/**
 * @module ol/proj/epsg3857
 */
import {cosh} from '../math.js';
import Projection from './Projection.js';
import Units from './Units.js';


/**
 * Radius of WGS84 sphere
 *
 * @const
 * @type {number}
 */
export const RADIUS = 6378137;


/**
 * @const
 * @type {number}
 */
export const HALF_SIZE = Math.PI * RADIUS;


/**
 * @const
 * @type {import("../extent.js").Extent}
 */
export const EXTENT = [
  -HALF_SIZE, -HALF_SIZE,
  HALF_SIZE, HALF_SIZE
];


/**
 * @const
 * @type {import("../extent.js").Extent}
 */
export const WORLD_EXTENT = [-180, -85, 180, 85];


/**
 * @classdesc
 * Projection object for web/spherical Mercator (EPSG:3857).
 */
class EPSG3857Projection extends Projection {

  /**
   * @param {string} code Code.
   */
  constructor(code) {
    super({
      code: code,
      units: Units.METERS,
      extent: EXTENT,
      global: true,
      worldExtent: WORLD_EXTENT,
      getPointResolution: function(resolution, point) {
        return resolution / cosh(point[1] / RADIUS);
      }
    });

  }

}


/**
 * Projections equal to EPSG:3857.
 *
 * @const
 * @type {Array<import("./Projection.js").default>}
 */
export const PROJECTIONS = [
  new EPSG3857Projection('EPSG:3857'),
  new EPSG3857Projection('EPSG:102100'),
  new EPSG3857Projection('EPSG:102113'),
  new EPSG3857Projection('EPSG:900913'),
  new EPSG3857Projection('urn:ogc:def:crs:EPSG:6.18:3:3857'),
  new EPSG3857Projection('urn:ogc:def:crs:EPSG::3857'),
  new EPSG3857Projection('http://www.opengis.net/gml/srs/epsg.xml#3857')
];


/**
 * Transformation from EPSG:4326 to EPSG:3857.
 *
 * @param {Array<number>} input Input array of coordinate values.
 * @param {Array<number>=} opt_output Output array of coordinate values.
 * @param {number=} opt_dimension Dimension (default is `2`).
 * @return {Array<number>} Output array of coordinate values.
 */
export function fromEPSG4326(input, opt_output, opt_dimension) {
  const length = input.length;
  const dimension = opt_dimension > 1 ? opt_dimension : 2;
  let output = opt_output;
  if (output === undefined) {
    if (dimension > 2) {
      // preserve values beyond second dimension
      output = input.slice();
    } else {
      output = new Array(length);
    }
  }
  const halfSize = HALF_SIZE;
  for (let i = 0; i < length; i += dimension) {
    output[i] = halfSize * input[i] / 180;
    let y = RADIUS *
        Math.log(Math.tan(Math.PI * (+input[i + 1] + 90) / 360));
    if (y > halfSize) {
      y = halfSize;
    } else if (y < -halfSize) {
      y = -halfSize;
    }
    output[i + 1] = y;
  }
  return output;
}


/**
 * Transformation from EPSG:3857 to EPSG:4326.
 *
 * @param {Array<number>} input Input array of coordinate values.
 * @param {Array<number>=} opt_output Output array of coordinate values.
 * @param {number=} opt_dimension Dimension (default is `2`).
 * @return {Array<number>} Output array of coordinate values.
 */
export function toEPSG4326(input, opt_output, opt_dimension) {
  const length = input.length;
  const dimension = opt_dimension > 1 ? opt_dimension : 2;
  let output = opt_output;
  if (output === undefined) {
    if (dimension > 2) {
      // preserve values beyond second dimension
      output = input.slice();
    } else {
      output = new Array(length);
    }
  }
  for (let i = 0; i < length; i += dimension) {
    output[i] = 180 * input[i] / HALF_SIZE;
    output[i + 1] = 360 * Math.atan(
      Math.exp(input[i + 1] / RADIUS)) / Math.PI - 90;
  }
  return output;
}