feat(export): add save/select/delete export presets

src/main/ExportPresets.js

@@ -0,0 +1,92 @@
+'use strict';
+
+/**
+ * Export preset persistence (Task 21 — export presets/profiles).
+ *
+ * Pure list operations over the `exportPresets` array kept in the app's
+ * settings.json store (the `store.get`/`store.set` helpers defined in
+ * src/main.js — the same store that holds headerFooterSettings and
+ * pageSettings). The store is injected so the logic is unit-testable with a
+ * fake store (see tests/main/ExportPresets.test.js); src/main.js wires these
+ * functions to the get-export-presets / save-export-preset /
+ * delete-export-preset invoke channels.
+ *
+ * Preset shape: { id: string, name: string, format: string|null, options: object }
+ * — `options` is the export-options snapshot captured from the renderer's
+ * export dialog, so selecting a preset can pre-fill that dialog exactly.
+ */
+
+const PRESET_KEY = 'exportPresets';
+const MAX_PRESETS = 50;
+const MAX_NAME_LENGTH = 100;
+
+/**
+ * Read the stored presets, defensively skipping corrupt data.
+ * @param {{get: Function, set: Function}} store settings store
+ * @returns {Array<{id: string, name: string, format: string|null, options: Object}>}
+ */
+function loadPresets(store) {
+  const stored = store.get(PRESET_KEY, []);
+  if (!Array.isArray(stored)) return [];
+  return stored.filter(
+    (preset) =>
+      preset &&
+      typeof preset === 'object' &&
+      typeof preset.id === 'string' &&
+      typeof preset.name === 'string'
+  );
+}
+
+/**
+ * Validate, normalize, and upsert a preset by id. A missing id gets a newly
+ * generated one (insert); an id that already exists is replaced (update).
+ * @param {{get: Function, set: Function}} store settings store
+ * @param {{id?: string, name?: string, format?: string, options?: Object}} preset
+ * @returns {Array} the updated preset list (also persisted)
+ * @throws when the preset is not an object, the name is empty, or the cap is hit
+ */
+function savePreset(store, preset) {
+  if (!preset || typeof preset !== 'object') {
+    throw new Error('Preset must be an object');
+  }
+  const name = typeof preset.name === 'string' ? preset.name.trim().slice(0, MAX_NAME_LENGTH) : '';
+  if (!name) {
+    throw new Error('Preset name is required');
+  }
+  const options = preset.options && typeof preset.options === 'object' ? preset.options : {};
+  const format = typeof preset.format === 'string' ? preset.format : null;
+
+  const presets = loadPresets(store);
+  const id = typeof preset.id === 'string' && preset.id ? preset.id : createPresetId();
+  const entry = { id, name, format, options };
+
+  const index = presets.findIndex((existing) => existing.id === id);
+  if (index >= 0) {
+    presets[index] = entry;
+  } else {
+    if (presets.length >= MAX_PRESETS) {
+      throw new Error(`Cannot store more than ${MAX_PRESETS} export presets`);
+    }
+    presets.push(entry);
+  }
+  store.set(PRESET_KEY, presets);
+  return presets;
+}
+
+/**
+ * Remove the preset with the given id (idempotent).
+ * @param {{get: Function, set: Function}} store settings store
+ * @param {string} presetId
+ * @returns {Array} the updated preset list (also persisted)
+ */
+function deletePreset(store, presetId) {
+  const presets = loadPresets(store).filter((preset) => preset.id !== presetId);
+  store.set(PRESET_KEY, presets);
+  return presets;
+}
+
+function createPresetId() {
+  return `preset-${Date.now().toString(36)}-${Math.random().toString(36).slice(2, 8)}`;
+}
+
+module.exports = { loadPresets, savePreset, deletePreset, PRESET_KEY, MAX_PRESETS };