using System.Globalization;
using System.Text.Json;
using Distribution.Data;
using Distribution.Features.Grn;
using Distribution.Features.SysConfig;
using Distribution.Infra.UoW;
using Distribution.Models;
using Microsoft.EntityFrameworkCore;

namespace Distribution.Features.GeneralLedger;

public record GlLine(string AccountCode, decimal Debit, decimal Credit);

/// <summary>What closing a financial year would post. Closable is false with a Reason when it cannot be closed.</summary>
public record YearEndPreview(int Year, string StartDate, string EndDate, decimal TotalIncome, decimal TotalExpenses,
    decimal NetProfit, bool Closable, string? Reason, bool AlreadyClosed);

/// <summary>
/// One opening balance: Account is a key from OpeningAccounts (e.g. "Inventory", "ShareCapital") or "BankAccount"
/// with BankAccountId. Amount is the account's normal balance (>= 0); the debit/credit side comes from the account.
/// </summary>
public record OpeningBalanceLine(string Account, Guid? BankAccountId, decimal Amount);

/// <summary>
/// Mirrors Distribution business events into the General Ledger as journal entries. Every public Post* method is
/// called AFTER the business transaction has committed and never throws: a GL problem is recorded in GlPostingLogs
/// (status Failed, payload kept) and can be retried later, so it can never block a sale, payment or cheque action.
/// </summary>
public class GlPostingService(
    IGeneralLedgerClient gl,
    ISysConfigRepository configRepo,
    GlSetupService setup,
    AppDBContext context,
    IUnitOfWork uow,
    ILogger<GlPostingService> logger)
{
    private record Payload(string EntryDate, string JournalType, string SourceModule, string Reference, string Narration,
        string PreparedBy, List<PayloadLine> Lines);

    private record PayloadLine(string AccountCode, decimal DebitAmount, decimal CreditAmount);

    // ── Events ───────────────────────────────────────────────────────────────

    public Task PostInvoiceFinalizedAsync(Models.Invoice invoice, CancellationToken ct = default) =>
        PostAsync("InvoiceFinalized", invoice.Id, invoice.FinalizedAt ?? DateTime.Now, "INVOICE", $"Invoice {invoice.Id} finalized",
            async () => invoice.TotalAmount <= 0 ? null :
            [
                new GlLine(await Acct(GlKeys.Receivable), invoice.TotalAmount, 0),
                new GlLine(await Acct(GlKeys.Sales), 0, invoice.TotalAmount)
            ], ct);

    public Task PostCustomerPaymentAsync(Models.Payment payment, CancellationToken ct = default) =>
        PostAsync("CustomerPayment", payment.Id, payment.CollectedAt, "PAYMENT", $"Customer payment for invoice {payment.FK_InvoiceId}",
            async () =>
            {
                if (payment.Amount <= 0 || payment.Method == PaymentMethod.Credit) return null;
                var debit = payment.Method == PaymentMethod.Cash
                    ? await BankCode(payment.FK_BankAccountId)
                    : await Acct(GlKeys.ChequesInHand);
                return [new GlLine(debit, payment.Amount, 0), new GlLine(await Acct(GlKeys.Receivable), 0, payment.Amount)];
            }, ct);

    /// <summary>Deposit / Return / Cancel of a received cheque that came from a customer payment.</summary>
    public Task PostReceivedChequeAsync(Models.ReceivedCheque cheque, ReceivedChequeStatusAction action, CancellationToken ct = default)
    {
        if (action is not (ReceivedChequeStatusAction.Deposit or ReceivedChequeStatusAction.Return or ReceivedChequeStatusAction.Cancel))
            return Task.CompletedTask;

        var date = action == ReceivedChequeStatusAction.Deposit ? cheque.DepositDate ?? DateTime.Now : DateTime.Now;
        return PostAsync($"ReceivedCheque{action}", cheque.Id, date, "CHEQUE", $"Received cheque {cheque.ChequeNo} {action}",
            async () =>
            {
                // Only cheques created by a customer payment were posted to Cheques-in-hand, so only they can move.
                if (!await context.Payments.AnyAsync(p => p.FK_ReceivedChequeId == cheque.Id, ct)) return null;
                var inHand = await Acct(GlKeys.ChequesInHand);
                return action switch
                {
                    ReceivedChequeStatusAction.Deposit =>
                        [new GlLine(await BankCode(cheque.FK_DepositBankAccountId), cheque.Amount, 0), new GlLine(inHand, 0, cheque.Amount)],
                    ReceivedChequeStatusAction.Return =>
                        [new GlLine(inHand, cheque.Amount, 0), new GlLine(await BankCode(cheque.FK_DepositBankAccountId), 0, cheque.Amount)],
                    _ => [new GlLine(await Acct(GlKeys.Receivable), cheque.Amount, 0), new GlLine(inHand, 0, cheque.Amount)]
                };
            }, ct);
    }

    public Task PostGrnAsync(Models.GoodsReceipt grn, CancellationToken ct = default) =>
        PostAsync("Grn", grn.Id, grn.ReceivedAt, "GRN", $"Goods received {grn.Id}",
            async () =>
            {
                decimal net = 0, nbt = 0, vat = 0;
                foreach (var i in grn.Items.Where(i => i.IsActive))
                {
                    var a = GrnPricing.Line(i.AcceptedQuantity, i.UnitCost, i.DiscountPercent, i.NbtPercent, i.VatPercent);
                    net += a.Gross - a.Discount;
                    nbt += a.Nbt;
                    vat += a.Vat;
                }
                var total = net + nbt + vat;
                if (total <= 0) return null;

                var lines = new List<GlLine> { new(await Acct(GlKeys.Inventory), net, 0) };
                if (nbt > 0) lines.Add(new GlLine(await Acct(GlKeys.InputNbt), nbt, 0));
                if (vat > 0) lines.Add(new GlLine(await Acct(GlKeys.InputVat), vat, 0));
                lines.Add(new GlLine(await Acct(GlKeys.Payable), 0, total));
                return lines;
            }, ct);

    public Task PostSupplierPaymentAsync(Models.SupplierPayment payment, CancellationToken ct = default) =>
        PostAsync("SupplierPayment", payment.Id, payment.PaidAt, "SUPPLIER_PAYMENT", $"Supplier payment {payment.Id}",
            async () =>
            {
                if (payment.Amount <= 0) return null;
                var credit = payment.Method == PaymentMethod.Cash
                    ? await BankCode(payment.FK_BankAccountId)
                    : await Acct(GlKeys.ChequesIssued);
                return [new GlLine(await Acct(GlKeys.Payable), payment.Amount, 0), new GlLine(credit, 0, payment.Amount)];
            }, ct);

    /// <summary>Clear / Bounce / Cancel of a cheque issued through a supplier payment.</summary>
    public Task PostIssuedChequeAsync(Models.ChequePage page, ChequePageStatusAction action, CancellationToken ct = default)
    {
        if (action == ChequePageStatusAction.Void) return Task.CompletedTask;

        var date = action == ChequePageStatusAction.Clear ? page.ClearedDate ?? DateTime.Now : DateTime.Now;
        return PostAsync($"IssuedCheque{action}", page.Id, date, "CHEQUE", $"Issued cheque {page.ChequeNo} {action}",
            async () =>
            {
                var amount = page.Amount ?? 0;
                if (amount <= 0 || !await context.SupplierPayments.AnyAsync(p => p.FK_ChequePageId == page.Id, ct)) return null;
                var issued = await Acct(GlKeys.ChequesIssued);
                if (action == ChequePageStatusAction.Clear)
                {
                    var bookBankId = await context.ChequeBooks.Where(b => b.Id == page.FK_ChequeBookId)
                        .Select(b => (Guid?)b.FK_BankAccountId).FirstOrDefaultAsync(ct);
                    return [new GlLine(issued, amount, 0), new GlLine(await BankCode(bookBankId), 0, amount)];
                }
                // Bounce / Cancel: the cheque no longer settles the payable, so put it back.
                return [new GlLine(issued, amount, 0), new GlLine(await Acct(GlKeys.Payable), 0, amount)];
            }, ct);
    }

    /// <summary>
    /// Posts the opening balances (asset side debited, liability/equity side credited). Zero amounts are skipped, so the
    /// form can list every account with a default of 0. Reports the outcome so the caller can show a failure.
    /// </summary>
    public async Task<GlPostingLog> PostOpeningBalanceAsync(DateOnly date, string? narration, List<OpeningBalanceLine> input, CancellationToken ct = default)
    {
        if ((await configRepo.GetByKeyAsync(GlKeys.SetupDone))?.Value != "true")
            throw new InvalidOperationException("Run the General Ledger setup first.");

        var lines = new List<GlLine>();
        foreach (var l in input ?? [])
        {
            if (l.Amount < 0) throw new InvalidOperationException($"'{l.Account}': the amount cannot be negative.");
            if (l.Amount == 0) continue;

            if (l.Account == "BankAccount")
            {
                lines.Add(new GlLine(await BankCode(l.BankAccountId), l.Amount, 0));
                continue;
            }
            if (!OpeningAccounts.TryGetValue(l.Account, out var def))
                throw new InvalidOperationException($"Unknown account '{l.Account}'.");
            var code = await Acct(def.Key);
            lines.Add(def.DebitNormal ? new GlLine(code, l.Amount, 0) : new GlLine(code, 0, l.Amount));
        }

        if (lines.Count == 0)
            throw new InvalidOperationException("Enter at least one opening balance greater than zero.");

        var debit = lines.Sum(x => x.Debit);
        var credit = lines.Sum(x => x.Credit);
        if (debit != credit)
            throw new InvalidOperationException(
                $"The opening balances do not balance: assets (debits) total {debit:N2} but liabilities + equity (credits) total {credit:N2}. " +
                "Adjust Share Capital / Retained Earnings so they match.");

        var sourceId = Guid.NewGuid();
        await PostAsync("OpeningBalance", sourceId, date.ToDateTime(TimeOnly.MinValue), "OPENING_BALANCE",
            string.IsNullOrWhiteSpace(narration) ? "Opening balances" : narration.Trim(), () => Task.FromResult<List<GlLine>?>(lines), ct);

        return await context.GlPostingLogs.FirstOrDefaultAsync(l => l.Event == "OpeningBalance" && l.SourceId == sourceId, ct)
            ?? throw new InvalidOperationException("The opening balances could not be prepared. Check the server log.");
    }

    /// <summary>Accounts that can carry an opening balance (besides individual cash/bank accounts) and their normal side.</summary>
    public static readonly Dictionary<string, (string Key, bool DebitNormal)> OpeningAccounts = new()
    {
        ["ChequesInHand"] = (GlKeys.ChequesInHand, true),
        ["Receivable"] = (GlKeys.Receivable, true),
        ["Inventory"] = (GlKeys.Inventory, true),
        ["InputVat"] = (GlKeys.InputVat, true),
        ["InputNbt"] = (GlKeys.InputNbt, true),
        ["Drawings"] = (GlKeys.Drawings, true),
        ["Payable"] = (GlKeys.Payable, false),
        ["ChequesIssued"] = (GlKeys.ChequesIssued, false),
        ["ShareCapital"] = (GlKeys.ShareCapital, false),
        ["RetainedEarnings"] = (GlKeys.RetainedEarnings, false),
        ["GeneralReserve"] = (GlKeys.GeneralReserve, false),
        ["RevaluationReserve"] = (GlKeys.RevaluationReserve, false),
    };

    // ── Year-end close ───────────────────────────────────────────────────────

    private const string YearEndEvent = "YearEndClose";

    private static Guid YearEndSourceId(int year) =>
        new(System.Security.Cryptography.MD5.HashData(System.Text.Encoding.UTF8.GetBytes($"{YearEndEvent}:{year}")));

    /// <summary>Years that have a posted closing journal.</summary>
    public async Task<List<int>> GetClosedYearsAsync(CancellationToken ct = default) =>
        (await context.GlPostingLogs
            .Where(l => l.Event == YearEndEvent && l.Status == GlPostingStatus.Posted)
            .Select(l => l.Reference)
            .ToListAsync(ct))
        .Select(r => int.TryParse(r.Split(':').Last(), out var y) ? y : 0)
        .Where(y => y > 0).OrderBy(y => y).ToList();

    private record CloseBuild(List<GlLine> Lines, decimal Income, decimal Expenses);

    /// <summary>Reads the year's own P&amp;L from GL (which excludes earlier closing journals) and builds the closing lines.</summary>
    private async Task<CloseBuild> BuildYearEndCloseAsync(int year, CancellationToken ct)
    {
        var result = await gl.SendAsync(HttpMethod.Get,
            $"v1/reports?reportType=ProfitAndLoss&outputFormat=Json&periodStart={year}-01-01&periodEnd={year}-12-31", null, ct);
        if (!result.Success || GlJson.Data(result) is not { } pl)
            throw new InvalidOperationException($"Could not read the {year} profit and loss from the General Ledger: {GlJson.Message(result) ?? result.StatusCode.ToString()}");

        // Net CREDIT balance per account: income sections carry their amount as is, expense sections are reported
        // as positive debits (so flip), unclassified rows are already credit - debit.
        var netCredit = new Dictionary<string, decimal>();
        decimal income = 0, expenses = 0;
        void Collect(string section, int sign)
        {
            if (GlJson.Get(pl, section) is not { } s || GlJson.Get(s, "lines") is not { ValueKind: JsonValueKind.Array } sectionLines) return;
            foreach (var l in sectionLines.EnumerateArray())
            {
                var code = GlJson.GetString(l, "accountCode");
                if (code is null || !decimal.TryParse(GlJson.GetString(l, "amount"), NumberStyles.Any, CultureInfo.InvariantCulture, out var amount)) continue;
                var credit = sign * amount;
                netCredit[code] = netCredit.GetValueOrDefault(code) + credit;
                if (credit > 0) income += credit; else expenses += -credit;
            }
        }
        Collect("sales", 1); Collect("otherIncome", 1);
        Collect("costOfSales", -1); Collect("distributionExpenses", -1); Collect("administrationExpenses", -1);
        Collect("otherExpenses", -1); Collect("financialExpenses", -1);
        Collect("unclassified", 1);

        // Closing: an account with a net credit balance is debited, one with a net debit balance is credited.
        var lines = netCredit.Where(kv => kv.Value != 0)
            .Select(kv => kv.Value > 0 ? new GlLine(kv.Key, kv.Value, 0) : new GlLine(kv.Key, 0, -kv.Value)).ToList();
        var debit = lines.Sum(x => x.Debit);
        var credit2 = lines.Sum(x => x.Credit);
        if (debit != credit2)
        {
            var retained = await Acct(GlKeys.RetainedEarnings);
            lines.Add(debit > credit2 ? new GlLine(retained, 0, debit - credit2) : new GlLine(retained, credit2 - debit, 0));
        }
        return new CloseBuild(lines, income, expenses);
    }

    public async Task<YearEndPreview> GetYearEndPreviewAsync(int year, CancellationToken ct = default)
    {
        var start = $"{year}-01-01";
        var end = $"{year}-12-31";

        if ((await configRepo.GetByKeyAsync(GlKeys.SetupDone))?.Value != "true")
            return new(year, start, end, 0, 0, 0, false, "Run the General Ledger setup first.", false);

        var sourceId = YearEndSourceId(year);
        var existing = await context.GlPostingLogs.FirstOrDefaultAsync(l => l.Event == YearEndEvent && l.SourceId == sourceId, ct);
        if (existing?.Status == GlPostingStatus.Posted)
            return new(year, start, end, 0, 0, 0, false, $"{year} has already been closed.", true);

        var build = await BuildYearEndCloseAsync(year, ct);
        var net = build.Income - build.Expenses;
        string? reason = null;
        if (new DateOnly(year, 12, 31) > DateOnly.FromDateTime(DateTime.Now))
            reason = $"{year} has not ended yet. A year can only be closed after 31 December.";
        else if (await context.GlPostingLogs.AnyAsync(l => l.Status != GlPostingStatus.Posted && !(l.Event == YearEndEvent && l.SourceId == sourceId), ct))
            reason = "There are failed or pending General Ledger postings. Retry them first so the year's figures are complete.";
        else if (build.Lines.Count == 0)
            reason = $"There is no income or expense activity in {year} to close.";

        return new(year, start, end, build.Income, build.Expenses, net, reason is null, reason, false);
    }

    /// <summary>Posts the closing journal for the year (income/expense into Retained Earnings), then locks the year's periods.</summary>
    public async Task<object> CloseYearAsync(int year, CancellationToken ct = default)
    {
        var preview = await GetYearEndPreviewAsync(year, ct);
        if (!preview.Closable) throw new InvalidOperationException(preview.Reason ?? "This year cannot be closed.");

        var build = await BuildYearEndCloseAsync(year, ct);
        var sourceId = YearEndSourceId(year);
        await PostAsync(YearEndEvent, sourceId, new DateTime(year, 12, 31), "YEAR_END_CLOSE", $"Year-end closing entry for {year}",
            () => Task.FromResult<List<GlLine>?>(build.Lines), ct, journalType: "CLOSING", reference: $"{YearEndEvent}:{year}");

        var row = await context.GlPostingLogs.FirstOrDefaultAsync(l => l.Event == YearEndEvent && l.SourceId == sourceId, ct)
            ?? throw new InvalidOperationException("The closing entry could not be prepared. Check the server log.");
        if (row.Status != GlPostingStatus.Posted)
            throw new InvalidOperationException((row.Error ?? "The General Ledger did not accept the closing entry.") + " Fix the cause and press Close again.");

        var locked = await LockYearPeriodsAsync(year, ct);
        return new { year, glJournalNo = row.GlJournalNo, netProfit = preview.NetProfit, periodsLocked = locked };
    }

    private async Task<int> LockYearPeriodsAsync(int year, CancellationToken ct)
    {
        var ids = new HashSet<long>();
        for (var month = 1; month <= 12; month++)
        {
            var p = await gl.SendAsync(HttpMethod.Get, $"v1/fiscal-years/periods/by-date?date={year}-{month:00}-15", null, ct);
            if (p.Success && GlJson.Data(p) is { } pd && GlJson.GetLong(pd, "periodId") is { } id) ids.Add(id);
        }

        var locked = 0;
        foreach (var id in ids)
        {
            var r = await gl.SendAsync(HttpMethod.Put, $"v1/periods/{id}/lock", new { action = "Close", reason = $"Year-end close {year}" }, ct);
            if (r.Success) locked++;
            else logger.LogWarning("Could not lock GL period {PeriodId} after closing {Year}: {Message}", id, year, GlJson.Message(r));
        }
        return locked;
    }

    // ── Retry ────────────────────────────────────────────────────────────────

    /// <summary>Re-sends every Failed/Pending posting. Returns how many are now Posted.</summary>
    public async Task<int> RetryFailedAsync(CancellationToken ct = default)
    {
        var rows = await context.GlPostingLogs
            .Where(l => l.Status != GlPostingStatus.Posted)
            .OrderBy(l => l.CreatedAt)
            .ToListAsync(ct);

        var posted = 0;
        foreach (var row in rows)
        {
            await SendAsync(row, ct);
            if (row.Status == GlPostingStatus.Posted) posted++;
        }
        return posted;
    }

    // ── Core ─────────────────────────────────────────────────────────────────

    private async Task PostAsync(string evt, Guid sourceId, DateTime date, string sourceModule, string narration,
        Func<Task<List<GlLine>?>> buildLines, CancellationToken ct, string journalType = "GENERAL", string? reference = null)
    {
        try
        {
            if ((await configRepo.GetByKeyAsync(GlKeys.SetupDone))?.Value != "true") return; // GL not set up yet

            var row = await context.GlPostingLogs.FirstOrDefaultAsync(l => l.Event == evt && l.SourceId == sourceId, ct);
            if (row is not null && row.Status == GlPostingStatus.Posted) return;

            if (row is null)
            {
                var lines = await buildLines();
                if (lines is null || lines.Count == 0) return;

                reference ??= $"{evt}:{sourceId}";
                var payload = new Payload(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture), journalType, sourceModule, reference,
                    narration, "Distribution", lines.Select(l => new PayloadLine(l.AccountCode, l.Debit, l.Credit)).ToList());

                row = new GlPostingLog
                {
                    Event = evt,
                    SourceId = sourceId,
                    Reference = reference,
                    PayloadJson = JsonSerializer.Serialize(payload, JsonOptions)
                };
                await uow.BeginAsync(ct);
                try { await context.GlPostingLogs.AddAsync(row, ct); await uow.CommitAsync(ct); }
                catch { await uow.RollbackAsync(ct); throw; }
            }

            await SendAsync(row, ct);
        }
        catch (Exception ex)
        {
            logger.LogError(ex, "GL posting {Event}:{SourceId} failed before it could be sent", evt, sourceId);
        }
    }

    private async Task SendAsync(GlPostingLog row, CancellationToken ct)
    {
        string? journalNo = null;
        string? error = null;
        try
        {
            var payload = JsonSerializer.Deserialize<JsonElement>(row.PayloadJson);
            var entryDate = payload.GetProperty("entryDate").GetString()!;

            var period = await gl.SendAsync(HttpMethod.Get, $"v1/fiscal-years/periods/by-date?date={entryDate}", null, ct);
            var periodId = period.Success && GlJson.Data(period) is { } pd ? GlJson.GetLong(pd, "periodId") : null;
            if (periodId is null)
            {
                error = $"No accounting period in GL covers {entryDate}. Run GL setup for that year.";
            }
            else
            {
                var body = JsonSerializer.Deserialize<Dictionary<string, JsonElement>>(row.PayloadJson, JsonOptions)!;
                body["periodId"] = JsonSerializer.SerializeToElement(periodId.Value);
                var result = await gl.SendAsync(HttpMethod.Post, "v1/journal-entries", body, ct);
                if (result.Success)
                    journalNo = GlJson.Data(result) is { } d ? GlJson.GetString(d, "journalNo") ?? "" : "";
                else
                    error = GlJson.Message(result) ?? $"GL returned HTTP {result.StatusCode}";
            }
        }
        catch (Exception ex)
        {
            error = ex.Message;
            logger.LogWarning(ex, "GL posting {Reference} failed", row.Reference);
        }

        row.Attempts++;
        row.LastAttemptAt = DateTime.Now;
        row.Status = error is null ? GlPostingStatus.Posted : GlPostingStatus.Failed;
        row.GlJournalNo = journalNo;
        row.Error = error is null ? null : error.Length > 1000 ? error[..1000] : error;

        await uow.BeginAsync(ct);
        try { context.GlPostingLogs.Update(row); await uow.CommitAsync(ct); }
        catch { await uow.RollbackAsync(ct); throw; }
    }

    // ── Account lookups ──────────────────────────────────────────────────────

    private async Task<string> Acct(string key) =>
        (await configRepo.GetByKeyAsync(key))?.Value is { Length: > 0 } code
            ? code
            : throw new InvalidOperationException($"GL account mapping '{key}' is missing. Run GL setup.");

    private async Task<string> BankCode(Guid? bankAccountId)
    {
        if (bankAccountId is null) throw new InvalidOperationException("No cash/bank account on this transaction.");
        var account = await context.BankAccounts.FirstOrDefaultAsync(a => a.Id == bankAccountId.Value)
            ?? throw new InvalidOperationException("Cash/bank account not found.");
        return await setup.EnsureBankAccountAsync(account)
            ?? throw new InvalidOperationException("Could not map the cash/bank account to a GL account. Run GL setup.");
    }

    private static readonly JsonSerializerOptions JsonOptions = new() { PropertyNamingPolicy = JsonNamingPolicy.CamelCase };
}