solution by vojtech.kolomicenko@intraworlds.com

new.php

@@ -0,0 +1,102 @@
+<?php
+
+// implementing classes apply a filter to a string
+interface Filter {
+    function filter(string $str): string;
+}
+
+abstract class CascadeFilter implements Filter {
+    private $_previousFilter = null;
+
+    function __construct(?Filter $filter) {
+        $this->_previousFilter = $filter;
+    }
+
+    function filter(string $str): string {
+        if ($this->_previousFilter) {
+            return $this->_previousFilter->filter($str);
+        } else {
+            return $str;
+        }
+    }
+}
+
+class IsNotDebug extends CascadeFilter {
+    function filter(string $str): string {
+        $str = parent::filter($str);
+        return $str == 'debug' ? '' : $str;
+    }
+}
+
+class ExtractLogLevel extends CascadeFilter {
+    const PATTERN = '/test\.(\w+)/';
+
+    function filter(string $str): string {
+        $str = parent::filter($str);
+
+        if (preg_match(self::PATTERN, $str, $matches)) {
+            return strtolower($matches[1]);
+        } else {
+            return '';
+        }
+    }
+}
+
+
+class FileRowReader extends FilterIterator {
+    private $_filter = null;
+
+    function __construct(string $filename, Filter $filter) {
+        $this->_filter = $filter;
+
+        // parent is a generator
+        parent::__construct(
+            (function($filename){
+                $f = fopen($filename, 'r');
+                try {
+                    while ($row = fgets($f)) {
+                        yield $row;
+                    }
+                } finally {
+                    fclose($f);
+                }
+            })($filename)
+        );
+    }
+
+    public function current() {
+        return $this->_filter->filter($this->getInnerIterator()->current());
+    }
+
+    public function accept() {
+        if ($this->current() == '') {
+            return false;
+        }
+        return true;
+    }
+}
+
+// read and parse file
+$filter = new IsNotDebug(new ExtractLogLevel(null));
+$fileReader = new FileRowReader($argv[1], $filter);
+
+// build stats
+$stats = new class($fileReader) extends ArrayIterator {
+    function __construct(Iterable $iterator) {
+        $stats = array();
+        foreach ($iterator as $level) {
+            if (array_key_exists($level, $stats)) {
+                $stats[$level]++;
+            } else {
+                $stats[$level] = 1;
+            }
+        }
+        arsort($stats);
+        parent::__construct($stats);
+    }
+};
+
+// show stats
+foreach ($stats as $level => $count) {
+    echo "$level: $count" . PHP_EOL;
+}