package com.prolog.eis.utils;

import java.util.ArrayList;
import java.util.List;

/**
 * @author zhanghan
 */
public class ListPageUtils {

    /**
     * 开始分页
     *
     * @param list
     * @param pageNum  页码
     * @param pageSize 每页多少条数据
     * @return
     */
    public static List startPage(List list, Integer pageNum,
                                 Integer pageSize) {
        if (list == null) {
            return null;
        }
        if (list.size() == 0) {
            return null;
        }

        Integer count = list.size(); // 记录总数
        Integer pageCount = 0; // 页数
        if (count % pageSize == 0) {
            pageCount = count / pageSize;
        } else {
            pageCount = count / pageSize + 1;
        }

        int fromIndex = 0; // 开始索引
        int toIndex = 0; // 结束索引

        if(pageNum > pageCount) {
            return new ArrayList();
        }else if (pageNum != pageCount){
            fromIndex = (pageNum - 1) * pageSize;
            toIndex = fromIndex + pageSize;
        }else {
            fromIndex = (pageNum - 1) * pageSize;
            toIndex = count;
        }

        if (toIndex > list.size()) {
            return list.subList(fromIndex, list.size());
        } else {
            return list.subList(fromIndex, toIndex);
        }
    }
}