<?php

/**
 * This file is part of the Nette Framework (https://nette.org)
 * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
 */

declare(strict_types=1);

namespace Nette\Utils;

use Nette;


/**
 * Paginating math.
 *
 * @property   int $page
 * @property-read int $firstPage
 * @property-read int|null $lastPage
 * @property-read int<0,max> $firstItemOnPage
 * @property-read int<0,max> $lastItemOnPage
 * @property   int $base
 * @property-read bool $first
 * @property-read bool $last
 * @property-read int<0,max>|null $pageCount
 * @property   positive-int $itemsPerPage
 * @property   int<0,max>|null $itemCount
 * @property-read int<0,max> $offset
 * @property-read int<0,max>|null $countdownOffset
 * @property-read int<0,max> $length
 */
class Paginator
{
    use Nette\SmartObject;

    private int $base = 1;

    /** @var positive-int */
    private int $itemsPerPage = 1;

    private int $page = 1;

    /** @var int<0, max>|null */
    private ?int $itemCount = null;


    /**
     * Sets current page number.
     */
    public function setPage(int $page): static
    {
        $this->page = $page;
        return $this;
    }


    /**
     * Returns current page number.
     */
    public function getPage(): int
    {
        return $this->base + $this->getPageIndex();
    }


    /**
     * Returns first page number.
     */
    public function getFirstPage(): int
    {
        return $this->base;
    }


    /**
     * Returns last page number.
     */
    public function getLastPage(): ?int
    {
        return $this->itemCount === null
            ? null
            : $this->base + max(0, $this->getPageCount() - 1);
    }


    /**
     * Returns the sequence number of the first element on the page
     * @return int<0, max>
     */
    public function getFirstItemOnPage(): int
    {
        return $this->itemCount !== 0
            ? $this->offset + 1
            : 0;
    }


    /**
     * Returns the sequence number of the last element on the page
     * @return int<0, max>
     */
    public function getLastItemOnPage(): int
    {
        return $this->offset + $this->length;
    }


    /**
     * Sets first page (base) number.
     */
    public function setBase(int $base): static
    {
        $this->base = $base;
        return $this;
    }


    /**
     * Returns first page (base) number.
     */
    public function getBase(): int
    {
        return $this->base;
    }


    /**
     * Returns zero-based page number.
     * @return int<0, max>
     */
    protected function getPageIndex(): int
    {
        $index = max(0, $this->page - $this->base);
        return $this->itemCount === null
            ? $index
            : min($index, max(0, $this->getPageCount() - 1));
    }


    /**
     * Is the current page the first one?
     */
    public function isFirst(): bool
    {
        return $this->getPageIndex() === 0;
    }


    /**
     * Is the current page the last one?
     */
    public function isLast(): bool
    {
        return $this->itemCount === null
            ? false
            : $this->getPageIndex() >= $this->getPageCount() - 1;
    }


    /**
     * Returns the total number of pages.
     * @return int<0, max>|null
     */
    public function getPageCount(): ?int
    {
        return $this->itemCount === null
            ? null
            : (int) ceil($this->itemCount / $this->itemsPerPage);
    }


    /**
     * Sets the number of items to display on a single page.
     */
    public function setItemsPerPage(int $itemsPerPage): static
    {
        $this->itemsPerPage = max(1, $itemsPerPage);
        return $this;
    }


    /**
     * Returns the number of items to display on a single page.
     * @return positive-int
     */
    public function getItemsPerPage(): int
    {
        return $this->itemsPerPage;
    }


    /**
     * Sets the total number of items.
     */
    public function setItemCount(?int $itemCount = null): static
    {
        $this->itemCount = $itemCount === null ? null : max(0, $itemCount);
        return $this;
    }


    /**
     * Returns the total number of items.
     * @return int<0, max>|null
     */
    public function getItemCount(): ?int
    {
        return $this->itemCount;
    }


    /**
     * Returns the absolute index of the first item on current page.
     * @return int<0, max>
     */
    public function getOffset(): int
    {
        return $this->getPageIndex() * $this->itemsPerPage;
    }


    /**
     * Returns the absolute index of the first item on current page in countdown paging.
     * @return int<0, max>|null
     */
    public function getCountdownOffset(): ?int
    {
        return $this->itemCount === null
            ? null
            : max(0, $this->itemCount - ($this->getPageIndex() + 1) * $this->itemsPerPage);
    }


    /**
     * Returns the number of items on current page.
     * @return int<0, max>
     */
    public function getLength(): int
    {
        return $this->itemCount === null
            ? $this->itemsPerPage
            : min($this->itemsPerPage, $this->itemCount - $this->getPageIndex() * $this->itemsPerPage);
    }
}

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