Extract React preview helpers to shared module

Author: kyoshino

src/lib/services/contents/api/react-helpers.js

@@ -0,0 +1,97 @@
+import { fromJS } from 'immutable';
+
+import { getAssetByPath } from '$lib/services/assets';
+import { AssetProxy } from '$lib/services/contents/api/asset-proxy';
+import { getEntriesByCollection } from '$lib/services/contents/collection/entries';
+import { getCollectionFileEntry } from '$lib/services/contents/collection/files';
+import { getField } from '$lib/services/contents/entry/fields';
+
+/**
+ * @import { Entry, GetFieldArgs, InternalLocaleCode } from '$lib/types/private';
+ * @import { ApiAsset, FieldKeyPath } from '$lib/types/public';
+ */
+
+/**
+ * Create an asset getter function for React components (preview templates and custom widgets).
+ * @param {object} args Arguments.
+ * @param {Entry} args.entry Entry object.
+ * @param {string} args.collectionName Collection name.
+ * @param {string} [args.fileName] File name.
+ * @returns {(path: string) => ApiAsset | undefined} Function that gets asset URLs.
+ */
+export const createGetAsset =
+  ({ entry, collectionName, fileName }) =>
+  /**
+   * Get the asset URL for a given asset path.
+   * @param {string} path Path to the asset.
+   * @returns {ApiAsset | undefined} Asset item.
+   */
+  (path) => {
+    const asset = getAssetByPath({ value: path, entry, collectionName, fileName });
+
+    if (asset) {
+      return new AssetProxy(asset);
+    }
+
+    return undefined;
+  };
+
+/**
+ * Get metadata for fields. For relation fields, looks up and stores the referenced entry content
+ * keyed by collection name and value, matching the `fieldsMetaData` structure expected by
+ * Netlify/Decap CMS preview templates and custom widgets.
+ * @param {object} args Arguments.
+ * @param {InternalLocaleCode} args.locale Current locale.
+ * @param {Omit<GetFieldArgs, 'keyPath'>} args.getFieldArgs Arguments for getField function.
+ * @returns {import('immutable').MapOf<any>} Immutable Map of entry metadata.
+ */
+export const getMetaData = ({ locale, getFieldArgs }) => {
+  const { valueMap = {} } = getFieldArgs;
+  /** @type {Record<string, any>} */
+  const metaData = {};
+  /** @type {Map<string, Entry[]>} */
+  const refEntriesCache = new Map();
+
+  Object.entries(valueMap).forEach(([key, value]) => {
+    const keyPath = /** @type {FieldKeyPath} */ (key.replace(/\.\d+$/, ''));
+    const field = getField({ ...getFieldArgs, keyPath });
+
+    // Populate metadata for relation fields by looking up referenced entries
+    if (field?.widget === 'relation') {
+      const {
+        value_field: valueField = '{{slug}}',
+        collection: refCollection,
+        file: refFile,
+      } = field;
+
+      const refEntries = (() => {
+        const cacheKey = `${refCollection}:${refFile ?? ''}`;
+        const cache = refEntriesCache.get(cacheKey);
+
+        if (cache) {
+          return cache;
+        }
+
+        const entries = (
+          refFile
+            ? [getCollectionFileEntry(refCollection, refFile)]
+            : getEntriesByCollection(refCollection)
+        ).filter((entry) => !!entry);
+
+        refEntriesCache.set(cacheKey, entries);
+
+        return entries;
+      })();
+
+      metaData[keyPath] ??= {};
+      metaData[keyPath][refCollection] ??= {};
+      metaData[keyPath][refCollection][value] = refEntries.find((entry) =>
+        valueField === '{{slug}}'
+          ? entry.slug === value
+          : entry.locales[locale]?.content?.[valueField] === value,
+      )?.locales[locale]?.content;
+    }
+  });
+
+  return /** @type {import('immutable').MapOf<any>} */ (fromJS(metaData));
+};