Image File Translator

/**
 * Translates text within an image using OCR and simulated translation.
 *
 * @param {Image} originalImg The original image object to process.
 * @param {string} targetLang The target language for translation (e.g., 'eng', 'rus', 'deu'). Note: This is for API compatibility; the actual translation is simulated.
 * @returns {Promise<HTMLCanvasElement>} A canvas element with the text replaced.
 */
async function processImage(originalImg, targetLang = 'eng') {

    // Helper function to dynamically load the Tesseract.js library from a CDN.
    // This ensures the library is available without needing to add it to the HTML.
    const loadTesseract = () => {
        return new Promise((resolve, reject) => {
            // If Tesseract is already loaded, resolve immediately.
            if (window.Tesseract) {
                return resolve();
            }
            const script = document.createElement('script');
            script.src = 'https://cdn.jsdelivr.net/npm/tesseract.js@5/dist/tesseract.min.js';
            script.onload = () => resolve();
            script.onerror = (err) => reject(new Error(`Failed to load Tesseract.js: ${err}`));
            document.head.appendChild(script);
        });
    };

    try {
        await loadTesseract();
    } catch (error) {
        console.error(error);
        // Return a canvas with an error message if the library fails to load.
        const errorCanvas = document.createElement('canvas');
        errorCanvas.width = originalImg.naturalWidth;
        errorCanvas.height = originalImg.naturalHeight;
        const ctx = errorCanvas.getContext('2d');
        ctx.fillStyle = 'red';
        ctx.font = '16px sans-serif';
        ctx.fillText('Error: Could not load Tesseract.js library.', 10, 20);
        return errorCanvas;
    }


    // 1. Setup the canvas
    const canvas = document.createElement('canvas');
    canvas.width = originalImg.naturalWidth;
    canvas.height = originalImg.naturalHeight;
    const ctx = canvas.getContext('2d');
    ctx.drawImage(originalImg, 0, 0);

    // 2. Initialize Tesseract
    // We load both English and Russian to handle a wider range of source images.
    const worker = await Tesseract.createWorker('eng+rus', 1, {
       logger: m => console.log(m) // Optional: logs progress to the console
    });

    // 3. Perform OCR
    const { data: { lines } } = await worker.recognize(canvas);

    // 4. Process the recognized text: First, erase all identified text areas.
    // This prevents overlapping text boxes from interfering with each other.
    ctx.fillStyle = 'white'; // Use white to "erase" the text.
    ctx.strokeStyle = '#e0e0e0'; // Use a light border for visual debugging.
    ctx.lineWidth = 1;

    for (const line of lines) {
        // Only process text with a reasonable confidence score to avoid erasing non-text.
        if (line.confidence > 50) {
            const bbox = line.bbox;
            ctx.fillRect(bbox.x0, bbox.y0, bbox.width, bbox.height);
            ctx.strokeRect(bbox.x0, bbox.y0, bbox.width, bbox.height);
        }
    }

    // 5. "Translate" and draw placeholders
    // This loop runs after all areas have been erased.
    ctx.fillStyle = 'black';
    ctx.textAlign = 'left';
    ctx.textBaseline = 'top';

    for (const line of lines) {
        if (line.confidence > 50) {
            const bbox = line.bbox;
            const originalText = line.text;

            // --- SIMULATED TRANSLATION ---
            // In a real-world application with a server or API key, you would call a
            // translation service here:
            // const translatedText = await translateAPI(originalText, targetLang);
            //
            // For this client-side example, we create a placeholder of block characters
            // that has the same length as the original text.
            const placeholderText = '█'.repeat(originalText.replace(/\s/g, '').length);

            // Dynamically calculate font size to fit the placeholder text within the box.
            let fontSize = bbox.height;
            ctx.font = `${fontSize}px sans-serif`;
            let textWidth = ctx.measureText(placeholderText).width;

            // Reduce font size until the text fits within the bounding box width.
            while (textWidth > bbox.width && fontSize > 8) {
                fontSize -= 1;
                ctx.font = `${fontSize}px sans-serif`;
                textWidth = ctx.measureText(placeholderText).width;
            }
            
            // Vertically center the text within the bounding box.
            const y = bbox.y0 + (bbox.height - fontSize) / 2;
            ctx.fillText(placeholderText, bbox.x0, y);
        }
    }

    // 6. Clean up the Tesseract worker
    await worker.terminate();

    // 7. Return the final canvas
    return canvas;
}