using AutoMapper;
using PowderCoating.Shared.Constants;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;
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;

/// <summary>
/// Manages vendor (supplier) records: company details, payment terms, preferred-vendor flag, and the
/// default expense account used when AP bills are created for this vendor. Vendors link to inventory
/// items (indicating their source supplier) and purchase orders. Deletion is blocked when live
/// inventory items reference the vendor, protecting referential integrity without resorting to a
/// cascade delete that would silently break historical records.
/// </summary>
[Authorize(Policy = AppConstants.Policies.CanManageVendors)]
public class VendorsController : Controller
{
    private readonly IUnitOfWork _unitOfWork;
    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,
        IFinancialReportService financialReports,
        ITenantContext tenantContext)
    {
        _unitOfWork = unitOfWork;
        _mapper = mapper;
        _userManager = userManager;
        _logger = logger;
        _financialReports = financialReports;
        _tenantContext = tenantContext;
    }

    /// <summary>
    /// Displays a paginated, sortable, searchable vendor list. Search covers company name, contact
    /// name, email, phone, and city so a user can locate a vendor by any of its common identifiers.
    /// Inventory items are eagerly loaded solely to compute the per-vendor item count badge shown in
    /// the grid; the count explicitly excludes soft-deleted items so only live references are shown.
    /// </summary>
    public async Task<IActionResult> Index(
        string? searchTerm,
        string? sortColumn,
        string sortDirection = "asc",
        int pageNumber = 1,
        int pageSize = 25)
    {
        try
        {
            // Create and validate grid request
            var gridRequest = new GridRequest
            {
                PageNumber = pageNumber,
                PageSize = pageSize,
                SortColumn = sortColumn ?? "CompanyName",
                SortDirection = sortDirection,
                SearchTerm = searchTerm
            };
            gridRequest.Validate();

            // Build search filter
            System.Linq.Expressions.Expression<Func<Vendor, bool>>? filter = null;
            if (!string.IsNullOrWhiteSpace(searchTerm))
            {
                var search = searchTerm.ToLower();
                filter = s => s.CompanyName.ToLower().Contains(search)
                    || (s.ContactName != null && s.ContactName.ToLower().Contains(search))
                    || (s.Email != null && s.Email.ToLower().Contains(search))
                    || (s.Phone != null && s.Phone.ToLower().Contains(search))
                    || (s.City != null && s.City.ToLower().Contains(search));
            }

            // Build orderBy function
            Func<IQueryable<Vendor>, IOrderedQueryable<Vendor>> orderBy = gridRequest.SortColumn switch
            {
                "CompanyName" => q => gridRequest.SortDirection == "asc" ? q.OrderBy(s => s.CompanyName) : q.OrderByDescending(s => s.CompanyName),
                "ContactName" => q => gridRequest.SortDirection == "asc" ? q.OrderBy(s => s.ContactName) : q.OrderByDescending(s => s.ContactName),
                "Phone" => q => gridRequest.SortDirection == "asc" ? q.OrderBy(s => s.Phone) : q.OrderByDescending(s => s.Phone),
                "Email" => q => gridRequest.SortDirection == "asc" ? q.OrderBy(s => s.Email) : q.OrderByDescending(s => s.Email),
                "IsActive" => q => gridRequest.SortDirection == "asc" ? q.OrderBy(s => s.IsActive) : q.OrderByDescending(s => s.IsActive),
                "IsPreferred" => q => gridRequest.SortDirection == "asc" ? q.OrderBy(s => s.IsPreferred) : q.OrderByDescending(s => s.IsPreferred),
                _ => q => q.OrderBy(s => s.CompanyName)
            };

            // Get paged data with inventory items eager loading for count
            var (items, totalCount) = await _unitOfWork.Vendors.GetPagedAsync(
                gridRequest.PageNumber,
                gridRequest.PageSize,
                filter,
                orderBy,
                s => s.InventoryItems);

            // Map to DTOs
            var vendorDtos = items.Select(s => new VendorListDto
            {
                Id = s.Id,
                CompanyName = s.CompanyName,
                ContactName = s.ContactName,
                Phone = s.Phone,
                Email = s.Email,
                IsActive = s.IsActive,
                IsPreferred = s.IsPreferred,
                InventoryItemCount = s.InventoryItems.Count(i => !i.IsDeleted)
            }).ToList();

            var pagedResult = PagedResult<VendorListDto>.From(gridRequest, vendorDtos, totalCount);

            // Set ViewBag for sorting
            ViewBag.SearchTerm = searchTerm;
            ViewBag.SortColumn = gridRequest.SortColumn;
            ViewBag.SortDirection = gridRequest.SortDirection;

            return View(pagedResult);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error retrieving vendors");
            TempData["Error"] = "An error occurred while loading vendors.";
            return View(new PagedResult<VendorListDto>());
        }
    }

    /// <summary>
    /// Shows full vendor detail including linked inventory items and the human-readable default expense
    /// account name. The account name is resolved via a direct <c>_context.Accounts.FindAsync</c>
    /// call rather than an eager-load because the Account entity lives outside the standard
    /// <c>IUnitOfWork</c> pattern and is only needed for display here.
    /// </summary>
    public async Task<IActionResult> Details(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        try
        {
            var vendor = await _unitOfWork.Vendors.GetByIdAsync(id.Value, false, s => s.InventoryItems);
            if (vendor == null)
            {
                return NotFound();
            }

            var vendorDto = _mapper.Map<VendorDto>(vendor);
            if (vendor.DefaultExpenseAccountId.HasValue)
            {
                var acct = await _unitOfWork.Accounts.GetByIdAsync(vendor.DefaultExpenseAccountId.Value);
                vendorDto.DefaultExpenseAccountName = acct != null ? $"{acct.AccountNumber} – {acct.Name}" : null;
            }
            return View(vendorDto);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error retrieving vendor {VendorId}", id);
            TempData["Error"] = "An error occurred while loading the vendor.";
            return RedirectToAction(nameof(Index));
        }
    }

    /// <summary>
    /// Renders the Create form with the expense account dropdown pre-populated.
    /// When <paramref name="inline"/> is true the layout is stripped so the HTML can be injected
    /// into a modal; the form will POST back with the same flag and return JSON instead of a redirect.
    /// </summary>
    public async Task<IActionResult> Create(bool inline = false)
    {
        await PopulateExpenseAccountsAsync();
        if (inline)
            return PartialView(new CreateVendorDto());
        return View(new CreateVendorDto());
    }

    /// <summary>
    /// Persists a new vendor, stamping it with the current user's <c>CompanyId</c> so multi-tenant
    /// isolation is enforced at creation rather than relying solely on query filters. Redirects to
    /// Details on success so the user can immediately verify the saved record.
    /// When <paramref name="inline"/> is true (quick-add modal path) returns JSON {success, id, name}
    /// instead of a redirect so the caller can add the new option to the originating select element.
    /// </summary>
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Create(CreateVendorDto dto, bool inline = false)
    {
        if (!ModelState.IsValid)
        {
            if (inline)
            {
                var errors = ModelState.Values
                    .SelectMany(v => v.Errors)
                    .Select(e => e.ErrorMessage);
                return Json(new { success = false, errors });
            }
            await PopulateExpenseAccountsAsync();
            return View(dto);
        }

        try
        {
            var currentUser = await _userManager.GetUserAsync(User);
            var vendor = _mapper.Map<Vendor>(dto);
            vendor.CompanyId = currentUser!.CompanyId;

            await _unitOfWork.Vendors.AddAsync(vendor);
            await _unitOfWork.CompleteAsync();

            if (inline)
                return Json(new { success = true, id = vendor.Id, name = vendor.CompanyName });

            TempData["Success"] = $"Vendor '{vendor.CompanyName}' created successfully.";
            return RedirectToAction(nameof(Details), new { id = vendor.Id });
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error creating vendor");
            if (inline)
                return Json(new { success = false, errors = new[] { "An error occurred while saving." } });
            TempData["Error"] = "An error occurred while creating the vendor.";
            return View(dto);
        }
    }

    /// <summary>
    /// Renders the Edit form for an existing vendor.
    /// </summary>
    public async Task<IActionResult> Edit(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        try
        {
            var vendor = await _unitOfWork.Vendors.GetByIdAsync(id.Value);
            if (vendor == null)
            {
                return NotFound();
            }

            var dto = _mapper.Map<UpdateVendorDto>(vendor);
            await PopulateExpenseAccountsAsync();
            return View(dto);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error loading vendor {VendorId} for edit", id);
            TempData["Error"] = "An error occurred while loading the vendor.";
            return RedirectToAction(nameof(Index));
        }
    }

    /// <summary>
    /// Applies edits to an existing vendor. Uses AutoMapper's map-onto-existing-entity overload so
    /// EF Core's change tracker only marks modified columns dirty, preserving audit timestamps and
    /// <c>CompanyId</c> that are not present in the DTO.
    /// </summary>
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Edit(int id, UpdateVendorDto dto)
    {
        if (id != dto.Id)
        {
            return NotFound();
        }

        if (!ModelState.IsValid)
        {
            await PopulateExpenseAccountsAsync();
            return View(dto);
        }

        try
        {
            var vendor = await _unitOfWork.Vendors.GetByIdAsync(id);
            if (vendor == null)
            {
                return NotFound();
            }

            _mapper.Map(dto, vendor);
            await _unitOfWork.Vendors.UpdateAsync(vendor);
            await _unitOfWork.CompleteAsync();

            TempData["Success"] = $"Vendor '{vendor.CompanyName}' updated successfully.";
            return RedirectToAction(nameof(Details), new { id = vendor.Id });
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error updating vendor {VendorId}", id);
            TempData["Error"] = "An error occurred while updating the vendor.";
            return View(dto);
        }
    }

    /// <summary>
    /// Shows the Delete confirmation page with the vendor's active inventory item count, so the user
    /// understands the impact before confirming. The count is surfaced here to avoid a surprise
    /// block error on the POST — surfacing the constraint on the GET gives the user an opportunity to
    /// reassign items first.
    /// </summary>
    public async Task<IActionResult> Delete(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        try
        {
            var vendor = await _unitOfWork.Vendors.GetByIdAsync(id.Value, false, s => s.InventoryItems);
            if (vendor == null)
            {
                return NotFound();
            }

            var vendorDto = _mapper.Map<VendorDto>(vendor);
            ViewBag.InventoryItemCount = vendor.InventoryItems.Count(i => !i.IsDeleted);
            return View(vendorDto);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error loading vendor {VendorId} for deletion", id);
            TempData["Error"] = "An error occurred while loading the vendor.";
            return RedirectToAction(nameof(Index));
        }
    }

    /// <summary>
    /// Soft-deletes a vendor after a business-rule guard: deletion is blocked when the vendor is
    /// still referenced by one or more active (non-soft-deleted) inventory items. The block is
    /// enforced in application code rather than via a DB foreign key constraint because soft deletes
    /// make constraint-based blocking unreliable — a DB constraint would fire even on logically
    /// deleted items. Soft delete is used so purchase order and AP bill history that references this
    /// vendor remains intact.
    /// </summary>
    [HttpPost, ActionName("Delete")]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> DeleteConfirmed(int id)
    {
        try
        {
            var vendor = await _unitOfWork.Vendors.GetByIdAsync(id, false, s => s.InventoryItems);
            if (vendor == null)
            {
                return NotFound();
            }

            var inventoryItemCount = vendor.InventoryItems.Count(i => !i.IsDeleted);
            if (inventoryItemCount > 0)
            {
                TempData["Error"] = $"Cannot delete vendor '{vendor.CompanyName}' because it is currently used by {inventoryItemCount} inventory item(s). Please reassign or remove those items first.";
                return RedirectToAction(nameof(Delete), new { id });
            }

            var vendorName = vendor.CompanyName;
            await _unitOfWork.Vendors.SoftDeleteAsync(id);
            await _unitOfWork.CompleteAsync();

            TempData["Success"] = $"Vendor '{vendorName}' has been deleted.";
            return RedirectToAction(nameof(Index));
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error deleting vendor {VendorId}", id);
            TempData["Error"] = "An error occurred while deleting the vendor.";
            return RedirectToAction(nameof(Index));
        }
    }

    /// <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
    /// the field is optional — not every vendor needs a default account pre-set.
    /// </summary>
    private async Task PopulateExpenseAccountsAsync()
    {
        var accounts = (await _unitOfWork.Accounts.FindAsync(
                a => a.IsActive && (a.AccountType == AccountType.Expense ||
                                    a.AccountType == AccountType.CostOfGoods ||
                                    a.AccountType == AccountType.Asset)))
            .OrderBy(a => a.AccountNumber)
            .Select(a => new SelectListItem($"{a.AccountNumber} – {a.Name}", a.Id.ToString()))
            .ToList();

        accounts.Insert(0, new SelectListItem("— None —", ""));
        ViewBag.ExpenseAccounts = accounts;
    }
}