initial draft

src/Domain/ImageReference.php

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+<?php
+
+namespace Liip\ImagineBundle\Domain;
+
+interface ImageReference
+{
+    public function getContent(): string;
+
+    public function getMimeType(): ?string;
+
+    public function getFormat(): ?string;
+}

src/Domain/ImageReferenceFile.php

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+<?php
+
+namespace Liip\ImagineBundle\Domain;
+
+interface ImageReferenceFile extends ImageReference
+{
+    public function getPath(): string;
+}

src/Domain/Imagine/Filter/FilterExecutor.php

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+<?php
+
+/*
+ * This file is part of the `liip/LiipImagineBundle` project.
+ *
+ * (c) https://github.com/liip/LiipImagineBundle/graphs/contributors
+ *
+ * For the full copyright and license information, please view the LICENSE.md
+ * file that was distributed with this source code.
+ */
+
+namespace Liip\ImagineBundle\Domain\Imagine\Filter;
+
+use Imagine\Image\ImageInterface;
+
+interface FilterExecutor
+{
+    /**
+     * Loads and applies a filter on the given image.
+     */
+    public function applyTo(ImageInterface $image, array $options = []): ImageInterface;
+}

src/Domain/ImagineTransformer.php

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+<?php
+
+namespace Liip\ImagineBundle\Domain;
+
+/**
+ * Main entry point into the imagine system.
+ *
+ * The transformer takes an image id, does all necessary transformations (and potentially caching) and gives the URL to the result image.
+ */
+interface ImagineTransformer
+{
+    /**
+     * Determine the URL to the transformed image.
+     *
+     * For performance reasons, this method SHOULD cache the resulting images and skip transformation when it already exists.
+     *
+     * Calling the URL must result in the image being returned.
+     * If possible, the image should only be generated on the fly when the URL is called.
+     *
+     * @param string $sourceImageId Identifier for the image, for example a file system path
+     * @param string $stackName     The stack name as configured
+     * @param string $targetFormat  Output format to generate
+     *
+     * @return string URL to where the image is available
+     *
+     * @throws ImageNotFoundException
+     * @throws StackNotFoundException
+     * @throws FormatNotSupportedException The requested image format can not be generated by the system (The transformer does not know about browser capabilities)
+     * @throws TransformingException       Something went wrong while transforming the image
+     */
+    public function transformToUrl(string $sourceImageId, string $stackName, string $targetFormat): string;
+
+    /**
+     * Force generating the transformed image.
+     *
+     * If the result image is already cached, it will be regenerated and overwritten.
+     *
+     * There is no cache lifetime defined. The application is expected to use active invalidation if the source image changes.
+     *
+     * @param string $sourceImageId Identifier for the image, for example a file system path
+     * @param string[] $stackNames
+     * @param string[] $targetFormats
+     */
+    public function warmupCache(string $sourceImageId, array $stackNames, array $targetFormats): void;
+
+    /**
+     * Remove cached images for the specified source image.
+     *
+     * @param string $sourceImageId Identifier for the image, for example a file system path
+     * @param string[] $stackNames Limit invalidation to the specified stacks. If empty, all stacks are invalidated.
+     */
+    public function invalidateCache(string $sourceImageId, array $stackNames = []): void;
+}

src/Domain/LiipImagineTransformer.php

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+<?php
+
+namespace Liip\ImagineBundle\Domain;
+
+use Liip\ImagineBundle\Domain\Stack\TransformerStackExecutor;
+use Liip\ImagineBundle\Domain\Storage\ImageLoader;
+use Liip\ImagineBundle\Domain\Storage\ImageStore;
+
+/**
+ * Main entry point into the imagine system.
+ *
+ * The transformer takes an image id, does all necessary transformations (and potentially caching) and gives the URL to the result image.
+ */
+final class LiipImagineTransformer implements ImagineTransformer
+{
+    public function __construct(
+        private ImageLoader $sourceImageLoader,
+        private TransformerStackExecutor $transformerStackExecutor,
+        private ImageStore $imageStore,
+    ) {}
+
+    public function transformToUrl(string $sourceImageId, string $stackName, string $targetFormat): string
+    {
+        if ($this->imageStore->supportsOnDemandCreation()
+            || $this->imageStore->exists($sourceImageId, $stackName, $targetFormat)
+        ) {
+            return $this->imageStore->getUrl($sourceImageId, $stackName, $targetFormat);
+        }
+
+        $this->warmupCache($sourceImageId, [$stackName], [$targetFormat]);
+
+        return $this->imageStore->getUrl($sourceImageId, $stackName, $targetFormat);
+    }
+
+    public function warmupCache(string $sourceImageId, array $stackNames, array $targetFormats): void
+    {
+        if (0 === count($stackNames)) {
+            throw new \Exception('TODO: implement determining all stack names');
+        }
+        $sourceImage = $this->sourceImageLoader->loadImage($sourceImageId);
+        foreach ($stackNames as $stackName) {
+            foreach ($targetFormats as $targetFormat) {
+                // TODO: if we would separate stack executor creation and execution, we could build the stack only once and apply it for each target format
+                $transformedImage = $this->transformerStackExecutor->apply($stackName, $sourceImage);
+                $this->imageStore->store($transformedImage, $sourceImageId, $stackName, $targetFormat);
+            }
+        }
+    }
+
+    public function invalidateCache(string $sourceImageId, array $stackNames = []): void
+    {
+        $this->imageStore->delete($sourceImageId, $stackNames);
+    }
+}

src/Domain/PostProcessor/PostProcessor.php

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+<?php
+
+/*
+ * This file is part of the `liip/LiipImagineBundle` project.
+ *
+ * (c) https://github.com/liip/LiipImagineBundle/graphs/contributors
+ *
+ * For the full copyright and license information, please view the LICENSE.md
+ * file that was distributed with this source code.
+ */
+
+namespace Liip\ImagineBundle\Domain\PostProcessor;
+
+use Liip\ImagineBundle\Domain\ImageReference;
+
+/**
+ * Post processors do additional work on the resulting image after filters have been applied.
+ *
+ * @author Konstantin Tjuterev <[email protected]>
+ */
+interface PostProcessor
+{
+    /**
+     * Allows processing a BinaryInterface, with run-time options, so PostProcessors remain stateless.
+     *
+     * @param array<mixed> $options Operation-specific options
+     */
+    public function process(ImageReference $binary, array $options = []): ImageReference;
+}

src/Domain/Stack/LiipTransformerStack.php

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+<?php
+
+namespace Liip\ImagineBundle\Domain\Stack;
+
+use Liip\ImagineBundle\Domain\ImageReference;
+use Liip\ImagineBundle\Imagine\Filter\PostProcessor\PostProcessorInterface;
+
+class LiipTransformerStack implements TransformerStack
+{
+    /**
+     * @param FilterInterface[] $filters # used to be Filter\Loader\LoaderInterface
+     * @param PostProcessorInterface[] $postProcessors
+     */
+    public function __construct(
+        private array $filters,
+        private array $postProcessors,
+    ) {}
+
+    public function applyTo(ImageReference $image): ImageReference
+    {
+        foreach ($this->filters as $filter) {
+            $image = $filter->applyTo($image);
+        }
+
+        foreach ($this->postProcessors as $postProcessor) {
+            $image = $postProcessor->process($image);
+        }
+
+        return $image;
+    }
+}