/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
import React, { CSSProperties } from 'react';

export interface PaginationProps {
  pageCount: number; // number of pages
  currentPage?: number; // index of current page, zero-based
  maxPageItemCount?: number;
  ellipsis?: string; // content for ellipsis item
  onPageChange: (page: number) => void; // `page` is zero-based
  style?: CSSProperties;
}

// first, ..., prev, current, next, ..., last
const MINIMAL_PAGE_ITEM_COUNT = 7;

/**
 * Generate numeric page items around current page.
 *   - Always include first and last page
 *   - Add ellipsis if needed
 */
export function generatePageItems(total: number, current: number, width: number) {
  if (width < MINIMAL_PAGE_ITEM_COUNT) {
    throw new Error(`Must allow at least ${MINIMAL_PAGE_ITEM_COUNT} page items`);
  }
  if (width % 2 === 0) {
    throw new Error(`Must allow odd number of page items`);
  }
  if (total < width) {
    return [...new Array(total).keys()];
  }
  const left = Math.max(0, Math.min(total - width, current - Math.floor(width / 2)));
  const items: (string | number)[] = new Array(width);
  for (let i = 0; i < width; i += 1) {
    items[i] = i + left;
  }
  // replace non-ending items with placeholders
  if (items[0] > 0) {
    items[0] = 0;
    items[1] = 'prev-more';
  }
  if (items[items.length - 1] < total - 1) {
    items[items.length - 1] = total - 1;
    items[items.length - 2] = 'next-more';
  }
  return items;
}

export default React.memo(
  React.forwardRef(function Pagination(
    { style, pageCount, currentPage = 0, maxPageItemCount = 9, onPageChange }: PaginationProps,
    ref: React.Ref<HTMLDivElement>,
  ) {
    const pageItems = generatePageItems(pageCount, currentPage, maxPageItemCount);
    return (
      <div ref={ref} className="dt-pagination" style={style}>
        <ul className="pagination pagination-sm">
          {pageItems.map(item =>
            typeof item === 'number' ? (
              // actual page number
              <li key={item} className={currentPage === item ? 'active' : undefined}>
                <a
                  href={`#page-${item}`}
                  role="button"
                  onClick={e => {
                    e.preventDefault();
                    onPageChange(item);
                  }}
                >
                  {item + 1}
                </a>
              </li>
            ) : (
              <li key={item} className="dt-pagination-ellipsis">
                <span>…</span>
              </li>
            ),
          )}
        </ul>
      </div>
    );
  }),
);