using Microsoft.EntityFrameworkCore;
using PowderCoating.Core.Entities;
using PowderCoating.Core.Enums;
using PowderCoating.Infrastructure.Data;
using System.Text.Json;

namespace PowderCoating.Web.BackgroundServices;

/// <summary>
/// Singleton background service that wakes hourly and generates bills or expenses for any
/// <see cref="RecurringTemplate"/> whose <c>NextFireDate</c> is today or in the past.
/// Bills are created as Draft so users can review; Expenses are recorded immediately.
/// NextFireDate is advanced after each successful fire. Templates are deactivated automatically
/// when <c>MaxOccurrences</c> is reached or <c>EndDate</c> has passed.
/// </summary>
public class RecurringTransactionService : BackgroundService
{
    private readonly IServiceScopeFactory _scopeFactory;
    private readonly ILogger<RecurringTransactionService> _logger;

    public RecurringTransactionService(
        IServiceScopeFactory scopeFactory,
        ILogger<RecurringTransactionService> logger)
    {
        _scopeFactory = scopeFactory;
        _logger = logger;
    }

    /// <summary>
    /// Loops forever, sleeping one hour between passes.
    /// Uses <see cref="IServiceScopeFactory"/> to resolve scoped services (DbContext) from the
    /// singleton because BackgroundService lives for the application lifetime.
    /// </summary>
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("RecurringTransactionService started.");

        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                await RunAsync(stoppingToken);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "RecurringTransactionService run failed.");
            }

            try
            {
                await Task.Delay(TimeSpan.FromHours(1), stoppingToken);
            }
            catch (OperationCanceledException)
            {
                break;
            }
        }

        _logger.LogInformation("RecurringTransactionService stopped.");
    }

    /// <summary>
    /// Loads all active templates whose NextFireDate is on or before today and fires each one.
    /// Uses IgnoreQueryFilters to bypass the HTTP-context-dependent tenant filter.
    /// </summary>
    private async Task RunAsync(CancellationToken ct)
    {
        using var scope = _scopeFactory.CreateScope();
        var db = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>();

        var today = DateTime.UtcNow.Date;

        var due = await db.RecurringTemplates
            .IgnoreQueryFilters()
            .Where(t => !t.IsDeleted && t.IsActive && t.NextFireDate.Date <= today)
            .ToListAsync(ct);

        if (due.Count == 0) return;

        _logger.LogInformation("RecurringTransactionService: {Count} template(s) due.", due.Count);

        foreach (var template in due)
        {
            if (ct.IsCancellationRequested) break;
            await FireTemplateAsync(db, template, ct);
        }
    }

    /// <summary>
    /// Fires a single template: creates the document, updates OccurrenceCount + NextFireDate,
    /// and deactivates the template when limits are reached. Errors are captured in LastError
    /// so the service loop continues to process other templates.
    /// </summary>
    private async Task FireTemplateAsync(
        ApplicationDbContext db,
        RecurringTemplate template,
        CancellationToken ct)
    {
        try
        {
            if (template.TemplateType == RecurringTemplateType.Bill)
                await CreateBillAsync(db, template, ct);
            else
                await CreateExpenseAsync(db, template, ct);

            template.OccurrenceCount++;
            template.NextFireDate = AdvanceDate(template.NextFireDate, template.Frequency, template.IntervalCount);
            template.LastError = null;

            // Deactivate when limits reached
            if (template.MaxOccurrences.HasValue && template.OccurrenceCount >= template.MaxOccurrences.Value)
            {
                template.IsActive = false;
                _logger.LogInformation("Template {Id} ({Name}) deactivated: MaxOccurrences reached.", template.Id, template.Name);
            }
            else if (template.EndDate.HasValue && template.NextFireDate.Date > template.EndDate.Value.Date)
            {
                template.IsActive = false;
                _logger.LogInformation("Template {Id} ({Name}) deactivated: EndDate passed.", template.Id, template.Name);
            }

            await db.SaveChangesAsync(ct);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to fire recurring template {Id} ({Name}).", template.Id, template.Name);
            template.LastError = ex.Message;
            try { await db.SaveChangesAsync(ct); } catch { /* best-effort */ }
        }
    }

    // -------------------------------------------------------------------------
    // Bill creation
    // -------------------------------------------------------------------------

    /// <summary>
    /// Deserializes the template's JSON payload and inserts a Draft <see cref="Bill"/> with
    /// its line items. GL posting is deferred — the user posts the Draft bill manually after review.
    /// </summary>
    private async Task CreateBillAsync(ApplicationDbContext db, RecurringTemplate template, CancellationToken ct)
    {
        var data = JsonSerializer.Deserialize<BillTemplateData>(template.TemplateData)
                   ?? throw new InvalidOperationException("Invalid bill template data.");

        var bill = new Bill
        {
            BillNumber        = await NextBillNumberAsync(db, ct),
            VendorId          = data.VendorId,
            APAccountId       = data.APAccountId,
            BillDate          = DateTime.UtcNow,
            DueDate           = data.Terms != null ? ParseDueDate(data.Terms) : null,
            Status            = BillStatus.Draft,
            Terms             = data.Terms,
            Memo              = $"[Recurring] {data.Memo}".Trim(),
            SubTotal          = data.LineItems?.Sum(l => l.Quantity * l.UnitPrice) ?? 0,
            TaxPercent        = data.TaxPercent,
            TaxAmount         = 0,
            Total             = 0,
            CompanyId         = template.CompanyId,
            CreatedBy         = "Recurring",
            CreatedAt         = DateTime.UtcNow
        };
        bill.TaxAmount = Math.Round(bill.SubTotal * bill.TaxPercent / 100, 2);
        bill.Total     = bill.SubTotal + bill.TaxAmount;

        db.Bills.Add(bill);
        await db.SaveChangesAsync(ct); // get bill.Id

        int order = 1;
        foreach (var line in data.LineItems ?? [])
        {
            db.BillLineItems.Add(new BillLineItem
            {
                BillId       = bill.Id,
                AccountId    = line.AccountId,
                Description  = line.Description,
                Quantity     = line.Quantity,
                UnitPrice    = line.UnitPrice,
                Amount       = Math.Round(line.Quantity * line.UnitPrice, 2),
                DisplayOrder = order++,
                CompanyId    = template.CompanyId,
                CreatedAt    = DateTime.UtcNow
            });
        }

        _logger.LogInformation("Recurring bill {BillNumber} created for template {Id}.", bill.BillNumber, template.Id);
    }

    // -------------------------------------------------------------------------
    // Expense creation
    // -------------------------------------------------------------------------

    /// <summary>
    /// Deserializes the template's JSON payload and inserts an <see cref="Expense"/> immediately.
    /// Expenses are already-paid transactions so no user review is required.
    /// </summary>
    private async Task CreateExpenseAsync(ApplicationDbContext db, RecurringTemplate template, CancellationToken ct)
    {
        var data = JsonSerializer.Deserialize<ExpenseTemplateData>(template.TemplateData)
                   ?? throw new InvalidOperationException("Invalid expense template data.");

        var expense = new Expense
        {
            ExpenseNumber    = await NextExpenseNumberAsync(db, ct),
            Date             = DateTime.UtcNow,
            VendorId         = data.VendorId == 0 ? null : data.VendorId,
            ExpenseAccountId = data.ExpenseAccountId,
            PaymentAccountId = data.PaymentAccountId,
            PaymentMethod    = (PaymentMethod)data.PaymentMethod,
            Amount           = data.Amount,
            Memo             = $"[Recurring] {data.Memo}".Trim(),
            CompanyId        = template.CompanyId,
            CreatedBy        = "Recurring",
            CreatedAt        = DateTime.UtcNow
        };

        db.Expenses.Add(expense);

        _logger.LogInformation("Recurring expense {ExpenseNumber} created for template {Id}.", expense.ExpenseNumber, template.Id);
    }

    // -------------------------------------------------------------------------
    // Helpers
    // -------------------------------------------------------------------------

    /// <summary>Advances a date by one period (Frequency × IntervalCount).</summary>
    private static DateTime AdvanceDate(DateTime date, RecurringFrequency freq, int interval)
    {
        return freq switch
        {
            RecurringFrequency.Daily     => date.AddDays(interval),
            RecurringFrequency.Weekly    => date.AddDays(7 * interval),
            RecurringFrequency.BiWeekly  => date.AddDays(14 * interval),
            RecurringFrequency.Monthly   => date.AddMonths(interval),
            RecurringFrequency.Quarterly => date.AddMonths(3 * interval),
            RecurringFrequency.Annually  => date.AddYears(interval),
            _                            => date.AddMonths(interval)
        };
    }

    /// <summary>
    /// Generates the next sequential bill number (BILL-YYMM-####).
    /// Uses IgnoreQueryFilters so soft-deleted bills are included in the sequence scan.
    /// </summary>
    private static async Task<string> NextBillNumberAsync(ApplicationDbContext db, CancellationToken ct)
    {
        var prefix = $"BILL-{DateTime.Now:yyMM}-";
        var last = await db.Bills
            .IgnoreQueryFilters()
            .Where(b => b.BillNumber.StartsWith(prefix))
            .OrderByDescending(b => b.BillNumber)
            .Select(b => b.BillNumber)
            .FirstOrDefaultAsync(ct);

        int next = 1;
        if (last != null && int.TryParse(last[prefix.Length..], out int n)) next = n + 1;
        return $"{prefix}{next:D4}";
    }

    /// <summary>
    /// Generates the next sequential expense number (EXP-YYMM-####).
    /// Uses IgnoreQueryFilters so soft-deleted expenses are included in the sequence scan.
    /// </summary>
    private static async Task<string> NextExpenseNumberAsync(ApplicationDbContext db, CancellationToken ct)
    {
        var prefix = $"EXP-{DateTime.Now:yyMM}-";
        var last = await db.Expenses
            .IgnoreQueryFilters()
            .Where(e => e.ExpenseNumber.StartsWith(prefix))
            .OrderByDescending(e => e.ExpenseNumber)
            .Select(e => e.ExpenseNumber)
            .FirstOrDefaultAsync(ct);

        int next = 1;
        if (last != null && int.TryParse(last[prefix.Length..], out int n)) next = n + 1;
        return $"{prefix}{next:D4}";
    }

    /// <summary>Best-effort due date from a payment terms string (delegates to the same patterns as PaymentTermsParser).</summary>
    private static DateTime? ParseDueDate(string terms)
    {
        var t = terms.Trim().ToUpperInvariant();
        if (t is "DUE ON RECEIPT" or "COD" or "IMMEDIATE") return DateTime.UtcNow.Date;

        // "Net 30", "NET30", "2/10 Net 30" → extract trailing number
        var parts = t.Split(' ', StringSplitOptions.RemoveEmptyEntries);
        var last = parts.LastOrDefault();
        if (last != null && int.TryParse(last, out int days) && days > 0)
            return DateTime.UtcNow.Date.AddDays(days);

        return null;
    }

    // -------------------------------------------------------------------------
    // JSON payload records (must match RecurringTemplatesController serialization)
    // -------------------------------------------------------------------------

    internal sealed record BillTemplateData(
        int VendorId,
        int APAccountId,
        string? Terms,
        string? Memo,
        decimal TaxPercent,
        List<BillLineData>? LineItems);

    internal sealed record BillLineData(
        int? AccountId,
        string Description,
        decimal Quantity,
        decimal UnitPrice);

    internal sealed record ExpenseTemplateData(
        int VendorId,
        int ExpenseAccountId,
        int PaymentAccountId,
        int PaymentMethod,
        decimal Amount,
        string? Memo);
}