using AutoMapper;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using PowderCoating.Application.DTOs.Common;
using PowderCoating.Application.DTOs.PurchaseOrder;
using PowderCoating.Application.Interfaces;
using PowderCoating.Core.Entities;
using PowderCoating.Core.Enums;
using PowderCoating.Core.Interfaces;
using PowderCoating.Core.Interfaces.Repositories;
using PowderCoating.Shared.Constants;
using PowderCoating.Web.Helpers;

namespace PowderCoating.Web.Controllers;

[Authorize(Policy = AppConstants.Policies.CanManagePurchaseOrders)]
public class PurchaseOrdersController : Controller
{
    private readonly IUnitOfWork _unitOfWork;
    private readonly IMapper _mapper;
    private readonly UserManager<ApplicationUser> _userManager;
    private readonly ILogger<PurchaseOrdersController> _logger;
    private readonly IPdfService _pdfService;
    private readonly ICompanyLogoService _logoService;

    public PurchaseOrdersController(
        IUnitOfWork unitOfWork,
        IMapper mapper,
        UserManager<ApplicationUser> userManager,
        ILogger<PurchaseOrdersController> logger,
        IPdfService pdfService,
        ICompanyLogoService logoService)
    {
        _unitOfWork = unitOfWork;
        _mapper = mapper;
        _userManager = userManager;
        _logger = logger;
        _pdfService = pdfService;
        _logoService = logoService;
    }

    // -----------------------------------------------------------------------
    // GET: /PurchaseOrders
    // -----------------------------------------------------------------------
    /// <summary>
    /// Lists purchase orders with server-side filtering, sorting, and pagination. Summary KPI
    /// cards (total count, open count, committed value, overdue count) are computed from a
    /// lightweight projection of all non-deleted POs for the company — independent of the current
    /// filter — so the cards always reflect the global state rather than the filtered subset.
    /// Cancelled POs are excluded from committed value because they carry no financial obligation.
    /// </summary>
    public async Task<IActionResult> Index(
        string? searchTerm,
        PurchaseOrderStatus? statusFilter,
        int? vendorId,
        DateTime? dateFrom,
        DateTime? dateTo,
        string? sortColumn,
        string sortDirection = "desc",
        int pageNumber = 1,
        int pageSize = 25)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        pageSize = Math.Clamp(pageSize, 10, 100);
        pageNumber = Math.Max(1, pageNumber);

        var (items, totalCount) = await _unitOfWork.PurchaseOrders.GetPagedAsync(
            currentUser.CompanyId, pageNumber, pageSize,
            statusFilter, vendorId, dateFrom, dateTo,
            searchTerm, sortColumn, sortDirection);

        var dtos = _mapper.Map<List<PurchaseOrderListDto>>(items);

        var result = new PagedResult<PurchaseOrderListDto>
        {
            Items = dtos,
            TotalCount = totalCount,
            PageNumber = pageNumber,
            PageSize = pageSize
        };

        // Stats (server-side projection — only three columns fetched)
        var stats = await _unitOfWork.PurchaseOrders.GetStatsAsync(currentUser.CompanyId);
        ViewBag.TotalCount = stats.TotalCount;
        ViewBag.OpenCount = stats.OpenCount;
        ViewBag.CommittedValue = stats.CommittedValue;
        ViewBag.OverdueCount = stats.OverdueCount;

        await PopulateVendorFilterDropdownAsync(currentUser.CompanyId);
        ViewBag.SearchTerm = searchTerm;
        ViewBag.StatusFilter = statusFilter;
        ViewBag.VendorId = vendorId;
        ViewBag.DateFrom = dateFrom?.ToString("yyyy-MM-dd");
        ViewBag.DateTo = dateTo?.ToString("yyyy-MM-dd");
        ViewBag.SortColumn = sortColumn ?? "orderdate";
        ViewBag.SortDirection = sortDirection;

        return View(result);
    }

    // -----------------------------------------------------------------------
    // GET: /PurchaseOrders/Details/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Displays full PO detail including vendor info, linked bill (if one has been created), and
    /// all non-deleted line items with their associated inventory items.
    /// </summary>
    public async Task<IActionResult> Details(int id)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        var po = await _unitOfWork.PurchaseOrders.LoadForViewAsync(id, currentUser.CompanyId);
        if (po == null) return NotFound();

        var dto = _mapper.Map<PurchaseOrderDto>(po);
        return View(dto);
    }

    // -----------------------------------------------------------------------
    // GET: /PurchaseOrders/Create
    // -----------------------------------------------------------------------
    /// <summary>
    /// Returns the blank PO creation form with today's date pre-filled. Vendors and inventory
    /// items are loaded via <see cref="PopulateCreateViewBagAsync"/> and serialised to JSON so
    /// the dynamic line-item UI can look up unit-of-measure and last purchase price without
    /// additional round trips.
    /// </summary>
    public async Task<IActionResult> Create()
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        await PopulateCreateViewBagAsync(currentUser.CompanyId);
        return View(new CreatePurchaseOrderDto { OrderDate = DateTime.Today });
    }

    // -----------------------------------------------------------------------
    // POST: /PurchaseOrders/Create
    // -----------------------------------------------------------------------
    /// <summary>
    /// Persists a new purchase order in <c>Draft</c> status. POs start as drafts so purchasing
    /// staff can review before formally submitting to the vendor via <see cref="Submit"/>.
    /// Custom line items (those without a linked inventory item) must have an explicit description
    /// because the item name cannot be inferred from inventory. LineTotal and PO totals are
    /// computed server-side from quantity × unit cost to prevent client-side manipulation.
    /// </summary>
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Create(CreatePurchaseOrderDto dto)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        if (!dto.Items.Any())
            ModelState.AddModelError("", "At least one line item is required.");

        foreach (var item in dto.Items.Where(i => !i.InventoryItemId.HasValue))
        {
            if (string.IsNullOrWhiteSpace(item.Description))
                ModelState.AddModelError("", "Custom line items require a description.");
        }

        if (!ModelState.IsValid)
        {
            await PopulateCreateViewBagAsync(currentUser.CompanyId);
            return View(dto);
        }

        try
        {
            var poNumber = await GeneratePoNumberAsync(currentUser.CompanyId);

            var po = _mapper.Map<PurchaseOrder>(dto);
            po.PoNumber = poNumber;
            po.Status = PurchaseOrderStatus.Draft;
            po.CompanyId = currentUser.CompanyId;

            foreach (var itemDto in dto.Items)
            {
                var item = _mapper.Map<PurchaseOrderItem>(itemDto);
                item.LineTotal = item.QuantityOrdered * item.UnitCost;
                item.CompanyId = currentUser.CompanyId;
                po.Items.Add(item);
            }

            po.SubTotal = po.Items.Sum(i => i.LineTotal);
            po.TotalAmount = po.SubTotal + po.ShippingCost;

            await _unitOfWork.PurchaseOrders.AddAsync(po);
            await _unitOfWork.CompleteAsync();

            this.ToastSuccess($"Purchase Order {po.PoNumber} created.");
            return RedirectToAction(nameof(Details), new { id = po.Id });
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error creating purchase order");
            ModelState.AddModelError("", "An error occurred while creating the purchase order.");
            await PopulateCreateViewBagAsync(currentUser.CompanyId);
            return View(dto);
        }
    }

    // -----------------------------------------------------------------------
    // GET: /PurchaseOrders/Edit/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Returns the edit form for a draft PO. Only <c>Draft</c> POs are editable; once submitted
    /// the vendor may have already received and acted on the order so changes would cause
    /// discrepancies between what the vendor was told and what is recorded internally.
    /// </summary>
    public async Task<IActionResult> Edit(int id)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        var po = await _unitOfWork.PurchaseOrders.LoadForViewAsync(id, currentUser.CompanyId);
        if (po == null) return NotFound();
        if (po.Status != PurchaseOrderStatus.Draft)
        {
            TempData["Error"] = "Only Draft purchase orders can be edited.";
            return RedirectToAction(nameof(Details), new { id });
        }

        var dto = new UpdatePurchaseOrderDto
        {
            VendorId = po.VendorId,
            OrderDate = po.OrderDate,
            ExpectedDeliveryDate = po.ExpectedDeliveryDate,
            ShippingCost = po.ShippingCost,
            Notes = po.Notes,
            InternalNotes = po.InternalNotes,
            Items = po.Items.Select(i => new CreatePurchaseOrderItemDto
            {
                InventoryItemId = i.InventoryItemId,
                Description = i.Description,
                UnitOfMeasure = i.UnitOfMeasure,
                QuantityOrdered = i.QuantityOrdered,
                UnitCost = i.UnitCost,
                Notes = i.Notes
            }).ToList()
        };

        await PopulateCreateViewBagAsync(currentUser.CompanyId);
        ViewBag.PoId = id;
        ViewBag.PoNumber = po.PoNumber;
        return View(dto);
    }

    // -----------------------------------------------------------------------
    // POST: /PurchaseOrders/Edit/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Saves PO edits using a soft-delete + re-insert pattern for line items so that previously
    /// submitted item records are preserved in the database for audit purposes. Active item
    /// subtotals and shipping are recomputed after the new items are added to keep
    /// <c>SubTotal</c> and <c>TotalAmount</c> consistent.
    /// </summary>
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Edit(int id, UpdatePurchaseOrderDto dto)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        var po = await _unitOfWork.PurchaseOrders.LoadForViewAsync(id, currentUser.CompanyId);
        if (po == null) return NotFound();
        if (po.Status != PurchaseOrderStatus.Draft)
        {
            TempData["Error"] = "Only Draft purchase orders can be edited.";
            return RedirectToAction(nameof(Details), new { id });
        }

        if (!dto.Items.Any())
            ModelState.AddModelError("", "At least one line item is required.");

        foreach (var item in dto.Items.Where(i => !i.InventoryItemId.HasValue))
        {
            if (string.IsNullOrWhiteSpace(item.Description))
                ModelState.AddModelError("", "Custom line items require a description.");
        }

        if (!ModelState.IsValid)
        {
            await PopulateCreateViewBagAsync(currentUser.CompanyId);
            ViewBag.PoId = id;
            ViewBag.PoNumber = po.PoNumber;
            return View(dto);
        }

        try
        {
            _mapper.Map(dto, po);

            // Soft-delete existing items then add fresh ones
            foreach (var existing in po.Items)
            {
                existing.IsDeleted = true;
                existing.UpdatedAt = DateTime.UtcNow;
            }

            foreach (var itemDto in dto.Items)
            {
                var item = _mapper.Map<PurchaseOrderItem>(itemDto);
                item.LineTotal = item.QuantityOrdered * item.UnitCost;
                item.CompanyId = currentUser.CompanyId;
                po.Items.Add(item);
            }

            var activeItems = po.Items.Where(i => !i.IsDeleted).ToList();
            po.SubTotal = activeItems.Sum(i => i.LineTotal);
            po.TotalAmount = po.SubTotal + po.ShippingCost;
            po.UpdatedAt = DateTime.UtcNow;

            await _unitOfWork.CompleteAsync();

            this.ToastSuccess($"Purchase Order {po.PoNumber} updated.");
            return RedirectToAction(nameof(Details), new { id });
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error updating purchase order {PoId}", id);
            ModelState.AddModelError("", "An error occurred while updating the purchase order.");
            await PopulateCreateViewBagAsync(currentUser.CompanyId);
            ViewBag.PoId = id;
            ViewBag.PoNumber = po.PoNumber;
            return View(dto);
        }
    }

    // -----------------------------------------------------------------------
    // GET: /PurchaseOrders/Delete/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Returns the delete confirmation page for a PO. Only <c>Draft</c> or <c>Cancelled</c> POs
    /// may be deleted; submitted/received POs have inventory and accounting implications that
    /// prevent safe removal.
    /// </summary>
    public async Task<IActionResult> Delete(int id)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        var po = await _unitOfWork.PurchaseOrders.LoadForViewAsync(id, currentUser.CompanyId);
        if (po == null) return NotFound();

        if (po.Status != PurchaseOrderStatus.Draft && po.Status != PurchaseOrderStatus.Cancelled)
        {
            TempData["Error"] = "Only Draft or Cancelled purchase orders can be deleted.";
            return RedirectToAction(nameof(Details), new { id });
        }

        return View(_mapper.Map<PurchaseOrderListDto>(po));
    }

    // -----------------------------------------------------------------------
    // POST: /PurchaseOrders/Delete/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Soft-deletes a draft or cancelled PO. The PO number is preserved in the database (via
    /// soft delete rather than physical removal) so the sequence cannot be reused and the number
    /// gap is explainable in audit logs.
    /// </summary>
    [HttpPost, ActionName("Delete")]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> DeleteConfirmed(int id)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        var po = await _unitOfWork.PurchaseOrders.GetByIdAsync(id);
        if (po == null || po.CompanyId != currentUser.CompanyId) return NotFound();

        if (po.Status != PurchaseOrderStatus.Draft && po.Status != PurchaseOrderStatus.Cancelled)
        {
            TempData["Error"] = "Only Draft or Cancelled purchase orders can be deleted.";
            return RedirectToAction(nameof(Details), new { id });
        }

        try
        {
            await _unitOfWork.PurchaseOrders.SoftDeleteAsync(id);
            await _unitOfWork.CompleteAsync();

            this.ToastSuccess($"Purchase Order {po.PoNumber} deleted.");
            return RedirectToAction(nameof(Index));
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error deleting purchase order {PoId}", id);
            TempData["Error"] = "An error occurred while deleting the purchase order.";
            return RedirectToAction(nameof(Details), new { id });
        }
    }

    // -----------------------------------------------------------------------
    // POST: /PurchaseOrders/Submit/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Advances a PO from <c>Draft</c> to <c>Submitted</c>, signalling that the order has been
    /// formally sent to the vendor. A PO with no line items cannot be submitted because the
    /// vendor would have nothing to fulfil. Submitted POs become read-only; any changes require
    /// cancelling and creating a new PO (or discussing an amendment with the vendor off-system).
    /// </summary>
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Submit(int id)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        var po = await _unitOfWork.PurchaseOrders.LoadForViewAsync(id, currentUser.CompanyId);
        if (po == null) return NotFound();

        if (po.Status != PurchaseOrderStatus.Draft)
        {
            TempData["Error"] = "Only Draft purchase orders can be submitted.";
            return RedirectToAction(nameof(Details), new { id });
        }

        if (!po.Items.Any())
        {
            TempData["Error"] = "Cannot submit a purchase order with no line items.";
            return RedirectToAction(nameof(Details), new { id });
        }

        po.Status = PurchaseOrderStatus.Submitted;
        po.UpdatedAt = DateTime.UtcNow;
        await _unitOfWork.CompleteAsync();

        this.ToastSuccess($"Purchase Order {po.PoNumber} submitted.");
        return RedirectToAction(nameof(Details), new { id });
    }

    // -----------------------------------------------------------------------
    // POST: /PurchaseOrders/Cancel/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Cancels a PO at any status except <c>Received</c>. Received POs cannot be cancelled
    /// because the goods have already entered inventory and a vendor bill may exist; undoing
    /// receipt would require separate inventory adjustments and bill voids. Cancelled POs are
    /// excluded from committed-spend reporting but remain in the database for audit purposes.
    /// </summary>
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Cancel(int id)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        var po = await _unitOfWork.PurchaseOrders.GetByIdAsync(id);
        if (po == null || po.CompanyId != currentUser.CompanyId) return NotFound();

        if (po.Status == PurchaseOrderStatus.Received)
        {
            TempData["Error"] = "Received purchase orders cannot be cancelled.";
            return RedirectToAction(nameof(Details), new { id });
        }

        po.Status = PurchaseOrderStatus.Cancelled;
        po.UpdatedAt = DateTime.UtcNow;
        await _unitOfWork.CompleteAsync();

        this.ToastSuccess($"Purchase Order {po.PoNumber} cancelled.");
        return RedirectToAction(nameof(Details), new { id });
    }

    // -----------------------------------------------------------------------
    // GET: /PurchaseOrders/Receive/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Returns the goods-receipt form pre-filled with each line item's remaining-to-receive
    /// quantity (ordered minus already received). Only <c>Submitted</c> or
    /// <c>PartiallyReceived</c> POs can accept receipts — <c>Draft</c> POs have not been sent
    /// and <c>Received</c> POs are already complete.
    /// </summary>
    public async Task<IActionResult> Receive(int id)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        var po = await _unitOfWork.PurchaseOrders.LoadForViewAsync(id, currentUser.CompanyId);

        if (po == null) return NotFound();

        if (po.Status != PurchaseOrderStatus.Submitted && po.Status != PurchaseOrderStatus.PartiallyReceived)
        {
            TempData["Error"] = "Only Submitted or Partially Received purchase orders can receive goods.";
            return RedirectToAction(nameof(Details), new { id });
        }

        var dto = new ReceivePurchaseOrderDto
        {
            ReceivedDate = DateTime.Today,
            Items = po.Items.Select(i => new ReceiveItemDto
            {
                PurchaseOrderItemId = i.Id,
                InventoryItemId = i.InventoryItemId,
                ItemName = i.InventoryItem?.Name ?? i.Description ?? string.Empty,
                ItemSKU = i.InventoryItem?.SKU ?? string.Empty,
                UnitOfMeasure = i.InventoryItem?.UnitOfMeasure ?? i.UnitOfMeasure ?? string.Empty,
                QuantityOrdered = i.QuantityOrdered,
                QuantityAlreadyReceived = i.QuantityReceived,
                QuantityRemaining = Math.Max(0, i.QuantityOrdered - i.QuantityReceived),
                QuantityToReceive = Math.Max(0, i.QuantityOrdered - i.QuantityReceived)
            }).ToList()
        };

        ViewBag.PoNumber = po.PoNumber;
        ViewBag.VendorName = po.Vendor?.CompanyName;
        ViewBag.OrderDate = po.OrderDate;
        ViewBag.PoId = id;
        return View(dto);
    }

    // -----------------------------------------------------------------------
    // POST: /PurchaseOrders/Receive/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Records the physical receipt of goods and updates inventory stock levels atomically inside
    /// a database transaction. For each linked inventory item the weighted-average cost is
    /// recalculated as <c>(existingQty * existingAvgCost + receivedQty * poUnitCost) / newTotalQty</c>
    /// so that the running average reflects the blended acquisition cost over multiple purchases.
    /// An <see cref="InventoryTransaction"/> of type <c>Purchase</c> is written for each item
    /// received to provide a complete stock ledger. Quantities are clamped to the remaining
    /// receivable amount to prevent over-receipt. PO status advances to <c>PartiallyReceived</c>
    /// or <c>Received</c> based on whether all items have been fully received.
    /// </summary>
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Receive(int id, ReceivePurchaseOrderDto dto)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        var po = await _unitOfWork.PurchaseOrders.LoadForViewAsync(id, currentUser.CompanyId);

        if (po == null) return NotFound();

        if (po.Status != PurchaseOrderStatus.Submitted && po.Status != PurchaseOrderStatus.PartiallyReceived)
        {
            TempData["Error"] = "Only Submitted or Partially Received purchase orders can receive goods.";
            return RedirectToAction(nameof(Details), new { id });
        }

        var hasAnyQuantity = dto.Items.Any(i => i.QuantityToReceive > 0);
        if (!hasAnyQuantity)
        {
            TempData["Error"] = "Enter a quantity greater than 0 for at least one item.";
            ViewBag.PoNumber = po.PoNumber;
            ViewBag.VendorName = po.Vendor?.CompanyName;
            ViewBag.OrderDate = po.OrderDate;
            ViewBag.PoId = id;
            return View(dto);
        }

        var allReceived = false;
        try
        {
        await _unitOfWork.ExecuteInTransactionAsync(async () =>
        {
            foreach (var receiveDto in dto.Items.Where(i => i.QuantityToReceive > 0))
            {
                var poItem = po.Items.FirstOrDefault(i => i.Id == receiveDto.PurchaseOrderItemId);
                if (poItem == null) continue;

                // Clamp to remaining quantity
                var maxReceivable = poItem.QuantityOrdered - poItem.QuantityReceived;
                var qtyToReceive = Math.Min(receiveDto.QuantityToReceive, maxReceivable);
                if (qtyToReceive <= 0) continue;

                // Only update inventory for linked inventory items
                if (poItem.InventoryItemId.HasValue)
                {
                    var inventoryItem = poItem.InventoryItem;
                    if (inventoryItem != null)
                    {
                        // Recalculate weighted average cost
                        var newTotalQty = inventoryItem.QuantityOnHand + qtyToReceive;
                        if (newTotalQty > 0)
                        {
                            inventoryItem.AverageCost = Math.Round(
                                (inventoryItem.QuantityOnHand * inventoryItem.AverageCost + qtyToReceive * poItem.UnitCost)
                                / newTotalQty, 4);
                        }

                        inventoryItem.QuantityOnHand += qtyToReceive;
                        inventoryItem.LastPurchasePrice = poItem.UnitCost;
                        inventoryItem.LastPurchaseDate = dto.ReceivedDate;

                        var transaction = new InventoryTransaction
                        {
                            InventoryItemId = poItem.InventoryItemId.Value,
                            TransactionType = InventoryTransactionType.Purchase,
                            Quantity = qtyToReceive,
                            UnitCost = poItem.UnitCost,
                            TotalCost = qtyToReceive * poItem.UnitCost,
                            TransactionDate = dto.ReceivedDate,
                            Reference = po.PoNumber,
                            Notes = dto.Notes,
                            BalanceAfter = inventoryItem.QuantityOnHand,
                            PurchaseOrderId = po.Id,
                            CompanyId = po.CompanyId
                        };

                        await _unitOfWork.InventoryTransactions.AddAsync(transaction);
                    }
                }

                poItem.QuantityReceived += qtyToReceive;
                poItem.LineTotal = poItem.QuantityOrdered * poItem.UnitCost;
                poItem.UpdatedAt = DateTime.UtcNow;
            }

            // Recalculate PO totals and status
            var activeItems = po.Items.Where(i => !i.IsDeleted).ToList();
            po.SubTotal = activeItems.Sum(i => i.LineTotal);
            po.TotalAmount = po.SubTotal + po.ShippingCost;

            allReceived = activeItems.All(i => i.QuantityReceived >= i.QuantityOrdered);
            var anyReceived = activeItems.Any(i => i.QuantityReceived > 0);

            if (allReceived)
            {
                po.Status = PurchaseOrderStatus.Received;
                po.ReceivedDate = dto.ReceivedDate;
            }
            else if (anyReceived)
            {
                po.Status = PurchaseOrderStatus.PartiallyReceived;
            }

            po.UpdatedAt = DateTime.UtcNow;

        }); // end ExecuteInTransactionAsync — SaveChangesAsync called automatically before commit

            this.ToastSuccess(allReceived
                ? $"All items received for {po.PoNumber}."
                : $"Partial receipt recorded for {po.PoNumber}.");

            return RedirectToAction(nameof(Details), new { id });
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error receiving goods for PO {PoId}", id);
            TempData["Error"] = "An error occurred while recording the receipt.";
            return RedirectToAction(nameof(Receive), new { id });
        }
    }

    // -----------------------------------------------------------------------
    // GET: /PurchaseOrders/DownloadPdf/5
    // -----------------------------------------------------------------------
    /// <summary>
    /// Generates and streams a PDF version of the PO suitable for emailing to the vendor.
    /// Company logo and contact details are embedded in the PDF header using the tenant's
    /// stored logo bytes and <c>CompanyInfoDto</c>. PDF generation is delegated to
    /// <see cref="IPdfService.GeneratePurchaseOrderPdfAsync"/>.
    /// </summary>
    public async Task<IActionResult> DownloadPdf(int id)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        try
        {
            var po = await _unitOfWork.PurchaseOrders.LoadForViewAsync(id, currentUser.CompanyId);

            if (po == null) return NotFound();

            var dto = _mapper.Map<PurchaseOrderDto>(po);

            var company  = await _unitOfWork.Companies.GetByIdAsync(currentUser.CompanyId);
            var companyInfo = new Application.DTOs.Company.CompanyInfoDto
            {
                CompanyName          = company?.CompanyName ?? string.Empty,
                Phone                = company?.Phone,
                Address              = company?.Address,
                City                 = company?.City,
                State                = company?.State,
                ZipCode              = company?.ZipCode,
                PrimaryContactEmail  = company?.PrimaryContactEmail
            };

            var (logoData, logoContentType) = await LoadCompanyLogoAsync(company);
            var pdfBytes = await _pdfService.GeneratePurchaseOrderPdfAsync(
                dto, logoData, logoContentType, companyInfo);

            return File(pdfBytes, "application/pdf", $"{po.PoNumber}.pdf");
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error generating PDF for PO {Id}", id);
            TempData["Error"] = "An error occurred while generating the PDF.";
            return RedirectToAction(nameof(Details), new { id });
        }
    }

    // -----------------------------------------------------------------------
    // GET: /PurchaseOrders/CreateFromLowStock
    // -----------------------------------------------------------------------
    /// <summary>
    /// Shortcut that pre-populates a new PO from the low-stock inventory alert list. Only items
    /// with a <c>PrimaryVendorId</c> are eligible because the vendor field is required on a PO.
    /// Items are grouped by vendor so the user can choose which vendor's low-stock items to order
    /// in a single PO (you cannot mix vendors on one PO). When a vendor is selected the DTO is
    /// pre-filled with each low-stock item's <c>ReorderQuantity</c> (or 1 if not set) and the
    /// last purchase price as the default unit cost, saving manual data entry.
    /// </summary>
    public async Task<IActionResult> CreateFromLowStock(int? vendorId)
    {
        var currentUser = await _userManager.GetUserAsync(User);
        if (currentUser == null) return Unauthorized();

        // Find low-stock items that have a primary vendor
        var lowStockItems = (await _unitOfWork.InventoryItems.FindAsync(
            i => i.IsActive && i.CompanyId == currentUser.CompanyId &&
                 i.PrimaryVendorId != null && i.QuantityOnHand <= i.ReorderPoint,
            false,
            i => i.PrimaryVendor!))
            .ToList();

        if (!lowStockItems.Any())
        {
            TempData["Info"] = "No low-stock items with a primary vendor were found.";
            return RedirectToAction(nameof(Create));
        }

        // Group by vendor for the selection step
        var vendorGroups = lowStockItems
            .GroupBy(i => new { i.PrimaryVendorId, VendorName = i.PrimaryVendor?.CompanyName ?? "Unknown" })
            .Select(g => new
            {
                VendorId = g.Key.PrimaryVendorId!.Value,
                VendorName = g.Key.VendorName,
                ItemCount = g.Count()
            })
            .OrderBy(v => v.VendorName)
            .ToList();

        // If no vendor selected yet, show selection page
        if (!vendorId.HasValue)
        {
            ViewBag.VendorGroups = vendorGroups;
            return View("SelectLowStockVendor");
        }

        // Pre-populate a Create form for the selected vendor
        var vendorItems = lowStockItems.Where(i => i.PrimaryVendorId == vendorId.Value).ToList();
        if (!vendorItems.Any())
        {
            TempData["Info"] = "No low-stock items found for that vendor.";
            return RedirectToAction(nameof(CreateFromLowStock));
        }

        var dto = new CreatePurchaseOrderDto
        {
            VendorId = vendorId.Value,
            OrderDate = DateTime.Today,
            Items = vendorItems.Select(i => new CreatePurchaseOrderItemDto
            {
                InventoryItemId = i.Id,
                QuantityOrdered = i.ReorderQuantity > 0 ? i.ReorderQuantity : 1,
                UnitCost = i.LastPurchasePrice > 0 ? i.LastPurchasePrice : i.UnitCost
            }).ToList()
        };

        await PopulateCreateViewBagAsync(currentUser.CompanyId);
        ViewBag.FromLowStock = true;
        return View("Create", dto);
    }

    // -----------------------------------------------------------------------
    // Private helpers
    // -----------------------------------------------------------------------

    /// <summary>
    /// Generates a sequential PO number in the format <c>PO-YYMM-####</c>. Uses
    /// <c>IgnoreQueryFilters()</c> to include soft-deleted POs in the scan so numbers are never
    /// reused. Scoped to the current company so each tenant has its own independent sequence.
    /// </summary>
    private async Task<string> GeneratePoNumberAsync(int companyId)
    {
        var prefix = $"PO-{DateTime.UtcNow:yy}{DateTime.UtcNow.Month:D2}-";

        var existingPos = await _unitOfWork.PurchaseOrders.FindAsync(
            po => po.CompanyId == companyId && po.PoNumber.StartsWith(prefix),
            ignoreQueryFilters: true);
        var existing = existingPos.Select(po => po.PoNumber).ToList();

        var maxNum = 0;
        foreach (var num in existing)
        {
            var suffix = num.Length >= prefix.Length + 4 ? num.Substring(prefix.Length) : "";
            if (int.TryParse(suffix, out int n) && n > maxNum)
                maxNum = n;
        }

        return $"{prefix}{(maxNum + 1):D4}";
    }

    /// <summary>
    /// Loads Create/Edit form dropdowns: active vendors and active inventory items. Inventory
    /// items are serialised to a JSON blob in <c>ViewBag.InventoryItemsJson</c> so the dynamic
    /// line-item UI can look up unit-of-measure and cost on the client side without extra AJAX
    /// calls. The cost preference order is last purchase price then catalog unit cost.
    /// </summary>
    private async Task PopulateCreateViewBagAsync(int companyId)
    {
        var vendorEntities = await _unitOfWork.Vendors.FindAsync(
            v => v.CompanyId == companyId && v.IsActive);
        var vendors = vendorEntities
            .OrderBy(v => v.CompanyName)
            .Select(v => new SelectListItem(v.CompanyName, v.Id.ToString()))
            .ToList();
        vendors.Insert(0, new SelectListItem("— Select Vendor —", ""));
        ViewBag.Vendors = vendors;

        var inventoryEntities = await _unitOfWork.InventoryItems.FindAsync(
            i => i.CompanyId == companyId && i.IsActive);
        var inventoryItems = inventoryEntities
            .OrderBy(i => i.Name)
            .Select(i => new
            {
                value = i.Id,
                text = i.Name + (!string.IsNullOrEmpty(i.SKU) ? $" ({i.SKU})" : ""),
                uom = i.UnitOfMeasure ?? "units",
                cost = i.LastPurchasePrice > 0 ? i.LastPurchasePrice : i.UnitCost
            })
            .ToList();
        ViewBag.InventoryItemsJson = System.Text.Json.JsonSerializer.Serialize(inventoryItems);
    }

    /// <summary>
    /// Loads the vendor filter dropdown for the Index view. Unlike
    /// <see cref="PopulateCreateViewBagAsync"/> this includes inactive vendors so that historical
    /// POs for deactivated vendors remain searchable.
    /// </summary>
    private async Task PopulateVendorFilterDropdownAsync(int companyId)
    {
        var vendorEntities = await _unitOfWork.Vendors.FindAsync(v => v.CompanyId == companyId);
        var vendors = vendorEntities
            .OrderBy(v => v.CompanyName)
            .Select(v => new SelectListItem(v.CompanyName, v.Id.ToString()))
            .ToList();
        vendors.Insert(0, new SelectListItem("All Vendors", ""));
        ViewBag.VendorList = vendors;
    }

    private async Task<(byte[]? LogoData, string? LogoContentType)> LoadCompanyLogoAsync(Company? company)
    {
        if (company == null) return (null, null);
        if (!string.IsNullOrEmpty(company.LogoFilePath))
        {
            var (ok, content, contentType, _) = await _logoService.GetCompanyLogoAsync(company.LogoFilePath);
            if (ok) return (content, contentType);
        }
        return (company.LogoData, company.LogoContentType);
    }
}