var msfnz = require('../common/msfnz');
var HALF_PI = Math.PI/2;
var EPSLN = 1.0e-10;
var R2D = 57.29577951308232088;
var adjust_lon = require('../common/adjust_lon');
var FORTPI = Math.PI/4;
var tsfnz = require('../common/tsfnz');
var phi2z = require('../common/phi2z');
exports.init = function() {
  var con = this.b / this.a;
  this.es = 1 - con * con;
  if(!('x0' in this)){
    this.x0 = 0;
  }
  if(!('y0' in this)){
    this.y0 = 0;
  }
  this.e = Math.sqrt(this.es);
  if (this.lat_ts) {
    if (this.sphere) {
      this.k0 = Math.cos(this.lat_ts);
    }
    else {
      this.k0 = msfnz(this.e, Math.sin(this.lat_ts), Math.cos(this.lat_ts));
    }
  }
  else {
    if (!this.k0) {
      if (this.k) {
        this.k0 = this.k;
      }
      else {
        this.k0 = 1;
      }
    }
  }
};

/* Mercator forward equations--mapping lat,long to x,y
  --------------------------------------------------*/

exports.forward = function(p) {
  var lon = p.x;
  var lat = p.y;
  // convert to radians
  if (lat * R2D > 90 && lat * R2D < -90 && lon * R2D > 180 && lon * R2D < -180) {
    return null;
  }

  var x, y;
  if (Math.abs(Math.abs(lat) - HALF_PI) <= EPSLN) {
    return null;
  }
  else {
    if (this.sphere) {
      x = this.x0 + this.a * this.k0 * adjust_lon(lon - this.long0);
      y = this.y0 + this.a * this.k0 * Math.log(Math.tan(FORTPI + 0.5 * lat));
    }
    else {
      var sinphi = Math.sin(lat);
      var ts = tsfnz(this.e, lat, sinphi);
      x = this.x0 + this.a * this.k0 * adjust_lon(lon - this.long0);
      y = this.y0 - this.a * this.k0 * Math.log(ts);
    }
    p.x = x;
    p.y = y;
    return p;
  }
};


/* Mercator inverse equations--mapping x,y to lat/long
  --------------------------------------------------*/
exports.inverse = function(p) {

  var x = p.x - this.x0;
  var y = p.y - this.y0;
  var lon, lat;

  if (this.sphere) {
    lat = HALF_PI - 2 * Math.atan(Math.exp(-y / (this.a * this.k0)));
  }
  else {
    var ts = Math.exp(-y / (this.a * this.k0));
    lat = phi2z(this.e, ts);
    if (lat === -9999) {
      return null;
    }
  }
  lon = adjust_lon(this.long0 + x / (this.a * this.k0));

  p.x = lon;
  p.y = lat;
  return p;
};

exports.names = ["Mercator", "Popular Visualisation Pseudo Mercator", "Mercator_1SP", "Mercator_Auxiliary_Sphere", "merc"];