Phase F: Customer/Vendor Statements, Payment Terms Parser, Tax Rates

F1: GetCustomerStatementAsync/GetVendorStatementAsync on IFinancialReportService;
    StatementLineDto; CustomerStatementDto/VendorStatementDto; Statement action on
    CustomersController + VendorsController; Statement views + PDF download via
    StatementPdfHelper (QuestPDF); Statement button on Customer/Vendor Details pages.

F2: PaymentTermsParser static helper (CalculateDueDate, ParseEarlyPaymentDiscount);
    EarlyPaymentDiscountPercent/Days on Invoice entity; GetCustomerPaymentTerms AJAX
    endpoint on InvoicesController auto-populates Terms + due date on customer select;
    early payment discount notice on Invoice Create.

F3: TaxRate entity (Name/Rate/State/IsDefault/IsActive, tenant-filtered);
    IUnitOfWork.TaxRates + UnitOfWork + ApplicationDbContext; TaxRatesController
    (Index/Create/Edit/Delete/ToggleActive, CompanyAdminOnly); GetTaxRateForCustomer
    AJAX endpoint; Tax Rates in Settings gear menu.

Also fixes AddVendorCredits migration: VendorCreditApplications FKs changed from
CASCADE to NoAction to resolve SQL Server error 1785 (multiple cascade paths).
Migration: AddPaymentTermsAndTaxRates applied locally; 200/200 unit tests pass.

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

src/PowderCoating.Web/Controllers/CustomersController.cs

@@ -26,6 +26,7 @@ public class CustomersController : Controller
     private readonly ISubscriptionService _subscriptionService;
     private readonly ITenantContext _tenantContext;
     private readonly UserManager<ApplicationUser> _userManager;
+    private readonly IFinancialReportService _financialReports;
 
     public CustomersController(
         IUnitOfWork unitOfWork,
@@ -34,7 +35,8 @@ public class CustomersController : Controller
         INotificationService notificationService,
         ISubscriptionService subscriptionService,
         ITenantContext tenantContext,
-        UserManager<ApplicationUser> userManager)
+        UserManager<ApplicationUser> userManager,
+        IFinancialReportService financialReports)
     {
         _unitOfWork = unitOfWork;
         _mapper = mapper;
@@ -43,6 +45,7 @@ public class CustomersController : Controller
         _subscriptionService = subscriptionService;
         _tenantContext = tenantContext;
         _userManager = userManager;
+        _financialReports = financialReports;
     }
 
     /// <summary>
@@ -935,6 +938,30 @@ public class CustomersController : Controller
         return RedirectToAction(nameof(Details), new { id });
     }
 
+    /// <summary>
+    /// Displays or downloads a dated activity statement for a customer.
+    /// Pass <c>pdf=true</c> to download the QuestPDF version; otherwise renders the HTML view.
+    /// </summary>
+    [HttpGet]
+    public async Task<IActionResult> Statement(int id, DateTime? from, DateTime? to, bool pdf = false)
+    {
+        var companyId = _tenantContext.GetCurrentCompanyId() ?? 0;
+        var fromDate  = from ?? new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1);
+        var toDate    = to   ?? DateTime.Today;
+
+        var dto = await _financialReports.GetCustomerStatementAsync(companyId, id, fromDate, toDate);
+
+        if (pdf)
+        {
+            var bytes = StatementPdfHelper.Generate(
+                dto.CustomerName, dto.CompanyName, dto.CustomerAddress,
+                dto.From, dto.To, dto.OpeningBalance, dto.Lines, dto.ClosingBalance, isVendor: false);
+            return File(bytes, "application/pdf", $"Statement-{dto.CustomerName}-{toDate:yyyyMMdd}.pdf");
+        }
+
+        return View(dto);
+    }
+
     /// <summary>
     /// Generates the next sequential credit memo number in CM-YYMM-#### format.
     /// Uses <c>ignoreQueryFilters: true</c> when scanning all existing memos so that

src/PowderCoating.Web/Controllers/InvoicesController.cs

@@ -1851,6 +1851,54 @@ public class InvoicesController : Controller
         return $"{prefix}{(maxNum + 1):D4}";
     }
 
+    /// <summary>
+    /// Returns the customer's payment terms, derived due date, and early-payment discount info
+    /// for the Invoice Create form so JavaScript can auto-populate those fields on customer selection.
+    /// </summary>
+    [HttpGet]
+    public async Task<IActionResult> GetCustomerPaymentTerms(int customerId)
+    {
+        var customer = await _unitOfWork.Customers.GetByIdAsync(customerId);
+        if (customer == null) return NotFound();
+
+        var invoiceDate = DateTime.Today;
+        var dueDate     = PaymentTermsParser.CalculateDueDate(customer.PaymentTerms, invoiceDate);
+        var (discountPercent, discountDays) = PaymentTermsParser.ParseEarlyPaymentDiscount(customer.PaymentTerms);
+
+        return Json(new
+        {
+            paymentTerms               = customer.PaymentTerms,
+            dueDate                    = dueDate?.ToString("yyyy-MM-dd"),
+            earlyPaymentDiscountPercent = discountPercent,
+            earlyPaymentDiscountDays   = discountDays,
+            isTaxExempt                = customer.IsTaxExempt
+        });
+    }
+
+    /// <summary>
+    /// Returns the default active tax rate for the current company, or zero for tax-exempt customers.
+    /// Called by the Invoice Create form when the customer selection changes.
+    /// </summary>
+    [HttpGet]
+    public async Task<IActionResult> GetTaxRateForCustomer(int customerId)
+    {
+        var companyId = _tenantContext.GetCurrentCompanyId() ?? 0;
+        var customer  = await _unitOfWork.Customers.GetByIdAsync(customerId);
+        if (customer == null) return NotFound();
+
+        if (customer.IsTaxExempt)
+            return Json(new { taxPercent = 0m, taxRateName = (string?)null });
+
+        var defaultRate = await _unitOfWork.TaxRates
+            .FirstOrDefaultAsync(r => r.IsDefault && r.IsActive && !r.IsDeleted);
+
+        return Json(new
+        {
+            taxPercent  = defaultRate?.Rate ?? 0m,
+            taxRateName = defaultRate?.Name
+        });
+    }
+
     /// <summary>
     /// Populates ViewBag data used by both Create GET and Create POST (on validation failure re-display):
     /// — Active customer list for the customer dropdown.

src/PowderCoating.Web/Controllers/TaxRatesController.cs

@@ -0,0 +1,139 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using PowderCoating.Core.Entities;
+using PowderCoating.Core.Interfaces;
+using PowderCoating.Shared.Constants;
+
+namespace PowderCoating.Web.Controllers;
+
+/// <summary>
+/// Manages named tax rates used to pre-fill the tax percent field on invoices when a taxable
+/// customer is selected. Only one rate may be marked as default at a time; that default is
+/// auto-applied via the GetTaxRateForCustomer AJAX endpoint on the Invoice Create form.
+/// </summary>
+[Authorize(Policy = AppConstants.Policies.CompanyAdminOnly)]
+public class TaxRatesController : Controller
+{
+    private readonly IUnitOfWork _unitOfWork;
+    private readonly ITenantContext _tenantContext;
+    private readonly ILogger<TaxRatesController> _logger;
+
+    public TaxRatesController(
+        IUnitOfWork unitOfWork,
+        ITenantContext tenantContext,
+        ILogger<TaxRatesController> logger)
+    {
+        _unitOfWork = unitOfWork;
+        _tenantContext = tenantContext;
+        _logger = logger;
+    }
+
+    /// <summary>Lists all tax rates for the current company.</summary>
+    public async Task<IActionResult> Index()
+    {
+        var rates = await _unitOfWork.TaxRates.GetAllAsync();
+        return View(rates.OrderBy(r => r.Name).ToList());
+    }
+
+    [HttpGet]
+    public IActionResult Create() => View(new TaxRate());
+
+    /// <summary>Creates a new tax rate. Enforces that only one rate is the default.</summary>
+    [HttpPost]
+    [ValidateAntiForgeryToken]
+    public async Task<IActionResult> Create(TaxRate model)
+    {
+        if (!ModelState.IsValid) return View(model);
+
+        if (model.IsDefault)
+            await ClearOtherDefaultsAsync(0);
+
+        await _unitOfWork.TaxRates.AddAsync(model);
+        await _unitOfWork.CompleteAsync();
+
+        TempData["Success"] = $"Tax rate \"{model.Name}\" created.";
+        return RedirectToAction(nameof(Index));
+    }
+
+    [HttpGet]
+    public async Task<IActionResult> Edit(int id)
+    {
+        var rate = await _unitOfWork.TaxRates.GetByIdAsync(id);
+        if (rate == null) return NotFound();
+        return View(rate);
+    }
+
+    /// <summary>Updates an existing tax rate. Clears default flag on other rates when IsDefault is set.</summary>
+    [HttpPost]
+    [ValidateAntiForgeryToken]
+    public async Task<IActionResult> Edit(int id, TaxRate model)
+    {
+        if (id != model.Id) return BadRequest();
+        if (!ModelState.IsValid) return View(model);
+
+        var rate = await _unitOfWork.TaxRates.GetByIdAsync(id);
+        if (rate == null) return NotFound();
+
+        if (model.IsDefault && !rate.IsDefault)
+            await ClearOtherDefaultsAsync(id);
+
+        rate.Name        = model.Name;
+        rate.Rate        = model.Rate;
+        rate.State       = model.State;
+        rate.Description = model.Description;
+        rate.IsDefault   = model.IsDefault;
+        rate.IsActive    = model.IsActive;
+
+        await _unitOfWork.CompleteAsync();
+
+        TempData["Success"] = $"Tax rate \"{rate.Name}\" updated.";
+        return RedirectToAction(nameof(Index));
+    }
+
+    /// <summary>Toggles IsActive without a full page reload.</summary>
+    [HttpPost]
+    [ValidateAntiForgeryToken]
+    public async Task<IActionResult> ToggleActive(int id)
+    {
+        var rate = await _unitOfWork.TaxRates.GetByIdAsync(id);
+        if (rate == null) return NotFound();
+
+        rate.IsActive = !rate.IsActive;
+        if (!rate.IsActive) rate.IsDefault = false;
+
+        await _unitOfWork.CompleteAsync();
+        return RedirectToAction(nameof(Index));
+    }
+
+    /// <summary>Soft-deletes a tax rate. Blocked when the rate is currently the default.</summary>
+    [HttpPost]
+    [ValidateAntiForgeryToken]
+    public async Task<IActionResult> Delete(int id)
+    {
+        var rate = await _unitOfWork.TaxRates.GetByIdAsync(id);
+        if (rate == null) return NotFound();
+
+        if (rate.IsDefault)
+        {
+            TempData["Error"] = "Cannot delete the default tax rate. Set another rate as default first.";
+            return RedirectToAction(nameof(Index));
+        }
+
+        await _unitOfWork.TaxRates.SoftDeleteAsync(id);
+        await _unitOfWork.CompleteAsync();
+
+        TempData["Success"] = $"Tax rate \"{rate.Name}\" deleted.";
+        return RedirectToAction(nameof(Index));
+    }
+
+    /// <summary>
+    /// Clears IsDefault on all rates except the one with <paramref name="exceptId"/>.
+    /// Called before saving a newly-designated default to enforce the single-default invariant.
+    /// </summary>
+    private async Task ClearOtherDefaultsAsync(int exceptId)
+    {
+        var others = await _unitOfWork.TaxRates.FindAsync(r => r.IsDefault && r.Id != exceptId);
+        foreach (var r in others)
+            r.IsDefault = false;
+    }
+}

src/PowderCoating.Web/Controllers/VendorsController.cs

@@ -7,9 +7,11 @@ using Microsoft.AspNetCore.Mvc.Rendering;
 using Microsoft.EntityFrameworkCore;
 using PowderCoating.Application.DTOs.Common;
 using PowderCoating.Application.DTOs.Vendor;
+using PowderCoating.Application.Interfaces;
 using PowderCoating.Core.Entities;
 using PowderCoating.Core.Enums;
 using PowderCoating.Core.Interfaces;
+using PowderCoating.Web.Helpers;
 
 namespace PowderCoating.Web.Controllers;
 
@@ -27,17 +29,23 @@ public class VendorsController : Controller
     private readonly IMapper _mapper;
     private readonly UserManager<ApplicationUser> _userManager;
     private readonly ILogger<VendorsController> _logger;
+    private readonly IFinancialReportService _financialReports;
+    private readonly ITenantContext _tenantContext;
 
     public VendorsController(
         IUnitOfWork unitOfWork,
         IMapper mapper,
         UserManager<ApplicationUser> userManager,
-        ILogger<VendorsController> logger)
+        ILogger<VendorsController> logger,
+        IFinancialReportService financialReports,
+        ITenantContext tenantContext)
     {
         _unitOfWork = unitOfWork;
         _mapper = mapper;
         _userManager = userManager;
         _logger = logger;
+        _financialReports = financialReports;
+        _tenantContext = tenantContext;
     }
 
     /// <summary>
@@ -377,6 +385,29 @@ public class VendorsController : Controller
 
     /// <summary>
     /// Populates <c>ViewBag.ExpenseAccounts</c> with active Expense, Cost of Goods, and Asset accounts
+    /// <summary>
+    /// Displays or downloads a dated activity statement for a vendor.
+    /// </summary>
+    [HttpGet]
+    public async Task<IActionResult> Statement(int id, DateTime? from, DateTime? to, bool pdf = false)
+    {
+        var companyId = _tenantContext.GetCurrentCompanyId() ?? 0;
+        var fromDate  = from ?? new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1);
+        var toDate    = to   ?? DateTime.Today;
+
+        var dto = await _financialReports.GetVendorStatementAsync(companyId, id, fromDate, toDate);
+
+        if (pdf)
+        {
+            var bytes = StatementPdfHelper.Generate(
+                dto.VendorName, dto.CompanyName, null,
+                dto.From, dto.To, dto.OpeningBalance, dto.Lines, dto.ClosingBalance, isVendor: true);
+            return File(bytes, "application/pdf", $"Statement-{dto.VendorName}-{toDate:yyyyMMdd}.pdf");
+        }
+
+        return View(dto);
+    }
+
     /// for the vendor's default expense account dropdown. All three account types are included because
     /// vendor bills can legitimately be coded to COGS (powder, materials) or asset accounts (equipment
     /// purchases) in addition to regular operating expenses. A "— None —" placeholder is prepended so