using Fitness_core_BE.Infra.Tenancy;

namespace Fitness_core_BE.Services
{
    /// <summary>
    /// Daily sweep (01:00 Sri Lanka time) that checks every provisioned tenant schema for
    /// CustomerSubscriptions due for renewal (RenewalDate on or before today) and creates an
    /// unapproved (IsActive=false) renewal invoice for each -- see SubscriptionRenewalRunner for
    /// the actual per-subscription algorithm (Paid vs. Pending/Partial carry-forward). Nothing on
    /// the subscription itself changes here; approving/changing-plan/rejecting the invoice
    /// (SubscriptionRenewalApprovalService) is what advances RenewalDate or replaces the plan.
    /// Own, independent loop from OverdueLockJob's 6-hour cadence -- deliberately not merged with it.
    ///
    /// Same as OverdueLockJob, this is a background service with no HttpContext, so it can't
    /// rely on TenantConnectionResolver's per-request tenant resolution -- it loops every
    /// provisioned tenant schema directly via TenantSchemaIterator instead.
    /// </summary>
    public class SubscriptionRenewalJob : BackgroundService
    {
        private const string JobName = "SubscriptionRenewalJob";

        // 01:00 Sri Lanka local time (UTC+5:30, no DST observed since 2006) -- the gyms this
        // runs for are all Sri Lanka-based, so the trigger point is anchored to local time
        // rather than UTC. The actual RenewalDate/candidate comparisons inside
        // SubscriptionRenewalRunner still use DateTime.UtcNow, unaffected by this -- only the
        // wake-up point shifts.
        private static readonly TimeSpan RunAtLocal = TimeSpan.FromHours(1);
        private static readonly TimeZoneInfo SriLankaTimeZone = ResolveSriLankaTimeZone();

        private readonly IServiceScopeFactory _scopeFactory;
        private readonly ILogger<SubscriptionRenewalJob> _logger;

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

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                var delay = ComputeDelayUntilNextRun(DateTime.UtcNow);
                _logger.LogInformation(
                    "SubscriptionRenewalJob: next run scheduled at {NextRunUtc:u} UTC (in {Delay}).",
                    DateTime.UtcNow.Add(delay), delay);

                try
                {
                    await Task.Delay(delay, stoppingToken);
                }
                catch (TaskCanceledException)
                {
                    // Shutting down.
                    break;
                }

                try
                {
                    _logger.LogInformation("SubscriptionRenewalJob: daily run starting.");
                    await RunOnceAsync(stoppingToken);
                    _logger.LogInformation("SubscriptionRenewalJob: daily run finished.");
                }
                catch (Exception ex)
                {
                    _logger.LogError(ex, "SubscriptionRenewalJob run failed.");
                }
            }
        }

        private static TimeZoneInfo ResolveSriLankaTimeZone()
        {
            try
            {
                return TimeZoneInfo.FindSystemTimeZoneById("Sri Lanka Standard Time"); // Windows ID
            }
            catch (TimeZoneNotFoundException)
            {
                try
                {
                    return TimeZoneInfo.FindSystemTimeZoneById("Asia/Colombo"); // IANA ID (Linux/macOS)
                }
                catch (TimeZoneNotFoundException)
                {
                    // Neither ID resolved (e.g. no tzdata on the host) -- Sri Lanka has kept a
                    // fixed UTC+5:30 offset with no DST since 2006, so a custom fixed-offset
                    // zone is a safe fallback rather than failing the whole job.
                    return TimeZoneInfo.CreateCustomTimeZone(
                        "Sri Lanka (fixed +05:30)", TimeSpan.FromMinutes(330), "Sri Lanka Time", "Sri Lanka Time");
                }
            }
        }

        // Delay-then-run, not run-then-delay: a fixed daily time trigger shouldn't fire an extra
        // run just because the app happened to restart. Internal + static so it's unit-testable
        // without spinning up the whole hosted service.
        internal static TimeSpan ComputeDelayUntilNextRun(DateTime nowUtc)
        {
            var nowLocal = TimeZoneInfo.ConvertTimeFromUtc(nowUtc, SriLankaTimeZone);
            var todayRunLocal = nowLocal.Date + RunAtLocal;
            var nextRunLocal = nowLocal < todayRunLocal ? todayRunLocal : todayRunLocal.AddDays(1);
            var nextRunUtc = TimeZoneInfo.ConvertTimeToUtc(
                DateTime.SpecifyKind(nextRunLocal, DateTimeKind.Unspecified), SriLankaTimeZone);
            return nextRunUtc - nowUtc;
        }

        private async Task RunOnceAsync(CancellationToken ct)
        {
            using var scope = _scopeFactory.CreateScope();
            var iterator = scope.ServiceProvider.GetRequiredService<TenantSchemaIterator>();
            var runner = scope.ServiceProvider.GetRequiredService<SubscriptionRenewalRunner>();
            var history = scope.ServiceProvider.GetRequiredService<IJobRunHistory>();

            var now = DateTime.UtcNow;

            await foreach (var (clientId, schemaName) in iterator.GetProvisionedRegistrationsAsync(ct))
            {
                // Declared outside the try so the catch block can still use schemaCtx.Central to
                // record the failure -- central is one fixed database regardless of tenant, so
                // it's safe to reuse (or lazily open) here even though the schema-specific work failed.
                TenantSchemaContext? schemaCtx = null;
                try
                {
                    schemaCtx = iterator.OpenSchema(clientId, schemaName);
                    var result = await runner.RunForSchemaAsync(schemaCtx, now, ct);

                    await history.RecordAsync(schemaCtx.Central, new JobRunRecord(
                        JobName, clientId, now,
                        result.Failed > 0 ? "PartialFailure" : "Success",
                        result.Renewed,
                        result.Failed > 0 ? string.Join("; ", result.Notes) : null), ct);

                    if (result.Renewed > 0 || result.Failed > 0)
                    {
                        _logger.LogInformation(
                            "SubscriptionRenewalJob: client {ClientId} ({Schema}) -- {Candidates} candidate(s), {Renewed} renewed, {Failed} failed.",
                            clientId, schemaName, result.Candidates, result.Renewed, result.Failed);
                    }
                }
                catch (Exception ex)
                {
                    _logger.LogError(ex, "SubscriptionRenewalJob failed for client {ClientId} schema {Schema}.", clientId, schemaName);
                    schemaCtx ??= iterator.OpenSchema(clientId, schemaName);
                    await history.RecordAsync(schemaCtx.Central, new JobRunRecord(JobName, clientId, now, "Failed", 0, ex.Message), ct);
                }
                finally
                {
                    if (schemaCtx != null)
                        await schemaCtx.DisposeAsync();
                }
            }
        }
    }
}