Arrgh\Arrgh

Complexity

Total Complexity

149

Size/Duplication

Total Lines	1100
Duplicated Lines	0 %

Coupling/Cohesion

Components	2
Dependencies	0

54 Methods

Rating	Name	Duplication	Size	Complexity
A	__construct()	0	10	2
A	__call()	0	4	1
A	toArray()	0	10	2
A	keepChain()	0	6	1
A	keep()	0	4	1
A	keepOnce()	0	4	1
A	breakChain()	0	4	1
A	offsetExists()	0	4	1
A	offsetGet()	0	4	2
A	offsetSet()	0	8	2
A	offsetUnset()	0	4	1
A	current()	0	8	2
A	key()	0	4	1
A	next()	0	4	1
A	rewind()	0	4	1
A	valid()	0	4	1
A	arr()	0	4	1
A	chain()	0	4	1
A	__callStatic()	0	13	3
A	allFunctions()	0	12	1
B	getSortDirection()	0	11	5
A	wrapCallable()	0	11	2
C	invoke()	0	72	15
B	findFunction()	0	27	6
A	handleCaseAsort()	0	5	1
A	handleCaseArrayColumn()	0	20	4
A	_call()	0	4	1
A	_rotateRight()	0	6	1
A	_swapTwoFirst()	0	8	1
A	_copy()	0	6	1
A	_copyMultiple()	0	14	4
A	_copyValue()	0	9	2
A	_arrgh()	0	5	1
A	arr_map_assoc()	0	5	1
B	arr_sort_by()	0	18	6
A	arr_collapse()	0	10	2
A	arr_contains()	0	11	2
B	arr_except()	0	21	5
B	arr_only()	0	23	6
A	arr_get()	0	9	2
C	_arr_get_traverse()	0	61	14
C	_arr_get_traverse_collection()	0	35	11
A	_arr_get_traverse_next_node_index()	0	14	4
B	_arr_get_traverse_next_node_key()	0	20	7
A	_arr_get_traverse_apply_custom_function()	0	7	1
A	arr_is_collection()	0	4	2
B	arr_depth()	0	20	5
A	arr_partition()	0	13	2
A	arr_even()	0	4	1
A	arr_odd()	0	4	1
A	arr_head()	0	4	1
A	arr_first()	0	7	2
A	arr_last()	0	7	2
A	arr_tail()	0	4	1

<?php

namespace Arrgh;

use \Closure;
use \InvalidArgumentException;

/**
 * A chainable array API or a set of static functions, or both.
 *
 * Note: arr_* global functions are defined at the end of the file
 *
 * @method  collapse(array $input)
 * @method  contains(array $haystack, string $needle, string $key)
 * @method  except(array $input, array|string $keys)
 * @method  only(array $input, array|string $keys)
 * @method  map_assoc(array $input, \Closure $callable)
 * @method  sort_by(array $input, string $key)
 * @method  depth(array $input)
 * @method  even(array $input)
 * @method  first(array $input)
 * @method  get(array, $input, array|string, $path, bool $collapse)
 * @method  head(array $input)
 * @method  is_collection(array $input)
 * @method  last(array $input)
 * @method  odd(array $input)
 * @method  partition(array $input, \Closure $callable)
 * @method  tail(array $input)
 */
class Arrgh implements \ArrayAccess, \Iterator
{
    const PHP_SORT_DIRECTION_56 = 1;
    const PHP_SORT_DIRECTION_7 = -1;

    private $array;
    private $array_position;
    private $original_array;
    private $terminate;
    private $keep_once;
    private $last_value;

    private static $php_version;
    private static $php_sort_direction;

    /**
     * Creates a new Arrgh object
     *
     * @method __construct
     * @param  mixed      $array Optional parameter that can be either an array or another Arrgh object.
     */
    public function __construct($array = [])
    {
        $this->array = $array;
        $this->array_position = 0;
        if ($array instanceof Arrgh) {
            $this->array = $array->toArray();
        }
        $this->original_array = $this->array;
        $this->terminate = true;
    }

    /**
     * Invoke calls for Arrgh instances.
     * @internal
     */
    public function __call($method, $args)
    {
        return self::invoke($method, $args, $this);
    }

    /**
     * Returns a native array.
     *
     * @method toArray
     * @return array  Returns an array.
     */
    public function toArray()
    {
        $array = array_map(function($item) {
            if ($item instanceof Arrgh) {
                return $item->toArray();
            }
            return $item;
        }, $this->array);
        return $array;
    }

    /**
     * Tells Arrgh to either return iteself or a value where it would otherwise
     * had terminated the chain and return a value.
     *
     * The default behaviour is to break the chain on terminating methods like:
     *
     * - join
     * - pop
     *
     * @method keepChain
     * @param  bool      $value      Set true to keep and false to terminate.
     * @param  bool      $keep_once  Set true to automatically switch of again
     *                               after one call to a terminating method.
     * @see keep
     * @see keepOnce
     * @see breakChain
     * @return Arrgh\Arrgh self
     */
    public function keepChain($value = true, $keep_once = false)
    {
        $this->terminate = !$value;
        $this->keep_once = $keep_once;
        return $this;
    }

    /**
     * Tells Arrgh to return itself where it would otheriwse had terminated
     * the chain and returned a value.
     *
     * @method keep
     * @see keepChain
     * @return Arrgh\Arrgh self
     */
    public function keep()
    {
        return $this->keepChain(true);
    }

    /**
     * Tells Arrgh to return iteself where it would otherwise had terminated
     * the chain and return a value, but do it just once.
     *
     * @method keepOnce
     * @see keepChain
     * @return Arrgh\Arrgh self
     */
    public function keepOnce()
    {
        return $this->keepChain(true, true);
    }

    /**
     * Tells Arrgh to return to its normal behaviour and return values rather
     * than itself when terminating methods are called.
     *
     * @method breakChain
     * @see keepChain
     * @return Arrgh\Arrgh self
     */
    public function breakChain()
    {
        return $this->keepChain(false);
    }

    /**
     * ArrayAccess
     * @internal
     */
    public function offsetExists($offset)
    {
        return isset($this->array[$offset]);
    }

    /**
     * ArrayAccess
     * @internal
     */
    public function offsetGet($offset)
    {
        return isset($this->array[$offset]) ? $this->array[$offset] : null;
    }

    /**
     * ArrayAccess
     * @internal
     */
    public function offsetSet($offset, $value)
    {
        if (is_null($offset)) {
            $this->array[] = $value;
        } else {
            $this->array[$offset] = $value;
        }
    }

    /**
     * ArrayAccess
     * @internal
     */
    public function offsetUnset($offset)
    {
        unset($this->array[$offset]);
    }

    /**
     * Iterator
     * @internal
     */
    public function current()
    {
        $value = $this->array[$this->array_position];
        if (is_array($value)) {
            return new Arrgh($value);
        }
        return $value;
    }

    /**
     * Iterator
     * @internal
     */
    public function key()
    {
        return $this->array_position;
    }

    /**
     * Iterator
     * @internal
     */
    public function next()
    {
        ++$this->array_position;
    }

    /**
     * Iterator
     * @internal
     */
    public function rewind()
    {
        $this->array_position = 0;
    }

    /**
     * Iterator
     * @internal
     */
    public function valid()
    {
        return isset($this->array[$this->array_position]);
    }

    /**
     * Creates a new Arrgh object (chain)
     *
     * @param  mixed      $array Optional parameter that can be either an array or another Arrgh object.
     * @see chain
     * @return Arrgh\Arrgh       A new Arrgh object
     */
    public static function arr($array = [])
    {
        return new self($array);
    }

    /**
     * Creates a new Arrgh object (chain)
     *
     * @param  mixed      $array Optional parameter that can be either an array or another Arrgh object.
     * @see arr
     * @return Arrgh\Arrgh       A new Arrgh object
     */
    public static function chain($array = [])
    {
        return new self($array);
    }

    /**
     * Invoke calls for static Arrgh calls.
     * @internal
     */
    public static function __callStatic($method, $args)
    {
        if ($method[0] === "_") {
            $method = substr($method, 1);
            $_args = $args;
            $first_argument = array_shift($args);
            if (is_array($first_argument)) {
                return self::chain($first_argument)->$method(...$args);
            }
            return self::chain()->$method(...$_args);
        }
        return self::invoke($method, $args);
    }

    /**
     * Returns list of supported functions partitioned into types of functions.
     *
     * @method allFunctions
     * @return array       Associative array with function type as key point
     *                     to a list of functions of that type
     */
    public static function allFunctions()
    {
        return [
            "_arrgh"        => self::$arr_functions,
            "_call"         => self::$simple_functions,
            "_rotateRight"  => self::$reverse_functions,
            "_swapTwoFirst" => self::$swapped_functions,
            "_copy"         => self::$mutable_functions,
            "_copyMultiple" => self::$mutable_functions_multiple,
            "_copyValue"    => self::$mutable_value_functions,
        ];
    }

    /**
     * Given the PHP version this functions returns the sort integer to use
     * for equal values in functions like `usort`. Optionally you can pass in
     * the existing value like so:
     *
     * usort($input, function ($a, $b) {
     *     return Arrgh::getSortDirection($a - $b);
     * });
     *
     * This will ensure that the custom sort function will work in both PHP
     * version 5.6.x and 7.x
     *
     * @method getSortDirection
     * @param  integer           $direction An integer like value
     * @return integer                      Returns a sort integer for a sort or compare function
     */
    public static function getSortDirection($direction = null)
    {
        if (self::$php_version === null) {
            self::$php_version = explode(".", phpversion());
            self::$php_sort_direction = self::$php_version[0] >= 7 ? self::PHP_SORT_DIRECTION_7 : self::PHP_SORT_DIRECTION_56;
        }
        if ($direction === null || $direction === 0) {
            return self::$php_sort_direction;
        }
        return $direction;
    }

    /**
     * Wraps a callable with the purpose of fixing bad PHP sort implementations.
     *
     * @internal
     *
     * @method wrapCallable
     * @param  \Closure      $callable A sort function
     * @return \Closure                A new closeure
     */
    private static function wrapCallable(Closure $callable)
    {
        $direction = self::getSortDirection();
        return function($a, $b) use ($direction, $callable) {
            $result = $callable($a, $b);
            if ($result === 0) {
                return $direction;
            }
            return $result;
        };
    }


    /**
     * Transforms the incoming calls to native calls.
     *
     * @internal
     *
     * @method invoke
     * @param  string $method Name of method to invoke.
     * @param  array  $args   Arguments for method.
     * @param  Arrgh  $object Optionally invoke on $object.
     *
     * @return mixed          Can return anything.
     */
    private static function invoke($method, $args, Arrgh $object = null)
    {
        self::getSortDirection();

        list($matching_handler, $matching_function, $post_handler) = self::findFunction($method);

        switch ($matching_function) {
            case "asort":
                self::handleCaseAsort(
                    /* ref */ $matching_function,
                    /* ref */ $args
                );
                break;
            case "array_column":
                self::handleCaseArrayColumn(
                    /* ref */ $matching_handler,
                    /* ref */ $matching_function,
                    /* ref */ $post_handler,
                    /* ref */ $args
                );
                break;
            default:
                break;
        }

        // If chain unshift array onto argument stack
        if ($object && !in_array($matching_function, self::$starters)) {
            array_unshift($args, $object->array);
        }

        // If some arrays are Arrghs map to array or if callable, wrap it in
        // new callable with info about sort direction.
        $args = array_map(function($arg) use ($matching_function) {
            if ($arg instanceof Arrgh) {
                return $arg->array;
            } else if ($arg instanceof Closure) {
                if (in_array($matching_function, self::$reverse_result_functions) && self::$php_version[0] < 7) {
                    return self::wrapCallable($arg);
                }
            }
            return $arg;
        }, $args);

        // Invoke handler
        $matching_handler_derefed = $matching_handler; // bug in 7.0.3, internally the var is no longer a string but a pointer
        $result = self::$matching_handler_derefed($matching_function, $args, $object);

        // If a post handler is registered let it modify the result
        if ($post_handler) {
            $result = $post_handler($result);
        }

        if ($object) {
            if (in_array($matching_function, self::$terminators)) {
                if ($object->terminate) {
                    if (is_array($result)) {
                        return new Arrgh($result);
                    }
                    return $result;
                }
                if ($object->keep_once) {
                    $object->terminate = true;
                    $object->keep_once = false;
                }
                $object->last_value = $result;
                return $object;
            }
            $object->array = $result;
            return $object;
        }
        return $result;
    }

    /**
     * Based on input method finds handler, function and post handler.
     *
     * @internal
     *
     * @return array Returns a tuble of [handler, function, postHandler]
     */
    private static function findFunction($method)
    {
        $snake = strtolower(preg_replace('/\B([A-Z])/', '_\1', $method));
        $function_name = $snake;
        $function_name_prefixed = stripos($method, "array_") === 0 ? $snake : "array_" . $snake;

        $all_function_names = [$function_name, $function_name_prefixed];
        $all_functions      = self::allFunctions();

        $matching_handler  = null;
        $matching_function = null;
        $post_handler      = null;
        foreach ($all_functions as $handler => $functions) {
            foreach ($all_function_names as $function) {
                if (in_array($function, $functions)) {
                    $matching_handler  = $handler;
                    $matching_function = $function;
                    break 2;
                }
            }
        }

        if ($matching_function === null) {
            throw new InvalidArgumentException("Method {$method} doesn't exist");
        }
        return [$matching_handler, $matching_function, $post_handler];
    }

    /**
     * Handles special case: asort - In PHP5 reverses equals ("arsort" doen't mess up for some reason)
     *
     * @internal
     */
    private static function handleCaseAsort(&$matching_function, &$args)
    {
        $matching_function = "uasort";
        array_push($args, function($a, $b) { return strcasecmp($a, $b); });
    }

    /**
     * Handles special case: array_column - Native array_column filters away null values.
     *
     * That means you cannot use array_column for multisort since array size no longer matches.
     * This version of array_column returns null if the column is missing.
     *
     * @internal
     */
    private static function handleCaseArrayColumn(&$matching_handler, &$matching_function, &$post_handler, &$args)
    {
        $matching_handler  = "_rotateRight";
        $matching_function = "array_map";
        $column_array = $args[0];
        $column_key   = $args[1];
        if (count($args) === 3) {
            $column_id = $args[2];
            $column_ids_new = array_map(function($item) use ($column_id) {
                return isset($item[$column_id]) ? $item[$column_id] : null;
            }, $column_array);
            $post_handler = function($result) use ($column_ids_new) {
                return array_combine($column_ids_new, $result);
            };
        }
        $args = [$column_array];
        array_push($args, function($item) use ($column_key) {
            return isset($item[$column_key]) ? $item[$column_key] : null;
        });
    }

    /**
     * Handler: _call
     *
     * Calls the native function directly.
     *
     * @internal
     */
    private static function _call($function, $args)
    {
        return $function(...$args);
    }

    /**
     * Handler: _rotateRight
     *
     * Shifts of the first argument (callable) and pushes it to the end.
     *
     * @internal
     */
    private static function _rotateRight($function, $args)
    {
        $first_argument = array_pop($args);
        array_unshift($args, $first_argument);
        return $function(...$args);
    }

    /**
     * Handler: _swapTwoFirst
     *
     * Swaps the first two args.
     *
     * @internal
     */
    private static function _swapTwoFirst($function, $args)
    {
        $first_argument = array_shift($args);
        $second_argument = array_shift($args);
        array_unshift($args, $first_argument);
        array_unshift($args, $second_argument);
        return $function(...$args);
    }

    /**
     * Handler: _copy
     *
     * Makes a copy of the array and returns it after invoking function.
     *
     * @internal
     */
    private static function _copy($function, $args)
    {
        $array = array_shift($args);
        $function($array, ...$args);
        return $array;
    }

    /**
     * Handler: _copyMultiple
     *
     * If multiple arrays are passed as arguments mulitple will be returned.
     * Otherwise _copy is used.
     *
     * @internal
     */
    private static function _copyMultiple($function, $args)
    {
        $function(...$args);
        $arrays = [];
        foreach ($args as $arg) {
            if (is_array($arg)) {
                $arrays[] = $arg;
            }
        }
        if (count($arrays) === 1) {
            return $arrays[0];
        }
        return $arrays;
    }

    /**
     * Handler: _copyValue
     *
     * Makes a copy of the array and returns it after invoking function.
     *
     * @internal
     */
    private static function _copyValue($function, $args, $object = null)
    {
        $array = array_shift($args);
        $result = $function($array, ...$args);
        if ($object) {
            $object->array = $array;
        }
        return $result;
    }

    /**
     * Handler: _arrgh
     *
     * The handler for non-native functions
     *
     * @internal
     */
    private static function _arrgh($function, $args)
    {
        $function = "arr_" . $function;
        return self::$function(...$args);
    }

    /**
     * A mapping function for associative arrays (keeps keys).
     *
     * @method map_assoc
     *
     * @param  array         $array    Array or array-like value.
     * @param  Closure       $callable Mapping function
     *
     * @return array                   Returns mapped associative array.
     */
    private static function arr_map_assoc($array, Closure $callable)
    {
        $keys = array_keys($array);
        return array_combine($keys, array_map($callable, $keys, $array));
    }

    /**
     * Sort an array of associative arrays by key. It checks the first two values for type
     * either sorts by number or using strcmp. If a key is missing entries are moved to the top
     * (or bottom depending on $direction)
     */
    private static function arr_sort_by($array, $key, $direction = "ASC")
    {
        $direction_int = strtoupper($direction) === "ASC" ? 1 : -1;

        if ($key instanceof Closure) {
            usort($array, self::wrapCallable($key));
            if ($direction_int === -1) {
                return array_reverse($array);
            }
            return $array;
        }

        $column = array_map(function($item) use ($key) {
            return isset($item[$key]) ? $item[$key] : null;
        }, $array);
        array_multisort($column, ($direction_int === 1 ? SORT_ASC : SORT_DESC), $array);
        return $array;
    }

    private static function arr_collapse($array)
    {
        return array_reduce($array, function($merged, $item) {
            if (is_array($item)) {
                return array_merge($merged, $item);
            }
            $merged[] = $item;
            return $merged;
        }, []);
    }

    private static function arr_contains($array, $search, $key = null)
    {
        if ($key) {
            $haystack = array_column($array, $key);
        } else {
            $haystack = array_reduce($array, function($merged, $item) {
                return array_merge($merged, array_values($item));
            }, []);
        }
        return array_search($search, $haystack) !== false;
    }

    private static function arr_except($array, $except)
    {
        if (is_string($except)) {
            $except = [$except];
        }

        $is_collection = self::arr_is_collection($array);
        $array = $is_collection ? $array : [$array];

        $result = array_map(function($item) use ($except) {
            foreach ($except as $key) {
                unset($item[$key]);
            }
            return $item;
        }, $array);

        if ($is_collection) {
            return $result;
        }
        return $result[0];
    }

    private static function arr_only($array, $only)
    {
        if (is_string($only)) {
            $only = [$only];
        }

        $is_collection = self::arr_is_collection($array);
        $array = $is_collection ? $array : [$array];

        $result = array_map(function($item) use ($only) {
            foreach ($item as $key => $value) {
                if (!in_array($key, $only)) {
                    unset($item[$key]);
                }
            }
            return $item;
        }, $array);

        if ($is_collection) {
            return $result;
        }
        return $result[0];
    }

    /**
     *  Get for multi-dimensional arrays
     *
     *  @param array      An array to query on
     *  @param path|array A string representing the path to traverse.
     *                    Optionally pass as [ $path, ...$functions ] if `!$` is used
     *  @param bool       Collapse resulting data-set
     *  @throws InvalidArgumentException Thrown when a path cannot be reached in case $array does
     *                    not correspond to path type. E.g. collection expected
     *                    but a simple value was encountered.
     */
    private static function arr_get($array, $path, $collapse = false)
    {
        $path_string = $path;
        if (is_array($path)) {
            $path_string = array_shift($path);
        }
        $path_segments = explode(".", $path_string);
        return self::_arr_get_traverse($array, $path_segments, $collapse, /* functions */ $path);
    }

    /* arr_get: Traverses path to get value */
    private static function _arr_get_traverse($data, $path, $collapse = false, $functions = [])
    {
        $next_key      = array_shift($path);
        $plug_index    = is_numeric($next_key) ? (int) $next_key : null;
        $is_collection = self::isCollection($data);

        // Apply custom function
        if ($next_key === '!$') {
            if ($is_collection) {
                list($data, $path, $functions, $next_key) = self::_arr_get_traverse_apply_custom_function($data, $functions, $path);
            } else {
                throw new InvalidArgumentException("Invalid path trying to invoke function on non-collection");
            }
        }

        // Select data either by index or key
        if ($plug_index === null) {
            $next_node = self::_arr_get_traverse_next_node_key($data, $is_collection, $next_key);
        } else {
            if ($is_collection) {
                $next_node = self::_arr_get_traverse_next_node_index($data, $plug_index);
            } else {
                throw new InvalidArgumentException("Invalid path trying to plug item but data is not a collection");
            }
        }

        // If nothing matched break path and return
        if (empty($next_node)) {
            return null;
        }

        // If path is at the end return
        if (count($path) === 0) {
            if (is_array($next_node) && $collapse) {
                return array_filter($next_node);
            }
            return $next_node;
        }

        // If path is not completed
        if (is_array($next_node)) {

            // Recurse
            if (self::arr_is_collection($next_node)) {
                $result = self::_arr_get_traverse_collection($path, $next_node, $collapse, $functions);
            } else {
                $result = self::_arr_get_traverse($next_node, $path, $collapse, $functions);
            }

            // Collapse result if needed
            if (is_array($result)) {
                // Collapse collections greater than 1
                if (self::arr_depth($result) > 1) {
                    $result = self::arr_collapse($result);
                }
                return array_filter($result);
            }
            return $result;
        }
        return null;
    }

    private static function _arr_get_traverse_collection($path, $next_node, $collapse, $functions)
    {
        $node_depth = self::arr_depth($next_node);

        // Collapse collections
        $is_intermediary_collection = !is_numeric($path[0]) && $path[0] !== "!$" && $node_depth > 0;
        if ($collapse && $is_intermediary_collection) {
            $next_node = self::arr_collapse($next_node);
        }

        if (is_numeric($path[0]) && $node_depth < 1) {
            $result = self::_arr_get_traverse($next_node, $path, $collapse, $functions);
        } else {
            // Collect data from sub-tree
            $result = [];
            foreach ($next_node as $node) {
                if ($node === null) {
                    $result[] = null;
                } else {
                    $partial = self::_arr_get_traverse($node, $path, $collapse, $functions);
                    if ($collapse) {
                        $result[] = $partial;
                    } else {
                        $result[] = [$partial];
                    }
                }
            }
        }

        // Since collection functions inject an array segment we must collapse the result
        if ($path[0] === "!$") {
            $result = self::arr_collapse($result);
        }
        return $result;
    }

    /* arr_get: Find next node by index */
    private static function _arr_get_traverse_next_node_index($data, $plug_index)
    {
        // Adjust negative index
        if ($plug_index < 0) {
            $count = count($data);
            $plug_index = $count === 1 ? 0 : $count + ($plug_index % $count);
        }

        // Plug data
        if (isset($data[$plug_index])) {
            return $data[$plug_index];
        }
        return null;
    }

    /* arr_get: Find next node by key */
    private static function _arr_get_traverse_next_node_key($data, $is_collection, $next_key)
    {
        if ($next_key === null) {
            return $data;
        }
        if ($is_collection) {
            return array_map(function($item) use ($next_key) {
                if ($item !== null && array_key_exists($next_key, $item)) {
                    return $item[$next_key];
                }
                return null;
            }, $data);
        } else if (is_array($data)) {
            if (array_key_exists($next_key, $data)) {
                return $data[$next_key];
            }
            return null;
        }
        throw new InvalidArgumentException("Path ...$next_key does not exist");
    }

    /* arr_get: Invoke custom filter function on path */
    private static function _arr_get_traverse_apply_custom_function($data, $functions, $path)
    {
        $function  = array_shift($functions);
        $data      = array_values(array_filter($data, $function, ARRAY_FILTER_USE_BOTH));
        $next_key  = array_shift($path);
        return [$data, $path, $functions, $next_key];
    }

    private static function arr_is_collection($mixed)
    {
        return is_array($mixed) && array_values($mixed) === $mixed;
    }

    /**
     * Return the depth of a collection hiearchy. Zero based.
     *
     * @param array A collection
     * @return int `null` if $array is not a collection.
     */
    private static function arr_depth($array)
    {
        // Empty arrays are assumed to be collections, thus returning 0-depth
        if (empty($array) && is_array($array)) {
            return 0;
        }

        // Associative arrays are not collections, return null
        if (!self::arr_is_collection($array)) {
            return null;
        }

        $depth = 0;
        $child = array_shift($array);
        while (self::arr_is_collection($child)) {
            $depth += 1;
            $child = array_shift($child);
        }
        return $depth;
    }

    /**
     * Partion the input based on the result of the callback function.
     *
     * @param array     $array    A collection
     * @param \Closeure $callable A callable returning true or false depending on which way to partion the element—left or right.
     * @return array An array with two arrays—left and right: [left, right]
     */
    private static function arr_partition($array, Closure $callable)
    {
        $left = [];
        $right = [];
        array_walk($array, function($item, $key) use (&$left, &$right, $callable) {
            if ($callable($item, $key)) {
                $left[] = $item;
            } else {
                $right[] = $item;
            }
        });
        return [$left, $right];
    }

    private static function arr_even($array)
    {
        return self::arr_partition($array, function($item, $key) { return $key % 2 === 0; })[0];
    }

    private static function arr_odd($array)
    {
        return self::arr_partition($array, function($item, $key) { return $key % 2 === 1; })[0];
    }

    /* Synonym of shift */
    private static function arr_head($array)
    {
        return self::shift($array);
    }

    private static function arr_first($array)
    {
        if (count($array)) {
            return $array[0];
        }
        return null;
    }

    private static function arr_last($array)
    {
        if (count($array)) {
            return $array[count($array) - 1];
        }
        return null;
    }

    private static function arr_tail($array)
    {
        return self::chain($array)->keep()->shift()->toArray();

The method shift does not exist on object<Arrgh\Arrgh>? Since you implemented __call, maybe consider adding a @method annotation.

    }

    // _arrgh
    static private $arr_functions = [
        "collapse",
        "contains",
        "except",
        "map_assoc",
        "only",
        "sort_by",
        'depth',
        'even',
        'first',
        'get',
        'head',
        'is_collection',
        'last',
        'odd',
        'partition',
        'tail',
    ];

    // _call
    static private $simple_functions = [
        "array_change_key_case",
        "array_chunk",
        "array_column",
        "array_combine",
        "array_count_values",
        "array_diff",
        "array_diff_assoc",
        "array_diff_key",
        "array_diff_uassoc",
        "array_diff_ukey",
        "array_fill",
        "array_fill_keys",
        "array_filter",
        "array_flip",
        "array_intersect",
        "array_intersect_assoc",
        "array_intersect_key",
        "array_intersect_uassoc",
        "array_intersect_ukey",
        "array_keys",
        "array_merge",
        "array_merge_recursive",
        "array_pad",
        "array_product",
        "array_rand",
        "array_reduce",
        "array_replace",
        "array_replace_recursive",
        "array_reverse",
        "array_slice",
        "array_sum",
        "array_udiff",
        "array_udiff_assoc",
        "array_udiff_uassoc",
        "array_uintersect",
        "array_uintersect_assoc",
        "array_uintersect_uassoc",
        "array_unique",
        "array_values",
        "count",
        "max",
        "min",
        "range",
        "sizeof",
    ];

    // _copy
    static private $mutable_functions = [
        "array_push",
        "array_splice",
        "array_unshift",
        "array_walk",
        "array_walk_recursive",
        "arsort",
        "asort",
        "krsort",
        "ksort",
        "natcasesort",
        "natsort",
        "rsort",
        "shuffle",
        "sort",
        "uasort",
        "uksort",
        "usort",
    ];

    // _copyMultiple
    static private $mutable_functions_multiple = [
        "array_multisort",
    ];

    // _copyValue
    static private $mutable_value_functions = [
        "array_pop",
        "array_shift",
        "end",
    ];

    // _rotateRight
    static private $reverse_functions = [
        "array_map",
    ];

    // _swapTwoFirst
    static private $swapped_functions = [
        "array_key_exists",
        "array_search",
        "implode",
        "in_array",
        "join",
    ];

    static private $starters = [
        "array_fill",
        "array_fill_keys",
        "range",
    ];

    static private $terminators = [
        "array_pop",
        "array_shift",
        "array_sum",
        "count",
        "first",
        "head",
        "join",
        "last",
        "max",
        "min",
        "sizeof",
    ];

    static private $reverse_result_functions = [
        "uasort",
        "uksort",
        "usort",
        "asort",
    ];
}