using System.Text.Json;
using Marathon.Application.Abstractions;
using Marathon.Domain.Entities;
using Marathon.Domain.Enums;
using Marathon.Domain.ValueObjects;
using DomainEventId = Marathon.Domain.ValueObjects.EventId;

namespace Marathon.UI.Services;

/// <summary>
/// Repository-backed anomaly browsing service. Loads anomalies + their
/// originating events in a single pass, parses <c>EvidenceJson</c>, and shapes
/// <see cref="AnomalyListItem"/> / <see cref="AnomalyDetailVm"/> records for
/// the UI to consume directly.
/// </summary>
public sealed class AnomalyBrowsingService : IAnomalyBrowsingService
{
    private readonly IAnomalyRepository _anomalies;
    private readonly IEventRepository _events;

    public AnomalyBrowsingService(IAnomalyRepository anomalies, IEventRepository events)
    {
        _anomalies = anomalies ?? throw new ArgumentNullException(nameof(anomalies));
        _events = events ?? throw new ArgumentNullException(nameof(events));
    }

    public async Task<IReadOnlyList<AnomalyListItem>> ListAsync(AnomalyFilter filter, CancellationToken ct)
    {
        ArgumentNullException.ThrowIfNull(filter);

        // Date filter pushed to SQL; severity needs the parsed score and sport needs
        // the event join, so those two stay in memory over the smaller returned set.
        var all = await _anomalies.ListByDateRangeAsync(filter.From, filter.To, ct).ConfigureAwait(false);
        if (all.Count == 0) return Array.Empty<AnomalyListItem>();

        // Resolve event metadata in one batched pass — distinct EventIds only.
        var eventLookup = await BuildEventLookupAsync(all, ct).ConfigureAwait(false);

        var items = new List<AnomalyListItem>(all.Count);
        foreach (var anomaly in all)
        {
            ct.ThrowIfCancellationRequested();
            if (TryProject(anomaly, eventLookup, out var item))
            {
                items.Add(item);
            }
        }

        // Remaining filters in-memory (page-sized set).
        IEnumerable<AnomalyListItem> filtered = items;

        if (filter.MinSeverity is { } minSeverity)
        {
            filtered = filtered.Where(i => AnomalySeverityRules.MeetsThreshold(i.Severity, minSeverity));
        }

        if (filter.SportCodes is { Count: > 0 } sports)
        {
            filtered = filtered.Where(i => sports.Contains(i.Sport.Value));
        }

        if (filter.Kinds is { Count: > 0 } kinds)
        {
            filtered = filtered.Where(i => kinds.Contains(i.Kind));
        }

        // DetectedAt is the tiebreak for the score/gap sorts so order stays stable.
        var sorted = filter.Sort switch
        {
            AnomalySort.HighestScore =>
                filtered.OrderByDescending(i => i.Score).ThenByDescending(i => i.DetectedAt),
            AnomalySort.LongestGap =>
                filtered.OrderByDescending(i => i.SuspensionGapSeconds).ThenByDescending(i => i.DetectedAt),
            _ => filtered.OrderByDescending(i => i.DetectedAt),
        };

        return sorted.ToList();
    }

    public async Task<AnomalyDetailVm?> GetByIdAsync(Guid id, CancellationToken ct)
    {
        var anomaly = await _anomalies.GetAsync(id, ct).ConfigureAwait(false);
        if (anomaly is null) return null;

        var eventLookup = await BuildEventLookupAsync(new[] { anomaly }, ct).ConfigureAwait(false);
        if (!TryProject(anomaly, eventLookup, out var item)) return null;

        if (!TryParseEvidence(anomaly.EvidenceJson, out var dto)) return null;

        var pre = ToSnapshot(dto.PreSuspension);
        var post = ToSnapshot(dto.PostSuspension);

        return new AnomalyDetailVm(item, pre, post);
    }

    public Task<int> GetUnreadCountAsync(DateTimeOffset since, CancellationToken ct)
        // Server-side COUNT(*) — no longer materialises the table to count.
        => _anomalies.CountSinceAsync(since, ct);

    public async Task<IReadOnlyList<int>> ListKnownSportCodesAsync(CancellationToken ct)
    {
        var all = await _anomalies.ListAsync(ct).ConfigureAwait(false);
        if (all.Count == 0) return Array.Empty<int>();

        var lookup = await BuildEventLookupAsync(all, ct).ConfigureAwait(false);
        return all
            .Select(a => lookup.TryGetValue(a.EventId, out var ev) ? ev.Sport.Value : (int?)null)
            .Where(static x => x.HasValue)
            .Select(static x => x!.Value)
            .Distinct()
            .OrderBy(static x => x)
            .ToList();
    }

    // ---------------- internals ----------------

    private async Task<IReadOnlyDictionary<DomainEventId, Event>> BuildEventLookupAsync(
        IReadOnlyCollection<Anomaly> anomalies,
        CancellationToken ct)
    {
        var distinct = anomalies
            .Select(a => a.EventId)
            .Distinct()
            .ToList();

        // Single batched query instead of one GetAsync per distinct event (N+1).
        return await _events.GetManyAsync(distinct, ct).ConfigureAwait(false);
    }

    private static bool TryProject(
        Anomaly anomaly,
        IReadOnlyDictionary<DomainEventId, Event> events,
        out AnomalyListItem item)
    {
        item = default!;
        if (!TryParseEvidence(anomaly.EvidenceJson, out var dto)) return false;

        var severity = AnomalySeverityRules.FromScore(anomaly.Score);

        // Skip orphan anomalies whose event has been pruned — degrade gracefully rather
        // than throwing on a sentinel SportCode(0). Anomalies have an FK to events so this
        // is defensive; the feed already drops rows whose evidence won't parse.
        if (!events.TryGetValue(anomaly.EventId, out var ev) || ev is null)
            return false;

        var sport = ev.Sport;
        var country = ev.CountryCode;
        var league = ev.LeagueId;
        var title = ev.Title;

        var preSnap = ToSnapshot(dto.PreSuspension);
        var postSnap = ToSnapshot(dto.PostSuspension);

        var twoWay = dto.PreSuspension.PDraw is null && dto.PostSuspension.PDraw is null;

        item = new AnomalyListItem(
            anomaly.Id,
            anomaly.EventId,
            title,
            sport,
            country,
            league,
            anomaly.DetectedAt,
            anomaly.Score,
            severity,
            anomaly.Kind,
            dto.SuspensionGapSeconds,
            preSnap.Rate1,
            preSnap.RateDraw,
            preSnap.Rate2,
            postSnap.Rate1,
            postSnap.RateDraw,
            postSnap.Rate2,
            preSnap.Favourite,
            postSnap.Favourite,
            twoWay);

        return true;
    }

    private static bool TryParseEvidence(string evidenceJson, out EvidenceDto dto)
    {
        dto = default!;
        if (string.IsNullOrWhiteSpace(evidenceJson)) return false;
        try
        {
            var parsed = JsonSerializer.Deserialize<EvidenceDto>(evidenceJson, JsonOptions);
            if (parsed?.PreSuspension is null || parsed.PostSuspension is null) return false;
            dto = parsed;
            return true;
        }
        catch (JsonException)
        {
            return false;
        }
    }

    private static AnomalyEvidenceSnapshot ToSnapshot(EvidenceSnapshotDto dto)
    {
        var fav = ResolveFavourite(dto.P1, dto.PDraw, dto.P2);
        return new AnomalyEvidenceSnapshot(
            dto.CapturedAt,
            dto.Rate1,
            dto.RateDraw,
            dto.Rate2,
            dto.P1,
            dto.PDraw,
            dto.P2,
            fav);
    }

    private static AnomalyFavourite ResolveFavourite(decimal? p1, decimal? pDraw, decimal? p2)
    {
        // Favourite = side with the highest implied probability (lowest odds).
        var best = AnomalyFavourite.None;
        decimal bestValue = decimal.MinValue;

        if (p1 is { } v1 && v1 > bestValue) { bestValue = v1; best = AnomalyFavourite.Side1; }
        if (pDraw is { } vd && vd > bestValue) { bestValue = vd; best = AnomalyFavourite.Draw; }
        if (p2 is { } v2 && v2 > bestValue) { best = AnomalyFavourite.Side2; }

        return best;
    }

    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNameCaseInsensitive = true,
    };

    private sealed class EvidenceDto
    {
        public int SuspensionGapSeconds { get; set; }
        public EvidenceSnapshotDto PreSuspension { get; set; } = default!;
        public EvidenceSnapshotDto PostSuspension { get; set; } = default!;
    }

    private sealed class EvidenceSnapshotDto
    {
        public DateTimeOffset CapturedAt { get; set; }
        public decimal? P1 { get; set; }
        public decimal? PDraw { get; set; }
        public decimal? P2 { get; set; }
        public decimal? Rate1 { get; set; }
        public decimal? RateDraw { get; set; }
        public decimal? Rate2 { get; set; }
    }
}