Implement interpolation

3 files changed, 83 insertions, 3 deletions

diff --git a/README.md b/README.md
index b19e38b..dcefc94 100644
--- a/README.md
+++ b/README.md
@@ -22,11 +22,19 @@ Loggr is very simple to use, and looks like this:
 
 ```php
 $loggr = new Loggr(new FileSystemDriver('path-to-logs'));
-$loggr->info('context');
+$loggr->info('message', ['some-data' => 'goes-here']);
 ```
 
 All you have to do is instantiate Loggr with the appropriate driver for your use case and then simply 
-log away with any data you want to give it. It takes scalar values, as well as arrays and objects.
+log away with any data you want to give it. As per the PSR-3 standard, you can also interpolate context values 
+into the message placeholder, like so:
+
+```php
+$loggr = new Loggr(new FileSystemDriver('path-to-logs'));
+$loggr->info('Hello {who}', ['who' => 'World']);
+```
+
+Which would then output `Hello World` as the message.
 
 ### Methods
 
diff --git a/src/Loggr.php b/src/Loggr.php
index 82d5681..e641a18 100644
--- a/src/Loggr.php
+++ b/src/Loggr.php
@@ -50,12 +50,67 @@ class Loggr implements LoggerInterface
         $this->driver->log($this->format->serialize(new Message(
             level: $level,
             trace: $this->trace,
-            content: $message,
+            content: $this->interpolate($message, $context),
             context: $context,
         )));
     }
 
     /**
+     * @param string $message
+     * @param mixed|null $context
+     * @return string
+     */
+    private function interpolate(string $message, mixed $context = null): string
+    {
+        // $context has to be present, an array or an object.
+        if (!is_array($context) && !is_object($context)) return $message;
+
+        /** @var string|null $parsed_message */
+        $parsed_message = preg_replace_callback('/{(?<var>.*?)}/', function ($matches) use ($context) {
+            return $this->parseInterpolation($matches['var'], $context);
+        }, $message);
+
+        if ($parsed_message === null) {
+            $this->error = "Error parsing interpolation.";
+            return $message;
+        }
+
+        return $parsed_message;
+    }
+
+    /**
+     * @param string $var
+     * @param mixed|null $context
+     * @return string
+     */
+    private function parseInterpolation(string $var, mixed $context = null): string
+    {
+        $parts = explode('.', $var);
+        $value = $context;
+
+        foreach ($parts as $part) {
+            if (is_array($value) && array_key_exists($part, $value)) {
+                $value = $value[$part];
+                continue;
+            }
+
+            if (is_object($value) && property_exists($value, $part)) {
+                $value = $value->{$part};
+                continue;
+            }
+
+            return '';
+        }
+
+        return match(gettype($value)) {
+            'string' => $value,
+            'integer', 'boolean', 'double' => (string)$value,
+            'NULL' => 'null',
+            default => ''
+        };
+    }
+
+    /**
      * Logs an emergency level message with optional context.
      *
      * @param string|\Stringable $message
diff --git a/tests/LoggrTest.php b/tests/LoggrTest.php
index a7c3628..2172907 100644
--- a/tests/LoggrTest.php
+++ b/tests/LoggrTest.php
@@ -4,6 +4,7 @@ namespace Asko\Loggr\Tests;
 
 use Asko\Loggr\Drivers\OutputDriver;
 use Asko\Loggr\Loggr;
+use DateTime;
 use PHPUnit\Framework\TestCase;
 
 class LoggrTest extends TestCase
@@ -22,4 +23,20 @@ class LoggrTest extends TestCase
         $loggr->info('test');
         $this->assertEquals("Driver or format not set.", $loggr->error);
     }
+
+    public function testInterpolation(): void
+    {
+        $full_date = (new DateTime())->format('Y-m-d H:i:s');
+        $this->expectOutputString("[{$full_date}] LoggrTest.INFO: test something - {\"interpolation\":\"something\"}");
+        $loggr = new Loggr(new OutputDriver());
+        $loggr->info('test {interpolation}', ['interpolation' => 'something']);
+    }
+
+    public function testNestedInterpolation(): void
+    {
+        $full_date = (new DateTime())->format('Y-m-d H:i:s');
+        $this->expectOutputString("[{$full_date}] LoggrTest.INFO: test something - {\"nested\":{\"interpolation\":\"something\"}}");
+        $loggr = new Loggr(new OutputDriver());
+        $loggr->info('test {nested.interpolation}', ['nested' => ['interpolation' => 'something']]);
+    }
 }
\ No newline at end of file