// QSC projection rewritten from the original PROJ4
// https://github.com/OSGeo/proj.4/blob/master/src/PJ_qsc.c

import {EPSLN, TWO_PI, SPI, HALF_PI, FORTPI} from '../constants/values';

/* constants */
var FACE_ENUM = {
    FRONT: 1,
    RIGHT: 2,
    BACK: 3,
    LEFT: 4,
    TOP: 5,
    BOTTOM: 6
};

var AREA_ENUM = {
    AREA_0: 1,
    AREA_1: 2,
    AREA_2: 3,
    AREA_3: 4
};

export function init() {

  this.x0 = this.x0 || 0;
  this.y0 = this.y0 || 0;
  this.lat0 = this.lat0 || 0;
  this.long0 = this.long0 || 0;
  this.lat_ts = this.lat_ts || 0;
  this.title = this.title || "Quadrilateralized Spherical Cube";

  /* Determine the cube face from the center of projection. */
  if (this.lat0 >= HALF_PI - FORTPI / 2.0) {
    this.face = FACE_ENUM.TOP;
  } else if (this.lat0 <= -(HALF_PI - FORTPI / 2.0)) {
    this.face = FACE_ENUM.BOTTOM;
  } else if (Math.abs(this.long0) <= FORTPI) {
    this.face = FACE_ENUM.FRONT;
  } else if (Math.abs(this.long0) <= HALF_PI + FORTPI) {
    this.face = this.long0 > 0.0 ? FACE_ENUM.RIGHT : FACE_ENUM.LEFT;
  } else {
    this.face = FACE_ENUM.BACK;
  }

  /* Fill in useful values for the ellipsoid <-> sphere shift
   * described in [LK12]. */
  if (this.es !== 0) {
    this.one_minus_f = 1 - (this.a - this.b) / this.a;
    this.one_minus_f_squared = this.one_minus_f * this.one_minus_f;
  }
}

// QSC forward equations--mapping lat,long to x,y
// -----------------------------------------------------------------
export function forward(p) {
  var xy = {x: 0, y: 0};
  var lat, lon;
  var theta, phi;
  var t, mu;
  /* nu; */
  var area = {value: 0};

  // move lon according to projection's lon
  p.x -= this.long0;

  /* Convert the geodetic latitude to a geocentric latitude.
   * This corresponds to the shift from the ellipsoid to the sphere
   * described in [LK12]. */
  if (this.es !== 0) {//if (P->es != 0) {
    lat = Math.atan(this.one_minus_f_squared * Math.tan(p.y));
  } else {
    lat = p.y;
  }

  /* Convert the input lat, lon into theta, phi as used by QSC.
   * This depends on the cube face and the area on it.
   * For the top and bottom face, we can compute theta and phi
   * directly from phi, lam. For the other faces, we must use
   * unit sphere cartesian coordinates as an intermediate step. */
  lon = p.x; //lon = lp.lam;
  if (this.face === FACE_ENUM.TOP) {
    phi = HALF_PI - lat;
    if (lon >= FORTPI && lon <= HALF_PI + FORTPI) {
      area.value = AREA_ENUM.AREA_0;
      theta = lon - HALF_PI;
    } else if (lon > HALF_PI + FORTPI || lon <= -(HALF_PI + FORTPI)) {
      area.value = AREA_ENUM.AREA_1;
      theta = (lon > 0.0 ? lon - SPI : lon + SPI);
    } else if (lon > -(HALF_PI + FORTPI) && lon <= -FORTPI) {
      area.value = AREA_ENUM.AREA_2;
      theta = lon + HALF_PI;
    } else {
      area.value = AREA_ENUM.AREA_3;
      theta = lon;
    }
  } else if (this.face === FACE_ENUM.BOTTOM) {
    phi = HALF_PI + lat;
    if (lon >= FORTPI && lon <= HALF_PI + FORTPI) {
      area.value = AREA_ENUM.AREA_0;
      theta = -lon + HALF_PI;
    } else if (lon < FORTPI && lon >= -FORTPI) {
      area.value = AREA_ENUM.AREA_1;
      theta = -lon;
    } else if (lon < -FORTPI && lon >= -(HALF_PI + FORTPI)) {
      area.value = AREA_ENUM.AREA_2;
      theta = -lon - HALF_PI;
    } else {
      area.value = AREA_ENUM.AREA_3;
      theta = (lon > 0.0 ? -lon + SPI : -lon - SPI);
    }
  } else {
    var q, r, s;
    var sinlat, coslat;
    var sinlon, coslon;

    if (this.face === FACE_ENUM.RIGHT) {
      lon = qsc_shift_lon_origin(lon, +HALF_PI);
    } else if (this.face === FACE_ENUM.BACK) {
      lon = qsc_shift_lon_origin(lon, +SPI);
    } else if (this.face === FACE_ENUM.LEFT) {
      lon = qsc_shift_lon_origin(lon, -HALF_PI);
    }
    sinlat = Math.sin(lat);
    coslat = Math.cos(lat);
    sinlon = Math.sin(lon);
    coslon = Math.cos(lon);
    q = coslat * coslon;
    r = coslat * sinlon;
    s = sinlat;

    if (this.face === FACE_ENUM.FRONT) {
      phi = Math.acos(q);
      theta = qsc_fwd_equat_face_theta(phi, s, r, area);
    } else if (this.face === FACE_ENUM.RIGHT) {
      phi = Math.acos(r);
      theta = qsc_fwd_equat_face_theta(phi, s, -q, area);
    } else if (this.face === FACE_ENUM.BACK) {
      phi = Math.acos(-q);
      theta = qsc_fwd_equat_face_theta(phi, s, -r, area);
    } else if (this.face === FACE_ENUM.LEFT) {
      phi = Math.acos(-r);
      theta = qsc_fwd_equat_face_theta(phi, s, q, area);
    } else {
      /* Impossible */
      phi = theta = 0;
      area.value = AREA_ENUM.AREA_0;
    }
  }

  /* Compute mu and nu for the area of definition.
   * For mu, see Eq. (3-21) in [OL76], but note the typos:
   * compare with Eq. (3-14). For nu, see Eq. (3-38). */
  mu = Math.atan((12 / SPI) * (theta + Math.acos(Math.sin(theta) * Math.cos(FORTPI)) - HALF_PI));
  t = Math.sqrt((1 - Math.cos(phi)) / (Math.cos(mu) * Math.cos(mu)) / (1 - Math.cos(Math.atan(1 / Math.cos(theta)))));

  /* Apply the result to the real area. */
  if (area.value === AREA_ENUM.AREA_1) {
    mu += HALF_PI;
  } else if (area.value === AREA_ENUM.AREA_2) {
    mu += SPI;
  } else if (area.value === AREA_ENUM.AREA_3) {
    mu += 1.5 * SPI;
  }

  /* Now compute x, y from mu and nu */
  xy.x = t * Math.cos(mu);
  xy.y = t * Math.sin(mu);
  xy.x = xy.x * this.a + this.x0;
  xy.y = xy.y * this.a + this.y0;

  p.x = xy.x;
  p.y = xy.y;
  return p;
}

// QSC inverse equations--mapping x,y to lat/long
// -----------------------------------------------------------------
export function inverse(p) {
  var lp = {lam: 0, phi: 0};
  var mu, nu, cosmu, tannu;
  var tantheta, theta, cosphi, phi;
  var t;
  var area = {value: 0};

  /* de-offset */
  p.x = (p.x - this.x0) / this.a;
  p.y = (p.y - this.y0) / this.a;

  /* Convert the input x, y to the mu and nu angles as used by QSC.
   * This depends on the area of the cube face. */
  nu = Math.atan(Math.sqrt(p.x * p.x + p.y * p.y));
  mu = Math.atan2(p.y, p.x);
  if (p.x >= 0.0 && p.x >= Math.abs(p.y)) {
    area.value = AREA_ENUM.AREA_0;
  } else if (p.y >= 0.0 && p.y >= Math.abs(p.x)) {
    area.value = AREA_ENUM.AREA_1;
    mu -= HALF_PI;
  } else if (p.x < 0.0 && -p.x >= Math.abs(p.y)) {
    area.value = AREA_ENUM.AREA_2;
    mu = (mu < 0.0 ? mu + SPI : mu - SPI);
  } else {
    area.value = AREA_ENUM.AREA_3;
    mu += HALF_PI;
  }

  /* Compute phi and theta for the area of definition.
   * The inverse projection is not described in the original paper, but some
   * good hints can be found here (as of 2011-12-14):
   * http://fits.gsfc.nasa.gov/fitsbits/saf.93/saf.9302
   * (search for "Message-Id: <9302181759.AA25477 at fits.cv.nrao.edu>") */
  t = (SPI / 12) * Math.tan(mu);
  tantheta = Math.sin(t) / (Math.cos(t) - (1 / Math.sqrt(2)));
  theta = Math.atan(tantheta);
  cosmu = Math.cos(mu);
  tannu = Math.tan(nu);
  cosphi = 1 - cosmu * cosmu * tannu * tannu * (1 - Math.cos(Math.atan(1 / Math.cos(theta))));
  if (cosphi < -1) {
    cosphi = -1;
  } else if (cosphi > +1) {
    cosphi = +1;
  }

  /* Apply the result to the real area on the cube face.
   * For the top and bottom face, we can compute phi and lam directly.
   * For the other faces, we must use unit sphere cartesian coordinates
   * as an intermediate step. */
  if (this.face === FACE_ENUM.TOP) {
    phi = Math.acos(cosphi);
    lp.phi = HALF_PI - phi;
    if (area.value === AREA_ENUM.AREA_0) {
      lp.lam = theta + HALF_PI;
    } else if (area.value === AREA_ENUM.AREA_1) {
      lp.lam = (theta < 0.0 ? theta + SPI : theta - SPI);
    } else if (area.value === AREA_ENUM.AREA_2) {
      lp.lam = theta - HALF_PI;
    } else /* area.value == AREA_ENUM.AREA_3 */ {
      lp.lam = theta;
    }
  } else if (this.face === FACE_ENUM.BOTTOM) {
    phi = Math.acos(cosphi);
    lp.phi = phi - HALF_PI;
    if (area.value === AREA_ENUM.AREA_0) {
      lp.lam = -theta + HALF_PI;
    } else if (area.value === AREA_ENUM.AREA_1) {
      lp.lam = -theta;
    } else if (area.value === AREA_ENUM.AREA_2) {
      lp.lam = -theta - HALF_PI;
    } else /* area.value == AREA_ENUM.AREA_3 */ {
      lp.lam = (theta < 0.0 ? -theta - SPI : -theta + SPI);
    }
  } else {
    /* Compute phi and lam via cartesian unit sphere coordinates. */
    var q, r, s;
    q = cosphi;
    t = q * q;
    if (t >= 1) {
      s = 0;
    } else {
      s = Math.sqrt(1 - t) * Math.sin(theta);
    }
    t += s * s;
    if (t >= 1) {
      r = 0;
    } else {
      r = Math.sqrt(1 - t);
    }
    /* Rotate q,r,s into the correct area. */
    if (area.value === AREA_ENUM.AREA_1) {
      t = r;
      r = -s;
      s = t;
    } else if (area.value === AREA_ENUM.AREA_2) {
      r = -r;
      s = -s;
    } else if (area.value === AREA_ENUM.AREA_3) {
      t = r;
      r = s;
      s = -t;
    }
    /* Rotate q,r,s into the correct cube face. */
    if (this.face === FACE_ENUM.RIGHT) {
      t = q;
      q = -r;
      r = t;
    } else if (this.face === FACE_ENUM.BACK) {
      q = -q;
      r = -r;
    } else if (this.face === FACE_ENUM.LEFT) {
      t = q;
      q = r;
      r = -t;
    }
    /* Now compute phi and lam from the unit sphere coordinates. */
    lp.phi = Math.acos(-s) - HALF_PI;
    lp.lam = Math.atan2(r, q);
    if (this.face === FACE_ENUM.RIGHT) {
      lp.lam = qsc_shift_lon_origin(lp.lam, -HALF_PI);
    } else if (this.face === FACE_ENUM.BACK) {
      lp.lam = qsc_shift_lon_origin(lp.lam, -SPI);
    } else if (this.face === FACE_ENUM.LEFT) {
      lp.lam = qsc_shift_lon_origin(lp.lam, +HALF_PI);
    }
  }

  /* Apply the shift from the sphere to the ellipsoid as described
   * in [LK12]. */
  if (this.es !== 0) {
    var invert_sign;
    var tanphi, xa;
    invert_sign = (lp.phi < 0 ? 1 : 0);
    tanphi = Math.tan(lp.phi);
    xa = this.b / Math.sqrt(tanphi * tanphi + this.one_minus_f_squared);
    lp.phi = Math.atan(Math.sqrt(this.a * this.a - xa * xa) / (this.one_minus_f * xa));
    if (invert_sign) {
      lp.phi = -lp.phi;
    }
  }

  lp.lam += this.long0;
  p.x = lp.lam;
  p.y = lp.phi;
  return p;
}

/* Helper function for forward projection: compute the theta angle
 * and determine the area number. */
function qsc_fwd_equat_face_theta(phi, y, x, area) {
  var theta;
  if (phi < EPSLN) {
    area.value = AREA_ENUM.AREA_0;
    theta = 0.0;
  } else {
    theta = Math.atan2(y, x);
    if (Math.abs(theta) <= FORTPI) {
      area.value = AREA_ENUM.AREA_0;
    } else if (theta > FORTPI && theta <= HALF_PI + FORTPI) {
      area.value = AREA_ENUM.AREA_1;
      theta -= HALF_PI;
    } else if (theta > HALF_PI + FORTPI || theta <= -(HALF_PI + FORTPI)) {
      area.value = AREA_ENUM.AREA_2;
      theta = (theta >= 0.0 ? theta - SPI : theta + SPI);
    } else {
      area.value = AREA_ENUM.AREA_3;
      theta += HALF_PI;
    }
  }
  return theta;
}

/* Helper function: shift the longitude. */
function qsc_shift_lon_origin(lon, offset) {
  var slon = lon + offset;
  if (slon < -SPI) {
    slon += TWO_PI;
  } else if (slon > +SPI) {
    slon -= TWO_PI;
  }
  return slon;
}

export var names = ["Quadrilateralized Spherical Cube", "Quadrilateralized_Spherical_Cube", "qsc"];
export default {
  init: init,
  forward: forward,
  inverse: inverse,
  names: names
};