var utils = require('../utils')
  , nodes = require('../nodes');

/**
 * Color component name map.
 */

var componentMap = {
    red: 'r'
  , green: 'g'
  , blue: 'b'
  , alpha: 'a'
  , hue: 'h'
  , saturation: 's'
  , lightness: 'l'
};

/**
 * Color component unit type map.
 */

var unitMap = {
    hue: 'deg'
  , saturation: '%'
  , lightness: '%'
};

/**
 * Color type map.
 */

var typeMap = {
    red: 'rgba'
  , blue: 'rgba'
  , green: 'rgba'
  , alpha: 'rgba'
  , hue: 'hsla'
  , saturation: 'hsla'
  , lightness: 'hsla'
};

/**
 * Return component `name` for the given `color`.
 *
 * @param {RGBA|HSLA} color
 * @param {String} name
 * @return {Unit}
 * @api public
 */

module.exports = function component(color, name) {
  utils.assertColor(color, 'color');
  utils.assertString(name, 'name');
  var name = name.string
    , unit = unitMap[name]
    , type = typeMap[name]
    , name = componentMap[name];
  if (!name) throw new Error('invalid color component "' + name + '"');
  return new nodes.Unit(color[type][name], unit);
};