Bookshelf

Book

<?php

class Book implements ItemInterface
{
    /**
     * @var string
     */
    private string $title;

    /**
     * @var string
     */
    private string $author;

    use ReadContentTrait;

    /**
     * @return string
     */
    public function getTitle(): string
    {
        return $this->title;
    }

    /**
     * @param string $title
     */
    public function setTitle(string $title): void
    {
        $this->title = $title;
    }

    /**
     * @return string
     */
    public function getAuthor(): string
    {
        return $this->author;
    }

    /**
     * @param string $author
     */
    public function setAuthor(string $author): void
    {
        $this->author = $author;
    }
}

Bookshelf

<?php
class Bookshelf
{
    private array $items;

    private int $maxItems;
    
    public function storeItem(ItemInterface $item):void {
        $this->items[] = $item;
    }

    public function retrieveItem(int $itemNumber) {
        return (key_exists($itemNumber, $this->items) ? $this->items[$itemNumber] : false);
    }

    public function getState():array
    {
        return [
            'elementCount' => count($this->items),
            'spaceLeft' => $this->maxItems - count($this->items)
        ];
    }

    public function searchItems(string $contentToSearch) {
        /** @var ItemInterface $item */
        foreach ($this->items as $item) {
            for ($pageNumber=1;$pageNumber<=$item->countPages();$pageNumber++) {
                if (strstr($item->readPageContent($pageNumber), $contentToSearch)!== false) {
                    return $item;
                }
            }
        }
        return false;
    }
}

ItemInterface

<?php

interface ItemInterface
{
    /**
     * @param int $page
     * @return mixed
     */
    public function readPageContent(int $page);

    public function countPages():array;
}

Magazine

<?php

class Magazine implements ItemInterface
{
    private string $name;

    private DateTime $publicationDate;

    use ReadContentTrait;

    /**
     * @return string
     */
    public function getName(): string
    {
        return $this->name;
    }

    /**
     * @param string $name
     */
    public function setName(string $name): void
    {
        $this->name = $name;
    }

    /**
     * @return DateTime
     */
    public function getPublicationDate(): DateTime
    {
        return $this->publicationDate;
    }

    /**
     * @param DateTime $publicationDate
     */
    public function setPublicationDate(DateTime $publicationDate): void
    {
        $this->publicationDate = $publicationDate;
    }


}

Notebook

<?php

class Notebook implements ItemInterface
{
    private string $owner;

    use ReadContentTrait;

    /**
     * @return string
     */
    public function getOwner(): string
    {
        return $this->owner;
    }

    /**
     * @param string $owner
     */
    public function setOwner(string $owner): void
    {
        $this->owner = $owner;
    }
}

ReadContentTrait

<?php
trait ReadContentTrait
{
    private array $pages;

    public function readPageContent(int $page)
    {
        return (key_exists($page,$this->pages))? $this->pages[$page]:null;
    }

    public function countPages():array
    {
        return count($this->pages);
    }
}