using System.Security.Claims;
using SeaHaven.DataServices.Interfaces;
using SeaHaven.DataServices.Models;
using SeaHaven.Services.DTOs;
using SeaHaven.Services.Exceptions;
using SeaHaven.Services.Helpers;
using SeaHaven.Services.Interfaces;

namespace SeaHaven.Services.Implementation
{
    public class NotificationFeedService : INotificationFeedService
    {
        /// <summary>Most items returned per per-work-order section; section counts stay exact.</summary>
        public const int SectionItemLimit = 50;

        /// <summary>How long an assignment, comment, mention or uplift decision stays in the feed.</summary>
        public static readonly TimeSpan RecentActivityWindow = TimeSpan.FromDays(7);

        /// <summary>Most source rows read per personal event type before grouping.</summary>
        public const int PersonalCandidateLimit = 500;

        private static readonly TimeSpan NoVendorLeadTime = TimeSpan.FromHours(48);

        private readonly INotificationFeedDataService _data;
        private readonly IVendorOperationsDataService _vendorData;
        private readonly IWorkOrderAccountResolver _accountResolver;
        private readonly TimeProvider _timeProvider;

        public NotificationFeedService(
            INotificationFeedDataService data,
            IVendorOperationsDataService vendorData,
            IWorkOrderAccountResolver accountResolver,
            TimeProvider timeProvider)
        {
            _data = data;
            _vendorData = vendorData;
            _accountResolver = accountResolver;
            _timeProvider = timeProvider;
        }

        public async Task<NotificationFeedDto> GetFeedAsync(ClaimsPrincipal user, CancellationToken cancellationToken)
        {
            var accountId = _accountResolver.ResolveAccountFilter(user);
            var (dispatcherId, seesUnassigned) = ResolveAudience(user);
            var scope = new NotificationFeedScope(accountId, dispatcherId);
            var now = _timeProvider.GetUtcNow().UtcDateTime;

            var sections = new List<(string Reason, int Count, IReadOnlyList<NotificationItemDto> Items)>();
            if (seesUnassigned)
                sections.Add(await UnassignedAsync(accountId, now, cancellationToken));
            sections.Add(await NoVendorAsync(scope, now, cancellationToken));
            sections.Add(await AvetaMissingAsync(scope, now, cancellationToken));
            sections.Add(await VendorConflictsAsync(scope, cancellationToken));

            var userId = user.FindFirstValue(ClaimTypes.NameIdentifier);
            if (!string.IsNullOrWhiteSpace(userId))
                sections.AddRange(await PersonalSectionsAsync(new NotificationPersonalScope(accountId, userId), now, cancellationToken));

            return new NotificationFeedDto
            {
                GeneratedAt = now,
                Sections = NotificationFeedOrdering.Order(sections)
            };
        }

        // Dispatchers see their own work orders. Roles that already see every dispatcher's
        // work on the dashboard see the whole account, including work nobody owns yet.
        private static (string? DispatcherId, bool SeesUnassigned) ResolveAudience(ClaimsPrincipal user)
        {
            if (user.IsInRole("Dispatcher"))
            {
                var dispatcherId = user.FindFirstValue(ClaimTypes.NameIdentifier);
                if (string.IsNullOrWhiteSpace(dispatcherId))
                    throw new WorkOrderBoardValidationException("Forbidden", "Dispatcher identity is required.");
                return (dispatcherId, false);
            }

            if (user.IsInRole("Admin") || user.IsInRole("Manager") || user.IsInRole("Scheduler"))
                return (null, true);

            throw new WorkOrderBoardValidationException("Forbidden", "Notifications require an authorized role.");
        }

        // Items addressed to the signed-in user whatever their role: assignments to them, comments on
        // work they take part in, mentions of them, and decisions on uplifts they requested. The
        // account scope still applies; the dispatcher scope does not, because a mention or an uplift
        // request can concern a work order owned by another dispatcher.
        private async Task<IReadOnlyList<(string, int, IReadOnlyList<NotificationItemDto>)>> PersonalSectionsAsync(
            NotificationPersonalScope scope, DateTime now, CancellationToken cancellationToken)
        {
            var since = now.Subtract(RecentActivityWindow);
            var comments = await _data.GetUnansweredCommentsAsync(scope, since, PersonalCandidateLimit, cancellationToken);
            var assignments = await _data.GetRecentAssignmentsAsync(scope, since, PersonalCandidateLimit, cancellationToken);
            var decisions = await _data.GetUpliftDecisionsAsync(scope, since, PersonalCandidateLimit, cancellationToken);

            var mentions = NotificationActivityItems.Mentions(comments, scope.UserId);
            var activity = NotificationActivityItems.Comments(comments, scope.UserId)
                .Concat(NotificationActivityItems.Assignments(assignments))
                .Concat(NotificationActivityItems.UpliftDecisions(decisions))
                .ToList();

            return new[]
            {
                BoundedSection(NotificationReasons.Mentions, mentions),
                BoundedSection(NotificationReasons.Activity, activity)
            };
        }

        // Counts every work order the section covers; returns the most severe, most recent items.
        private static (string, int, IReadOnlyList<NotificationItemDto>) BoundedSection(
            string reason, IReadOnlyList<NotificationItemDto> items)
        {
            var workOrderCount = items.SelectMany(item => item.WorkOrders).Select(w => w.Id).Distinct().Count();
            var bounded = items
                .OrderByDescending(item => NotificationSeverities.Rank(item.Severity))
                .ThenByDescending(item => item.TriggeredAt)
                .ThenBy(item => item.Id, StringComparer.Ordinal)
                .Take(SectionItemLimit)
                .ToList();
            return (reason, workOrderCount, bounded);
        }

        private async Task<(string, int, IReadOnlyList<NotificationItemDto>)> UnassignedAsync(
            int? accountId, DateTime now, CancellationToken cancellationToken)
        {
            var summary = await _data.GetUnassignedSummaryAsync(accountId, cancellationToken);
            if (summary.Count == 0)
                return (NotificationReasons.Unassigned, 0, Array.Empty<NotificationItemDto>());

            var item = new NotificationItemDto
            {
                Id = NotificationReasons.Unassigned,
                Reason = NotificationReasons.Unassigned,
                Severity = NotificationSeverities.High,
                Title = summary.Count == 1
                    ? "1 work order is unassigned"
                    : $"{summary.Count} work orders are unassigned",
                Count = summary.Count,
                TriggeredAt = summary.LatestCreatedAt ?? now,
                Target = new NotificationTargetDto
                {
                    Kind = NotificationTargetKinds.Queue,
                    Queue = NotificationQueues.Unassigned
                }
            };
            return (NotificationReasons.Unassigned, summary.Count, new[] { item });
        }

        private async Task<(string, int, IReadOnlyList<NotificationItemDto>)> NoVendorAsync(
            NotificationFeedScope scope, DateTime now, CancellationToken cancellationToken)
        {
            var page = await _data.GetNoVendorAsync(scope, now.Add(NoVendorLeadTime), SectionItemLimit, cancellationToken);
            var items = page.Items.Select(candidate => new NotificationItemDto
            {
                Id = $"no-vendor-{candidate.Id}",
                Reason = NotificationReasons.NoVendor,
                Severity = NotificationSeverities.Medium,
                Title = $"{WorkOrderLabel(candidate.Id, candidate.Number)} starts within 48h with no vendor assigned",
                Count = 1,
                TriggeredAt = candidate.ScheduledDate.Subtract(NoVendorLeadTime),
                Target = WorkOrderTarget(candidate.Id, NotificationWorkOrderTabs.Info),
                WorkOrders = new[] { new NotificationWorkOrderRefDto { Id = candidate.Id, Number = candidate.Number } }
            }).ToList();
            return (NotificationReasons.NoVendor, page.Total, items);
        }

        private async Task<(string, int, IReadOnlyList<NotificationItemDto>)> AvetaMissingAsync(
            NotificationFeedScope scope, DateTime now, CancellationToken cancellationToken)
        {
            var today = NotificationBusinessTime.Today(now);
            var page = await _data.GetAvetaMissingAsync(scope, today, SectionItemLimit, cancellationToken);
            var items = page.Items.Select(candidate => new NotificationItemDto
            {
                Id = $"aveta-missing-{candidate.Id}",
                Reason = NotificationReasons.AvetaMissing,
                Severity = NotificationSeverities.Medium,
                Title = $"{WorkOrderLabel(candidate.Id, candidate.Number)} is missing the Aveta document",
                Count = 1,
                // The one-day window opens the day before the scheduled date.
                TriggeredAt = candidate.ScheduledDate.Date.AddDays(-1),
                Target = WorkOrderTarget(candidate.Id, NotificationWorkOrderTabs.Extras),
                WorkOrders = new[] { new NotificationWorkOrderRefDto { Id = candidate.Id, Number = candidate.Number } }
            }).ToList();
            return (NotificationReasons.AvetaMissing, page.Total, items);
        }

        private async Task<(string, int, IReadOnlyList<NotificationItemDto>)> VendorConflictsAsync(
            NotificationFeedScope scope, CancellationToken cancellationToken)
        {
            var dispatches = await _vendorData.GetActiveScheduledDispatchesAsync(scope.AccountId, cancellationToken);
            var pairs = VendorConflictPairs.Build(dispatches)
                .Where(pair => scope.DispatcherId == null
                    || pair.Left.AssignTo == scope.DispatcherId
                    || pair.Right.AssignTo == scope.DispatcherId)
                .ToList();
            var workOrderCount = pairs
                .SelectMany(pair => new[] { pair.Left.WorkOrderId, pair.Right.WorkOrderId })
                .Distinct()
                .Count();

            // Cap by recency like the other sections: keep the newest overlaps so a section that
            // exceeds the limit never drops a more recent conflict in favour of an older one.
            var items = pairs
                .OrderByDescending(pair => pair.Left.Start < pair.Right.Start ? pair.Left.Start : pair.Right.Start)
                .ThenByDescending(pair => pair.Left.Id)
                .ThenByDescending(pair => pair.Right.Id)
                .Take(SectionItemLimit)
                .Select(pair => new NotificationItemDto
                {
                    Id = $"vendor-conflict-{pair.Left.Id}-{pair.Right.Id}",
                    Reason = NotificationReasons.VendorConflict,
                    Severity = NotificationSeverities.Medium,
                    Title = $"{(string.IsNullOrWhiteSpace(pair.Left.VendorName) ? "Vendor" : pair.Left.VendorName)} has overlapping appointments",
                    Count = 2,
                    TriggeredAt = pair.Left.Start < pair.Right.Start ? pair.Left.Start : pair.Right.Start,
                    Target = WorkOrderTarget(pair.Left.WorkOrderId, NotificationWorkOrderTabs.Info),
                    WorkOrders = new[]
                {
                    new NotificationWorkOrderRefDto { Id = pair.Left.WorkOrderId, Number = pair.Left.WorkOrderNumber },
                    new NotificationWorkOrderRefDto { Id = pair.Right.WorkOrderId, Number = pair.Right.WorkOrderNumber }
                }
                }).ToList();
            return (NotificationReasons.VendorConflict, workOrderCount, items);
        }

        private static NotificationTargetDto WorkOrderTarget(int workOrderId, string tab) => new()
        {
            Kind = NotificationTargetKinds.WorkOrder,
            WorkOrderId = workOrderId,
            Tab = tab
        };

        private static string WorkOrderLabel(int id, string? number)
            => NotificationActivityItems.WorkOrderLabel(id, number);
    }
}