refactor: extract BACKEND_MESSAGES + tBackend to src/main/domain/i18n-backend + 8 tests

Pure variant takes language as parameter. main.ts retains 2-arg adapter
that injects config.language so call-sites are unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/main.ts

@@ -8,6 +8,7 @@ import { autoUpdater } from 'electron-updater';
 import { compareUpdateVersions, isNewerUpdateVersion, normalizeUpdateVersion } from './main/domain/update-version-utils';
 import { writeFileAtomicSync } from './main/infra/fs-atomic';
 import { parseDuration, formatDuration, formatDurationDashed } from './main/infra/duration';
+import { tBackend as tBackendCore, type BackendMessageKey } from './main/domain/i18n-backend';
 import { CustomClip, MergeGroupItem, MergeGroup, QueueItem, DownloadProgress, DownloadResult } from './types';
 import {
     setDebugLogFn, initToolDirs,
@@ -86,102 +87,11 @@ function getMergeGroupPhaseText(phase: string): string {
 // ==========================================
 // BACKEND I18N
 // ==========================================
-// User-visible messages produced in main.ts. Keep keys stable — the renderer
+// Backend-Messages sind in src/main/domain/i18n-backend.ts.
-// no longer translates these (renderer.ts:downloadClip used to translate a
+// tBackend bleibt als 2-Arg-Adapter hier — pure Variante uebernimmt language
-// hardcoded set, which was brittle as the strings drifted). Internal
+// als 3. Parameter, der hier aus config.language injected wird.
-// debug log messages stay English-only since they're developer-facing.
-const BACKEND_MESSAGES = {
-    de: {
-        invalidVodUrl: 'Ungueltige VOD-URL',
-        invalidClipUrl: 'Ungueltige Clip-URL',
-        clipNotFound: 'Clip nicht gefunden',
-        streamlinkAutoInstallFailed: 'Streamlink fehlt und konnte nicht automatisch installiert werden. Siehe debug.log.',
-        streamlinkMissing: 'Streamlink fehlt.',
-        streamlinkNotFound: 'Streamlink nicht gefunden. Installiere Streamlink oder Python+streamlink (py -3 -m pip install streamlink).',
-        streamlinkExitCode: 'Streamlink Fehlercode {code}',
-        ffmpegMissing: 'FFmpeg fehlt.',
-        ffmpegMergeFailed: 'FFmpeg Merge fehlgeschlagen.',
-        ffmpegSplitFailed: 'FFmpeg Split fehlgeschlagen.',
-        fileTooSmall: 'Datei zu klein ({bytes} Bytes)',
-        clipFileTooSmall: 'Clip-Datei zu klein ({bytes} Bytes) - Twitch hat den Stream evtl. nicht ausgeliefert.',
-        integrityNoVideo: 'Integritaetspruefung fehlgeschlagen: Kein Videostream gefunden.',
-        integrityTooShort: 'Integritaetspruefung fehlgeschlagen: Dauer zu kurz ({duration}s).',
-        integrityDurationMismatch: 'Integritaetspruefung fehlgeschlagen: {actual}s statt erwarteter ~{expected}s.',
-        integrityFailedGeneric: 'Integritaetspruefung fehlgeschlagen.',
-        downloadCancelled: 'Download wurde abgebrochen.',
-        downloadPaused: 'Download wurde pausiert.',
-        downloadFailedExitCode: 'Download fehlgeschlagen (Exit-Code {code})',
-        unknownDownloadError: 'Unbekannter Fehler beim Download',
-        notAllClipPartsDownloaded: 'Nicht alle Clip-Teile konnten heruntergeladen werden.',
-        notAllPartsDownloaded: 'Nicht alle Teile konnten heruntergeladen werden.',
-        mergeGroupFileMissing: 'Heruntergeladene Datei {index} fehlt.',
-        diskSpaceShortFor: 'Zu wenig Speicherplatz fur {context}: frei {free}, benoetigt ~{required}.',
-        diskSpaceShortGeneric: 'Zu wenig Speicherplatz.',
-        attemptFailed: 'Versuch {attempt}/{max} fehlgeschlagen ({errorClass}): {error}',
-        retryingIn: 'Neuer Versuch in {seconds}s ({errorClass})...',
-        statusCheckingTools: 'Prufe Download-Tools...',
-        statusDownloadStarted: 'Download gestartet',
-        statusBytesDownloaded: '{bytes} heruntergeladen',
-        statusFetchingChatReplay: 'Chat-Replay wird heruntergeladen...',
-        statusChatMessagesFetched: 'Chat-Nachrichten geladen: {count}',
-        preflightNoInternet: 'Keine Internetverbindung erkannt.',
-        preflightStreamlinkMissing: 'Streamlink fehlt oder ist nicht startbar.',
-        preflightFfmpegMissing: 'FFmpeg fehlt oder ist nicht startbar.',
-        preflightFfprobeMissing: 'FFprobe fehlt oder ist nicht startbar.',
-        preflightDownloadPathNotWritable: 'Download-Ordner ist nicht beschreibbar.'
-    },
-    en: {
-        invalidVodUrl: 'Invalid VOD URL',
-        invalidClipUrl: 'Invalid clip URL',
-        clipNotFound: 'Clip not found',
-        streamlinkAutoInstallFailed: 'Streamlink is missing and could not be auto-installed. See debug.log.',
-        streamlinkMissing: 'Streamlink is missing.',
-        streamlinkNotFound: 'Streamlink not found. Install streamlink or Python+streamlink (py -3 -m pip install streamlink).',
-        streamlinkExitCode: 'Streamlink exit code {code}',
-        ffmpegMissing: 'FFmpeg is missing.',
-        ffmpegMergeFailed: 'FFmpeg merge failed.',
-        ffmpegSplitFailed: 'FFmpeg split failed.',
-        fileTooSmall: 'File too small ({bytes} bytes)',
-        clipFileTooSmall: 'Clip file too small ({bytes} bytes) - Twitch may not have served the stream.',
-        integrityNoVideo: 'Integrity check failed: no video stream found.',
-        integrityTooShort: 'Integrity check failed: duration too short ({duration}s).',
-        integrityDurationMismatch: 'Integrity check failed: {actual}s instead of expected ~{expected}s.',
-        integrityFailedGeneric: 'Integrity check failed.',
-        downloadCancelled: 'Download was cancelled.',
-        downloadPaused: 'Download was paused.',
-        downloadFailedExitCode: 'Download failed (exit code {code})',
-        unknownDownloadError: 'Unknown download error',
-        notAllClipPartsDownloaded: 'Not all clip parts could be downloaded.',
-        notAllPartsDownloaded: 'Not all parts could be downloaded.',
-        mergeGroupFileMissing: 'Downloaded file {index} is missing.',
-        diskSpaceShortFor: 'Not enough disk space for {context}: free {free}, need ~{required}.',
-        diskSpaceShortGeneric: 'Not enough disk space.',
-        attemptFailed: 'Attempt {attempt}/{max} failed ({errorClass}): {error}',
-        retryingIn: 'Retrying in {seconds}s ({errorClass})...',
-        statusCheckingTools: 'Checking download tools...',
-        statusDownloadStarted: 'Download started',
-        statusBytesDownloaded: '{bytes} downloaded',
-        statusFetchingChatReplay: 'Fetching chat replay...',
-        statusChatMessagesFetched: 'Chat messages fetched: {count}',
-        preflightNoInternet: 'No internet connection detected.',
-        preflightStreamlinkMissing: 'Streamlink is missing or not runnable.',
-        preflightFfmpegMissing: 'FFmpeg is missing or not runnable.',
-        preflightFfprobeMissing: 'FFprobe is missing or not runnable.',
-        preflightDownloadPathNotWritable: 'Download folder is not writable.'
-    }
-} as const;
-
-type BackendMessageKey = keyof typeof BACKEND_MESSAGES.de;
-
 function tBackend(key: BackendMessageKey, params?: Record<string, string | number>): string {
-    const lang: 'de' | 'en' = config.language === 'en' ? 'en' : 'de';
+    return tBackendCore(key, params, config?.language ?? 'de');
-    let template: string = BACKEND_MESSAGES[lang][key];
-    if (params) {
-        for (const [k, v] of Object.entries(params)) {
-            template = template.replace(`{${k}}`, String(v));
-        }
-    }
-    return template;
 }
 
 // Ensure directories exist

src/main/domain/i18n-backend.test.ts

@@ -0,0 +1,49 @@
+import { test, expect, describe } from 'vitest';
+import { tBackend, BACKEND_MESSAGES, type BackendMessageKey } from './i18n-backend';
+
+describe('tBackend', () => {
+    test('returns DE message for known key (default language)', () => {
+        expect(tBackend('invalidVodUrl', undefined, 'de')).toBe(BACKEND_MESSAGES.de.invalidVodUrl);
+    });
+
+    test('returns EN message when language=en', () => {
+        expect(tBackend('invalidVodUrl', undefined, 'en')).toBe(BACKEND_MESSAGES.en.invalidVodUrl);
+    });
+
+    test('unknown language falls back to de', () => {
+        expect(tBackend('invalidVodUrl', undefined, 'fr')).toBe(BACKEND_MESSAGES.de.invalidVodUrl);
+        expect(tBackend('invalidVodUrl', undefined, '')).toBe(BACKEND_MESSAGES.de.invalidVodUrl);
+    });
+
+    test('substitutes single {param}', () => {
+        const result = tBackend('streamlinkExitCode', { code: 42 }, 'en');
+        expect(result).toBe('Streamlink exit code 42');
+    });
+
+    test('substitutes multiple {params}', () => {
+        const result = tBackend('integrityDurationMismatch', { actual: 100, expected: 120 }, 'de');
+        expect(result).toContain('100');
+        expect(result).toContain('120');
+        expect(result).not.toContain('{actual}');
+        expect(result).not.toContain('{expected}');
+    });
+
+    test('numeric params stringify', () => {
+        const result = tBackend('fileTooSmall', { bytes: 256 }, 'en');
+        expect(result).toBe('File too small (256 bytes)');
+    });
+
+    test('every DE key has an EN counterpart', () => {
+        const deKeys = Object.keys(BACKEND_MESSAGES.de) as BackendMessageKey[];
+        const enKeys = Object.keys(BACKEND_MESSAGES.en);
+        for (const k of deKeys) {
+            expect(enKeys).toContain(k);
+        }
+    });
+
+    test('no template literal left after substitution for typical params', () => {
+        // attemptFailed has {attempt}, {max}, {errorClass}, {error}
+        const result = tBackend('attemptFailed', { attempt: 1, max: 3, errorClass: 'network', error: 'ETIMEDOUT' }, 'en');
+        expect(result).toBe('Attempt 1/3 failed (network): ETIMEDOUT');
+    });
+});

src/main/domain/i18n-backend.ts

@@ -0,0 +1,101 @@
+// Backend-Messages (User-visible aus main.ts produziert). Pure: Sprache wird
+// als Parameter uebergeben statt aus globalem config geholt.
+
+export const BACKEND_MESSAGES = {
+    de: {
+        invalidVodUrl: 'Ungueltige VOD-URL',
+        invalidClipUrl: 'Ungueltige Clip-URL',
+        clipNotFound: 'Clip nicht gefunden',
+        streamlinkAutoInstallFailed: 'Streamlink fehlt und konnte nicht automatisch installiert werden. Siehe debug.log.',
+        streamlinkMissing: 'Streamlink fehlt.',
+        streamlinkNotFound: 'Streamlink nicht gefunden. Installiere Streamlink oder Python+streamlink (py -3 -m pip install streamlink).',
+        streamlinkExitCode: 'Streamlink Fehlercode {code}',
+        ffmpegMissing: 'FFmpeg fehlt.',
+        ffmpegMergeFailed: 'FFmpeg Merge fehlgeschlagen.',
+        ffmpegSplitFailed: 'FFmpeg Split fehlgeschlagen.',
+        fileTooSmall: 'Datei zu klein ({bytes} Bytes)',
+        clipFileTooSmall: 'Clip-Datei zu klein ({bytes} Bytes) - Twitch hat den Stream evtl. nicht ausgeliefert.',
+        integrityNoVideo: 'Integritaetspruefung fehlgeschlagen: Kein Videostream gefunden.',
+        integrityTooShort: 'Integritaetspruefung fehlgeschlagen: Dauer zu kurz ({duration}s).',
+        integrityDurationMismatch: 'Integritaetspruefung fehlgeschlagen: {actual}s statt erwarteter ~{expected}s.',
+        integrityFailedGeneric: 'Integritaetspruefung fehlgeschlagen.',
+        downloadCancelled: 'Download wurde abgebrochen.',
+        downloadPaused: 'Download wurde pausiert.',
+        downloadFailedExitCode: 'Download fehlgeschlagen (Exit-Code {code})',
+        unknownDownloadError: 'Unbekannter Fehler beim Download',
+        notAllClipPartsDownloaded: 'Nicht alle Clip-Teile konnten heruntergeladen werden.',
+        notAllPartsDownloaded: 'Nicht alle Teile konnten heruntergeladen werden.',
+        mergeGroupFileMissing: 'Heruntergeladene Datei {index} fehlt.',
+        diskSpaceShortFor: 'Zu wenig Speicherplatz fur {context}: frei {free}, benoetigt ~{required}.',
+        diskSpaceShortGeneric: 'Zu wenig Speicherplatz.',
+        attemptFailed: 'Versuch {attempt}/{max} fehlgeschlagen ({errorClass}): {error}',
+        retryingIn: 'Neuer Versuch in {seconds}s ({errorClass})...',
+        statusCheckingTools: 'Prufe Download-Tools...',
+        statusDownloadStarted: 'Download gestartet',
+        statusBytesDownloaded: '{bytes} heruntergeladen',
+        statusFetchingChatReplay: 'Chat-Replay wird heruntergeladen...',
+        statusChatMessagesFetched: 'Chat-Nachrichten geladen: {count}',
+        preflightNoInternet: 'Keine Internetverbindung erkannt.',
+        preflightStreamlinkMissing: 'Streamlink fehlt oder ist nicht startbar.',
+        preflightFfmpegMissing: 'FFmpeg fehlt oder ist nicht startbar.',
+        preflightFfprobeMissing: 'FFprobe fehlt oder ist nicht startbar.',
+        preflightDownloadPathNotWritable: 'Download-Ordner ist nicht beschreibbar.'
+    },
+    en: {
+        invalidVodUrl: 'Invalid VOD URL',
+        invalidClipUrl: 'Invalid clip URL',
+        clipNotFound: 'Clip not found',
+        streamlinkAutoInstallFailed: 'Streamlink is missing and could not be auto-installed. See debug.log.',
+        streamlinkMissing: 'Streamlink is missing.',
+        streamlinkNotFound: 'Streamlink not found. Install streamlink or Python+streamlink (py -3 -m pip install streamlink).',
+        streamlinkExitCode: 'Streamlink exit code {code}',
+        ffmpegMissing: 'FFmpeg is missing.',
+        ffmpegMergeFailed: 'FFmpeg merge failed.',
+        ffmpegSplitFailed: 'FFmpeg split failed.',
+        fileTooSmall: 'File too small ({bytes} bytes)',
+        clipFileTooSmall: 'Clip file too small ({bytes} bytes) - Twitch may not have served the stream.',
+        integrityNoVideo: 'Integrity check failed: no video stream found.',
+        integrityTooShort: 'Integrity check failed: duration too short ({duration}s).',
+        integrityDurationMismatch: 'Integrity check failed: {actual}s instead of expected ~{expected}s.',
+        integrityFailedGeneric: 'Integrity check failed.',
+        downloadCancelled: 'Download was cancelled.',
+        downloadPaused: 'Download was paused.',
+        downloadFailedExitCode: 'Download failed (exit code {code})',
+        unknownDownloadError: 'Unknown download error',
+        notAllClipPartsDownloaded: 'Not all clip parts could be downloaded.',
+        notAllPartsDownloaded: 'Not all parts could be downloaded.',
+        mergeGroupFileMissing: 'Downloaded file {index} is missing.',
+        diskSpaceShortFor: 'Not enough disk space for {context}: free {free}, need ~{required}.',
+        diskSpaceShortGeneric: 'Not enough disk space.',
+        attemptFailed: 'Attempt {attempt}/{max} failed ({errorClass}): {error}',
+        retryingIn: 'Retrying in {seconds}s ({errorClass})...',
+        statusCheckingTools: 'Checking download tools...',
+        statusDownloadStarted: 'Download started',
+        statusBytesDownloaded: '{bytes} downloaded',
+        statusFetchingChatReplay: 'Fetching chat replay...',
+        statusChatMessagesFetched: 'Chat messages fetched: {count}',
+        preflightNoInternet: 'No internet connection detected.',
+        preflightStreamlinkMissing: 'Streamlink is missing or not runnable.',
+        preflightFfmpegMissing: 'FFmpeg is missing or not runnable.',
+        preflightFfprobeMissing: 'FFprobe is missing or not runnable.',
+        preflightDownloadPathNotWritable: 'Download folder is not writable.'
+    }
+} as const;
+
+export type BackendMessageKey = keyof typeof BACKEND_MESSAGES.de;
+export type BackendLanguage = 'de' | 'en';
+
+export function tBackend(
+    key: BackendMessageKey,
+    params: Record<string, string | number> | undefined,
+    language: BackendLanguage | string
+): string {
+    const lang: BackendLanguage = (language === 'en') ? 'en' : 'de';
+    let template: string = BACKEND_MESSAGES[lang][key];
+    if (params) {
+        for (const [k, v] of Object.entries(params)) {
+            template = template.replace(`{${k}}`, String(v));
+        }
+    }
+    return template;
+}