#include <errno.h>

#include <math.h>

#include "proj.h"

#include "proj_internal.h"

PROJ_HEAD(ocea, "Oblique Cylindrical Equal Area")

"\n\tCyl, Sph"

    "lonc= alpha= or\n\tlat_1= lat_2= lon_1= lon_2=";

namespace { // anonymous namespace

struct pj_ocea {

    double rok;

    double rtk;

    double sinphi;

    double cosphi;

};

} // anonymous namespace

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

    PJ_XY xy = {0.0, 0.0};

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

    double t;

    xy.y = sin(lp.lam);

    t = cos(lp.lam);

    xy.x = atan((tan(lp.phi) * Q->cosphi + Q->sinphi * xy.y) / t);

    if (t < 0.)

        xy.x += M_PI;

    xy.x *= Q->rtk;

    xy.y = Q->rok * (Q->sinphi * sin(lp.phi) - Q->cosphi * cos(lp.phi) * xy.y);

    return xy;

}

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

    PJ_LP lp = {0.0, 0.0};

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

    xy.y /= Q->rok;

    xy.x /= Q->rtk;

    const double t = sqrt(1. - xy.y * xy.y);

    const double s = sin(xy.x);

    lp.phi = asin(xy.y * Q->sinphi + t * Q->cosphi * s);

    lp.lam = atan2(t * Q->sinphi * s - xy.y * Q->cosphi, t * cos(xy.x));

    return lp;

}

PJ *PJ_PROJECTION(ocea) {

    double phi_1, phi_2, lam_1, lam_2, lonz, alpha;

    struct pj_ocea *Q =

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

    if (nullptr == Q)

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

    P->opaque = Q;

    Q->rok = 1. / P->k0;

    Q->rtk = P->k0;

    double lam_p, phi_p;

    /*If the keyword "alpha" is found in the sentence then use 1point+1azimuth*/

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

        /*Define Pole of oblique transformation from 1 point & 1 azimuth*/

        // ERO: I've added M_PI so that the alpha is the angle from point 1 to

        // point 2 from the North in a clockwise direction (to be consistent

        // with omerc behavior)

        alpha = M_PI + pj_param(P->ctx, P->params, "ralpha").f;

        lonz = pj_param(P->ctx, P->params, "rlonc").f;

        /*Equation 9-8 page 80 (http://pubs.usgs.gov/pp/1395/report.pdf)*/

        // Actually slightliy modified to use atan2(), as it is suggested by

        // Snyder for equation 9-1, but this is not mentioned here

        lam_p = atan2(-cos(alpha), -sin(P->phi0) * sin(alpha)) + lonz;

        /*Equation 9-7 page 80 (http://pubs.usgs.gov/pp/1395/report.pdf)*/

        phi_p = asin(cos(P->phi0) * sin(alpha));

        /*If the keyword "alpha" is NOT found in the sentence then use 2points*/

    } else {

        /*Define Pole of oblique transformation from 2 points*/

        phi_1 = pj_param(P->ctx, P->params, "rlat_1").f;

        phi_2 = pj_param(P->ctx, P->params, "rlat_2").f;

        lam_1 = pj_param(P->ctx, P->params, "rlon_1").f;

        lam_2 = pj_param(P->ctx, P->params, "rlon_2").f;

        /*Equation 9-1 page 80 (http://pubs.usgs.gov/pp/1395/report.pdf)*/

        lam_p = atan2(cos(phi_1) * sin(phi_2) * cos(lam_1) -

                          sin(phi_1) * cos(phi_2) * cos(lam_2),

                      sin(phi_1) * cos(phi_2) * sin(lam_2) -

                          cos(phi_1) * sin(phi_2) * sin(lam_1));

        /* take care of P->lam0 wrap-around when +lam_1=-90*/

        if (lam_1 == -M_HALFPI)

            lam_p = -lam_p;

        /*Equation 9-2 page 80 (http://pubs.usgs.gov/pp/1395/report.pdf)*/

        double cos_lamp_m_minus_lam_1 = cos(lam_p - lam_1);

        double tan_phi_1 = tan(phi_1);

        if (tan_phi_1 == 0.0) {

            // Not sure if we want to support this case, but at least this

            // avoids a division by zero, and gives the same result as the below

            // atan()

            phi_p = (cos_lamp_m_minus_lam_1 >= 0.0) ? -M_HALFPI : M_HALFPI;

        } else {

            phi_p = atan(-cos_lamp_m_minus_lam_1 / tan_phi_1);

        }

    }

    P->lam0 = lam_p + M_HALFPI;

    Q->cosphi = cos(phi_p);

    Q->sinphi = sin(phi_p);

    P->inv = ocea_s_inverse;

    P->fwd = ocea_s_forward;

    P->es = 0.;

    return P;

}