06/05 Optimize app

app/services/export_service.py

@@ -1,5 +1,10 @@
 """
 Export Service — CSV, Excel, and PDF generation for transactions and reports.
+
+Memory-efficient exports:
+  - CSV: streaming generator (rows written one at a time, never all in memory)
+  - Excel: openpyxl write-only mode + DB yield_per(500) avoids loading the full
+    result set into Python at once
 """
 
 import io
@@ -11,13 +16,20 @@ from app.models.transaction import Transaction
 
 # ── CSV export ────────────────────────────────────────────────────────────────
 
-def transactions_to_csv(transactions):
-    """Return a CSV string of transactions."""
-    output = io.StringIO()
-    writer = csv.writer(output)
+def transactions_csv_stream(query):
+    """
+    Generator that yields CSV text one row at a time.
+    Pass the SQLAlchemy *query* (not a list) — rows are fetched in 500-row batches.
+    Use with Flask's stream_with_context() for a true streaming response.
+    """
+    buf = io.StringIO()
+    writer = csv.writer(buf)
 
     writer.writerow(['Date', 'Type', 'Description', 'Category', 'Account', 'Amount', 'Notes'])
-    for txn in transactions:
+    yield buf.getvalue()
+    buf.seek(0); buf.truncate()
+
+    for txn in query.yield_per(500):
         writer.writerow([
             txn.date.strftime('%Y-%m-%d'),
             txn.transaction_type,
@@ -27,80 +39,87 @@ def transactions_to_csv(transactions):
             float(txn.amount),
             txn.notes or '',
         ])
-
-    output.seek(0)
-    return output.getvalue()
+        yield buf.getvalue()
+        buf.seek(0); buf.truncate()
 
 
 # ── Excel export ──────────────────────────────────────────────────────────────
 
-def transactions_to_excel(transactions, period_label='Transactions'):
-    """Return Excel bytes for a list of transactions."""
+def transactions_to_excel(query, period_label='Transactions'):
+    """
+    Return Excel bytes built from a SQLAlchemy *query* using openpyxl write-only
+    mode.  Rows are fetched 500 at a time so the full result set is never held in
+    Python memory simultaneously.
+    """
     from openpyxl import Workbook
-    from openpyxl.styles import Font, PatternFill, Alignment, Border, Side
+    from openpyxl.styles import Font, PatternFill, Alignment
+    from openpyxl.cell import WriteOnlyCell
     from openpyxl.utils import get_column_letter
 
-    wb = Workbook()
-    ws = wb.active
-    ws.title = period_label[:31]  # max 31 chars
-
     symbol = current_app.config.get('APP_CURRENCY_SYMBOL', '$')
 
-    # Header style
+    wb = Workbook(write_only=True)
+    ws = wb.create_sheet(title=period_label[:31])
+
+    col_widths = [12, 10, 40, 18, 18, 16, 30]
+    for i, w in enumerate(col_widths, 1):
+        ws.column_dimensions[get_column_letter(i)].width = w
+
     header_fill = PatternFill(start_color='0F172A', end_color='0F172A', fill_type='solid')
     header_font = Font(color='F1F5F9', bold=True, size=10)
-    thin = Side(style='thin', color='E2E8F0')
-    border = Border(bottom=Side(style='thin', color='E2E8F0'))
+    headers = ['Date', 'Type', 'Description', 'Category', 'Account',
+               f'Amount ({symbol})', 'Notes']
+    header_row = []
+    for h in headers:
+        c = WriteOnlyCell(ws, value=h)
+        c.font = header_font
+        c.fill = header_fill
+        header_row.append(c)
+    ws.append(header_row)
 
-    headers = ['Date', 'Type', 'Description', 'Category', 'Account', f'Amount ({symbol})', 'Notes']
-    col_widths = [12, 10, 40, 18, 18, 16, 30]
-
-    for col, (header, width) in enumerate(zip(headers, col_widths), 1):
-        cell = ws.cell(row=1, column=col, value=header)
-        cell.font = header_font
-        cell.fill = header_fill
-        cell.alignment = Alignment(horizontal='left', vertical='center')
-        ws.column_dimensions[get_column_letter(col)].width = width
-
-    ws.row_dimensions[1].height = 22
-
-    # Data rows
     income_fill = PatternFill(start_color='F0FDF4', end_color='F0FDF4', fill_type='solid')
     expense_fill = PatternFill(start_color='FFF7F7', end_color='FFF7F7', fill_type='solid')
+    row_font = Font(size=10)
+    amt_fmt = '#,##0.00'
 
-    for row_num, txn in enumerate(transactions, 2):
+    running_total = 0.0
+    for txn in query.yield_per(500):
         fill = income_fill if txn.transaction_type == 'income' else expense_fill
-        data = [
+        amt = float(txn.amount)
+        running_total += amt
+        row_vals = [
             txn.date.strftime('%Y-%m-%d'),
             txn.transaction_type.title(),
             txn.description,
             txn.category.name if txn.category else '',
             txn.account.name if txn.account else '',
-            float(txn.amount),
+            amt,
             txn.notes or '',
         ]
-        for col, value in enumerate(data, 1):
-            cell = ws.cell(row=row_num, column=col, value=value)
-            cell.fill = fill
-            cell.border = border
-            cell.font = Font(size=10)
-            if col == 6:
-                cell.number_format = f'#,##0.00'
-                cell.alignment = Alignment(horizontal='right')
+        row = []
+        for col_idx, value in enumerate(row_vals, 1):
+            c = WriteOnlyCell(ws, value=value)
+            c.font = row_font
+            c.fill = fill
+            if col_idx == 6:
+                c.number_format = amt_fmt
+                c.alignment = Alignment(horizontal='right')
+            row.append(c)
+        ws.append(row)
 
-    # Totals row
-    total_row = len(transactions) + 2
-    ws.cell(row=total_row, column=5, value='TOTAL').font = Font(bold=True, size=10)
-    total_cell = ws.cell(row=total_row, column=6,
-                          value=sum(float(t.amount) for t in transactions))
-    total_cell.font = Font(bold=True, size=10)
-    total_cell.number_format = f'#,##0.00'
-    total_cell.alignment = Alignment(horizontal='right')
+    # Totals row — plain cells (write-only, no random access)
+    total_lbl = WriteOnlyCell(ws, value='TOTAL')
+    total_lbl.font = Font(bold=True, size=10)
+    total_val = WriteOnlyCell(ws, value=running_total)
+    total_val.font = Font(bold=True, size=10)
+    total_val.number_format = amt_fmt
+    total_val.alignment = Alignment(horizontal='right')
+    ws.append(['', '', '', '', total_lbl, total_val, ''])
 
     output = io.BytesIO()
     wb.save(output)
     output.seek(0)
-    return output.getvalue()
+    return output.read()
 
 
 # ── PDF export ────────────────────────────────────────────────────────────────