUE);

        }

    } else

        Q->w = .5;

    if (pj_param(P->ctx, P->params, "tM").i) {

        Q->m = fabs(pj_param(P->ctx, P->params, "dM").f);

        if (Q->m <= 0.) {

            proj_log_error(P, _("Invalid value for M: it should be > 0"));

            return pj_default_destructor(P,

                                         PROJ_ERR_INVALID_OP_ILLEGAL_ARG_VALUE);

        }

    } else

        Q->m = 1.;

    Q->rm = 1. / Q->m;

    Q->m /= Q->w;

    P->es = 0.;

    P->fwd = hammer_s_forward;

    P->inv = hammer_s_inverse;

    return P;

}

#undef EPS