feat: create the Parser entry module, the user facing API

It exposes three public methods, parseFromURL(url), parseFromFile(filename) and
parseFromString(xml).

Author: Harrison Ifeanyichukwu

src/Parser.php

@@ -0,0 +1,80 @@
+<?php
+/**
+ * The parser module
+ *
+ * PHP Version 7.1
+ *
+ *@author Harrison ifeanyichukwu <[email protected]>
+*/
+declare(strict_types = 1);
+
+namespace Forensic\FeedParser;
+
+use Exception;
+use Forensic\FeedParser\Exceptions\InvalidURLException;
+use Forensic\FeedParser\Exceptions\ResourceNotFoundException;
+use Forensic\FeedParser\Exceptions\FileNotFoundException;
+
+/**
+ * Class Parser
+*/
+class Parser
+{
+    /**
+     * creates a feed parser, and xml document, feeds the document to the parser, and returns
+     * the result from the parser
+    */
+    private function parse(string $xml)
+    {
+        return null;
+    }
+
+    /**
+     * Fetches feed from a given url and parses it.
+     *
+     *@param string $url - the resource url
+    */
+    public function parseFromURL(string $url)
+    {
+        if (!filter_var($url, FILTER_VALIDATE_URL))
+            throw new InvalidURLException($url . ' is not a valid resource url');
+
+        try
+        {
+            $xml = file_get_contents($url);
+            if ($xml === false)
+                throw new Exception('xml resource not found');
+        }
+        catch(Exception $ex)
+        {
+            throw new ResourceNotFoundException($ex->getMessage());
+        }
+
+        return $this->parse($xml);
+    }
+
+    /**
+     * Fetches feed from a given file and parses it.
+     *
+     *@param string $filename - the file path
+    */
+    public function parseFromFile(string $filename)
+    {
+        if (!file_exists($filename))
+            throw new FileNotFoundException($filename . ' does not exist');
+
+        $xml = file_get_contents($filename);
+
+        return $this->parse($xml);
+    }
+
+    /**
+     * Parses feed from the given xml string
+     *
+     *@param string $xml - the xml string
+     */
+    public function parseFromString(string $xml)
+    {
+        return $this->parse($xml);
+    }
+}