Add merchant selection to EditTransaction page

Allow users to set or change the merchant for a transaction from the
EditTransaction page. Users can select from existing merchants or
create new ones on the fly.

Changes:
- Add merchant dropdown with existing merchants
- Support creating new merchants via custom input
- Update transaction merchant when saving
- Rename "Merchant Name" label to "Transaction Name" for clarity

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

MoneyMap/Pages/EditTransaction.cshtml

@@ -52,7 +52,7 @@
                     </div>
 
                     <div class="mb-3">
-                        <label class="form-label fw-bold">Merchant Name</label>
+                        <label class="form-label fw-bold">Transaction Name</label>
                         <div class="form-control-plaintext">@Model.Transaction.Name</div>
                     </div>
 
@@ -98,6 +98,29 @@
                         <span asp-validation-for="Transaction.Category" class="text-danger"></span>
                     </div>
 
+                    <div class="mb-3">
+                        <label class="form-label fw-bold">Merchant</label>
+                        <select class="form-select mb-2" id="merchantSelect" onchange="handleMerchantChange()">
+                            <option value="">(no merchant)</option>
+                            @foreach (var merchant in Model.AvailableMerchants)
+                            {
+                                <option value="@merchant.Id" selected="@(Model.Transaction.MerchantId == merchant.Id)">@merchant.Name</option>
+                            }
+                            <option value="__custom__" selected="@Model.UseCustomMerchant">+ Enter custom merchant</option>
+                        </select>
+
+                        <div id="customMerchantInput" style="display: @(Model.UseCustomMerchant ? "block" : "none")">
+                            <input asp-for="Transaction.MerchantName"
+                                   class="form-control"
+                                   placeholder="Enter merchant name" />
+                        </div>
+
+                        <input type="hidden" asp-for="Transaction.MerchantId" id="merchantHidden" />
+
+                        <div class="form-text">Select a merchant or create a new one</div>
+                        <span asp-validation-for="Transaction.MerchantId" class="text-danger"></span>
+                    </div>
+
                     <div class="mb-3">
                         <label asp-for="Transaction.Notes" class="form-label fw-bold">Notes</label>
                         <textarea asp-for="Transaction.Notes"
@@ -249,14 +272,32 @@
             }
         }
 
+        function handleMerchantChange() {
+            const select = document.getElementById('merchantSelect');
+            const customInput = document.getElementById('customMerchantInput');
+            const hiddenInput = document.getElementById('merchantHidden');
+            const merchantNameInput = document.querySelector('input[name="Transaction.MerchantName"]');
+
+            if (select.value === '__custom__') {
+                customInput.style.display = 'block';
+                hiddenInput.value = '';
+                merchantNameInput.value = '';
+                merchantNameInput.focus();
+            } else {
+                customInput.style.display = 'none';
+                hiddenInput.value = select.value;
+                merchantNameInput.value = '';
+            }
+        }
+
         // Update hidden field when custom input changes
         document.addEventListener('DOMContentLoaded', function() {
             const categoryInput = document.querySelector('input[name="Transaction.Category"]');
-            const select = document.getElementById('categorySelect');
+            const categorySelect = document.getElementById('categorySelect');
 
             if (categoryInput) {
                 categoryInput.addEventListener('input', function() {
-                    if (select.value === '__custom__') {
+                    if (categorySelect.value === '__custom__') {
                         // Keep custom selected when typing
                     }
                 });
@@ -264,6 +305,7 @@
 
             // Initialize on page load
             handleCategoryChange();
+            handleMerchantChange();
         });
     </script>
 }

MoneyMap/Pages/EditTransaction.cshtml.cs

@@ -33,7 +33,11 @@ namespace MoneyMap.Pages
         [BindProperty]
         public bool UseCustomCategory { get; set; }
 
+        [BindProperty]
+        public bool UseCustomMerchant { get; set; }
+
         public List<string> AvailableCategories { get; set; } = new();
+        public List<Merchant> AvailableMerchants { get; set; } = new();
         public List<ReceiptWithItems> Receipts { get; set; } = new();
 
         [TempData]
@@ -49,6 +53,7 @@ namespace MoneyMap.Pages
                     .ThenInclude(c => c!.Account)
                 .Include(t => t.Account)
                 .Include(t => t.TransferToAccount)
+                .Include(t => t.Merchant)
                 .Include(t => t.Receipts)
                     .ThenInclude(r => r.LineItems)
                 .FirstOrDefaultAsync(t => t.Id == id);
@@ -64,6 +69,7 @@ namespace MoneyMap.Pages
                 Memo = transaction.Memo,
                 Amount = transaction.Amount,
                 Category = transaction.Category ?? "",
+                MerchantId = transaction.MerchantId,
                 Notes = transaction.Notes ?? "",
                 CardLabel = transaction.PaymentMethodLabel,
                 AccountLabel = transaction.Card?.Account?.DisplayLabel ?? transaction.Account?.DisplayLabel ?? "None"
@@ -76,11 +82,16 @@ namespace MoneyMap.Pages
             }).ToList() ?? new List<ReceiptWithItems>();
 
             await LoadAvailableCategoriesAsync();
+            await LoadAvailableMerchantsAsync();
 
             // Check if current category exists in list
             UseCustomCategory = !string.IsNullOrWhiteSpace(Transaction.Category)
                 && !AvailableCategories.Contains(Transaction.Category);
 
+            // Check if current merchant exists in list
+            UseCustomMerchant = Transaction.MerchantId.HasValue
+                && !AvailableMerchants.Any(m => m.Id == Transaction.MerchantId.Value);
+
             return Page();
         }
 
@@ -92,6 +103,9 @@ namespace MoneyMap.Pages
                 ModelState.Remove("Transaction.Notes");
             }
 
+            // Remove MerchantName from validation (it's only used when creating new merchant)
+            ModelState.Remove("Transaction.MerchantName");
+
             if (!ModelState.IsValid)
             {
                 await LoadDataAsync();
@@ -111,6 +125,37 @@ namespace MoneyMap.Pages
                 ? ""
                 : Transaction.Notes.Trim();
 
+            // Update merchant
+            if (!string.IsNullOrWhiteSpace(Transaction.MerchantName))
+            {
+                // Create new merchant if custom name was entered
+                var merchantName = Transaction.MerchantName.Trim();
+                var existingMerchant = await _db.Merchants
+                    .FirstOrDefaultAsync(m => m.Name == merchantName);
+
+                if (existingMerchant != null)
+                {
+                    transaction.MerchantId = existingMerchant.Id;
+                }
+                else
+                {
+                    var newMerchant = new Merchant { Name = merchantName };
+                    _db.Merchants.Add(newMerchant);
+                    await _db.SaveChangesAsync();
+                    transaction.MerchantId = newMerchant.Id;
+                }
+            }
+            else if (Transaction.MerchantId.HasValue && Transaction.MerchantId.Value > 0)
+            {
+                // Existing merchant was selected
+                transaction.MerchantId = Transaction.MerchantId.Value;
+            }
+            else
+            {
+                // No merchant selected
+                transaction.MerchantId = null;
+            }
+
             await _db.SaveChangesAsync();
 
             SuccessMessage = "Transaction updated successfully!";
@@ -175,6 +220,7 @@ namespace MoneyMap.Pages
         private async Task LoadDataAsync()
         {
             await LoadAvailableCategoriesAsync();
+            await LoadAvailableMerchantsAsync();
 
             var transaction = await _db.Transactions
                 .Include(t => t.Receipts)
@@ -201,6 +247,13 @@ namespace MoneyMap.Pages
                 .ToListAsync();
         }
 
+        private async Task LoadAvailableMerchantsAsync()
+        {
+            AvailableMerchants = await _db.Merchants
+                .OrderBy(m => m.Name)
+                .ToListAsync();
+        }
+
         public class TransactionEditModel
         {
             public long Id { get; set; }
@@ -209,6 +262,8 @@ namespace MoneyMap.Pages
             public string Memo { get; set; } = "";
             public decimal Amount { get; set; }
             public string Category { get; set; } = "";
+            public int? MerchantId { get; set; }
+            public string? MerchantName { get; set; } = "";
             public string? Notes { get; set; } = "";
             public string CardLabel { get; set; } = "";
             public string AccountLabel { get; set; } = "";