/**
 * \file GravityModel.cpp
 * \brief Implementation for GeographicLib::GravityModel class
 *
 * Copyright (c) Charles Karney (2011-2017) <charles@karney.com> and licensed
 * under the MIT/X11 License. For more information, see
 * https://geographiclib.sourceforge.io/
 **********************************************************************/

#include <GeographicLib/GravityModel.hpp>
#include <fstream>
#include <GeographicLib/SphericalEngine.hpp>
#include <GeographicLib/GravityCircle.hpp>
#include <GeographicLib/Utility.hpp>

#if !defined(GEOGRAPHICLIB_DATA)
# if defined(_WIN32)
# define GEOGRAPHICLIB_DATA "C:/ProgramData/GeographicLib"
# else
# define GEOGRAPHICLIB_DATA "/usr/local/share/GeographicLib"
# endif
#endif

#if !defined(GEOGRAPHICLIB_GRAVITY_DEFAULT_NAME)
# define GEOGRAPHICLIB_GRAVITY_DEFAULT_NAME "egm96"
#endif

#if defined(_MSC_VER)
// Squelch warnings about unsafe use of getenv
# pragma warning (disable: 4996)
#endif

namespace GeographicLib {

 using namespace std;

 GravityModel::GravityModel(const std::string& name,const std::string& path)
 : _name(name)
 , _dir(path)
 , _description("NONE")
 , _date("UNKNOWN")
 , _amodel(Math::NaN())
 , _GMmodel(Math::NaN())
 , _zeta0(0)
 , _corrmult(1)
 , _norm(SphericalHarmonic::FULL)
 {
 if (_dir.empty())
 _dir = DefaultGravityPath();
 ReadMetadata(_name);
 {
 string coeff = _filename + ".cof";
 ifstream coeffstr(coeff.c_str(), ios::binary);
 if (!coeffstr.good())
 throw GeographicErr("Error opening " + coeff);
 char id[idlength_ + 1];
 coeffstr.read(id, idlength_);
 if (!coeffstr.good())
 throw GeographicErr("No header in " + coeff);
 id[idlength_] = '0円';
 if (_id != string(id))
 throw GeographicErr("ID mismatch: " + _id + " vs " + id);
 int N, M;
 SphericalEngine::coeff::readcoeffs(coeffstr, N, M, _Cx, _Sx);
 if (!(N >= 0 && M >= 0))
 throw GeographicErr("Degree and order must be at least 0");
 if (_Cx[0] != 0)
 throw GeographicErr("A degree 0 term should be zero");
 _Cx[0] = 1; // Include the 1/r term in the sum
 _gravitational = SphericalHarmonic(_Cx, _Sx, N, N, M, _amodel, _norm);
 SphericalEngine::coeff::readcoeffs(coeffstr, N, M, _CC, _CS);
 if (N < 0) {
 N = M = 0;
 _CC.resize(1, real(0));
 }
 _CC[0] += _zeta0 / _corrmult;
 _correction = SphericalHarmonic(_CC, _CS, N, N, M, real(1), _norm);
 int pos = int(coeffstr.tellg());
 coeffstr.seekg(0, ios::end);
 if (pos != coeffstr.tellg())
 throw GeographicErr("Extra data in " + coeff);
 }
 int nmx = _gravitational.Coefficients().nmx();
 // Adjust the normalization of the normal potential to match the model.
 real mult = _earth._GM / _GMmodel;
 real amult = Math::sq(_earth._a / _amodel);
 // The 0th term in _zonal should be is 1 + _dzonal0. Instead set it to 1
 // to give exact cancellation with the (0,0) term in the model and account
 // for _dzonal0 separately.
 _zonal.clear(); _zonal.push_back(1);
 _dzonal0 = (_earth.MassConstant() - _GMmodel) / _GMmodel;
 for (int n = 2; n <= nmx; n += 2) {
 // Only include as many normal zonal terms as matter. Figuring the limit
 // in this way works because the coefficients of the normal potential
 // (which is smooth) decay much more rapidly that the corresponding
 // coefficient of the model potential (which is bumpy). Typically this
 // goes out to n = 18.
 mult *= amult;
 real
 r = _Cx[n], // the model term
 s = - mult * _earth.Jn(n) / sqrt(real(2 * n + 1)), // the normal term
 t = r - s; // the difference
 if (t == r) // the normal term is negligible
 break;
 _zonal.push_back(0); // index = n - 1; the odd terms are 0
 _zonal.push_back(s);
 }
 int nmx1 = int(_zonal.size()) - 1;
 _disturbing = SphericalHarmonic1(_Cx, _Sx,
 _gravitational.Coefficients().N(),
 nmx, _gravitational.Coefficients().mmx(),
 _zonal,
 _zonal, // This is not accessed!
 nmx1, nmx1, 0,
 _amodel,
 SphericalHarmonic1::normalization(_norm));
 }

 void GravityModel::ReadMetadata(const std::string& name) {
 const char* spaces = " \t\n\v\f\r";
 _filename = _dir + "/" + name + ".egm";
 ifstream metastr(_filename.c_str());
 if (!metastr.good())
 throw GeographicErr("Cannot open " + _filename);
 string line;
 getline(metastr, line);
 if (!(line.size() >= 6 && line.substr(0,5) == "EGMF-"))
 throw GeographicErr(_filename + " does not contain EGMF-n signature");
 string::size_type n = line.find_first_of(spaces, 5);
 if (n != string::npos)
 n -= 5;
 string version(line, 5, n);
 if (version != "1")
 throw GeographicErr("Unknown version in " + _filename + ": " + version);
 string key, val;
 real a = Math::NaN(), GM = a, omega = a, f = a, J2 = a;
 while (getline(metastr, line)) {
 if (!Utility::ParseLine(line, key, val))
 continue;
 // Process key words
 if (key == "Name")
 _name = val;
 else if (key == "Description")
 _description = val;
 else if (key == "ReleaseDate")
 _date = val;
 else if (key == "ModelRadius")
 _amodel = Utility::val<real>(val);
 else if (key == "ModelMass")
 _GMmodel = Utility::val<real>(val);
 else if (key == "AngularVelocity")
 omega = Utility::val<real>(val);
 else if (key == "ReferenceRadius")
 a = Utility::val<real>(val);
 else if (key == "ReferenceMass")
 GM = Utility::val<real>(val);
 else if (key == "Flattening")
 f = Utility::fract<real>(val);
 else if (key == "DynamicalFormFactor")
 J2 = Utility::fract<real>(val);
 else if (key == "HeightOffset")
 _zeta0 = Utility::fract<real>(val);
 else if (key == "CorrectionMultiplier")
 _corrmult = Utility::fract<real>(val);
 else if (key == "Normalization") {
 if (val == "FULL" || val == "Full" || val == "full")
 _norm = SphericalHarmonic::FULL;
 else if (val == "SCHMIDT" || val == "Schmidt" || val == "schmidt")
 _norm = SphericalHarmonic::SCHMIDT;
 else
 throw GeographicErr("Unknown normalization " + val);
 } else if (key == "ByteOrder") {
 if (val == "Big" || val == "big")
 throw GeographicErr("Only little-endian ordering is supported");
 else if (!(val == "Little" || val == "little"))
 throw GeographicErr("Unknown byte ordering " + val);
 } else if (key == "ID")
 _id = val;
 // else unrecognized keywords are skipped
 }
 // Check values
 if (!(Math::isfinite(_amodel) && _amodel > 0))
 throw GeographicErr("Model radius must be positive");
 if (!(Math::isfinite(_GMmodel) && _GMmodel > 0))
 throw GeographicErr("Model mass constant must be positive");
 if (!(Math::isfinite(_corrmult) && _corrmult > 0))
 throw GeographicErr("Correction multiplier must be positive");
 if (!(Math::isfinite(_zeta0)))
 throw GeographicErr("Height offset must be finite");
 if (int(_id.size()) != idlength_)
 throw GeographicErr("Invalid ID");
 if (Math::isfinite(f) && Math::isfinite(J2))
 throw GeographicErr("Cannot specify both f and J2");
 _earth = NormalGravity(a, GM, omega,
 Math::isfinite(f) ? f : J2, Math::isfinite(f));
 }

 Math::real GravityModel::InternalT(real X, real Y, real Z,
 real& deltaX, real& deltaY, real& deltaZ,
 bool gradp, bool correct) const {
 // If correct, then produce the correct T = W - U. Otherwise, neglect the
 // n = 0 term (which is proportial to the difference in the model and
 // reference values of GM).
 if (_dzonal0 == 0)
 // No need to do the correction
 correct = false;
 real T, invR = correct ? 1 / Math::hypot(Math::hypot(X, Y), Z) : 1;
 if (gradp) {
 // initial values to suppress warnings
 deltaX = deltaY = deltaZ = 0;
 T = _disturbing(-1, X, Y, Z, deltaX, deltaY, deltaZ);
 real f = _GMmodel / _amodel;
 deltaX *= f;
 deltaY *= f;
 deltaZ *= f;
 if (correct) {
 invR = _GMmodel * _dzonal0 * invR * invR * invR;
 deltaX += X * invR;
 deltaY += Y * invR;
 deltaZ += Z * invR;
 }
 } else
 T = _disturbing(-1, X, Y, Z);
 T = (T / _amodel - (correct ? _dzonal0 : 0) * invR) * _GMmodel;
 return T;
 }

 Math::real GravityModel::V(real X, real Y, real Z,
 real& GX, real& GY, real& GZ) const {
 real
 Vres = _gravitational(X, Y, Z, GX, GY, GZ),
 f = _GMmodel / _amodel;
 Vres *= f;
 GX *= f;
 GY *= f;
 GZ *= f;
 return Vres;
 }

 Math::real GravityModel::W(real X, real Y, real Z,
 real& gX, real& gY, real& gZ) const {
 real fX, fY,
 Wres = V(X, Y, Z, gX, gY, gZ) + _earth.Phi(X, Y, fX, fY);
 gX += fX;
 gY += fY;
 return Wres;
 }

 void GravityModel::SphericalAnomaly(real lat, real lon, real h,
 real& Dg01, real& xi, real& eta) const {
 real X, Y, Z, M[Geocentric::dim2_];
 _earth.Earth().IntForward(lat, lon, h, X, Y, Z, M);
 real
 deltax, deltay, deltaz,
 T = InternalT(X, Y, Z, deltax, deltay, deltaz, true, false),
 clam = M[3], slam = -M[0],
 P = Math::hypot(X, Y),
 R = Math::hypot(P, Z),
 // psi is geocentric latitude
 cpsi = R != 0 ? P / R : M[7],
 spsi = R != 0 ? Z / R : M[8];
 // Rotate cartesian into spherical coordinates
 real MC[Geocentric::dim2_];
 Geocentric::Rotation(spsi, cpsi, slam, clam, MC);
 Geocentric::Unrotate(MC, deltax, deltay, deltaz, deltax, deltay, deltaz);
 // H+M, Eq 2-151c
 Dg01 = - deltaz - 2 * T / R;
 real gammaX, gammaY, gammaZ;
 _earth.U(X, Y, Z, gammaX, gammaY, gammaZ);
 real gamma = Math::hypot( Math::hypot(gammaX, gammaY), gammaZ);
 xi = -(deltay/gamma) / Math::degree();
 eta = -(deltax/gamma) / Math::degree();
 }

 Math::real GravityModel::GeoidHeight(real lat, real lon) const
 {
 real X, Y, Z;
 _earth.Earth().IntForward(lat, lon, 0, X, Y, Z, NULL);
 real
 gamma0 = _earth.SurfaceGravity(lat),
 dummy,
 T = InternalT(X, Y, Z, dummy, dummy, dummy, false, false),
 invR = 1 / Math::hypot(Math::hypot(X, Y), Z),
 correction = _corrmult * _correction(invR * X, invR * Y, invR * Z);
 // _zeta0 has been included in _correction
 return T/gamma0 + correction;
 }

 Math::real GravityModel::Gravity(real lat, real lon, real h,
 real& gx, real& gy, real& gz) const {
 real X, Y, Z, M[Geocentric::dim2_];
 _earth.Earth().IntForward(lat, lon, h, X, Y, Z, M);
 real Wres = W(X, Y, Z, gx, gy, gz);
 Geocentric::Unrotate(M, gx, gy, gz, gx, gy, gz);
 return Wres;
 }
 Math::real GravityModel::Disturbance(real lat, real lon, real h,
 real& deltax, real& deltay,
 real& deltaz) const {
 real X, Y, Z, M[Geocentric::dim2_];
 _earth.Earth().IntForward(lat, lon, h, X, Y, Z, M);
 real Tres = InternalT(X, Y, Z, deltax, deltay, deltaz, true, true);
 Geocentric::Unrotate(M, deltax, deltay, deltaz, deltax, deltay, deltaz);
 return Tres;
 }

 GravityCircle GravityModel::Circle(real lat, real h, unsigned caps) const {
 if (h != 0)
 // Disallow invoking GeoidHeight unless h is zero.
 caps &= ~(CAP_GAMMA0 | CAP_C);
 real X, Y, Z, M[Geocentric::dim2_];
 _earth.Earth().IntForward(lat, 0, h, X, Y, Z, M);
 // Y = 0, cphi = M[7], sphi = M[8];
 real
 invR = 1 / Math::hypot(X, Z),
 gamma0 = (caps & CAP_GAMMA0 ?_earth.SurfaceGravity(lat)
 : Math::NaN()),
 fx, fy, fz, gamma;
 if (caps & CAP_GAMMA) {
 _earth.U(X, Y, Z, fx, fy, fz); // fy = 0
 gamma = Math::hypot(fx, fz);
 } else
 gamma = Math::NaN();
 _earth.Phi(X, Y, fx, fy);
 return GravityCircle(GravityCircle::mask(caps),
 _earth._a, _earth._f, lat, h, Z, X, M[7], M[8],
 _amodel, _GMmodel, _dzonal0, _corrmult,
 gamma0, gamma, fx,
 caps & CAP_G ?
 _gravitational.Circle(X, Z, true) :
 CircularEngine(),
 // N.B. If CAP_DELTA is set then CAP_T should be too.
 caps & CAP_T ?
 _disturbing.Circle(-1, X, Z, (caps&CAP_DELTA) != 0) :
 CircularEngine(),
 caps & CAP_C ?
 _correction.Circle(invR * X, invR * Z, false) :
 CircularEngine());
 }

 std::string GravityModel::DefaultGravityPath() {
 string path;
 char* gravitypath = getenv("GEOGRAPHICLIB_GRAVITY_PATH");
 if (gravitypath)
 path = string(gravitypath);
 if (!path.empty())
 return path;
 char* datapath = getenv("GEOGRAPHICLIB_DATA");
 if (datapath)
 path = string(datapath);
 return (!path.empty() ? path : string(GEOGRAPHICLIB_DATA)) + "/gravity";
 }

 std::string GravityModel::DefaultGravityName() {
 string name;
 char* gravityname = getenv("GEOGRAPHICLIB_GRAVITY_NAME");
 if (gravityname)
 name = string(gravityname);
 return !name.empty() ? name : string(GEOGRAPHICLIB_GRAVITY_DEFAULT_NAME);
 }

} // namespace GeographicLib