feat: Convert data from ResourceStore based on preferences

src/storage/RepresentationConvertingStore.ts

@@ -0,0 +1,47 @@
+import { Conditions } from './Conditions';
+import { matchingMediaType } from '../util/Util';
+import { PassthroughStore } from './PassthroughStore';
+import { Representation } from '../ldp/representation/Representation';
+import { RepresentationConverter } from './conversion/RepresentationConverter';
+import { RepresentationPreferences } from '../ldp/representation/RepresentationPreferences';
+import { ResourceIdentifier } from '../ldp/representation/ResourceIdentifier';
+import { ResourceStore } from './ResourceStore';
+
+/**
+ * Store that overrides the `getRepresentation` function.
+ * Tries to convert the {@link Representation} it got from the source store
+ * so it matches one of the given type preferences.
+ *
+ * In the future this class should take the preferences of the request into account.
+ * Even if there is a match with the output from the store,
+ * if there is a low weight for that type conversions might still be preferred.
+ */
+export class RepresentationConvertingStore extends PassthroughStore {
+  private readonly converter: RepresentationConverter;
+
+  public constructor(source: ResourceStore, converter: RepresentationConverter) {
+    super(source);
+    this.converter = converter;
+  }
+
+  public async getRepresentation(identifier: ResourceIdentifier, preferences: RepresentationPreferences,
+    conditions?: Conditions): Promise<Representation> {
+    const representation = await super.getRepresentation(identifier, preferences, conditions);
+    if (this.matchesPreferences(representation, preferences)) {
+      return representation;
+    }
+    return this.converter.handleSafe({ identifier, representation, preferences });
+  }
+
+  private matchesPreferences(representation: Representation, preferences: RepresentationPreferences): boolean {
+    if (!preferences.type) {
+      return true;
+    }
+    return Boolean(
+      representation.metadata.contentType &&
+      preferences.type.some((type): boolean =>
+        type.weight > 0 &&
+        matchingMediaType(type.value, representation.metadata.contentType!)),
+    );
+  }
+}