Plan the run as physical labels, not one per part

A drawer with two part types is one label, so the page, the preview, the
print loop and the PDF all work from plan_groups rather than iterating
the selection. The preview takes the parts that share a label, and the
page reports how much tape the run will use.

app/routes/labels_tape.py

@@ -3,11 +3,15 @@ Tape printing - admin only. Drives the Brother VC-500W over the network.
 
 Routes (all under /admin/labels/tape):
     /                 choose labels, set tape options, see a live preview
-    /preview.png      rendered preview of one label
+    /preview.png      rendered preview of one physical label
     /print            send the job to the printer over IPP
     /download.pdf     the same labels as a PDF, for when you'd rather not
     /test             probe the printer: model, state, accepted formats
 
+A "physical label" is not the same as a PartLabel row: a drawer holding
+two part types prints as one 40 x 20mm label. tape_printer.plan_groups
+works that out, and everything here follows its plan.
+
 Created by: Jess Rogerson (yelling commands at Claude.AI)
 """
 
@@ -37,6 +41,8 @@ def printer_config():
         'format': (SiteSetting.get('tape_printer_format', '') or '').strip(),
         'tape': SiteSetting.get('tape_default', tape_printer.DEFAULT_TAPE),
         'rotate': SiteSetting.get_bool('tape_rotate_default', True),
+        'size_mode': SiteSetting.get('tape_size_mode',
+                                     tape_printer.DEFAULT_SIZE_MODE),
     }
 
 
@@ -51,6 +57,7 @@ def _options_query(options, labels):
         'ids': ','.join(str(l.id) for l in labels),
         tape_printer.FORM_MARKER: '1',
         'tape': options.tape,
+        'size_mode': options.size_mode,
         'copies': options.copies,
         'font_scale': options.font_scale,
         'image_percent': options.image_percent,
@@ -61,6 +68,8 @@ def _options_query(options, labels):
     # Checkboxes: only present when on, which is what the parser expects.
     if options.rotate:
         query['rotate'] = '1'
+    if options.group_drawers:
+        query['group_drawers'] = '1'
     if options.outline:
         query['outline'] = '1'
     if options.fixed_length_mm:
@@ -100,20 +109,27 @@ def index():
 
     config = printer_config()
     source = request.form if request.method == 'POST' else request.args
-    # rotate_default only applies when the form was not submitted, so an
-    # explicit untick on the page always wins over the saved preference.
+    # The *_default values only apply when the form was not submitted, so an
+    # explicit choice on the page always wins over the saved preference.
     options = tape_printer.options_from_form(
-        source, rotate_default=config['rotate'])
-    if not source.get('tape'):
-        options.tape = config['tape']
+        source, rotate_default=config['rotate'],
+        size_default=config['size_mode'], tape_default=config['tape'])
+
+    plan = tape_printer.plan_groups(labels, options)
+    tape = tape_printer.get_tape(options.tape)
 
     return render_template(
         'admin/labels/tape.html',
         labels=labels,
+        plan=plan,
         ids=','.join(str(l.id) for l in labels),
         options=options,
         tapes=tape_printer.TAPE_PRESETS,
-        tape=tape_printer.get_tape(options.tape),
+        tape=tape,
+        size_modes=tape_printer.SIZE_MODES,
+        label_width_mm=tape_printer.LABEL_WIDTH_MM,
+        tape_fits=tape_printer.tape_fits_label(options.tape),
+        tape_used_mm=tape_printer.tape_used_mm(plan, options.copies),
         field_options=[
             ('image', 'Part image'), ('name', 'Part name'),
             ('dimensions', 'Dimensions'), ('part_number', 'Part number'),
@@ -129,14 +145,27 @@ def index():
 @login_required
 @admin_required
 def preview():
-    label_id = request.args.get('id', type=int)
-    if not label_id:
-        abort(400, 'preview.png needs an ?id= of a label.')
-    label = PartLabel.query.get_or_404(label_id)
+    """
+    One physical label. `ids` is every part on it, because a drawer holding
+    two part types prints as a single 40 x 20mm label, not two labels.
+    """
+    raw = request.args.get('ids') or request.args.get('id') or ''
+    wanted = [int(v) for v in str(raw).split(',') if v.strip().isdigit()]
+    if not wanted:
+        abort(400, 'preview.png needs ?ids= of one or more labels.')
+
+    found = {row.id: row for row in
+             PartLabel.query.filter(PartLabel.id.in_(wanted)).all()}
+    group = [found[i] for i in wanted if i in found]
+    if not group:
+        abort(404)
+
+    config = printer_config()
     options = tape_printer.options_from_form(
-        request.args, rotate_default=printer_config()['rotate'])
+        request.args, rotate_default=config['rotate'],
+        size_default=config['size_mode'], tape_default=config['tape'])
     buffer = tape_printer.preview_png(
-        label, options, current_app.config['UPLOAD_FOLDER'])
+        group, options, current_app.config['UPLOAD_FOLDER'])
     return send_file(buffer, mimetype='image/png')
 
 
@@ -187,7 +216,8 @@ def print_tape():
 
     config = printer_config()
     options = tape_printer.options_from_form(
-        request.form, rotate_default=config['rotate'])
+        request.form, rotate_default=config['rotate'],
+        size_default=config['size_mode'], tape_default=config['tape'])
     host = config['host']
     if not host:
         flash('No tape printer address configured. Set it in Label '
@@ -213,26 +243,35 @@ def print_tape():
                                 **_options_query(options, labels)))
 
     upload_folder = current_app.config['UPLOAD_FOLDER']
+    plan = tape_printer.plan_groups(labels, options)
+
+    if options.is_fixed and not tape_printer.tape_fits_label(options.tape):
+        flash(f'{tape_printer.LABEL_WIDTH_MM:.0f}mm labels need 50mm tape - '
+              f'{tape_printer.get_tape(options.tape).name} is narrower, so '
+              'they were scaled down to fit.', 'warning')
+
     sent = 0
     failures = []
 
-    for label in labels:
+    for item in plan:
+        group = item['labels']
+        name = ' + '.join(l.display_title for l in group)
         try:
-            image = tape_printer.render_label(label, options, upload_folder)
+            image = tape_printer.render_group(group, options, upload_folder)
             document = tape_printer.image_to_bytes(image, mime_type)
             # copies is handled by repeating the job rather than the IPP
             # copies attribute: tape printers vary wildly in honouring it.
             for _ in range(options.copies):
                 ipp_client.print_job(
                     host, document, mime_type,
-                    job_name=f'LIM: {label.display_title}'[:120],
+                    job_name=f'LIM: {name}'[:120],
                     port=config['port'], path=config['path'])
                 sent += 1
         except ipp_client.IPPError as exc:
-            failures.append(f'{label.display_title}: {exc}')
+            failures.append(f'{name}: {exc}')
         except Exception as exc:
-            logger.exception('Tape print failed for label %s', label.id)
-            failures.append(f'{label.display_title}: {exc}')
+            logger.exception('Tape print failed for %s', name)
+            failures.append(f'{name}: {exc}')
 
     if sent:
         flash(f'Sent {sent} label{"" if sent == 1 else "s"} to the printer.',
@@ -253,9 +292,11 @@ def download_pdf():
         flash('Nothing selected.', 'warning')
         return redirect(url_for('labels.index'))
 
+    config = printer_config()
     source = request.form if request.method == 'POST' else request.args
     options = tape_printer.options_from_form(
-        source, rotate_default=printer_config()['rotate'])
+        source, rotate_default=config['rotate'],
+        size_default=config['size_mode'], tape_default=config['tape'])
     buffer = tape_printer.render_batch_pdf(
         labels, options, current_app.config['UPLOAD_FOLDER'])
     if buffer is None: