refactor(persistence): extract shared JSON I/O into json-store.ts; add parent-dir creation

src/main/json-store.ts

@@ -0,0 +1,32 @@
+// Tolerant JSON file primitives shared by the persistence modules
+// (project/recents/settings). Deliberately Electron-free so test harnesses
+// can bundle them alongside their consumers.
+//
+// Semantics every caller used to hand-roll:
+//   - read: missing/corrupt file resolves to null (caller picks the
+//     fallback shape: [], {}, or a thrown domain error)
+//   - write: pretty-printed UTF-8, parent directories created on demand.
+import fs from "fs";
+import path from "path";
+
+/** Parse a JSON file, or return null when it is missing or unreadable. */
+export function readJsonFile<T = unknown>(file: string): T | null {
+  try {
+    const raw = fs.readFileSync(file, "utf-8");
+    return JSON.parse(raw) as T;
+  } catch {
+    return null;
+  }
+}
+
+/** Read a JSON file expected to hold an array; anything else yields []. */
+export function readJsonArray<T = unknown>(file: string): T[] {
+  const parsed = readJsonFile<T[]>(file);
+  return Array.isArray(parsed) ? parsed : [];
+}
+
+/** Pretty-write a JSON file, creating parent directories when needed. */
+export function writeJsonFile(file: string, value: unknown): void {
+  fs.mkdirSync(path.dirname(file), { recursive: true });
+  fs.writeFileSync(file, JSON.stringify(value, null, 2), "utf-8");
+}

src/main/project.ts

@@ -1,5 +1,6 @@
 import fs from "fs";
 import path from "path";
+import { readJsonFile, readJsonArray, writeJsonFile } from "./json-store.js";
 
 export interface ChapterEntry {
   id: string;
@@ -103,9 +104,10 @@ export function createBook(bookPath: string, title: string): BookMeta {
 }
 
 export function loadBook(bookPath: string): BookMeta {
-  const raw = fs.readFileSync(metaPath(bookPath), "utf-8");
-  const data = JSON.parse(raw) as BookMeta;
-  if (data.app !== APP_ID) {
+  // Strict on purpose: a wrong app tag means "not a Folio book" and callers
+  // rely on the throw. This is domain validation, not generic JSON I/O.
+  const data = readJsonFile<BookMeta>(metaPath(bookPath));
+  if (!data || data.app !== APP_ID) {
     throw new Error(
       `Not a Folio book (no valid folio.json): ${bookPath}`
     );
@@ -117,38 +119,22 @@ export function loadBook(bookPath: string): BookMeta {
 }
 
 export function saveMeta(bookPath: string, meta: BookMeta): void {
-  fs.writeFileSync(
-    metaPath(bookPath),
-    JSON.stringify(meta, null, 2),
-    "utf-8"
-  );
-}
-
-function ensureParent(filePath: string): void {
-  fs.mkdirSync(path.dirname(filePath), { recursive: true });
+  writeJsonFile(metaPath(bookPath), meta);
 }
 
 export function listRecents(filePath: string): Recent[] {
-  try {
-    const raw = fs.readFileSync(filePath, "utf-8");
-    const arr = JSON.parse(raw);
-    return Array.isArray(arr) ? (arr as Recent[]) : [];
-  } catch {
-    return [];
-  }
+  return readJsonArray<Recent>(filePath);
 }
 
 export function addRecent(filePath: string, recent: Recent): Recent[] {
   const recents = listRecents(filePath).filter((r) => r.path !== recent.path);
   recents.unshift(recent);
-  ensureParent(filePath);
-  fs.writeFileSync(filePath, JSON.stringify(recents, null, 2), "utf-8");
+  writeJsonFile(filePath, recents);
   return recents;
 }
 
 export function removeRecent(filePath: string, recentPath: string): Recent[] {
   const recents = listRecents(filePath).filter((r) => r.path !== recentPath);
-  ensureParent(filePath);
-  fs.writeFileSync(filePath, JSON.stringify(recents, null, 2), "utf-8");
+  writeJsonFile(filePath, recents);
   return recents;
 }

src/main/recents.ts

@@ -1,13 +1,12 @@
 import fs from "fs";
 import path from "path";
 import { app } from "electron";
+import { APP_ID, hasBook } from "./project.js";
 import {
-  APP_ID,
-  hasBook,
-  listRecents as _listRecents,
   addRecent as _addRecent,
   removeRecent as _removeRecent,
 } from "./project.js";
+import { readJsonArray, writeJsonFile } from "./json-store.js";
 import type { Recent } from "./project.js";
 
 export type { Recent };
@@ -28,11 +27,10 @@ function legacyElectronRecentsFile(): string {
 }
 
 function loadRaw(file: string): Recent[] {
-  try {
-    return _listRecents(file).filter((r) => r && typeof r.path === "string");
-  } catch {
-    return [];
-  }
+  // Tolerate corrupt files ([]), then drop entries without a path.
+  return readJsonArray<Recent>(file).filter(
+    (r) => r && typeof r.path === "string"
+  );
 }
 
 // One-time migration: fold entries from a stray ~/.config/Electron recents
@@ -49,7 +47,7 @@ export function migrateLegacyRecents(): void {
     const known = new Set(current.map((r) => r.path));
     const merged = [...current, ...incoming.filter((r) => !known.has(r.path))];
     if (merged.length !== current.length) {
-      fs.writeFileSync(canonical, JSON.stringify(merged, null, 2), "utf-8");
+      writeJsonFile(canonical, merged);
     }
     fs.rmSync(legacy, { force: true });
   } catch {

src/main/settings.ts

@@ -1,7 +1,7 @@
-import fs from "fs";
 import path from "path";
 import { app } from "electron";
 import { APP_ID } from "./project.js";
+import { readJsonFile, writeJsonFile } from "./json-store.js";
 
 // Tiny per-user settings store (a JSON file in the Electron userData dir).
 // Used for preferences that should survive restarts, such as the theme.
@@ -12,13 +12,9 @@ let cache: Record<string, unknown> | null = null;
 
 function load(): Record<string, unknown> {
   if (cache) return cache;
-  try {
-    const raw = fs.readFileSync(SETTINGS_FILE(), "utf-8");
-    const parsed = JSON.parse(raw);
-    cache = parsed && typeof parsed === "object" ? parsed : {};
-  } catch {
-    cache = {};
-  }
+  // Missing or corrupt file both mean "no settings yet" -> {}.
+  cache =
+    readJsonFile<Record<string, unknown>>(SETTINGS_FILE()) ?? {};
   return cache as Record<string, unknown>;
 }
 
@@ -30,5 +26,5 @@ export function getSetting<T>(key: string, fallback: T): T {
 export function setSetting(key: string, value: unknown): void {
   const settings = load();
   settings[key] = value;
-  fs.writeFileSync(SETTINGS_FILE(), JSON.stringify(settings, null, 2), "utf-8");
+  writeJsonFile(SETTINGS_FILE(), settings);
 }