<?php

namespace SilverStripe\ORM;

use SilverStripe\Control\HTTP;
use SilverStripe\Control\HTTPRequest;
use SilverStripe\ORM\Queries\SQLSelect;
use SilverStripe\View\ArrayData;
use ArrayAccess;
use Exception;
use IteratorIterator;

/**
 * A decorator that wraps around a data list in order to provide pagination.
 */
class PaginatedList extends ListDecorator
{

    protected $request;
    protected $getVar = 'start';

    protected $pageLength = 10;
    protected $pageStart;
    protected $totalItems;
    protected $limitItems = true;

    /**
     * Constructs a new paginated list instance around a list.
     *
     * @param SS_List $list The list to paginate. The getRange method will
     *        be used to get the subset of objects to show.
     * @param array|ArrayAccess $request Either a map of request parameters or
     *        request object that the pagination offset is read from.
     * @throws Exception
     */
    public function __construct(SS_List $list, $request = [])
    {
        if (!is_array($request) && !$request instanceof ArrayAccess) {
            throw new Exception('The request must be readable as an array.');
        }

        $this->setRequest($request);
        parent::__construct($list);
    }

    /**
     * Returns the GET var that is used to set the page start. This defaults
     * to "start".
     *
     * If there is more than one paginated list on a page, it is necessary to
     * set a different get var for each using {@link setPaginationGetVar()}.
     *
     * @return string
     */
    public function getPaginationGetVar()
    {
        return $this->getVar;
    }

    /**
     * Sets the GET var used to set the page start.
     *
     * @param string $var
     * @return $this
     */
    public function setPaginationGetVar($var)
    {
        $this->getVar = $var;
        return $this;
    }

    /**
     * Returns the number of items displayed per page. This defaults to 10.
     *
     * @return int
     */
    public function getPageLength()
    {
        return $this->pageLength;
    }

    /**
     * Set the number of items displayed per page. Set to zero to disable paging.
     *
     * @param int $length
     * @return $this
     */
    public function setPageLength($length)
    {
        $this->pageLength = (int)$length;
        return $this;
    }

    /**
     * Sets the current page.
     *
     * @param int $page Page index beginning with 1
     * @return $this
     */
    public function setCurrentPage($page)
    {
        $this->pageStart = ((int)$page - 1) * $this->getPageLength();
        return $this;
    }

    /**
     * Returns the offset of the item the current page starts at.
     *
     * @return int
     */
    public function getPageStart()
    {
        $request = $this->getRequest();
        if ($this->pageStart === null) {
            if ($request
                && isset($request[$this->getPaginationGetVar()])
                && $request[$this->getPaginationGetVar()] > 0
            ) {
                $this->pageStart = (int)$request[$this->getPaginationGetVar()];
            } else {
                $this->pageStart = 0;
            }
        }

        return $this->pageStart;
    }

    /**
     * Sets the offset of the item that current page starts at. This should be
     * a multiple of the page length.
     *
     * @param int $start
     * @return $this
     */
    public function setPageStart($start)
    {
        $this->pageStart = (int)$start;
        return $this;
    }

    /**
     * Returns the total number of items in the unpaginated list.
     *
     * @return int
     */
    public function getTotalItems()
    {
        if ($this->totalItems === null) {
            $this->totalItems = count($this->list ?? []);
        }

        return $this->totalItems;
    }

    /**
     * Sets the total number of items in the list. This is useful when doing
     * custom pagination.
     *
     * @param int $items
     * @return $this
     */
    public function setTotalItems($items)
    {
        $this->totalItems = (int)$items;
        return $this;
    }

    /**
     * Sets the page length, page start and total items from a query object's
     * limit, offset and unlimited count. The query MUST have a limit clause.
     *
     * @param SQLSelect $query
     * @return $this
     */
    public function setPaginationFromQuery(SQLSelect $query)
    {
        if ($limit = $query->getLimit()) {
            $this->setPageLength($limit['limit']);
            $this->setPageStart($limit['start']);
            $this->setTotalItems($query->unlimitedRowCount());
        }
        return $this;
    }

    /**
     * Returns whether or not the underlying list is limited to the current
     * pagination range when iterating.
     *
     * By default the limit method will be called on the underlying list to
     * extract the subset for the current page. In some situations, if the list
     * is custom generated and already paginated you don't want to additionally
     * limit the list. You can use {@link setLimitItems} to control this.
     *
     * @return bool
     */
    public function getLimitItems()
    {
        return $this->limitItems;
    }

    /**
     * @param bool $limit
     * @return $this
     */
    public function setLimitItems($limit)
    {
        $this->limitItems = (bool)$limit;
        return $this;
    }

    /**
     * @return IteratorIterator
     */
    #[\ReturnTypeWillChange]
    public function getIterator()
    {
        $pageLength = $this->getPageLength();
        if ($this->limitItems && $pageLength) {
            $tmptList = clone $this->list;
            return new IteratorIterator(
                $tmptList->limit($pageLength, $this->getPageStart())
            );
        } else {
            return new IteratorIterator($this->list);
        }
    }

    /**
     * Returns a set of links to all the pages in the list. This is useful for
     * basic pagination.
     *
     * By default it returns links to every page, but if you pass the $max
     * parameter the number of pages will be limited to that number, centered
     * around the current page.
     *
     * @param  int $max
     * @return SS_List
     */
    public function Pages($max = null)
    {
        $result = new ArrayList();

        if ($max) {
            $start = ($this->CurrentPage() - floor($max / 2)) - 1;
            $end = $this->CurrentPage() + floor($max / 2);

            if ($start < 0) {
                $start = 0;
                $end = $max;
            }

            if ($end > $this->TotalPages()) {
                $end = $this->TotalPages();
                $start = max(0, $end - $max);
            }
        } else {
            $start = 0;
            $end = $this->TotalPages();
        }

        for ($i = $start; $i < $end; $i++) {
            $result->push(new ArrayData([
                'PageNum' => $i + 1,
                'Link' => HTTP::setGetVar(
                    $this->getPaginationGetVar(),
                    $i * $this->getPageLength(),
                    ($this->request instanceof HTTPRequest) ? $this->request->getURL(true) : null
                ),
                'CurrentBool' => $this->CurrentPage() == ($i + 1)
            ]));
        }

        return $result;
    }

    /**
     * Returns a summarised pagination which limits the number of pages shown
     * around the current page for visually balanced.
     *
     * Example: 25 pages total, currently on page 6, context of 4 pages
     * [prev] [1] ... [4] [5] [[6]] [7] [8] ... [25] [next]
     *
     * Example template usage:
     * <code>
     *    <% if MyPages.MoreThanOnePage %>
     *        <% if MyPages.NotFirstPage %>
     *            <a class="prev" href="$MyPages.PrevLink">Prev</a>
     *        <% end_if %>
     *        <% loop MyPages.PaginationSummary(4) %>
     *            <% if CurrentBool %>
     *                $PageNum
     *            <% else %>
     *                <% if Link %>
     *                    <a href="$Link">$PageNum</a>
     *                <% else %>
     *                    ...
     *                <% end_if %>
     *            <% end_if %>
     *        <% end_loop %>
     *        <% if MyPages.NotLastPage %>
     *            <a class="next" href="$MyPages.NextLink">Next</a>
     *        <% end_if %>
     *    <% end_if %>
     * </code>
     *
     * @param  int $context The number of pages to display around the current
     *         page. The number should be event, as half the number of each pages
     *         are displayed on either side of the current one.
     * @return SS_List
     */
    public function PaginationSummary($context = 4)
    {
        $result = new ArrayList();
        $current = $this->CurrentPage();
        $total = $this->TotalPages();

        // Make the number even for offset calculations.
        if ($context % 2) {
            $context--;
        }

        // If the first or last page is current, then show all context on one
        // side of it - otherwise show half on both sides.
        if ($current == 1 || $current == $total) {
            $offset = $context;
        } else {
            $offset = floor($context / 2);
        }

        $left = max($current - $offset, 1);
        $right = min($current + $offset, $total);
        $range = range($current - $offset, $current + $offset);

        if ($left + $context > $total) {
            $left = $total - $context;
        }

        for ($i = 0; $i < $total; $i++) {
            $link = HTTP::setGetVar(
                $this->getPaginationGetVar(),
                $i * $this->getPageLength(),
                ($this->request instanceof HTTPRequest) ? $this->request->getURL(true) : null
            );
            $num = $i + 1;

            $emptyRange = $num != 1 && $num != $total && (
                $num == $left - 1 || $num == $right + 1
            );

            if ($emptyRange) {
                $result->push(new ArrayData([
                    'PageNum' => null,
                    'Link' => null,
                    'CurrentBool' => false
                ]));
            } elseif ($num == 1 || $num == $total || in_array($num, $range ?? [])) {
                $result->push(new ArrayData([
                    'PageNum' => $num,
                    'Link' => $link,
                    'CurrentBool' => $current == $num
                ]));
            }
        }

        return $result;
    }

    /**
     * @return int
     */
    public function CurrentPage()
    {
        $pageLength = $this->getPageLength();
        return $pageLength
            ? floor($this->getPageStart() / $pageLength) + 1
            : 1;
    }

    /**
     * @return int
     */
    public function TotalPages()
    {
        $pageLength = $this->getPageLength();
        return $pageLength
            ? ceil($this->getTotalItems() / $pageLength)
            : min($this->getTotalItems(), 1);
    }

    /**
     * @return bool
     */
    public function MoreThanOnePage()
    {
        return $this->TotalPages() > 1;
    }

    /**
     * @return bool
     */
    public function FirstPage()
    {
        return $this->CurrentPage() == 1;
    }

    /**
     * @return bool
     */
    public function NotFirstPage()
    {
        return !$this->FirstPage();
    }

    /**
     * @return bool
     */
    public function LastPage()
    {
        return $this->CurrentPage() >= $this->TotalPages();
    }

    /**
     * @return bool
     */
    public function NotLastPage()
    {
        return !$this->LastPage();
    }

    /**
     * Returns the number of the first item being displayed on the current
     * page. This is useful for things like "displaying 10-20".
     *
     * @return int
     */
    public function FirstItem()
    {
        return ($start = $this->getPageStart()) ? $start + 1 : 1;
    }

    /**
     * Returns the number of the last item being displayed on this page.
     *
     * @return int
     */
    public function LastItem()
    {
        $pageLength = $this->getPageLength();
        if (!$pageLength) {
            return $this->getTotalItems();
        } elseif ($start = $this->getPageStart()) {
            return min($start + $pageLength, $this->getTotalItems());
        } else {
            return min($pageLength, $this->getTotalItems());
        }
    }

    /**
     * Returns a link to the first page.
     *
     * @return string
     */
    public function FirstLink()
    {
        return HTTP::setGetVar(
            $this->getPaginationGetVar(),
            0,
            ($this->request instanceof HTTPRequest) ? $this->request->getURL(true) : null
        );
    }

    /**
     * Returns a link to the last page.
     *
     * @return string
     */
    public function LastLink()
    {
        return HTTP::setGetVar(
            $this->getPaginationGetVar(),
            ($this->TotalPages() - 1) * $this->getPageLength(),
            ($this->request instanceof HTTPRequest) ? $this->request->getURL(true) : null
        );
    }

    /**
     * Returns a link to the next page, if there is another page after the
     * current one.
     *
     * @return string
     */
    public function NextLink()
    {
        if ($this->NotLastPage()) {
            return HTTP::setGetVar(
                $this->getPaginationGetVar(),
                $this->getPageStart() + $this->getPageLength(),
                ($this->request instanceof HTTPRequest) ? $this->request->getURL(true) : null
            );
        }
    }

    /**
     * Returns a link to the previous page, if the first page is not currently
     * active.
     *
     * @return string
     */
    public function PrevLink()
    {
        if ($this->NotFirstPage()) {
            return HTTP::setGetVar(
                $this->getPaginationGetVar(),
                $this->getPageStart() - $this->getPageLength(),
                ($this->request instanceof HTTPRequest) ? $this->request->getURL(true) : null
            );
        }
    }

    /**
     * Returns the total number of items in the list
     */
    public function TotalItems()
    {
        return $this->getTotalItems();
    }

    /**
     * Set the request object for this list
     *
     * @param HTTPRequest|ArrayAccess $request
     */
    public function setRequest($request)
    {
        $this->request = $request;
    }

    /**
     * Get the request object for this list
     */
    public function getRequest()
    {
        return $this->request;
    }
}