using Fitness_core_BE.Infra.Tenancy;
using Fitness_core_BE.Infra.UoW;
using Fitness_core_BE.Repos;
using Microsoft.EntityFrameworkCore;

namespace Fitness_core_BE.Services
{
    public sealed record SubscriptionRenewalRunResult(
        Guid ClientId, int Candidates, int Renewed, int Failed, IReadOnlyList<string> Notes);

    // The per-schema renewal algorithm, extracted from SubscriptionRenewalJob's daily loop so
    // the admin "trigger now" endpoint can call the exact same code path instead of duplicating it.
    //
    // Renewal-approval model: the daily sweep never touches the CustomerSubscription itself
    // (IsActive/RenewalDate/members/installments) -- it only computes whether a new invoice is
    // due and creates it as unapproved (IsActive=false). Advancing RenewalDate, and everything
    // else that used to happen automatically (deactivate old subscription, create a new one),
    // now only happens when staff approve/change-plan/reject via SubscriptionRenewalApprovalService.
    public class SubscriptionRenewalRunner(ILogger<SubscriptionRenewalRunner> logger)
    {
        private readonly ILogger<SubscriptionRenewalRunner> _logger = logger;

        public async Task<SubscriptionRenewalRunResult> RunForSchemaAsync(
            TenantSchemaContext schemaCtx, DateTime now, CancellationToken ct = default)
        {
            var tenant = schemaCtx.Tenant;
            var central = schemaCtx.Central;
            var today = now.Date;

            // DurationMode == "Rolling" is a hard requirement, not a preference: FixedRange
            // plans are fixed-date, non-renewing by design. RenewalDate (not ExpiryDate) drives
            // eligibility -- ExpiryDate is frozen at creation and never advances. The "no
            // already-pending invoice" exclusion is what makes this idempotent: once a renewal
            // invoice exists unapproved, the subscription is skipped on every subsequent run
            // until an approval action (approve/change-plan/reject) resolves it.
            var candidates = await tenant.CustomerSubscriptions
                .Include(s => s.CustomerPlan)
                .Where(s => s.IsActive
                         && s.RenewalDate != null && s.RenewalDate < today.AddDays(1)
                         && s.CustomerPlan.DurationMode == "Rolling"
                         && s.CustomerPlan.IsActive
                         && !tenant.CustomerInvoices.Any(i =>
                                i.FKCustomerSubscriptionId == s.SubscriptionId
                                && i.IsActive == false
                                && i.Status != "Cancelled"))
                .ToListAsync(ct);

            _logger.LogInformation(
                "SubscriptionRenewalJob: client {ClientId} -- {Candidates} subscription(s) due for renewal.",
                schemaCtx.ClientId, candidates.Count);

            var notes = new List<string>();
            int renewed = 0, failed = 0;

            var uow = new EFUnitOfWork(central, tenant);
            var subscriptionRepo = new CustomerSubscriptionRepository(tenant, central);
            var invoiceRepo = new CustomerInvoiceRepository(tenant);

            foreach (var oldSubscription in candidates)
            {
                try
                {
                    await RenewOneAsync(oldSubscription, tenant, uow, subscriptionRepo, invoiceRepo, _logger, ct);
                    renewed++;
                }
                catch (Exception ex)
                {
                    await uow.RollbackAsync(ct);
                    // RollbackAsync only rolls back the DB transaction -- it does not clear EF's
                    // change tracker. tenant/central are reused across every candidate in this
                    // loop, so a failed candidate's tracked-but-unsaved mutations (e.g. the
                    // "RolledOver" status flip) would otherwise still be flushed by the *next*
                    // candidate's SaveChanges/CommitAsync.
                    tenant.ChangeTracker.Clear();
                    central.ChangeTracker.Clear();
                    failed++;
                    var note = $"Renewal failed for subscription {oldSubscription.SubscriptionId} (customer {oldSubscription.FKCustomerId}): {ex.Message}";
                    notes.Add(note);
                    _logger.LogError(ex, "SubscriptionRenewalJob: {Note}", note);
                }
            }

            _logger.LogInformation(
                "SubscriptionRenewalJob: client {ClientId} done -- {Renewed} renewal invoice(s) created, {Failed} failed.",
                schemaCtx.ClientId, renewed, failed);

            return new SubscriptionRenewalRunResult(schemaCtx.ClientId, candidates.Count, renewed, failed, notes);
        }

        private static async Task RenewOneAsync(
            Fitness_core_BE.Models.CustomerSubscription oldSubscription,
            TenantDbContext tenant,
            EFUnitOfWork uow,
            CustomerSubscriptionRepository subscriptionRepo,
            CustomerInvoiceRepository invoiceRepo,
            ILogger logger,
            CancellationToken ct)
        {
            await uow.BeginAsync(ct);

            // By construction this is still the real, currently-collectible invoice: the
            // candidate query above already excludes subscriptions with a pending-approval
            // invoice, and nothing else sets CustomerInvoice.IsActive=false.
            var oldInvoice = await subscriptionRepo.GetLatestInvoiceAsync(oldSubscription.SubscriptionId, ct);
            if (oldInvoice == null)
            {
                throw new InvalidOperationException(
                    $"Subscription {oldSubscription.SubscriptionId} has no invoice to renew from.");
            }

            decimal carriedOverBalance;
            switch (oldInvoice.Status)
            {
                case "Paid":
                    carriedOverBalance = 0m;
                    logger.LogInformation(
                        "SubscriptionRenewalJob: subscription {SubscriptionId} -- prior invoice {InvoiceId} was Paid, no balance carried forward.",
                        oldSubscription.SubscriptionId, oldInvoice.CustomerInvoiceId);
                    break;

                case "Pending":
                case "Partial":
                    var approvedPaid = await subscriptionRepo.GetApprovedPaymentTotalAsync(oldInvoice.CustomerInvoiceId, ct);
                    carriedOverBalance = Math.Max(0m, oldInvoice.Amount - approvedPaid);

                    // GetLatestInvoiceAsync reads AsNoTracking -- re-fetch tracked to mutate it.
                    var trackedOldInvoice = await tenant.CustomerInvoices.FindAsync(
                        new object[] { oldInvoice.CustomerInvoiceId }, ct);
                    trackedOldInvoice!.Status = "RolledOver";

                    logger.LogInformation(
                        "SubscriptionRenewalJob: subscription {SubscriptionId} -- prior invoice {InvoiceId} was {OldStatus}, rolling over unpaid balance {CarriedOverBalance} and marking it RolledOver.",
                        oldSubscription.SubscriptionId, oldInvoice.CustomerInvoiceId, oldInvoice.Status, carriedOverBalance);
                    break;

                default:
                    // "Failed"/"Refunded" (or a stray "Cancelled"/"RolledOver" the candidate
                    // query's own invoice-state shouldn't produce) -- don't guess how to carry
                    // these forward; surfaces as a PartialFailure note for manual review.
                    throw new InvalidOperationException(
                        $"Subscription {oldSubscription.SubscriptionId}'s current invoice has unexpected status '{oldInvoice.Status}'.");
            }

            // Renewal invoices skip the onboarding fee (one-time, not a per-cycle charge) and
            // start unapproved (IsActive=false) -- staff must approve/change-plan/reject before
            // it counts. The subscription itself (IsActive, RenewalDate, members, installments)
            // is untouched here; all of that is deferred to the approval action.
            var newInvoice = await invoiceRepo.CreateRenewalInvoiceAsync(oldSubscription.SubscriptionId, carriedOverBalance, ct);

            await uow.CommitAsync(ct);

            logger.LogInformation(
                "SubscriptionRenewalJob: subscription {SubscriptionId} -- created unapproved renewal invoice {InvoiceId} (amount {Amount}), awaiting staff approval.",
                oldSubscription.SubscriptionId, newInvoice.CustomerInvoiceId, newInvoice.Amount);
        }
    }
}