Per-chart export: copy/download spec and PNG/SVG from the preview header

src/core/chart-export.ts

@@ -0,0 +1,91 @@
+/**
+ * Chart export — pure helpers for the single-chart export affordance
+ * (spec §08 → Per-chart export). Distinct from the workspace export envelope
+ * (`export-envelope.ts`): that backs up the whole library as one JSON file; this
+ * turns *one* snippet into a shareable artifact — its spec as `.vl.json`, or its
+ * rendered image as PNG/SVG.
+ *
+ * The naming is deterministic, and so is producing a **self-contained** spec —
+ * one with every saved-dataset reference replaced by its inline data, so the
+ * exported file renders without Astrolabe. Both live here and are tested. The
+ * clipboard write, the file download, and the image rasterization are browser-side
+ * and stay in `infrastructure/file-transfer` and the chart renderer.
+ */
+
+import { prepareSpecForRender, type ResolvableDataset } from './rendering';
+import { extractDatasetRefs } from './spec-refs';
+
+/** The formats a single chart can be exported as (file extension == the value). */
+export type ChartExportFormat = 'vl.json' | 'png' | 'svg';
+
+/** Cap on the derived base name so a very long snippet title can't blow up the
+ *  filename (filesystems and download shelves both balk past ~255 chars). */
+export const MAX_BASENAME_LEN = 60;
+
+/** C0 control characters + DEL, built from a string so no literal control byte
+ *  ever lands in this source file. Stripped from filenames. */
+// eslint-disable-next-line no-control-regex -- intentional: scrub control chars from names
+const CONTROL_CHARS = new RegExp('[\\u0000-\\u001f\\u007f]', 'g');
+
+/** Characters illegal on Windows or awkward across filesystems and URLs. */
+const ILLEGAL_CHARS = /[\\/:*?"<>|]/g;
+
+/**
+ * Turn a snippet's display name into a filesystem- and URL-safe base name.
+ *
+ * Keeps the user's words and **case**, and keeps letters of *any* script (a
+ * Cyrillic or CJK title stays itself — we never ASCII-fold, matching the app's
+ * full-script support). Swaps whitespace and dot runs for single dashes (so the
+ * extension stays unambiguous), drops control + illegal characters, collapses and
+ * trims dashes, and caps the length. Falls back to `"chart"` when nothing usable
+ * remains (a name of only punctuation or whitespace).
+ */
+export function snippetFileBasename(name: string): string {
+  const cleaned = name
+    .normalize('NFC')
+    .replace(CONTROL_CHARS, '')
+    .replace(ILLEGAL_CHARS, '')
+    .replace(/[.\s]+/g, '-') // dot and whitespace runs → one dash boundary
+    .replace(/-+/g, '-')
+    .replace(/^-+|-+$/g, '');
+  const capped = cleaned.slice(0, MAX_BASENAME_LEN).replace(/-+$/g, '');
+  return capped || 'chart';
+}
+
+/**
+ * Download filename for a single chart export, e.g. `sales-by-region.png`. The
+ * base is derived from the snippet name; `format` is both the extension and the
+ * artifact kind. No date or `astrolabe-` prefix (unlike the workspace export) —
+ * the user is exporting *one named chart* and wants its name on the file.
+ */
+export function chartExportFilename(name: string, format: ChartExportFormat): string {
+  return `${snippetFileBasename(name)}.${format}`;
+}
+
+/**
+ * The saved-dataset names a spec references via `{ data: { name } }` (deduped).
+ * A name the spec defines for itself via top-level `datasets` is excluded — those
+ * are already self-contained. Returns `[]` for spec text that doesn't parse. Drives
+ * whether the export offers an "inline referenced data" option at all.
+ */
+export function referencedDatasetNames(specText: string): string[] {
+  // extractDatasetRefs already safe-parses a string (→ [] on bad JSON) and dedups.
+  return extractDatasetRefs(specText);
+}
+
+/**
+ * Re-serialize a spec with every saved-dataset reference replaced by its inline
+ * data, so the exported file renders standalone (outside Astrolabe). Sizing is
+ * left exactly as authored — unlike the preview, no fit-mode is applied. Throws
+ * `DatasetNotFoundError` (from `prepareSpecForRender`) if the spec references a
+ * name not present in `datasets`; the caller surfaces that. `specText` must be
+ * valid JSON (it is the spec the editor is showing).
+ */
+export function inlineReferencedDatasets(
+  specText: string,
+  datasets: ReadonlyArray<ResolvableDataset>,
+): string {
+  const parsed: unknown = JSON.parse(specText);
+  const resolved = prepareSpecForRender(parsed, { datasets, fitMode: 'default' });
+  return JSON.stringify(resolved, null, 2);
+}