JsonlParser: improve truncating the file when poping and pushing items

src/JsonlParser.php

@@ -13,6 +13,15 @@ public function __construct(protected $stream)
     {
     }
 
+    /**
+     * Initialize the parser from the given file.
+     */
+    public static function fromFile(string $filename, string $mode = 'a+t'): self
+    {
+        $stream = fopen($filename, $mode);
+        return new self($stream);
+    }
+
     public function push(array|string $item): void
     {
         $encoded = json_encode($item);
@@ -65,9 +74,10 @@ public function pop(): null|array|string
 
         $buffer = strrev($buffer);
 
-        // truncate the stream and remove the trailing newline
+        // truncate the stream
+        // remove the trailing newline if the stream is now empty
         $pos = ftell($this->stream);
-        ftruncate($this->stream, $pos < 1 ? 0 : $pos-1);
+        ftruncate($this->stream, $pos <= strlen(self::LINES_SEPARATOR) ? 0 : $pos);
 
         return json_decode($buffer, associative: true);
     }
@@ -103,4 +113,12 @@ public function count(): int
 
         return $count;
     }
+
+    /**
+     * Checks if there are no items in the stream.
+     */
+    public function empty(): bool
+    {
+        return count($this) === 0;
+    }
 }

tests/JsonParserTest.php

@@ -126,4 +126,44 @@ public function testPushItemsToFile(): void
 
         fclose($stream); // this removes the file
     }
+
+    public function testFromFile(): void
+    {
+        $tmpFilename = tempnam(directory: sys_get_temp_dir(), prefix: 'jsonld');
+
+        $parser = JsonlParser::fromFile($tmpFilename);
+        $this->assertCount(0, $parser);
+        $this->assertTrue($parser->empty());
+
+        $parser->push(self::ITEM_ONE);
+        $parser->push(self::ITEM_TWO);
+        $this->assertCount(2, $parser);
+        $this->assertFalse($parser->empty());
+
+        // now get one and push the next item
+        $this->assertSame(self::ITEM_TWO, $parser->pop());
+        $this->assertStringEqualsFile(
+            expectedFile: $tmpFilename,
+            actualString: json_encode(self::ITEM_ONE) . JsonlParser::LINES_SEPARATOR
+        );
+        $this->assertCount(1, $parser);
+        $parser->push(self::ITEM);
+        $this->assertStringEqualsFile(
+            expectedFile: $tmpFilename,
+            actualString: json_encode(self::ITEM_ONE) . JsonlParser::LINES_SEPARATOR . json_encode(self::ITEM) . JsonlParser::LINES_SEPARATOR
+        );
+        $this->assertCount(2, $parser);
+
+        // now, empty the file
+        $parser->pop();
+        $parser->pop();
+        $this->assertCount(0, $parser);
+        $this->assertTrue($parser->empty());
+        $this->assertStringEqualsFile(
+            expectedFile: $tmpFilename,
+            actualString: ''
+        );
+
+        unlink($tmpFilename);
+    }
 }