feat: add date range option to create scan dialog

Adds a Rolling Window / Date Range toggle to the Parameters section.
Rolling Window mode (default) keeps the existing window_months stepper.
Date Range mode shows From/To date pickers and sends start_date/end_date
to the API instead of window_months. Validation covers empty dates,
past start dates, end ≤ start, and ranges exceeding 12 months.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

flight-comparator/frontend/src/pages/Scans.tsx

@@ -1,6 +1,6 @@
 import { useState } from 'react';
 import { useNavigate } from 'react-router-dom';
-import { Globe, PlaneTakeoff, Minus, Plus, ArrowRight, ArrowLeft } from 'lucide-react';
+import { Globe, PlaneTakeoff, Minus, Plus, ArrowRight, ArrowLeft, CalendarDays, CalendarRange } from 'lucide-react';
 import { scanApi } from '../api';
 import type { CreateScanRequest } from '../api';
 import AirportSearch from '../components/AirportSearch';
@@ -16,6 +16,8 @@ interface FormErrors {
   airports?: string;
   window_months?: string;
   adults?: string;
+  start_date?: string;
+  end_date?: string;
 }
 
 export default function Scans() {
@@ -34,6 +36,11 @@ export default function Scans() {
     adults: 1,
   });
 
+  // Window mode: rolling N months or specific date range
+  const [windowMode, setWindowMode] = useState<'window' | 'range'>('window');
+  const [startDate, setStartDate] = useState('');
+  const [endDate, setEndDate] = useState('');
+
   // Shared state
   const [selectedAirports, setSelectedAirports] = useState<string[]>([]);
   const [selectedOriginCountry, setSelectedOriginCountry] = useState('');
@@ -64,6 +71,26 @@ export default function Scans() {
       }
     }
 
+    if (windowMode === 'range') {
+      const today = new Date();
+      today.setHours(0, 0, 0, 0);
+      if (!startDate) {
+        next.start_date = 'Select a start date';
+      } else if (new Date(startDate) <= today) {
+        next.start_date = 'Start date must be in the future';
+      }
+      if (!endDate) {
+        next.end_date = 'Select an end date';
+      } else if (startDate && endDate <= startDate) {
+        next.end_date = 'End date must be after start date';
+      } else if (startDate && endDate) {
+        const s = new Date(startDate);
+        const e = new Date(endDate);
+        const months = (e.getFullYear() - s.getFullYear()) * 12 + (e.getMonth() - s.getMonth());
+        if (months > 12) next.end_date = 'Date range cannot exceed 12 months';
+      }
+    }
+
     setErrors(next);
     return Object.keys(next).length === 0;
   };
@@ -76,22 +103,26 @@ export default function Scans() {
     try {
       let requestData: CreateScanRequest;
 
+      const windowParams = windowMode === 'range'
+        ? { start_date: startDate, end_date: endDate }
+        : { window_months: formData.window_months };
+
       if (scanMode === 'reverse') {
         requestData = {
           scan_mode: 'reverse',
           origin: selectedOriginCountry,
           destinations: selectedAirports,
-          window_months: formData.window_months,
           seat_class: formData.seat_class,
           adults: formData.adults,
+          ...windowParams,
         };
       } else {
         requestData = {
           scan_mode: 'forward',
           origin: formData.origin,
-          window_months: formData.window_months,
           seat_class: formData.seat_class,
           adults: formData.adults,
+          ...windowParams,
           ...(destinationMode === 'country'
             ? { country: formData.country }
             : { destinations: selectedAirports }),
@@ -124,6 +155,16 @@ export default function Scans() {
       ? 'border-error focus:border-error focus:ring-2 focus:ring-error/20'
       : 'border-outline focus:border-primary focus:ring-2 focus:ring-primary/20');
 
+  const tomorrowStr = (() => {
+    const d = new Date();
+    d.setDate(d.getDate() + 1);
+    return d.toISOString().split('T')[0];
+  })();
+
+  const minEndDate = startDate
+    ? (() => { const d = new Date(startDate); d.setDate(d.getDate() + 1); return d.toISOString().split('T')[0]; })()
+    : tomorrowStr;
+
   return (
     <>
       <form onSubmit={handleSubmit} className="space-y-4 max-w-2xl">
@@ -331,12 +372,30 @@ export default function Scans() {
             Parameters
           </p>
 
-          <div className="grid grid-cols-1 sm:grid-cols-2 gap-4">
-            {/* Search Window */}
-            <div>
+          {/* Search Window toggle */}
+          <div className="mb-4">
             <label className="block text-sm font-medium text-on-surface-variant mb-1.5">
               Search Window
             </label>
+            <SegmentedButton
+              options={[
+                { value: 'window', label: 'Rolling Window', icon: CalendarDays },
+                { value: 'range',  label: 'Date Range',     icon: CalendarRange },
+              ]}
+              value={windowMode}
+              onChange={(v) => {
+                setWindowMode(v as 'window' | 'range');
+                setStartDate('');
+                setEndDate('');
+                setErrors(prev => ({ ...prev, start_date: undefined, end_date: undefined }));
+              }}
+            />
+          </div>
+
+          {windowMode === 'window' ? (
+            <div className="grid grid-cols-1 sm:grid-cols-2 gap-4">
+              {/* Stepper */}
+              <div>
                 <div className="flex items-center gap-2">
                   <button
                     type="button"
@@ -378,6 +437,75 @@ export default function Scans() {
                 </select>
               </div>
             </div>
+          ) : (
+            <>
+              {/* Date pickers */}
+              <div className="grid grid-cols-1 sm:grid-cols-2 gap-4">
+                <div>
+                  <label className="block text-sm font-medium text-on-surface-variant mb-1.5">
+                    From
+                  </label>
+                  <input
+                    type="date"
+                    value={startDate}
+                    min={tomorrowStr}
+                    onChange={(e) => {
+                      setStartDate(e.target.value);
+                      if (errors.start_date) setErrors(prev => ({ ...prev, start_date: undefined }));
+                    }}
+                    className={inputCls(!!errors.start_date)}
+                  />
+                  {errors.start_date ? (
+                    <p className="mt-1 text-xs text-error">{errors.start_date}</p>
+                  ) : (
+                    <p className="mt-1 text-xs text-on-surface-variant">First date to scan</p>
+                  )}
+                </div>
+                <div>
+                  <label className="block text-sm font-medium text-on-surface-variant mb-1.5">
+                    To
+                  </label>
+                  <input
+                    type="date"
+                    value={endDate}
+                    min={minEndDate}
+                    onChange={(e) => {
+                      setEndDate(e.target.value);
+                      if (errors.end_date) setErrors(prev => ({ ...prev, end_date: undefined }));
+                    }}
+                    className={inputCls(!!errors.end_date)}
+                  />
+                  {errors.end_date ? (
+                    <p className="mt-1 text-xs text-error">{errors.end_date}</p>
+                  ) : (
+                    <p className="mt-1 text-xs text-on-surface-variant">Last date to scan</p>
+                  )}
+                </div>
+              </div>
+              <p className="mt-2 text-xs text-on-surface-variant">
+                Flights will be sampled on the 15th of each month within this range
+              </p>
+
+              {/* Seat Class */}
+              <div className="mt-4 grid grid-cols-1 sm:grid-cols-2 gap-4">
+                <div>
+                  <label className="block text-sm font-medium text-on-surface-variant mb-1.5">
+                    Seat Class
+                  </label>
+                  <select
+                    value={formData.seat_class}
+                    onChange={(e) => setFormData(prev => ({ ...prev, seat_class: e.target.value as 'economy' | 'premium' | 'business' | 'first' }))}
+                    className={inputCls()}
+                  >
+                    <option value="economy">Economy</option>
+                    <option value="premium">Premium Economy</option>
+                    <option value="business">Business</option>
+                    <option value="first">First Class</option>
+                  </select>
+                </div>
+              </div>
+            </>
+          )}
 
           {/* Adults — full width below */}
           <div className="mt-4">