Implement option for automatic pruning of images

Closes #21.

Author: 0xEAB

tools/ddct-src/Util/ContainerBuilder.php

@@ -16,11 +16,15 @@
 
 final class ContainerBuilder
 {
+    private readonly bool $autoPruneImages;
+
     public function __construct(
         private readonly ContainerEngine $containerEngine,
         private readonly ContainerFileMap $map,
         private readonly Tagger $tagger,
+        ?bool $autoPruneImages = null,
     ) {
+        $this->autoPruneImages = $autoPruneImages ?? self::determineAutoPruneImages();
     }
 
     private function buildContainerImpl(ContainerFileRecipe $recipe, BaseImage $baseImage): ContainerBuilderStatus
@@ -59,6 +63,8 @@ private function buildContainer(ContainerFileRecipe $recipe, BaseImage $baseImag
         writeln('--> Updating tags.');
         $this->tagger->applyAll();
 
+        $this->pruneImagesIfEnabled();
+
         return $result;
     }
 
@@ -144,4 +150,32 @@ public function hasBuiltExact(string $app, ContainerVersionTag $version): ?Conta
 
         return null;
     }
+
+    private function pruneImagesIfEnabled(): void
+    {
+        if (!$this->autoPruneImages) {
+            return;
+        }
+
+        writeln('--> Pruning images.');
+        $this->containerEngine->pruneImages();
+    }
+
+    public static function determineAutoPruneImages(): bool
+    {
+        if (!isset($_SERVER['AUTO_PRUNE_IMAGES'])) {
+            return false;
+        }
+
+        $value = filter_var(
+            $_SERVER['AUTO_PRUNE_IMAGES'],
+            FILTER_VALIDATE_BOOL,
+            FILTER_NULL_ON_FAILURE,
+        );
+        if ($value === null) {
+            throw new Exception('Unsupported value for environment variable `AUTO_PRUNE_IMAGES`.');
+        }
+
+        return $value;
+    }
 }

tools/ddct-src/Util/ContainerEngine.php

@@ -159,6 +159,11 @@ public function removeImages(bool $force, string ...$images): void
         }
     }
 
+    public function pruneImages(): void
+    {
+        $this->passthruCommand('image', 'prune', '--force');
+    }
+
     public function pushImage(string $name): void
     {
         $this->passthruCommand('push', $name);