class NestedArray

class NestedArray {
    
    /**
     * Retrieves a value from a nested array with variable depth.
     *
     * This helper function should be used when the depth of the array element
     * being retrieved may vary (that is, the number of parent keys is variable).
     * It is primarily used for form structures and renderable arrays.
     *
     * Without this helper function the only way to get a nested array value with
     * variable depth in one line would be using eval(), which should be avoided:
     * @code
     * // Do not do this! Avoid eval().
     * // May also throw a PHP notice, if the variable array keys do not exist.
     * eval('$value = $array[\'' . implode("']['", $parents) . "'];");
     * @endcode
     *
     * Instead, use this helper function:
     * @code
     * $value = NestedArray::getValue($form, $parents);
     * @endcode
     *
     * A return value of NULL is ambiguous, and can mean either that the requested
     * key does not exist, or that the actual value is NULL. If it is required to
     * know whether the nested array key actually exists, pass a third argument
     * that is altered by reference:
     * @code
     * $key_exists = NULL;
     * $value = NestedArray::getValue($form, $parents, $key_exists);
     * if ($key_exists) {
     *   // Do something with $value.
     * }
     * @endcode
     *
     * However if the number of array parent keys is static, the value should
     * always be retrieved directly rather than calling this function.
     * For instance:
     * @code
     * $value = $form['signature_settings']['signature'];
     * @endcode
     *
     * @param array $array
     *   The array from which to get the value.
     * @param array $parents
     *   An array of parent keys of the value, starting with the outermost key.
     * @param bool $key_exists
     *   (optional) If given, an already defined variable that is altered by
     *   reference.
     *
     * @return mixed
     *   The requested nested value. Possibly NULL if the value is NULL or not all
     *   nested parent keys exist. $key_exists is altered by reference and is a
     *   Boolean that indicates whether all nested parent keys exist (TRUE) or not
     *   (FALSE). This allows to distinguish between the two possibilities when
     *   NULL is returned.
     *
     * @see NestedArray::setValue()
     * @see NestedArray::unsetValue()
     */
    public static function &getValue(array &$array, array $parents, &$key_exists = NULL) {
        $ref =& $array;
        foreach ($parents as $parent) {
            if (is_array($ref) && (isset($ref[$parent]) || array_key_exists($parent, $ref))) {
                $ref =& $ref[$parent];
            }
            else {
                $key_exists = FALSE;
                $null = NULL;
                return $null;
            }
        }
        $key_exists = TRUE;
        return $ref;
    }
    
    /**
     * Sets a value in a nested array with variable depth.
     *
     * This helper function should be used when the depth of the array element you
     * are changing may vary (that is, the number of parent keys is variable). It
     * is primarily used for form structures and renderable arrays.
     *
     * Example:
     * @code
     * // Assume you have a 'signature' element somewhere in a form. It might be:
     * $form['signature_settings']['signature'] = array(
     *   '#type' => 'text_format',
     *   '#title' => t('Signature'),
     * );
     * // Or, it might be further nested:
     * $form['signature_settings']['user']['signature'] = array(
     *   '#type' => 'text_format',
     *   '#title' => t('Signature'),
     * );
     * @endcode
     *
     * To deal with the situation, the code needs to figure out the route to the
     * element, given an array of parents that is either
     * @code array('signature_settings', 'signature') @endcode
     * in the first case or
     * @code array('signature_settings', 'user', 'signature') @endcode
     * in the second case.
     *
     * Without this helper function the only way to set the signature element in
     * one line would be using eval(), which should be avoided:
     * @code
     * // Do not do this! Avoid eval().
     * eval('$form[\'' . implode("']['", $parents) . '\'] = $element;');
     * @endcode
     *
     * Instead, use this helper function:
     * @code
     * NestedArray::setValue($form, $parents, $element);
     * @endcode
     *
     * However if the number of array parent keys is static, the value should
     * always be set directly rather than calling this function. For instance,
     * for the first example we could just do:
     * @code
     * $form['signature_settings']['signature'] = $element;
     * @endcode
     *
     * @param array $array
     *   A reference to the array to modify.
     * @param array $parents
     *   An array of parent keys, starting with the outermost key.
     * @param mixed $value
     *   The value to set.
     * @param bool $force
     *   (optional) If TRUE, the value is forced into the structure even if it
     *   requires the deletion of an already existing non-array parent value. If
     *   FALSE, PHP throws an error if trying to add into a value that is not an
     *   array. Defaults to FALSE.
     *
     * @see NestedArray::unsetValue()
     * @see NestedArray::getValue()
     */
    public static function setValue(array &$array, array $parents, $value, $force = FALSE) {
        $ref =& $array;
        foreach ($parents as $parent) {
            // PHP auto-creates container arrays and NULL entries without error if $ref
            // is NULL, but throws an error if $ref is set, but not an array.
            if ($force && isset($ref) && !is_array($ref)) {
                $ref = [];
            }
            $ref =& $ref[$parent];
        }
        $ref = $value;
    }
    
    /**
     * Unsets a value in a nested array with variable depth.
     *
     * This helper function should be used when the depth of the array element you
     * are changing may vary (that is, the number of parent keys is variable). It
     * is primarily used for form structures and renderable arrays.
     *
     * Example:
     * @code
     * // Assume you have a 'signature' element somewhere in a form. It might be:
     * $form['signature_settings']['signature'] = array(
     *   '#type' => 'text_format',
     *   '#title' => t('Signature'),
     * );
     * // Or, it might be further nested:
     * $form['signature_settings']['user']['signature'] = array(
     *   '#type' => 'text_format',
     *   '#title' => t('Signature'),
     * );
     * @endcode
     *
     * To deal with the situation, the code needs to figure out the route to the
     * element, given an array of parents that is either
     * @code array('signature_settings', 'signature') @endcode
     * in the first case or
     * @code array('signature_settings', 'user', 'signature') @endcode
     * in the second case.
     *
     * Without this helper function the only way to unset the signature element in
     * one line would be using eval(), which should be avoided:
     * @code
     * // Do not do this! Avoid eval().
     * eval('unset($form[\'' . implode("']['", $parents) . '\']);');
     * @endcode
     *
     * Instead, use this helper function:
     * @code
     * NestedArray::unset_nested_value($form, $parents, $element);
     * @endcode
     *
     * However if the number of array parent keys is static, the value should
     * always be set directly rather than calling this function. For instance, for
     * the first example we could just do:
     * @code
     * unset($form['signature_settings']['signature']);
     * @endcode
     *
     * @param array $array
     *   A reference to the array to modify.
     * @param array $parents
     *   An array of parent keys, starting with the outermost key and including
     *   the key to be unset.
     * @param bool $key_existed
     *   (optional) If given, an already defined variable that is altered by
     *   reference.
     *
     * @see NestedArray::setValue()
     * @see NestedArray::getValue()
     */
    public static function unsetValue(array &$array, array $parents, &$key_existed = NULL) {
        $unset_key = array_pop($parents);
        $ref =& self::getValue($array, $parents, $key_existed);
        if ($key_existed && is_array($ref) && (isset($ref[$unset_key]) || array_key_exists($unset_key, $ref))) {
            $key_existed = TRUE;
            unset($ref[$unset_key]);
        }
        else {
            $key_existed = FALSE;
        }
    }
    
    /**
     * Determines whether a nested array contains the requested keys.
     *
     * This helper function should be used when the depth of the array element to
     * be checked may vary (that is, the number of parent keys is variable). See
     * NestedArray::setValue() for details. It is primarily used for form
     * structures and renderable arrays.
     *
     * If it is required to also get the value of the checked nested key, use
     * NestedArray::getValue() instead.
     *
     * If the number of array parent keys is static, this helper function is
     * unnecessary and the following code can be used instead:
     * @code
     * $value_exists = isset($form['signature_settings']['signature']);
     * $key_exists = array_key_exists('signature', $form['signature_settings']);
     * @endcode
     *
     * @param array $array
     *   The array with the value to check for.
     * @param array $parents
     *   An array of parent keys of the value, starting with the outermost key.
     *
     * @return bool
     *   TRUE if all the parent keys exist, FALSE otherwise.
     *
     * @see NestedArray::getValue()
     */
    public static function keyExists(array $array, array $parents) {
        // Although this function is similar to PHP's array_key_exists(), its
        // arguments should be consistent with getValue().
        $key_exists = NULL;
        self::getValue($array, $parents, $key_exists);
        return $key_exists;
    }
    
    /**
     * Merges multiple arrays, recursively, and returns the merged array.
     *
     * This function is similar to PHP's array_merge_recursive() function, but it
     * handles non-array values differently. When merging values that are not both
     * arrays, the latter value replaces the former rather than merging with it.
     *
     * Example:
     * @code
     * $link_options_1 = array('fragment' => 'x', 'attributes' => array('title' => t('X'), 'class' => array('a', 'b')));
     * $link_options_2 = array('fragment' => 'y', 'attributes' => array('title' => t('Y'), 'class' => array('c', 'd')));
     *
     * // This results in array('fragment' => array('x', 'y'), 'attributes' => array('title' => array(t('X'), t('Y')), 'class' => array('a', 'b', 'c', 'd'))).
     * $incorrect = array_merge_recursive($link_options_1, $link_options_2);
     *
     * // This results in array('fragment' => 'y', 'attributes' => array('title' => t('Y'), 'class' => array('a', 'b', 'c', 'd'))).
     * $correct = NestedArray::mergeDeep($link_options_1, $link_options_2);
     * @endcode
     *
     * @param array ...
     *   Arrays to merge.
     *
     * @return array
     *   The merged array.
     *
     * @see NestedArray::mergeDeepArray()
     */
    public static function mergeDeep() {
        return self::mergeDeepArray(func_get_args());
    }
    
    /**
     * Merges multiple arrays, recursively, and returns the merged array.
     *
     * This function is equivalent to NestedArray::mergeDeep(), except the
     * input arrays are passed as a single array parameter rather than a variable
     * parameter list.
     *
     * The following are equivalent:
     * - NestedArray::mergeDeep($a, $b);
     * - NestedArray::mergeDeepArray(array($a, $b));
     *
     * The following are also equivalent:
     * - call_user_func_array('NestedArray::mergeDeep', $arrays_to_merge);
     * - NestedArray::mergeDeepArray($arrays_to_merge);
     *
     * @param array $arrays
     *   An arrays of arrays to merge.
     * @param bool $preserve_integer_keys
     *   (optional) If given, integer keys will be preserved and merged instead of
     *   appended. Defaults to FALSE.
     *
     * @return array
     *   The merged array.
     *
     * @see NestedArray::mergeDeep()
     */
    public static function mergeDeepArray(array $arrays, $preserve_integer_keys = FALSE) {
        $result = [];
        foreach ($arrays as $array) {
            foreach ($array as $key => $value) {
                // Renumber integer keys as array_merge_recursive() does unless
                // $preserve_integer_keys is set to TRUE. Note that PHP automatically
                // converts array keys that are integer strings (e.g., '1') to integers.
                if (is_int($key) && !$preserve_integer_keys) {
                    $result[] = $value;
                }
                elseif (isset($result[$key]) && is_array($result[$key]) && is_array($value)) {
                    $result[$key] = self::mergeDeepArray([
                        $result[$key],
                        $value,
                    ], $preserve_integer_keys);
                }
                else {
                    $result[$key] = $value;
                }
            }
        }
        return $result;
    }
    
    /**
     * Filters a nested array recursively.
     *
     * @param array $array
     *   The filtered nested array.
     * @param callable|null $callable
     *   The callable to apply for filtering.
     *
     * @return array
     *   The filtered array.
     */
    public static function filter(array $array, callable $callable = NULL) {
        $array = is_callable($callable) ? array_filter($array, $callable) : array_filter($array);
        foreach ($array as &$element) {
            if (is_array($element)) {
                $element = static::filter($element, $callable);
            }
        }
        return $array;
    }

}