Add label preview before full generation

backend/routes/uploads.py

@@ -1,7 +1,7 @@
 import json
 from flask import current_app, Blueprint, request, jsonify
 from auth.decorators import verify_session_auth
-from services.label_service import process_label_file
+from services.label_service import process_label_file, generate_label_preview
 from utils.security import validate_file_security, rate_limit, sanitize_input
 import logging
 
@@ -83,3 +83,73 @@ def upload_file():
     except Exception as e:
         logger.exception("Error processing upload for user %s", request.user_id)
         return jsonify({'error': 'An error occurred processing your file'}), 500
+
+
+@uploads_bp.route('/preview', methods=['POST'])
+@rate_limit("10 per hour")
+@verify_session_auth
+def preview_labels():
+    try:
+        if 'file' not in request.files:
+            return jsonify({'error': 'No file provided'}), 400
+
+        file = request.files['file']
+        user_id = request.user_id
+
+        file_size_mb = len(file.read()) / (1024 * 1024)
+        file.seek(0)
+        if file_size_mb > 25:
+            return jsonify({'error': 'File too large. Maximum 25MB.'}), 400
+
+        is_valid, result = validate_file_security(file)
+        if not is_valid:
+            return jsonify({'error': result}), 400
+
+        secure_filename_result = sanitize_input(result)
+
+        template_id = request.form.get('template_id', current_app.config['DEFAULT_TEMPLATE'])
+        templates = current_app.config['LABEL_TEMPLATES']
+        if template_id not in templates:
+            valid = ', '.join(templates.keys())
+            return jsonify({'error': f"Invalid template_id '{template_id}'. Valid templates: {valid}"}), 400
+
+        column_mapping = None
+        column_mapping_raw = request.form.get('column_mapping')
+        if column_mapping_raw:
+            try:
+                mapping = json.loads(column_mapping_raw)
+            except json.JSONDecodeError:
+                return jsonify({'error': 'Invalid column_mapping JSON'}), 400
+
+            barcode_col = mapping.get('barcode_column')
+            if barcode_col is None or not isinstance(barcode_col, int) or barcode_col < 1 or barcode_col > 100:
+                return jsonify({'error': 'barcode_column must be an integer between 1 and 100'}), 400
+
+            column_mapping = {
+                'barcode_column': barcode_col - 1,
+                'text_columns': [
+                    {'column': tc['column'] - 1, 'label': str(tc.get('label', f'Column {tc["column"]}'))[:50]}
+                    for tc in mapping.get('text_columns', [])
+                    if isinstance(tc.get('column'), int) and 1 <= tc['column'] <= 100
+                ],
+                'has_header_row': bool(mapping.get('has_header_row', False))
+            }
+
+        barcode_type = request.form.get('barcode_type', 'code128')
+        if barcode_type not in ('code128', 'qr'):
+            return jsonify({'error': f"Invalid barcode_type '{barcode_type}'. Valid types: code128, qr"}), 400
+
+        result = generate_label_preview(
+            file, user_id, secure_filename_result,
+            template_id=template_id,
+            column_mapping=column_mapping,
+            barcode_type=barcode_type
+        )
+        return jsonify(result)
+
+    except ValueError as e:
+        logger.warning("Preview validation error for user %s", request.user_id)
+        return jsonify({'error': str(e)}), 400
+    except Exception as e:
+        logger.exception("Error generating preview for user %s", request.user_id)
+        return jsonify({'error': 'An error occurred generating the preview'}), 500

backend/services/label_service.py

@@ -1,3 +1,4 @@
+import base64
 import pandas as pd
 import uuid
 import time
@@ -152,4 +153,82 @@ def process_label_file(file, user_id, secure_filename, template_id=None, column_
         logger.error("Processing failed, cleaning up temp files.")
         if os.path.exists(filepath):
             os.remove(filepath)
-        raise 
+        raise
+
+
+def generate_label_preview(file, user_id, secure_filename, template_id=None, column_mapping=None, barcode_type='code128'):
+    logger.info("Starting generate_label_preview for user %s", user_id)
+
+    if not column_mapping:
+        column_mapping = {
+            'barcode_column': 1,
+            'text_columns': [
+                {'column': 0, 'label': 'Location'},
+                {'column': 3, 'label': 'Unit'}
+            ],
+            'has_header_row': False
+        }
+
+    ext = os.path.splitext(secure_filename)[1]
+    saved_name = f"{uuid.uuid4().hex}{ext}"
+    filepath = os.path.join(current_app.config['UPLOAD_FOLDER'], saved_name)
+    file.save(filepath)
+
+    try:
+        header_arg = 0 if column_mapping.get('has_header_row') else None
+        if secure_filename.endswith(('.xlsx', '.xls')):
+            df = pd.read_excel(filepath, header=header_arg)
+        else:
+            df = pd.read_csv(filepath, header=header_arg)
+
+        barcode_col = column_mapping['barcode_column']
+        text_cols = column_mapping.get('text_columns', [])
+
+        labels = []
+        for _, row in df.iterrows():
+            if barcode_col >= len(row):
+                continue
+            barcode_value = str(row.iloc[barcode_col]).strip()[:100]
+            if not barcode_value or barcode_value == 'nan':
+                continue
+            text_lines = []
+            for tc in text_cols:
+                col_idx = tc['column']
+                if col_idx < len(row):
+                    val = str(row.iloc[col_idx]).strip()[:100]
+                    if val and val != 'nan':
+                        text_lines.append((tc['label'], val))
+            labels.append((barcode_value, text_lines))
+
+        if not labels:
+            raise ValueError('No valid data found in file')
+
+        label_count = len(labels)
+        if label_count > current_app.config['MAX_LABELS']:
+            raise ValueError(f'Too many labels. Maximum: {current_app.config["MAX_LABELS"]}')
+
+        template = None
+        if template_id:
+            template = current_app.config['LABEL_TEMPLATES'][template_id]
+        sheet_gen = PDFSheetGenerator(current_app.config['SHEET_FOLDER'], template)
+        pdf_bytes = sheet_gen.generate_preview_sheet(labels, barcode_type=barcode_type)
+
+        os.remove(filepath)
+
+        labels_per_sheet = sheet_gen.rows * sheet_gen.columns
+        total_sheets = (label_count + labels_per_sheet - 1) // labels_per_sheet
+
+        logger.info("Preview generated for user %s: %d labels, %d sheets", user_id, label_count, total_sheets)
+
+        return {
+            'preview_pdf': base64.b64encode(pdf_bytes).decode('utf-8'),
+            'label_count': label_count,
+            'total_sheets': total_sheets,
+            'labels_on_first_sheet': min(label_count, labels_per_sheet),
+        }
+
+    except Exception as e:
+        logger.error("Preview generation failed, cleaning up temp files.")
+        if os.path.exists(filepath):
+            os.remove(filepath)
+        raise

backend/utils/PDFSheetGenerator.py

@@ -1,3 +1,4 @@
+import io
 from reportlab.pdfgen import canvas
 from reportlab.lib.pagesizes import LETTER
 from reportlab.lib.units import inch
@@ -74,6 +75,27 @@ def _draw_debug_grid(self, c):
                 y = LETTER[1] - self.margin_top - (row + 1) * self.label_height - row * self.y_gap
                 c.rect(x, y, self.label_width, self.label_height)
 
+    def generate_preview_sheet(self, labels, barcode_type='code128'):
+        labels_per_sheet = self.rows * self.columns
+        preview_labels = labels[:labels_per_sheet]
+
+        barcode_gen = BarcodeGenerator(self.template, barcode_type=barcode_type)
+        barcode_gen.calibrate([bv for bv, _ in labels])
+
+        buf = io.BytesIO()
+        c = canvas.Canvas(buf, pagesize=LETTER)
+
+        for i, (barcode_value, text_lines) in enumerate(preview_labels):
+            row = i // self.columns
+            col = i % self.columns
+            x = self.margin_left + col * (self.label_width + self.x_gap)
+            y = LETTER[1] - self.margin_top - (row + 1) * self.label_height - row * self.y_gap
+            barcode_gen.draw_label_to_canvas(c, x, y, barcode_value, text_lines)
+
+        c.save()
+        buf.seek(0)
+        return buf.read()
+
     def _get_default_template(self):
         from config.settings import Config
         return Config.LABEL_TEMPLATES[Config.DEFAULT_TEMPLATE]

frontend-vite/react-ts/src/components/LabelPreview.tsx

@@ -0,0 +1,83 @@
+import { useEffect, useRef, useState } from 'react';
+import { X } from 'lucide-react';
+
+interface LabelPreviewProps {
+  pdfBase64: string;
+  labelCount: number;
+  totalSheets: number;
+  labelsOnFirstSheet: number;
+  onGenerateAll: () => void;
+  onClose: () => void;
+}
+
+function LabelPreview({ pdfBase64, labelCount, totalSheets, labelsOnFirstSheet, onGenerateAll, onClose }: LabelPreviewProps) {
+  const [pdfUrl, setPdfUrl] = useState<string | null>(null);
+  const [loaded, setLoaded] = useState(false);
+  const activeUrlRef = useRef<string | null>(null);
+
+  useEffect(() => {
+    setLoaded(false);
+    const bytes = Uint8Array.from(atob(pdfBase64), c => c.charCodeAt(0));
+    const blob = new Blob([bytes], { type: 'application/pdf' });
+    const url = URL.createObjectURL(blob);
+    activeUrlRef.current = url;
+    setPdfUrl(url);
+
+    return () => {
+      URL.revokeObjectURL(url);
+      activeUrlRef.current = null;
+    };
+  }, [pdfBase64]);
+
+  const sheetLabel = totalSheets === 1 ? 'sheet' : 'sheets';
+  const labelLabel = labelCount === 1 ? 'label' : 'labels';
+
+  return (
+    <div className="flex flex-col bg-card border border-border rounded-[16px] overflow-hidden" style={{ height: 'calc(100vh - 6rem)' }}>
+      {/* Header */}
+      <div className="px-6 py-4 border-b border-border flex items-center justify-between flex-shrink-0">
+        <div>
+          <h2 className="font-heading text-sm font-semibold text-foreground">First Sheet Preview</h2>
+          <p className="text-xs text-muted-foreground mt-0.5">
+            {labelsOnFirstSheet} of {labelCount} {labelLabel} · {totalSheets} {sheetLabel} total
+          </p>
+        </div>
+        <div className="flex items-center gap-3">
+          <button
+            onClick={onGenerateAll}
+            className="h-9 px-5 bg-primary text-primary-foreground font-heading text-sm font-medium rounded-full hover:bg-primary/90 transition-colors cursor-pointer"
+          >
+            Generate All
+          </button>
+          <button
+            onClick={onClose}
+            className="p-2 rounded-[10px] text-muted-foreground hover:bg-secondary hover:text-foreground transition-colors cursor-pointer bg-transparent border-none"
+            title="Close preview"
+          >
+            <X className="w-4 h-4" />
+          </button>
+        </div>
+      </div>
+
+      {/* PDF Viewer */}
+      <div className="flex-1 bg-[#3A3A3A] flex items-center justify-center p-6 relative overflow-hidden">
+        {!loaded && (
+          <div className="absolute inset-0 flex items-center justify-center">
+            <div className="animate-spin rounded-full h-6 w-6 border-b-2 border-white" />
+          </div>
+        )}
+        {pdfUrl && (
+          <iframe
+            src={pdfUrl}
+            title="Label Preview"
+            className={`w-full h-full rounded shadow-2xl transition-opacity duration-200 ${loaded ? 'opacity-100' : 'opacity-0'}`}
+            style={{ border: 'none' }}
+            onLoad={() => setLoaded(true)}
+          />
+        )}
+      </div>
+    </div>
+  );
+}
+
+export default LabelPreview;