var apply = require('./_apply'),

arrayMap = require('./_arrayMap'),
baseIteratee = require('./_baseIteratee'),
baseRest = require('./_baseRest');

/** Error message constants. */ var FUNC_ERROR_TEXT = 'Expected a function';

/**

* Creates a function that iterates over `pairs` and invokes the corresponding
* function of the first predicate to return truthy. The predicate-function
* pairs are invoked with the `this` binding and arguments of the created
* function.
*
* @static
* @memberOf _
* @since 4.0.0
* @category Util
* @param {Array} pairs The predicate-function pairs.
* @returns {Function} Returns the new composite function.
* @example
*
* var func = _.cond([
*   [_.matches({ 'a': 1 }),           _.constant('matches A')],
*   [_.conforms({ 'b': _.isNumber }), _.constant('matches B')],
*   [_.stubTrue,                      _.constant('no match')]
* ]);
*
* func({ 'a': 1, 'b': 2 });
* // => 'matches A'
*
* func({ 'a': 0, 'b': 1 });
* // => 'matches B'
*
* func({ 'a': '1', 'b': '2' });
* // => 'no match'
*/

function cond(pairs) {

var length = pairs == null ? 0 : pairs.length,
    toIteratee = baseIteratee;

pairs = !length ? [] : arrayMap(pairs, function(pair) {
  if (typeof pair[1] != 'function') {
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  return [toIteratee(pair[0]), pair[1]];
});

return baseRest(function(args) {
  var index = -1;
  while (++index < length) {
    var pair = pairs[index];
    if (apply(pair[0], this, args)) {
      return apply(pair[1], this, args);
    }
  }
});

}

module.exports = cond;