feat: integrate Tesseract.js with improved language availability and font handling

- Refactored OCR page recognition to utilize a configured Tesseract worker.
- Added functions to manage font URLs and asset filenames based on language.
- Implemented language availability checks and error handling for unsupported languages.
- Enhanced PDF workflow to display available OCR languages and handle user selections.
- Introduced utility functions for resolving Tesseract asset configurations.
- Added tests for OCR functionality, font loading, and Tesseract runtime behavior.
- Updated global types to include environment variables for Tesseract and font configurations.

src/js/utils/tesseract-runtime.ts

@@ -0,0 +1,130 @@
+import Tesseract from 'tesseract.js';
+import {
+  assertTesseractLanguagesAvailable,
+  TESSERACT_AVAILABLE_LANGUAGES_ENV_KEY,
+} from './tesseract-language-availability.js';
+
+const TESSERACT_ENV_KEYS = [
+  'VITE_TESSERACT_WORKER_URL',
+  'VITE_TESSERACT_CORE_URL',
+  'VITE_TESSERACT_LANG_URL',
+] as const;
+
+const TESSERACT_RUNTIME_ENV_KEYS = [
+  ...TESSERACT_ENV_KEYS,
+  TESSERACT_AVAILABLE_LANGUAGES_ENV_KEY,
+] as const;
+
+type TesseractRuntimeEnvKey = (typeof TESSERACT_RUNTIME_ENV_KEYS)[number];
+
+export type TesseractAssetEnv = Partial<
+  Pick<ImportMetaEnv, TesseractRuntimeEnvKey>
+>;
+
+export interface TesseractAssetConfig {
+  workerPath?: string;
+  corePath?: string;
+  langPath?: string;
+}
+
+export type TesseractLoggerMessage = Tesseract.LoggerMessage;
+export type TesseractWorkerOptions = Partial<Tesseract.WorkerOptions>;
+export type TesseractWorker = Tesseract.Worker;
+
+function getDefaultTesseractAssetEnv(): TesseractAssetEnv {
+  return import.meta.env;
+}
+
+function normalizeDirectoryUrl(url?: string): string | undefined {
+  const trimmed = url?.trim();
+  if (!trimmed) return undefined;
+  return trimmed.replace(/\/+$/, '');
+}
+
+function normalizeFileUrl(url?: string): string | undefined {
+  const trimmed = url?.trim();
+  if (!trimmed) return undefined;
+  return trimmed.replace(/\/+$/, '');
+}
+
+export function resolveTesseractAssetConfig(
+  env: TesseractAssetEnv = getDefaultTesseractAssetEnv()
+): TesseractAssetConfig {
+  return {
+    workerPath: normalizeFileUrl(env.VITE_TESSERACT_WORKER_URL),
+    corePath: normalizeDirectoryUrl(env.VITE_TESSERACT_CORE_URL),
+    langPath: normalizeDirectoryUrl(env.VITE_TESSERACT_LANG_URL),
+  };
+}
+
+export function hasConfiguredTesseractOverrides(
+  config: TesseractAssetConfig = resolveTesseractAssetConfig()
+): boolean {
+  return Boolean(config.workerPath || config.corePath || config.langPath);
+}
+
+export function hasCompleteTesseractOverrides(
+  config: TesseractAssetConfig = resolveTesseractAssetConfig()
+): boolean {
+  return Boolean(config.workerPath && config.corePath && config.langPath);
+}
+
+export function getIncompleteTesseractOverrideKeys(
+  config: TesseractAssetConfig = resolveTesseractAssetConfig()
+): Array<(typeof TESSERACT_ENV_KEYS)[number]> {
+  if (!hasConfiguredTesseractOverrides(config)) {
+    return [];
+  }
+
+  return TESSERACT_ENV_KEYS.filter((key) => {
+    switch (key) {
+      case 'VITE_TESSERACT_WORKER_URL':
+        return !config.workerPath;
+      case 'VITE_TESSERACT_CORE_URL':
+        return !config.corePath;
+      case 'VITE_TESSERACT_LANG_URL':
+        return !config.langPath;
+    }
+  });
+}
+
+export function buildTesseractWorkerOptions(
+  logger?: TesseractWorkerOptions['logger'],
+  env: TesseractAssetEnv = getDefaultTesseractAssetEnv()
+): TesseractWorkerOptions {
+  const config = resolveTesseractAssetConfig(env);
+
+  if (!hasConfiguredTesseractOverrides(config)) {
+    return logger ? { logger } : {};
+  }
+
+  if (!hasCompleteTesseractOverrides(config)) {
+    const missing = getIncompleteTesseractOverrideKeys(config).join(', ');
+    throw new Error(
+      `Self-hosted OCR assets are partially configured. Set ${missing} together with the other Tesseract asset URLs.`
+    );
+  }
+
+  return {
+    ...(logger ? { logger } : {}),
+    workerPath: config.workerPath,
+    corePath: config.corePath,
+    langPath: config.langPath,
+    gzip: true,
+  };
+}
+
+export async function createConfiguredTesseractWorker(
+  language: string,
+  oem: Tesseract.OEM,
+  logger?: TesseractWorkerOptions['logger'],
+  env: TesseractAssetEnv = getDefaultTesseractAssetEnv()
+): Promise<TesseractWorker> {
+  assertTesseractLanguagesAvailable(language, env);
+
+  return Tesseract.createWorker(
+    language,
+    oem,
+    buildTesseractWorkerOptions(logger, env)
+  );
+}