Add PDF archive store, raw-body IPC and export file helpers

The searchable PDF can be archived content-addressed under the local data
dir with its sha256 and layout fingerprint; a different PDF for an archived
invoice is refused and reads verify the hash. Export writes go through a
raw-body command that remembers the last folder; reveal-in-folder and open
fall back to xdg-open / explorer. Adds a Windows-safe export file name
builder. Migration M4 adds the archive columns and last export dir.

src/lib/filename.ts

@@ -0,0 +1,71 @@
+export type ExportMode = "searchable" | "flattened";
+
+export interface ExportFileNameInput {
+  /** Tokens: {number}, {client}, {date}. */
+  pattern?: string;
+  number: string;
+  client: string;
+  date: string;
+  mode: ExportMode;
+}
+
+const DEFAULT_PATTERN = "{number}_{client}_{date}";
+const MAX_STEM = 120;
+const FALLBACK = "invoice";
+
+// Characters Windows forbids in file names, plus control characters.
+// eslint-disable-next-line no-control-regex
+const FORBIDDEN = /[<>:"/\\|?*\u0000-\u001f\u007f]/g;
+// The device name matters even with an extension ("CON.txt" is still the console).
+const RESERVED = /^(con|prn|aux|nul|com[1-9¹²³]|lpt[1-9¹²³])$/i;
+const EDGE_JUNK = /^[.\s_-]+|[.\s_-]+$/g;
+
+function collapse(value: string): string {
+  return value
+    .replace(FORBIDDEN, "-")
+    .replace(/\s+/g, " ")
+    .replace(/-{2,}/g, "-")
+    .replace(/_{2,}/g, "_")
+    .replace(/ ?([-_]) ?/g, "$1");
+}
+
+function cleanPart(value: string): string {
+  return collapse(value.normalize("NFC")).replace(EDGE_JUNK, "");
+}
+
+/** Cut to at most `max` UTF-16 units without splitting a surrogate pair. */
+function truncate(value: string, max: number): string {
+  let out = "";
+  for (const ch of value) {
+    if (out.length + ch.length > max) break;
+    out += ch;
+  }
+  return out;
+}
+
+function fill(pattern: string, parts: { number: string; client: string; date: string }): string {
+  return pattern.replace(/\{(number|client|date)\}/g, (_, key: keyof typeof parts) => parts[key]);
+}
+
+/** A file name that is valid on Windows, macOS and Linux for an exported invoice PDF. */
+export function exportFileName(input: ExportFileNameInput): string {
+  const pattern = input.pattern?.trim() ? input.pattern : DEFAULT_PATTERN;
+  const parts = {
+    number: cleanPart(input.number),
+    client: cleanPart(input.client),
+    date: cleanPart(input.date),
+  };
+
+  let stem = fill(pattern, parts);
+  if (stem.length > MAX_STEM) {
+    // The invoice number is what identifies the file, so the client name gives way first.
+    const overflow = stem.length - MAX_STEM;
+    const client = truncate(parts.client, Math.max(0, parts.client.length - overflow));
+    stem = fill(pattern, { ...parts, client });
+  }
+  stem = cleanPart(truncate(cleanPart(stem), MAX_STEM));
+  if (!stem) stem = FALLBACK;
+  if (RESERVED.test(stem.split(".")[0])) stem = `_${stem}`;
+
+  return `${stem}${input.mode === "flattened" ? "-flat" : ""}.pdf`;
+}