using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using PowderCoating.Application.Interfaces;
using PowderCoating.Core.Entities;
using PowderCoating.Core.Enums;
using PowderCoating.Core.Interfaces;
using PowderCoating.Shared.Constants;

namespace PowderCoating.Web.Controllers;

[Authorize(Policy = AppConstants.Policies.CanViewData)]
public class VendorCreditsController : Controller
{
    private readonly IUnitOfWork _unitOfWork;
    private readonly ITenantContext _tenantContext;
    private readonly IAccountBalanceService _accountBalanceService;

    public VendorCreditsController(
        IUnitOfWork unitOfWork,
        ITenantContext tenantContext,
        IAccountBalanceService accountBalanceService)
    {
        _unitOfWork = unitOfWork;
        _tenantContext = tenantContext;
        _accountBalanceService = accountBalanceService;
    }

    private bool AllowAccounting() =>
        User.IsInRole("SuperAdmin") || User.IsInRole("Administrator") || User.IsInRole("Manager");

    // ── Index ────────────────────────────────────────────────────────────────

    /// <summary>Lists vendor credits grouped by status with unapplied balance summary.</summary>
    public async Task<IActionResult> Index(string? status)
    {
        if (!AllowAccounting()) return RedirectToAction("Landing", "Reports");

        var companyId = _tenantContext.GetCurrentCompanyId() ?? 0;

        var all = (await _unitOfWork.VendorCredits.FindAsync(
            vc => vc.CompanyId == companyId,
            false,
            vc => vc.Vendor))
            .OrderByDescending(vc => vc.CreditDate)
            .ThenByDescending(vc => vc.Id)
            .ToList();

        var displayed = status switch
        {
            "Open"    => all.Where(vc => vc.Status == VendorCreditStatus.Open).ToList(),
            "Partial" => all.Where(vc => vc.Status == VendorCreditStatus.PartiallyApplied).ToList(),
            "Applied" => all.Where(vc => vc.Status == VendorCreditStatus.Applied).ToList(),
            "Voided"  => all.Where(vc => vc.Status == VendorCreditStatus.Voided).ToList(),
            _         => all
        };

        ViewBag.StatusFilter    = status ?? "All";
        ViewBag.TotalCount      = all.Count;
        ViewBag.OpenCount       = all.Count(vc => vc.Status == VendorCreditStatus.Open);
        ViewBag.PartialCount    = all.Count(vc => vc.Status == VendorCreditStatus.PartiallyApplied);
        ViewBag.TotalUnapplied  = all
            .Where(vc => vc.Status is VendorCreditStatus.Open or VendorCreditStatus.PartiallyApplied)
            .Sum(vc => vc.RemainingAmount);

        return View(displayed);
    }

    // ── Create ───────────────────────────────────────────────────────────────

    [Authorize(Policy = AppConstants.Policies.CanManageJobs)]
    public async Task<IActionResult> Create()
    {
        if (!AllowAccounting()) return RedirectToAction("Landing", "Reports");
        await PopulateDropdownsAsync();
        return View(new VendorCredit { CreditDate = DateTime.Today });
    }

    [HttpPost]
    [Authorize(Policy = AppConstants.Policies.CanManageJobs)]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Create(
        VendorCredit model,
        int[] lineAccountIds,
        string[] lineDescriptions,
        decimal[] lineAmounts)
    {
        if (!AllowAccounting()) return RedirectToAction("Landing", "Reports");

        var lines = BuildLines(lineAccountIds, lineDescriptions, lineAmounts);
        if (lines.Count == 0)
        {
            TempData["Error"] = "At least one line item is required.";
            await PopulateDropdownsAsync();
            return View(model);
        }

        var companyId = _tenantContext.GetCurrentCompanyId() ?? 0;
        model.CreditNumber    = await GenerateCreditNumberAsync(companyId);
        model.Status          = VendorCreditStatus.Open;
        model.Total           = lines.Sum(l => l.Amount);
        model.RemainingAmount = model.Total;
        model.LineItems       = lines;

        await _unitOfWork.VendorCredits.AddAsync(model);
        await _unitOfWork.CompleteAsync();

        TempData["Success"] = $"Vendor credit {model.CreditNumber} created.";
        return RedirectToAction(nameof(Details), new { id = model.Id });
    }

    // ── Details ──────────────────────────────────────────────────────────────

    public async Task<IActionResult> Details(int id)
    {
        if (!AllowAccounting()) return RedirectToAction("Landing", "Reports");

        var vc = (await _unitOfWork.VendorCredits.FindAsync(
            v => v.Id == id,
            false,
            v => v.Vendor,
            v => v.APAccount,
            v => v.LineItems,
            v => v.Applications))
            .FirstOrDefault();

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

        // Load account names for lines
        var accountIds = vc.LineItems
            .Where(l => l.AccountId.HasValue)
            .Select(l => l.AccountId!.Value)
            .Distinct()
            .ToList();
        var accounts = await _unitOfWork.Accounts.FindAsync(a => accountIds.Contains(a.Id));
        ViewBag.AccountMap = accounts.ToDictionary(a => a.Id, a => $"{a.AccountNumber} – {a.Name}");

        // Load bills referenced by applications
        if (vc.Applications.Any())
        {
            var billIds = vc.Applications.Select(a => a.BillId).ToList();
            var bills   = await _unitOfWork.Bills.FindAsync(b => billIds.Contains(b.Id));
            ViewBag.BillMap = bills.ToDictionary(b => b.Id, b => b.BillNumber);
        }
        else
        {
            ViewBag.BillMap = new Dictionary<int, string>();
        }

        // Unapplied bills from the same vendor for the "Apply" panel
        if (vc.Status is VendorCreditStatus.Open or VendorCreditStatus.PartiallyApplied)
        {
            var openBills = await _unitOfWork.Bills.FindAsync(
                b => b.VendorId == vc.VendorId
                  && (b.Status == BillStatus.Open || b.Status == BillStatus.PartiallyPaid));
            ViewBag.OpenBills = openBills.OrderBy(b => b.DueDate).ToList();
        }

        return View(vc);
    }

    // ── Post ─────────────────────────────────────────────────────────────────

    /// <summary>
    /// Posts a vendor credit to the GL:
    ///   DR Accounts Payable (APAccountId) — vendor owes us, reduces AP
    ///   CR Expense/COGS accounts (each line) — reverses the original expense
    /// </summary>
    [HttpPost]
    [Authorize(Policy = AppConstants.Policies.CanManageJobs)]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Post(int id)
    {
        if (!AllowAccounting()) return RedirectToAction("Landing", "Reports");

        var vc = (await _unitOfWork.VendorCredits.FindAsync(
            v => v.Id == id,
            false,
            v => v.LineItems))
            .FirstOrDefault();

        if (vc == null) return NotFound();
        if (vc.Status != VendorCreditStatus.Open)
        {
            TempData["Error"] = "Only open (unposted) credits can be posted.";
            return RedirectToAction(nameof(Details), new { id });
        }

        await _unitOfWork.ExecuteInTransactionAsync(async () =>
        {
            // DR AP (reduces what we owe the vendor)
            await _accountBalanceService.DebitAsync(vc.APAccountId, vc.Total);

            // CR each expense account (reverses original expense)
            foreach (var line in vc.LineItems)
                await _accountBalanceService.CreditAsync(line.AccountId, line.Amount);

            // Record posting date so Void() can reverse only if GL entries were actually made.
            vc.PostedDate = DateTime.UtcNow;
            await _unitOfWork.VendorCredits.UpdateAsync(vc);

            // Status stays Open — the credit is now in the GL but not yet applied to a bill
            await _unitOfWork.CompleteAsync();
        });

        TempData["Success"] = $"Vendor credit {vc.CreditNumber} posted to GL.";
        return RedirectToAction(nameof(Details), new { id });
    }

    // ── Apply ─────────────────────────────────────────────────────────────────

    /// <summary>
    /// Applies a vendor credit against a vendor bill. Reduces Bill.AmountPaid (increasing balance)
    /// and VendorCredit.RemainingAmount. No additional GL posting — AP was already adjusted when
    /// the credit was posted.
    /// </summary>
    [HttpPost]
    [Authorize(Policy = AppConstants.Policies.CanManageJobs)]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Apply(int id, int billId, decimal amount)
    {
        if (!AllowAccounting()) return RedirectToAction("Landing", "Reports");

        var vc   = await _unitOfWork.VendorCredits.GetByIdAsync(id);
        var bill = await _unitOfWork.Bills.GetByIdAsync(billId);

        if (vc == null || bill == null) return NotFound();
        if (amount <= 0 || amount > vc.RemainingAmount || amount > bill.BalanceDue)
        {
            TempData["Error"] = "Invalid application amount.";
            return RedirectToAction(nameof(Details), new { id });
        }

        await _unitOfWork.ExecuteInTransactionAsync(async () =>
        {
            var application = new VendorCreditApplication
            {
                VendorCreditId = vc.Id,
                BillId         = bill.Id,
                Amount         = amount,
                AppliedDate    = DateTime.UtcNow
            };
            await _unitOfWork.VendorCreditApplications.AddAsync(application);

            // Update bill — treated as a payment against the balance
            bill.AmountPaid += amount;
            if (bill.AmountPaid >= bill.Total)
                bill.Status = BillStatus.Paid;
            else if (bill.AmountPaid > 0)
                bill.Status = BillStatus.PartiallyPaid;

            // Update credit
            vc.RemainingAmount -= amount;
            vc.Status = vc.RemainingAmount <= 0
                ? VendorCreditStatus.Applied
                : VendorCreditStatus.PartiallyApplied;

            await _unitOfWork.CompleteAsync();
        });

        TempData["Success"] = $"Applied {amount:C} of credit {vc.CreditNumber} to bill {bill.BillNumber}.";
        return RedirectToAction(nameof(Details), new { id });
    }

    // ── Void ─────────────────────────────────────────────────────────────────

    /// <summary>
    /// Voids a vendor credit. If the credit was previously posted (PostedDate is set), reverses the
    /// original GL entries: CR Accounts Payable / DR each expense line item, restoring both balances.
    /// Only the unapplied RemainingAmount of AP is reversed — applied portions reduced bill balances
    /// that are already settled and remain part of the immutable audit trail.
    /// </summary>
    [HttpPost]
    [Authorize(Policy = AppConstants.Policies.CompanyAdminOnly)]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Void(int id)
    {
        if (!AllowAccounting()) return RedirectToAction("Landing", "Reports");

        var vc = (await _unitOfWork.VendorCredits.FindAsync(
            v => v.Id == id, false,
            v => v.LineItems))
            .FirstOrDefault();
        if (vc == null) return NotFound();

        if (vc.Status == VendorCreditStatus.Applied)
        {
            TempData["Error"] = "Fully applied credits cannot be voided.";
            return RedirectToAction(nameof(Details), new { id });
        }

        await _unitOfWork.ExecuteInTransactionAsync(async () =>
        {
            // Reverse GL only if Post() was previously called; unposted credits have no GL entries.
            if (vc.PostedDate.HasValue && vc.RemainingAmount > 0)
            {
                // CR AP for the unapplied amount (undoes the debit made at Post time)
                await _accountBalanceService.CreditAsync(vc.APAccountId, vc.RemainingAmount);

                // DR each expense line proportionally (unapplied fraction of each line)
                var applyRatio = vc.Total > 0 ? vc.RemainingAmount / vc.Total : 1m;
                foreach (var line in vc.LineItems)
                    await _accountBalanceService.DebitAsync(line.AccountId, line.Amount * applyRatio);
            }

            vc.Status          = VendorCreditStatus.Voided;
            vc.RemainingAmount = 0;
            await _unitOfWork.VendorCredits.UpdateAsync(vc);
            await _unitOfWork.CompleteAsync();
        });

        TempData["Success"] = $"Vendor credit {vc.CreditNumber} voided.";
        return RedirectToAction(nameof(Index));
    }

    // ── Helpers ──────────────────────────────────────────────────────────────

    private static List<VendorCreditLineItem> BuildLines(
        int[] accountIds, string[] descriptions, decimal[] amounts)
    {
        var lines = new List<VendorCreditLineItem>();
        for (int i = 0; i < accountIds.Length; i++)
        {
            if (i < amounts.Length && amounts[i] > 0)
                lines.Add(new VendorCreditLineItem
                {
                    AccountId   = accountIds[i] > 0 ? accountIds[i] : null,
                    Description = i < descriptions.Length ? descriptions[i] : string.Empty,
                    Amount      = amounts[i]
                });
        }
        return lines;
    }

    /// <summary>
    /// Generates the next sequential credit number in the format VC-YYMM-####.
    /// Uses ignoreQueryFilters so voided/deleted records are included and numbers are never reused.
    /// </summary>
    private async Task<string> GenerateCreditNumberAsync(int companyId)
    {
        var prefix = $"VC-{DateTime.Now:yyMM}-";
        var all = await _unitOfWork.VendorCredits.FindAsync(
            vc => vc.CompanyId == companyId && vc.CreditNumber.StartsWith(prefix),
            ignoreQueryFilters: true);

        int next = 1;
        if (all.Any())
        {
            var nums = all
                .Select(vc => vc.CreditNumber[prefix.Length..])
                .Select(s => int.TryParse(s, out int n) ? n : 0);
            next = nums.Max() + 1;
        }

        return $"{prefix}{next:D4}";
    }

    private async Task PopulateDropdownsAsync()
    {
        var vendors  = await _unitOfWork.Vendors.FindAsync(v => v.IsActive);
        var accounts = await _unitOfWork.Accounts.FindAsync(a => a.IsActive);

        ViewBag.VendorList = vendors
            .OrderBy(v => v.CompanyName)
            .Select(v => new SelectListItem { Value = v.Id.ToString(), Text = v.CompanyName })
            .ToList();

        ViewBag.APAccountList = accounts
            .Where(a => a.AccountSubType == AccountSubType.AccountsPayable)
            .OrderBy(a => a.AccountNumber)
            .Select(a => new SelectListItem
            {
                Value = a.Id.ToString(),
                Text  = $"{a.AccountNumber} – {a.Name}"
            })
            .ToList();

        ViewBag.ExpenseAccountList = accounts
            .Where(a => a.AccountType is AccountType.Expense or AccountType.CostOfGoods)
            .OrderBy(a => a.AccountNumber)
            .Select(a => new SelectListItem
            {
                Value = a.Id.ToString(),
                Text  = $"{a.AccountNumber} – {a.Name}"
            })
            .ToList();
    }
}