using Data.SeaHavenIndustries;
using Microsoft.EntityFrameworkCore;
using SeaHaven.DataServices.Interfaces;

namespace SeaHaven.DataServices.Implementation
{
    public sealed class WorkOrderReconciliationDataService : IWorkOrderReconciliationDataService
    {
        private const int SingletonId = 1;
        private readonly ApplicationDbContext _context;

        public WorkOrderReconciliationDataService(ApplicationDbContext context)
        {
            _context = context;
        }

        public async Task<ReconciliationJobSnapshot> EnqueueAsync(
            string reason,
            DateTimeOffset now,
            CancellationToken cancellationToken)
        {
            var job = await GetOrCreateAsync(cancellationToken);
            if (job.State is not ("Pending" or "Running"))
            {
                job.RunId = Guid.NewGuid();
                job.FenceToken = null;
                job.State = "Pending";
                job.Reason = reason[..Math.Min(reason.Length, 128)];
                job.RequestedAt = now;
                job.StartedAt = null;
                job.LeaseExpiresAt = null;
                job.CompletedAt = null;
                job.WorkOrdersProcessed = 0;
                job.CommentsProcessed = 0;
                job.ErrorCode = null;
                try
                {
                    await _context.SaveChangesAsync(cancellationToken);
                }
                catch (DbUpdateConcurrencyException)
                {
                    _context.ChangeTracker.Clear();
                    job = await _context.WorkOrderReconciliationJobs
                        .SingleAsync(j => j.Id == SingletonId, cancellationToken);
                }
            }

            return Snapshot(job);
        }

        public async Task<ReconciliationLease?> TryAcquirePendingAsync(
            DateTimeOffset now,
            TimeSpan leaseDuration,
            CancellationToken cancellationToken)
        {
            var job = await GetOrCreateAsync(cancellationToken);
            var leaseExpired = job.State == "Running"
                && job.LeaseExpiresAt.HasValue
                && job.LeaseExpiresAt <= now;
            if (job.State != "Pending" && !leaseExpired)
                return null;

            job.State = "Running";
            job.StartedAt ??= now;
            job.LeaseExpiresAt = now.Add(leaseDuration);
            job.FenceToken = Guid.NewGuid();
            try
            {
                await _context.SaveChangesAsync(cancellationToken);
                return new ReconciliationLease(job.RunId, job.FenceToken.Value);
            }
            catch (DbUpdateConcurrencyException)
            {
                _context.ChangeTracker.Clear();
                return null;
            }
        }

        public async Task<ReconciliationJobSnapshot> GetStatusAsync(
            CancellationToken cancellationToken)
        {
            var job = await _context.WorkOrderReconciliationJobs
                .AsNoTracking()
                .SingleOrDefaultAsync(j => j.Id == SingletonId, cancellationToken);
            return job == null
                ? new ReconciliationJobSnapshot(null, "Idle", null, null, null, null, 0, 0, null)
                : Snapshot(job);
        }

        public async Task<bool> RenewLeaseAsync(
            Guid runId,
            Guid fenceToken,
            DateTimeOffset now,
            TimeSpan leaseDuration,
            CancellationToken cancellationToken)
        {
            var job = await _context.WorkOrderReconciliationJobs.SingleOrDefaultAsync(
                j => j.Id == SingletonId
                    && j.RunId == runId
                    && j.FenceToken == fenceToken
                    && j.State == "Running",
                cancellationToken);
            if (job == null)
                return false;

            job.LeaseExpiresAt = now.Add(leaseDuration);
            try
            {
                await _context.SaveChangesAsync(cancellationToken);
                return true;
            }
            catch (DbUpdateConcurrencyException)
            {
                _context.ChangeTracker.Clear();
                return false;
            }
        }

        public Task CompleteAsync(
            Guid runId,
            Guid fenceToken,
            DateTimeOffset completedAt,
            int workOrders,
            int comments,
            CancellationToken cancellationToken) =>
            FinishAsync(runId, fenceToken, completedAt, "Succeeded", workOrders, comments, null, cancellationToken);

        public Task FailAsync(
            Guid runId,
            Guid fenceToken,
            DateTimeOffset completedAt,
            string errorCode,
            CancellationToken cancellationToken) =>
            FinishAsync(runId, fenceToken, completedAt, "Failed", 0, 0, errorCode, cancellationToken);

        private async Task FinishAsync(
            Guid runId,
            Guid fenceToken,
            DateTimeOffset completedAt,
            string state,
            int workOrders,
            int comments,
            string? errorCode,
            CancellationToken cancellationToken)
        {
            var job = await _context.WorkOrderReconciliationJobs
                .SingleOrDefaultAsync(
                    j => j.Id == SingletonId
                        && j.RunId == runId
                        && j.FenceToken == fenceToken
                        && j.State == "Running",
                    cancellationToken);
            if (job == null)
                return;

            job.State = state;
            job.CompletedAt = completedAt;
            job.LeaseExpiresAt = null;
            job.WorkOrdersProcessed = workOrders;
            job.CommentsProcessed = comments;
            job.ErrorCode = errorCode;
            await _context.SaveChangesAsync(cancellationToken);
        }

        private async Task<WorkOrderReconciliationJob> GetOrCreateAsync(
            CancellationToken cancellationToken)
        {
            var job = await _context.WorkOrderReconciliationJobs
                .SingleOrDefaultAsync(j => j.Id == SingletonId, cancellationToken);
            if (job != null)
                return job;

            job = new WorkOrderReconciliationJob { Id = SingletonId, RunId = Guid.NewGuid() };
            _context.WorkOrderReconciliationJobs.Add(job);
            try
            {
                await _context.SaveChangesAsync(cancellationToken);
                return job;
            }
            catch (DbUpdateException)
            {
                _context.ChangeTracker.Clear();
                return await _context.WorkOrderReconciliationJobs
                    .SingleAsync(j => j.Id == SingletonId, cancellationToken);
            }
        }

        private static ReconciliationJobSnapshot Snapshot(WorkOrderReconciliationJob job) =>
            new(
                job.RunId,
                job.State,
                job.Reason,
                job.RequestedAt,
                job.StartedAt,
                job.CompletedAt,
                job.WorkOrdersProcessed,
                job.CommentsProcessed,
                job.ErrorCode);
    }
}