/**

* lodash (Custom Build) <https://lodash.com/>
* Build: `lodash modularize exports="npm" -o ./`
* Copyright jQuery Foundation and other contributors <https://jquery.org/>
* Released under MIT license <https://lodash.com/license>
* Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
* Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
*/

/** Used as references for various `Number` constants. */ var MAX_SAFE_INTEGER = 9007199254740991;

/** `Object#toString` result references. */ var argsTag = '[object Arguments]',

funcTag = '[object Function]',
genTag = '[object GeneratorFunction]';

/** Detect free variable `global` from Node.js. */ var freeGlobal = typeof global == 'object' && global && global.Object === Object && global;

/** Detect free variable `self`. */ var freeSelf = typeof self == 'object' && self && self.Object === Object && self;

/** Used as a reference to the global object. */ var root = freeGlobal || freeSelf || Function('return this')();

/**

* Appends the elements of `values` to `array`.
*
* @private
* @param {Array} array The array to modify.
* @param {Array} values The values to append.
* @returns {Array} Returns `array`.
*/

function arrayPush(array, values) {

var index = -1,
    length = values.length,
    offset = array.length;

while (++index < length) {
  array[offset + index] = values[index];
}
return array;

}

/** Used for built-in method references. */ var objectProto = Object.prototype;

/** Used to check objects for own properties. */ var hasOwnProperty = objectProto.hasOwnProperty;

/**

* Used to resolve the
* [`toStringTag`](http://ecma-international.org/ecma-262/7.0/#sec-object.prototype.tostring)
* of values.
*/

var objectToString = objectProto.toString;

/** Built-in value references. */ var Symbol = root.Symbol,

propertyIsEnumerable = objectProto.propertyIsEnumerable,
spreadableSymbol = Symbol ? Symbol.isConcatSpreadable : undefined;

/**

* The base implementation of `_.flatten` with support for restricting flattening.
*
* @private
* @param {Array} array The array to flatten.
* @param {number} depth The maximum recursion depth.
* @param {boolean} [predicate=isFlattenable] The function invoked per iteration.
* @param {boolean} [isStrict] Restrict to values that pass `predicate` checks.
* @param {Array} [result=[]] The initial result value.
* @returns {Array} Returns the new flattened array.
*/

function baseFlatten(array, depth, predicate, isStrict, result) {

var index = -1,
    length = array.length;

predicate || (predicate = isFlattenable);
result || (result = []);

while (++index < length) {
  var value = array[index];
  if (depth > 0 && predicate(value)) {
    if (depth > 1) {
      // Recursively flatten arrays (susceptible to call stack limits).
      baseFlatten(value, depth - 1, predicate, isStrict, result);
    } else {
      arrayPush(result, value);
    }
  } else if (!isStrict) {
    result[result.length] = value;
  }
}
return result;

}

/**

* Checks if `value` is a flattenable `arguments` object or array.
*
* @private
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is flattenable, else `false`.
*/

function isFlattenable(value) {

return isArray(value) || isArguments(value) ||
  !!(spreadableSymbol && value && value[spreadableSymbol]);

}

/**

* Flattens `array` a single level deep.
*
* @static
* @memberOf _
* @since 0.1.0
* @category Array
* @param {Array} array The array to flatten.
* @returns {Array} Returns the new flattened array.
* @example
*
* _.flatten([1, [2, [3, [4]], 5]]);
* // => [1, 2, [3, [4]], 5]
*/

function flatten(array) {

var length = array ? array.length : 0;
return length ? baseFlatten(array, 1) : [];

}

/**

* Checks if `value` is likely an `arguments` object.
*
* @static
* @memberOf _
* @since 0.1.0
* @category Lang
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is an `arguments` object,
*  else `false`.
* @example
*
* _.isArguments(function() { return arguments; }());
* // => true
*
* _.isArguments([1, 2, 3]);
* // => false
*/

function isArguments(value) {

// Safari 8.1 makes `arguments.callee` enumerable in strict mode.
return isArrayLikeObject(value) && hasOwnProperty.call(value, 'callee') &&
  (!propertyIsEnumerable.call(value, 'callee') || objectToString.call(value) == argsTag);

}

/**

* Checks if `value` is classified as an `Array` object.
*
* @static
* @memberOf _
* @since 0.1.0
* @category Lang
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is an array, else `false`.
* @example
*
* _.isArray([1, 2, 3]);
* // => true
*
* _.isArray(document.body.children);
* // => false
*
* _.isArray('abc');
* // => false
*
* _.isArray(_.noop);
* // => false
*/

var isArray = Array.isArray;

/**

* Checks if `value` is array-like. A value is considered array-like if it's
* not a function and has a `value.length` that's an integer greater than or
* equal to `0` and less than or equal to `Number.MAX_SAFE_INTEGER`.
*
* @static
* @memberOf _
* @since 4.0.0
* @category Lang
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is array-like, else `false`.
* @example
*
* _.isArrayLike([1, 2, 3]);
* // => true
*
* _.isArrayLike(document.body.children);
* // => true
*
* _.isArrayLike('abc');
* // => true
*
* _.isArrayLike(_.noop);
* // => false
*/

function isArrayLike(value) {

return value != null && isLength(value.length) && !isFunction(value);

}

/**

* This method is like `_.isArrayLike` except that it also checks if `value`
* is an object.
*
* @static
* @memberOf _
* @since 4.0.0
* @category Lang
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is an array-like object,
*  else `false`.
* @example
*
* _.isArrayLikeObject([1, 2, 3]);
* // => true
*
* _.isArrayLikeObject(document.body.children);
* // => true
*
* _.isArrayLikeObject('abc');
* // => false
*
* _.isArrayLikeObject(_.noop);
* // => false
*/

function isArrayLikeObject(value) {

return isObjectLike(value) && isArrayLike(value);

}

/**

* Checks if `value` is classified as a `Function` object.
*
* @static
* @memberOf _
* @since 0.1.0
* @category Lang
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is a function, else `false`.
* @example
*
* _.isFunction(_);
* // => true
*
* _.isFunction(/abc/);
* // => false
*/

function isFunction(value) {

// The use of `Object#toString` avoids issues with the `typeof` operator
// in Safari 8-9 which returns 'object' for typed array and other constructors.
var tag = isObject(value) ? objectToString.call(value) : '';
return tag == funcTag || tag == genTag;

}

/**

* Checks if `value` is a valid array-like length.
*
* **Note:** This method is loosely based on
* [`ToLength`](http://ecma-international.org/ecma-262/7.0/#sec-tolength).
*
* @static
* @memberOf _
* @since 4.0.0
* @category Lang
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is a valid length, else `false`.
* @example
*
* _.isLength(3);
* // => true
*
* _.isLength(Number.MIN_VALUE);
* // => false
*
* _.isLength(Infinity);
* // => false
*
* _.isLength('3');
* // => false
*/

function isLength(value) {

return typeof value == 'number' &&
  value > -1 && value % 1 == 0 && value <= MAX_SAFE_INTEGER;

}

/**

* Checks if `value` is the
* [language type](http://www.ecma-international.org/ecma-262/7.0/#sec-ecmascript-language-types)
* of `Object`. (e.g. arrays, functions, objects, regexes, `new Number(0)`, and `new String('')`)
*
* @static
* @memberOf _
* @since 0.1.0
* @category Lang
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is an object, else `false`.
* @example
*
* _.isObject({});
* // => true
*
* _.isObject([1, 2, 3]);
* // => true
*
* _.isObject(_.noop);
* // => true
*
* _.isObject(null);
* // => false
*/

function isObject(value) {

var type = typeof value;
return !!value && (type == 'object' || type == 'function');

}

/**

* Checks if `value` is object-like. A value is object-like if it's not `null`
* and has a `typeof` result of "object".
*
* @static
* @memberOf _
* @since 4.0.0
* @category Lang
* @param {*} value The value to check.
* @returns {boolean} Returns `true` if `value` is object-like, else `false`.
* @example
*
* _.isObjectLike({});
* // => true
*
* _.isObjectLike([1, 2, 3]);
* // => true
*
* _.isObjectLike(_.noop);
* // => false
*
* _.isObjectLike(null);
* // => false
*/

function isObjectLike(value) {

return !!value && typeof value == 'object';

}

module.exports = flatten;