feat(desktop): live-reload linked css theme files (#3099)

fluxer_desktop/src/main/ThemeLinkedFileWatch.ts

@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import {Buffer} from 'node:buffer';
+import fs from 'node:fs';
+import type {ThemeLinkedFileChange} from '@electron/common/Types';
+
+const THEME_CSS_MAX_BYTES = 1024 * 1024;
+
+interface ThemeLinkedFileWatchEntry {
+	listener: () => void;
+	generation: number;
+}
+
+export async function readThemeCssFile(filePath: string): Promise<ThemeLinkedFileChange> {
+	let handle: fs.promises.FileHandle | null = null;
+	try {
+		const linkStats = await fs.promises.lstat(filePath);
+		if (!linkStats.isFile()) {
+			return {path: filePath, error: 'not_file'};
+		}
+		handle = await fs.promises.open(filePath, fs.constants.O_RDONLY | (fs.constants.O_NOFOLLOW ?? 0));
+		const stats = await handle.stat();
+		if (!stats.isFile()) {
+			return {path: filePath, error: 'not_file'};
+		}
+		if (stats.size > THEME_CSS_MAX_BYTES) {
+			return {path: filePath, error: 'too_large'};
+		}
+		const buffer = Buffer.alloc(THEME_CSS_MAX_BYTES + 1);
+		let bytesRead = 0;
+		while (bytesRead < buffer.length) {
+			const result = await handle.read(buffer, bytesRead, buffer.length - bytesRead, bytesRead);
+			if (result.bytesRead === 0) break;
+			bytesRead += result.bytesRead;
+		}
+		if (bytesRead > THEME_CSS_MAX_BYTES) {
+			return {path: filePath, error: 'too_large'};
+		}
+		return {path: filePath, css: buffer.toString('utf8', 0, bytesRead).replace(/^\uFEFF/, '')};
+	} catch (error) {
+		const code = (error as NodeJS.ErrnoException | null)?.code;
+		if (code === 'ENOENT') {
+			return {path: filePath, error: 'missing'};
+		}
+		if (code === 'ELOOP') {
+			return {path: filePath, error: 'not_file'};
+		}
+		return {path: filePath, error: 'read_failed'};
+	} finally {
+		await handle?.close().catch(() => {});
+	}
+}
+
+export function createThemeLinkedFileWatchSet(
+	emit: (change: ThemeLinkedFileChange) => void,
+	intervalMs = 250,
+): {replace: (paths: ReadonlyArray<string>) => void; dispose: () => void} {
+	const entries = new Map<string, ThemeLinkedFileWatchEntry>();
+	const read = (filePath: string): void => {
+		const entry = entries.get(filePath);
+		if (!entry) return;
+		entry.generation += 1;
+		const generation = entry.generation;
+		void readThemeCssFile(filePath).then((change) => {
+			const current = entries.get(filePath);
+			if (current !== entry || current.generation !== generation) return;
+			emit(change);
+		});
+	};
+	const unwatch = (filePath: string): void => {
+		const entry = entries.get(filePath);
+		if (!entry) return;
+		fs.unwatchFile(filePath, entry.listener);
+		entries.delete(filePath);
+	};
+	return {
+		replace(paths) {
+			const next = new Set(paths);
+			for (const filePath of [...entries.keys()]) {
+				if (!next.has(filePath)) unwatch(filePath);
+			}
+			for (const filePath of next) {
+				if (entries.has(filePath)) continue;
+				const entry: ThemeLinkedFileWatchEntry = {listener: () => read(filePath), generation: 0};
+				entries.set(filePath, entry);
+				fs.watchFile(filePath, {interval: intervalMs, persistent: false}, entry.listener);
+				read(filePath);
+			}
+		},
+		dispose() {
+			for (const filePath of [...entries.keys()]) unwatch(filePath);
+		},
+	};
+}