'use strict';

module.exports = function (math) {
  var util = require('../../util/index'),

      BigNumber = math.type.BigNumber,
      Complex = require('../../type/Complex'),
      Unit = require('../../type/Unit'),
      collection = math.collection,

      isBoolean = util['boolean'].isBoolean,
      isNumber = util.number.isNumber,
      isString = util.string.isString,
      isComplex = Complex.isComplex,
      isUnit = Unit.isUnit,
      isCollection = collection.isCollection;

  /**
   * Add two values, `x + y`.
   * For matrices, the function is evaluated element wise.
   *
   * Syntax:
   *
   *    math.add(x, y)
   *
   * Examples:
   *
   *    math.add(2, 3);               // returns Number 5
   *
   *    var a = math.complex(2, 3);
   *    var b = math.complex(-4, 1);
   *    math.add(a, b);               // returns Complex -2 + 4i
   *
   *    math.add([1, 2, 3], 4);       // returns Array [5, 6, 7]
   *
   *    var c = math.unit('5 cm');
   *    var d = math.unit('2.1 mm');
   *    math.add(c, d);               // returns Unit 52.1 mm
   *
   * See also:
   *
   *    subtract
   *
   * @param  {Number | BigNumber | Boolean | Complex | Unit | String | Array | Matrix | null} x First value to add
   * @param  {Number | BigNumber | Boolean | Complex | Unit | String | Array | Matrix | null} y Second value to add
   * @return {Number | BigNumber | Complex | Unit | String | Array | Matrix} Sum of `x` and `y`
   */
  math.add = function add(x, y) {
    if (arguments.length != 2) {
      throw new math.error.ArgumentsError('add', arguments.length, 2);
    }

    if (isNumber(x)) {
      if (isNumber(y)) {
        // number + number
        return x + y;
      }
      else if (isComplex(y)) {
        // number + complex
        return new Complex(
            x + y.re,
            y.im
        );
      }
    }

    if (isComplex(x)) {
      if (isComplex(y)) {
        // complex + complex
        return new Complex(
            x.re + y.re,
            x.im + y.im
        );
      }
      else if (isNumber(y)) {
        // complex + number
        return new Complex(
            x.re + y,
            x.im
        );
      }
    }

    if (isUnit(x)) {
      if (isUnit(y)) {
        if (x.value == null) {
          throw new Error('Parameter x contains a unit with undefined value');
        }

        if (y.value == null) {
          throw new Error('Parameter y contains a unit with undefined value');
        }

        if (!x.equalBase(y)) {
          throw new Error('Units do not match');
        }

        var res = x.clone();
        res.value += y.value;
        res.fixPrefix = false;
        return res;
      }
    }

    if (x instanceof BigNumber) {
      // try to convert to big number
      if (isNumber(y)) {
        y = BigNumber.convert(y);
      }
      else if (isBoolean(y) || y === null) {
        y = new BigNumber(y ? 1 : 0);
      }

      if (y instanceof BigNumber) {
        return x.plus(y);
      }

      // downgrade to Number
      return add(x.toNumber(), y);
    }
    if (y instanceof BigNumber) {
      // try to convert to big number
      if (isNumber(x)) {
        x = BigNumber.convert(x);
      }
      else if (isBoolean(x) || x === null) {
        x = new BigNumber(x ? 1 : 0);
      }

      if (x instanceof BigNumber) {
        return x.plus(y);
      }

      // downgrade to Number
      return add(x, y.toNumber());
    }

    if (isCollection(x) || isCollection(y)) {
      return collection.deepMap2(x, y, add);
    }

    if (isString(x) || isString(y)) {
      return x + y;
    }

    if (isBoolean(x) || x === null) {
      return add(+x, y);
    }
    if (isBoolean(y) || y === null) {
      return add(x, +y);
    }

    throw new math.error.UnsupportedTypeError('add', math['typeof'](x), math['typeof'](y));
  };
};