Issue/390 (#397)

* Fiter items through `Result`. Fix #390

* Fix coding style

* remove backslash

* Advertise filtering ability

README.md

@@ -16,6 +16,7 @@
 - Enclosure support to handle external medias like audio content
 - Feed logo support (RSS + Atom)
 - PSR compliant logging
+- Content filtering to fetch only the newest items
 - DateTime detection and conversion
 - A generic HTTP ClientInterface
 - Guzzle Client integration
@@ -49,12 +50,6 @@ Let's suppose you installed feed-io using Composer, you can use its command line
 ./vendor/bin/feedio read http://php.net/feed.atom
 ```
 
-You can specify the number of items you want to read using the --count option. The instruction below will display the latest item :
-
-```shell
-./vendor/bin/feedio read -c 1 http://php.net/feed.atom
-```
-
 ## reading
 
 feed-io is designed to read feeds across the internet and to publish your own. Its main class is [FeedIo](https://github.com/alexdebril/feed-io/blob/master/src/FeedIo/FeedIo.php) :
@@ -76,6 +71,44 @@ foreach( $result->getFeed() as $item ) {
 }
 
 ```
+
+If you need to get only the new items since the last time you've consumed the feed, use the result's `getItemsSince()` method:
+
+```php
+// read a feed and specify the `$modifiedSince` limit to fetch only items newer than this date
+$result = $feedIo->read($url, $feed, $modifiedSince);
+
+// iterate through new items
+foreach( $result->getItemsSince() as $item ) {
+    echo $item->getTitle();
+}
+
+```
+
+You can also mix several filters to exclude items according to your needs:
+
+```php
+// read a feed
+$result = $feedIo->read($url, $feed, $modifiedSince);
+
+// remove items older than `$modifiedSince`
+$since = new FeedIo\Filter\Since($result->getModifiedSince());
+
+// Your own filter
+$database = new Acme\Filter\Database();
+
+$chain = new Chain();
+$chain
+    ->add($since)
+    ->add($database);
+
+// iterate through new items
+foreach( $result->getFilteredItems($chain) as $item ) {
+    echo $item->getTitle();
+}
+
+```
+
 In order to save bandwidth, feed-io estimates the next time it will be relevant to read the feed and get new items from it.
 
 ```php

src/FeedIo/Filter/Chain.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace FeedIo\Filter;
+
+use FeedIo\FeedInterface;
+
+class Chain
+{
+    private array $filters;
+
+    public function add(FilterInterface $filter): void
+    {
+        $this->filters[] = $filter;
+    }
+
+    public function filter(FeedInterface $feed): iterable
+    {
+        foreach ($feed as $item) {
+            foreach ($this->filters as $filter) {
+                if (!$filter->filter($item)) {
+                    continue 2;
+                }
+            }
+
+            yield $item;
+        }
+    }
+}

src/FeedIo/Filter/FilterInterface.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace FeedIo\Filter;
+
+use FeedIo\Feed\ItemInterface;
+
+interface FilterInterface
+{
+    /**
+     * Returns `true` if the item is to be returned.
+     *
+     * @param ItemInterface $item
+     * @return bool
+     */
+    public function filter(ItemInterface $item): bool;
+}

src/FeedIo/Filter/Since.php

@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace FeedIo\Filter;
+
+use DateTime;
+use FeedIo\Feed\ItemInterface;
+
+class Since implements FilterInterface
+{
+    private DateTime $date;
+
+    public function __construct(DateTime $date)
+    {
+        $this->date = $date;
+    }
+
+    public function filter(ItemInterface $item): bool
+    {
+        return $item->getLastModified() >= $this->date;
+    }
+}

src/FeedIo/Reader/Result.php

@@ -7,6 +7,8 @@
 use DateTime;
 use FeedIo\Adapter\ResponseInterface;
 use FeedIo\FeedInterface;
+use FeedIo\Filter\Chain;
+use FeedIo\Filter\Since;
 use FeedIo\Reader\Result\UpdateStats;
 
 /**
@@ -52,6 +54,19 @@ public function getFeed(): FeedInterface
         return $this->feed;
     }
 
+    public function getItemsSince(DateTime $since = null): iterable
+    {
+        $filter = new Chain();
+        $filter->add(new Since($since ?? $this->modifiedSince));
+
+        return $filter->filter($this->getFeed());
+    }
+
+    public function getFilteredItems(Chain $filterChain): iterable
+    {
+        return $filterChain->filter($this->feed);
+    }
+
     public function getModifiedSince(): ?DateTime
     {
         return $this->modifiedSince;

tests/FeedIo/Filter/ChainTest.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace FeedIo\Filter;
+
+use FeedIo\Feed;
+use FeedIo\Feed\Item;
+use PHPUnit\Framework\TestCase;
+
+class ChainTest extends TestCase
+{
+    public function testFilter()
+    {
+        $chain = new Chain();
+        $chain->add(new Since(new \DateTime('-1 day')));
+
+        $feed = new Feed();
+        $feed->add((new Item())->setLastModified(new \DateTime('-1 hour')));
+        $feed->add((new Item())->setLastModified(new \DateTime('-1 day')));
+        $feed->add((new Item())->setLastModified(new \DateTime('-1 month')));
+
+        $filtered = $chain->filter($feed);
+        $this->assertEquals(2, iterator_count($filtered));
+    }
+
+    public function testFancyFilter()
+    {
+        $chain = new Chain();
+        $fancyFilter = $this->getMockForAbstractClass('\FeedIo\Filter\FilterInterface');
+        $fancyFilter->expects($this->exactly(2))->method('filter')->will($this->returnCallback(function (Item $item) {
+            return $item->getTitle() === '1 day ago';
+        }));
+
+        $chain->add(new Since(new \DateTime('-1 day')));
+        $chain->add($fancyFilter);
+
+        $feed = new Feed();
+        $feed->add((new Item())->setTitle('1 hour ago')->setLastModified(new \DateTime('-1 hour')));
+        $feed->add((new Item())->setTitle('1 day ago')->setLastModified(new \DateTime('-1 day')));
+        $feed->add((new Item())->setTitle('1 month ago')->setLastModified(new \DateTime('-1 month')));
+
+        $filtered = $chain->filter($feed);
+        $count = 0;
+        foreach ($filtered as $item) {
+            $count++;
+        }
+        $this->assertEquals(1, $count);
+        $this->assertEquals('1 day ago', $item->getTitle());
+    }
+}

tests/FeedIo/Filter/SinceTest.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace FeedIo\Filter;
+
+use FeedIo\Feed\Item;
+use PHPUnit\Framework\TestCase;
+
+class FilterTest extends TestCase
+{
+    public function testFilter()
+    {
+        $filter = new Since(new \DateTime('-1 day'));
+        $this->assertTrue($filter->filter((new Item())->setLastModified(new \DateTime('-1 hour'))));
+        $this->assertTrue($filter->filter((new Item())->setLastModified(new \DateTime('-1 day'))));
+        $this->assertFalse($filter->filter((new Item())->setLastModified(new \DateTime('-2 day'))));
+    }
+}