Add metadata Pinia store for ExifTool queue preview reads.

Introduce preview entry types, resolveErrorMessage, and nullcart-style resolveAxiosErrorMessage for upcoming upload API errors.

frontend/src/stores/metadata.ts

@@ -0,0 +1,83 @@
+import { parseMetadata } from '@uswriting/exiftool';
+import { defineStore } from 'pinia';
+import { ref } from 'vue';
+import type { MetadataPreviewEntry } from '@/types/metadata/MetadataPreview';
+import { resolveErrorMessage } from '@/utils/resolveErrorMessage';
+
+export const useMetadataStore = defineStore('metadata', () => {
+    const previewsByKey = ref<Record<string, MetadataPreviewEntry>>({});
+
+    const readExifToolStdout = async (file: File): Promise<string> => {
+        const result = await parseMetadata(file);
+
+        if (!result.success) {
+            throw new Error(result.error);
+        }
+
+        return result.data;
+    };
+
+    const makeKeyFromFile = (file: File): string => `${file.name}\0${file.size}\0${file.lastModified}`;
+
+    const getPreview = (file: File): MetadataPreviewEntry => {
+        const key = makeKeyFromFile(file);
+
+        return previewsByKey.value[key] ?? { status: 'idle' };
+    };
+
+    const loadPreview = async (file: File): Promise<MetadataPreviewEntry> => {
+        const key = makeKeyFromFile(file);
+
+        previewsByKey.value = { ...previewsByKey.value, [key]: { status: 'loading' } };
+
+        try {
+            const output = await readExifToolStdout(file);
+
+            const entry: MetadataPreviewEntry = { status: 'ready', output };
+
+            previewsByKey.value = { ...previewsByKey.value, [key]: entry };
+
+            return entry;
+        } catch (error) {
+            const entry: MetadataPreviewEntry = {
+                status: 'error',
+                message: resolveErrorMessage(error, 'Could not read image metadata')
+            };
+
+            previewsByKey.value = { ...previewsByKey.value, [key]: entry };
+
+            return entry;
+        }
+    };
+
+    const loadPreviews = async (files: readonly File[]): Promise<void> => {
+        await Promise.all(files.map(file => loadPreview(file)));
+    };
+
+    const clearPreview = (file: File): void => {
+        const key = makeKeyFromFile(file);
+
+        if (!(key in previewsByKey.value)) {
+            return;
+        }
+
+        const next = { ...previewsByKey.value };
+
+        delete next[key];
+        previewsByKey.value = next;
+    };
+
+    const clearAllPreviews = (): void => {
+        previewsByKey.value = {};
+    };
+
+    return {
+        previewsByKey,
+        makeKeyFromFile,
+        getPreview,
+        loadPreview,
+        loadPreviews,
+        clearPreview,
+        clearAllPreviews
+    };
+});