var _clone = require('./internal/_clone');
var _curry3 = require('./internal/_curry3');
var _isTransformer = require('./internal/_isTransformer');
var _reduce = require('./internal/_reduce');
var _stepCat = require('./internal/_stepCat');


/**
 * Transforms the items of the list with the transducer and appends the
 * transformed items to the accumulator using an appropriate iterator function
 * based on the accumulator type.
 *
 * The accumulator can be an array, string, object or a transformer. Iterated
 * items will be appended to arrays and concatenated to strings. Objects will
 * be merged directly or 2-item arrays will be merged as key, value pairs.
 *
 * The accumulator can also be a transformer object that provides a 2-arity
 * reducing iterator function, step, 0-arity initial value function, init, and
 * 1-arity result extraction function result. The step function is used as the
 * iterator function in reduce. The result function is used to convert the
 * final accumulator into the return type and in most cases is R.identity. The
 * init function is used to provide the initial accumulator.
 *
 * The iteration is performed with [`R.reduce`](#reduce) after initializing the
 * transducer.
 *
 * @func
 * @memberOf R
 * @since v0.12.0
 * @category List
 * @sig a -> (b -> b) -> [c] -> a
 * @param {*} acc The initial accumulator value.
 * @param {Function} xf The transducer function. Receives a transformer and returns a transformer.
 * @param {Array} list The list to iterate over.
 * @return {*} The final, accumulated value.
 * @example
 *
 *      var numbers = [1, 2, 3, 4];
 *      var transducer = R.compose(R.map(R.add(1)), R.take(2));
 *
 *      R.into([], transducer, numbers); //=> [2, 3]
 *
 *      var intoArray = R.into([]);
 *      intoArray(transducer, numbers); //=> [2, 3]
 */
module.exports = _curry3(function into(acc, xf, list) {
  return _isTransformer(acc) ?
    _reduce(xf(acc), acc['@@transducer/init'](), list) :
    _reduce(xf(_stepCat(acc)), _clone(acc, [], [], false), list);
});