<?php

namespace Illuminate\Pagination;

use Closure;
use ArrayIterator;

abstract class AbstractPaginator
{
    /**
     * All of the items being paginated.
     *
     * @var \Illuminate\Support\Collection
     */
    protected $items;

    /**
     * The number of items to be shown per page.
     *
     * @var int
     */
    protected $perPage;

    /**
     * The current page being "viewed".
     *
     * @var int
     */
    protected $currentPage;

    /**
     * The base path to assign to all URLs.
     *
     * @var string
     */
    protected $path = '/';

    /**
     * The query parameters to add to all URLs.
     *
     * @var array
     */
    protected $query = [];

    /**
     * The URL fragment to add to all URLs.
     *
     * @var string|null
     */
    protected $fragment = null;

    /**
     * The query string variable used to store the page.
     *
     * @var string
     */
    protected $pageName = 'page';

    /**
     * The current page resolver callback.
     *
     * @var \Closure
     */
    protected static $currentPathResolver;

    /**
     * The current page resolver callback.
     *
     * @var \Closure
     */
    protected static $currentPageResolver;

    /**
     * The default presenter resolver.
     *
     * @var \Closure
     */
    protected static $presenterResolver;

    /**
     * Determine if the given value is a valid page number.
     *
     * @param  int  $page
     * @return bool
     */
    protected function isValidPageNumber($page)
    {
        return $page >= 1 && filter_var($page, FILTER_VALIDATE_INT) !== false;
    }

    /**
     * Create a range of pagination URLs.
     *
     * @param  int  $start
     * @param  int  $end
     * @return string
     */
    public function getUrlRange($start, $end)
    {
        $urls = [];

        for ($page = $start; $page <= $end; $page++) {
            $urls[$page] = $this->url($page);
        }

        return $urls;
    }

    /**
     * Get a URL for a given page number.
     *
     * @param  int  $page
     * @return string
     */
    public function url($page)
    {
        if ($page <= 0) {
            $page = 1;
        }

        // If we have any extra query string key / value pairs that need to be added
        // onto the URL, we will put them in query string form and then attach it
        // to the URL. This allows for extra information like sortings storage.
        $parameters = [$this->pageName => $page];

        if (count($this->query) > 0) {
            $parameters = array_merge($this->query, $parameters);
        }

        return $this->path.'?'
                        .http_build_query($parameters, '', '&')
                        .$this->buildFragment();
    }

    /**
     * Get the URL for the previous page.
     *
     * @return string|null
     */
    public function previousPageUrl()
    {
        if ($this->currentPage() > 1) {
            return $this->url($this->currentPage() - 1);
        }
    }

    /**
     * Get / set the URL fragment to be appended to URLs.
     *
     * @param  string|null  $fragment
     * @return $this|string|null
     */
    public function fragment($fragment = null)
    {
        if (is_null($fragment)) {
            return $this->fragment;
        }

        $this->fragment = $fragment;

        return $this;
    }

    /**
     * Add a set of query string values to the paginator.
     *
     * @param  array|string  $key
     * @param  string|null  $value
     * @return $this
     */
    public function appends($key, $value = null)
    {
        if (is_array($key)) {
            return $this->appendArray($key);
        }

        return $this->addQuery($key, $value);
    }

    /**
     * Add an array of query string values.
     *
     * @param  array  $keys
     * @return $this
     */
    protected function appendArray(array $keys)
    {
        foreach ($keys as $key => $value) {
            $this->addQuery($key, $value);
        }

        return $this;
    }

    /**
     * Add a query string value to the paginator.
     *
     * @param  string  $key
     * @param  string  $value
     * @return $this
     */
    public function addQuery($key, $value)
    {
        if ($key !== $this->pageName) {
            $this->query[$key] = $value;
        }

        return $this;
    }

    /**
     * Build the full fragment portion of a URL.
     *
     * @return string
     */
    protected function buildFragment()
    {
        return $this->fragment ? '#'.$this->fragment : '';
    }

    /**
     * Get the slice of items being paginated.
     *
     * @return array
     */
    public function items()
    {
        return $this->items->all();
    }

    /**
     * Get the number of the first item in the slice.
     *
     * @return int
     */
    public function firstItem()
    {
        return ($this->currentPage - 1) * $this->perPage + 1;
    }

    /**
     * Get the number of the last item in the slice.
     *
     * @return int
     */
    public function lastItem()
    {
        return $this->firstItem() + $this->count() - 1;
    }

    /**
     * Get the number of items shown per page.
     *
     * @return int
     */
    public function perPage()
    {
        return $this->perPage;
    }

    /**
     * Get the current page.
     *
     * @return int
     */
    public function currentPage()
    {
        return $this->currentPage;
    }

    /**
     * Determine if there are enough items to split into multiple pages.
     *
     * @return bool
     */
    public function hasPages()
    {
        return ! ($this->currentPage() == 1 && ! $this->hasMorePages());
    }

    /**
     * Resolve the current request path or return the default value.
     *
     * @param  string  $default
     * @return string
     */
    public static function resolveCurrentPath($default = '/')
    {
        if (isset(static::$currentPathResolver)) {
            return call_user_func(static::$currentPathResolver);
        }

        return $default;
    }

    /**
     * Set the current request path resolver callback.
     *
     * @param  \Closure  $resolver
     * @return void
     */
    public static function currentPathResolver(Closure $resolver)
    {
        static::$currentPathResolver = $resolver;
    }

    /**
     * Resolve the current page or return the default value.
     *
     * @param  string  $pageName
     * @param  int  $default
     * @return int
     */
    public static function resolveCurrentPage($pageName = 'page', $default = 1)
    {
        if (isset(static::$currentPageResolver)) {
            return call_user_func(static::$currentPageResolver, $pageName);
        }

        return $default;
    }

    /**
     * Set the current page resolver callback.
     *
     * @param  \Closure  $resolver
     * @return void
     */
    public static function currentPageResolver(Closure $resolver)
    {
        static::$currentPageResolver = $resolver;
    }

    /**
     * Set the default Presenter resolver.
     *
     * @param  \Closure  $resolver
     * @return void
     */
    public static function presenter(Closure $resolver)
    {
        static::$presenterResolver = $resolver;
    }

    /**
     * Get the query string variable used to store the page.
     *
     * @return string
     */
    public function getPageName()
    {
        return $this->pageName;
    }

    /**
     * Set the query string variable used to store the page.
     *
     * @param  string  $name
     * @return $this
     */
    public function setPageName($name)
    {
        $this->pageName = $name;

        return $this;
    }

    /**
     * Set the base path to assign to all URLs.
     *
     * @param  string  $path
     * @return $this
     */
    public function setPath($path)
    {
        $this->path = $path;

        return $this;
    }

    /**
     * Get an iterator for the items.
     *
     * @return \ArrayIterator
     */
    public function getIterator()
    {
        return new ArrayIterator($this->items->all());
    }

    /**
     * Determine if the list of items is empty or not.
     *
     * @return bool
     */
    public function isEmpty()
    {
        return $this->items->isEmpty();
    }

    /**
     * Get the number of items for the current page.
     *
     * @return int
     */
    public function count()
    {
        return $this->items->count();
    }

    /**
     * Get the paginator's underlying collection.
     *
     * @return \Illuminate\Support\Collection
     */
    public function getCollection()
    {
        return $this->items;
    }

    /**
     * Determine if the given item exists.
     *
     * @param  mixed  $key
     * @return bool
     */
    public function offsetExists($key)
    {
        return $this->items->has($key);
    }

    /**
     * Get the item at the given offset.
     *
     * @param  mixed  $key
     * @return mixed
     */
    public function offsetGet($key)
    {
        return $this->items->get($key);
    }

    /**
     * Set the item at the given offset.
     *
     * @param  mixed  $key
     * @param  mixed  $value
     * @return void
     */
    public function offsetSet($key, $value)
    {
        $this->items->put($key, $value);
    }

    /**
     * Unset the item at the given key.
     *
     * @param  mixed  $key
     * @return void
     */
    public function offsetUnset($key)
    {
        $this->items->forget($key);
    }

    /**
     * Make dynamic calls into the collection.
     *
     * @param  string  $method
     * @param  array  $parameters
     * @return mixed
     */
    public function __call($method, $parameters)
    {
        return call_user_func_array([$this->getCollection(), $method], $parameters);
    }

    /**
     * Render the contents of the paginator when casting to string.
     *
     * @return string
     */
    public function __toString()
    {
        return $this->render();
    }
}