ACF Pagination Gallery with categories

gallery.php

<?php /*
Template Name: Gallery
Gallery template based on Advanced Custom Fields gallery field
with pagination and categories.
ACF Fields for this page are:
- gallery (Gallery field) -> contain all images
- categories (Repeater field) -> images divided into categories
-- name
-- nice_name (for the url)
-- gallery
 */

get_header();

//Get current cat, if empty show all images
$current_cat = get_query_var('category_name');

if (have_posts()) {
    while (have_posts()) {
        the_post();

        echo '<div class="gallery-wrapper">';

        //Get categories
        $cats = get_field('categories');

        //if this is gallery category subpage find out which one
        if ($current_cat) {
            foreach ($cats as $k=>$c) {
                if ($c['nice_name']==$current_cat) {
                    $current_gallery = $c['gallery'];
                }
            }
        }else {
            //otherwise show whole gallery
            $current_gallery = get_field('gallery');
        }

        //Setup pagination variables
        $images = array(); // Set images array for current page

        $items_per_page  = 4; // How many items we should display on each page
        $total_items = count($current_gallery); // How many items we have in total
        $total_pages = ceil($total_items / $items_per_page); // How many pages we have in total
        //Get current page
        if ( get_query_var( 'paged' ) ) {
            $current_page = get_query_var( 'paged' );
        }elseif ( get_query_var( 'page' ) ) {
            $current_page = get_query_var( 'page' );
        }else {
            $current_page = 1;
        }

        $starting_point = (($current_page-1)*$items_per_page); // Get starting point for current page

        // Get elements for current page
        if ($current_gallery) {
            $images = array_slice($current_gallery, $starting_point, $items_per_page);
        }

        //Show category list
        if ($cats) {
            echo '<ul>';
            echo '<li><a href="'.get_permalink().'">All</a></li>';
            foreach ($cats as $c) {
                echo '<li><a href="'.get_permalink().$c['nice_name'].'/">'.$c['name'].'</a></li>';
            }
            echo '</ul>';
        }

        echo '<div id="gallery-items">';
        $i = $starting_point;
        if ($images) {
            foreach ($images as $g) {
                echo '<img src="'.$g['sizes']['thumb'].'" alt="'.$g['alt'].'">';
            }
        }
        echo '</div>';

        $big = 999999999; // need an unlikely integer
        $translated = __( 'Page', 'pixplus' ); // Supply translatable string
        $pagination = paginate_links( array(
                'base' => str_replace( $big, '%#%', esc_url( get_pagenum_link( $big ) ) ),
                'format' => '?paged=%#%',
                'current' => $current_page,
                'total' => $total_pages,
                'before_page_number' => '<span class="screen-reader-text">'.$translated.' </span>'
            ));
        if ($pagination) echo '<div class="pagination-wrapper">'.$pagination.'</div>';

        echo '</div>';
    }
}
get_footer();

gallery_acf_json.json

[
    {
        "key": "group_553ca48616132",
        "title": "Gallery with categories",
        "fields": [
            {
                "key": "field_553ca48ae5094",
                "label": "Gallery",
                "name": "gallery",
                "type": "gallery",
                "instructions": "",
                "required": 0,
                "conditional_logic": 0,
                "wrapper": {
                    "width": "",
                    "class": "",
                    "id": ""
                },
                "min": "",
                "max": "",
                "preview_size": "thumbnail",
                "library": "all",
                "min_width": "",
                "min_height": "",
                "min_size": "",
                "max_width": "",
                "max_height": "",
                "max_size": "",
                "mime_types": ""
            },
            {
                "key": "field_571ca023ac926",
                "label": "Categories",
                "name": "categories",
                "type": "repeater",
                "instructions": "",
                "required": 0,
                "conditional_logic": 0,
                "wrapper": {
                    "width": "",
                    "class": "",
                    "id": ""
                },
                "collapsed": "",
                "min": "",
                "max": "",
                "layout": "block",
                "button_label": "Add Category",
                "sub_fields": [
                    {
                        "key": "field_571ca035ac927",
                        "label": "Name",
                        "name": "name",
                        "type": "text",
                        "instructions": "",
                        "required": 0,
                        "conditional_logic": 0,
                        "wrapper": {
                            "width": "",
                            "class": "",
                            "id": ""
                        },
                        "default_value": "",
                        "placeholder": "",
                        "prepend": "",
                        "append": "",
                        "maxlength": "",
                        "readonly": 0,
                        "disabled": 0
                    },
                    {
                        "key": "field_571cb39ff8039",
                        "label": "Nice name",
                        "name": "nice_name",
                        "type": "text",
                        "instructions": "Slug, no spaces and special characters",
                        "required": 0,
                        "conditional_logic": 0,
                        "wrapper": {
                            "width": "",
                            "class": "",
                            "id": ""
                        },
                        "default_value": "",
                        "placeholder": "",
                        "prepend": "",
                        "append": "",
                        "maxlength": "",
                        "readonly": 0,
                        "disabled": 0
                    },
                    {
                        "key": "field_571ca03aac928",
                        "label": "Gallery",
                        "name": "gallery",
                        "type": "gallery",
                        "instructions": "",
                        "required": 0,
                        "conditional_logic": 0,
                        "wrapper": {
                            "width": "",
                            "class": "",
                            "id": ""
                        },
                        "min": "",
                        "max": "",
                        "preview_size": "thumbnail",
                        "library": "all",
                        "min_width": "",
                        "min_height": "",
                        "min_size": "",
                        "max_width": "",
                        "max_height": "",
                        "max_size": "",
                        "mime_types": ""
                    }
                ]
            }
        ],
        "location": [
            [
                {
                    "param": "page_template",
                    "operator": "==",
                    "value": "themename\/gallery.php"
                }
            ]
        ],
        "menu_order": 1,
        "position": "normal",
        "style": "default",
        "label_placement": "top",
        "instruction_placement": "label",
        "hide_on_screen": [
            "featured_image"
        ],
        "active": 1,
        "description": ""
    }
]

gallery_rewrites.php

/* Include this in functions.php */

add_action( 'init', 'gallery_cat_rewrite' );
function gallery_cat_rewrite() {
    //My subpage slug is "gallery" if you have something else, change gallery to that
    add_rewrite_rule(
        'gallery/([^/]+)/?$',
        'index.php?pagename=gallery&category_name=$matches[1]',
        'top' );

    add_rewrite_rule(
        'gallery/([^/]+)/page/([0-9]+)?$',
        'index.php?pagename=gallery&category_name=$matches[1]&paged=$matches[2]',
        'top' );

    // Remember to flush the rules once after modyfing something here.
    // After first page refresh comment this line so that rule wouldn't be flushed over and over again.
    flush_rewrite_rules();
}