using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using StellaOps.Signals.Models;
using StellaOps.Signals.Persistence;

namespace StellaOps.Signals.Services;

public sealed class RuntimeFactsIngestionService : IRuntimeFactsIngestionService
{
    private readonly IReachabilityFactRepository factRepository;
    private readonly TimeProvider timeProvider;
    private readonly ILogger<RuntimeFactsIngestionService> logger;

    public RuntimeFactsIngestionService(
        IReachabilityFactRepository factRepository,
        TimeProvider timeProvider,
        ILogger<RuntimeFactsIngestionService> logger)
    {
        this.factRepository = factRepository ?? throw new ArgumentNullException(nameof(factRepository));
        this.timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
        this.logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    public async Task<RuntimeFactsIngestResponse> IngestAsync(RuntimeFactsIngestRequest request, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(request);

        ValidateRequest(request);

        var subjectKey = request.Subject.ToSubjectKey();

        var existing = await factRepository.GetBySubjectAsync(subjectKey, cancellationToken).ConfigureAwait(false);
        var document = existing ?? new ReachabilityFactDocument
        {
            Subject = request.Subject,
            SubjectKey = subjectKey,
        };

        document.CallgraphId = request.CallgraphId;
        document.Subject = request.Subject;
        document.SubjectKey = subjectKey;
        document.ComputedAt = timeProvider.GetUtcNow();
        var aggregated = AggregateRuntimeFacts(request.Events);
        document.RuntimeFacts = MergeRuntimeFacts(document.RuntimeFacts, aggregated);
        document.Metadata = MergeMetadata(document.Metadata, request.Metadata);

        var persisted = await factRepository.UpsertAsync(document, cancellationToken).ConfigureAwait(false);

        logger.LogInformation(
            "Stored {RuntimeFactCount} runtime fact(s) for subject {SubjectKey} (callgraph={CallgraphId}).",
            persisted.RuntimeFacts?.Count ?? 0,
            subjectKey,
            request.CallgraphId);

        return new RuntimeFactsIngestResponse
        {
            FactId = persisted.Id,
            SubjectKey = subjectKey,
            CallgraphId = request.CallgraphId,
            RuntimeFactCount = persisted.RuntimeFacts?.Count ?? 0,
            TotalHitCount = persisted.RuntimeFacts?.Sum(f => f.HitCount) ?? 0,
            StoredAt = persisted.ComputedAt,
        };
    }

    private static void ValidateRequest(RuntimeFactsIngestRequest request)
    {
        if (request.Subject is null)
        {
            throw new RuntimeFactsValidationException("Subject is required.");
        }

        var subjectKey = request.Subject.ToSubjectKey();
        if (string.IsNullOrWhiteSpace(subjectKey))
        {
            throw new RuntimeFactsValidationException("Subject must include either scanId, imageDigest, or component/version.");
        }

        if (string.IsNullOrWhiteSpace(request.CallgraphId))
        {
            throw new RuntimeFactsValidationException("CallgraphId is required.");
        }

        if (request.Events is null || request.Events.Count == 0)
        {
            throw new RuntimeFactsValidationException("At least one runtime event is required.");
        }

        if (request.Events.Any(e => string.IsNullOrWhiteSpace(e.SymbolId)))
        {
            throw new RuntimeFactsValidationException("Runtime events must include symbolId.");
        }
    }

    private static List<RuntimeFactDocument> AggregateRuntimeFacts(IEnumerable<RuntimeFactEvent> events)
    {
        var map = new Dictionary<RuntimeFactKey, RuntimeFactDocument>(RuntimeFactKeyComparer.Instance);

        foreach (var evt in events)
        {
            if (string.IsNullOrWhiteSpace(evt.SymbolId))
            {
                continue;
            }

            var key = new RuntimeFactKey(evt.SymbolId.Trim(), evt.CodeId?.Trim(), evt.LoaderBase?.Trim());
            if (!map.TryGetValue(key, out var document))
            {
                document = new RuntimeFactDocument
                {
                    SymbolId = key.SymbolId,
                    CodeId = key.CodeId,
                    LoaderBase = key.LoaderBase,
                    ProcessId = evt.ProcessId,
                    ProcessName = Normalize(evt.ProcessName),
                    SocketAddress = Normalize(evt.SocketAddress),
                    ContainerId = Normalize(evt.ContainerId),
                    EvidenceUri = Normalize(evt.EvidenceUri),
                    Metadata = evt.Metadata != null
                        ? new Dictionary<string, string?>(evt.Metadata, StringComparer.Ordinal)
                        : null
                };

                map[key] = document;
            }
            else if (evt.Metadata != null && evt.Metadata.Count > 0)
            {
                document.Metadata ??= new Dictionary<string, string?>(StringComparer.Ordinal);
                foreach (var kvp in evt.Metadata)
                {
                    document.Metadata[kvp.Key] = kvp.Value;
                }
            }

            document.HitCount = Math.Clamp(document.HitCount + Math.Max(evt.HitCount, 1), 1, int.MaxValue);
        }

        return map.Values.ToList();
    }

    private static Dictionary<string, string?>? MergeMetadata(
        Dictionary<string, string?>? existing,
        Dictionary<string, string?>? incoming)
    {
        if (existing is null && incoming is null)
        {
            return null;
        }

        var merged = existing is null
            ? new Dictionary<string, string?>(StringComparer.Ordinal)
            : new Dictionary<string, string?>(existing, StringComparer.Ordinal);

        if (incoming != null)
        {
            foreach (var (metaKey, metaValue) in incoming)
            {
                merged[metaKey] = metaValue;
            }
        }

        return merged;
    }

    private static List<RuntimeFactDocument> MergeRuntimeFacts(
        List<RuntimeFactDocument>? existing,
        List<RuntimeFactDocument> incoming)
    {
        var map = new Dictionary<RuntimeFactKey, RuntimeFactDocument>(RuntimeFactKeyComparer.Instance);

        if (existing is { Count: > 0 })
        {
            foreach (var fact in existing)
            {
                var key = new RuntimeFactKey(fact.SymbolId, fact.CodeId, fact.LoaderBase);
                map[key] = new RuntimeFactDocument
                {
                    SymbolId = fact.SymbolId,
                    CodeId = fact.CodeId,
                    LoaderBase = fact.LoaderBase,
                    ProcessId = fact.ProcessId,
                    ProcessName = fact.ProcessName,
                    SocketAddress = fact.SocketAddress,
                    ContainerId = fact.ContainerId,
                    EvidenceUri = fact.EvidenceUri,
                    HitCount = fact.HitCount,
                    Metadata = fact.Metadata is null
                        ? null
                        : new Dictionary<string, string?>(fact.Metadata, StringComparer.Ordinal)
                };
            }
        }

        if (incoming.Count > 0)
        {
            foreach (var fact in incoming)
            {
                var key = new RuntimeFactKey(fact.SymbolId, fact.CodeId, fact.LoaderBase);
                if (!map.TryGetValue(key, out var existingFact))
                {
                    map[key] = new RuntimeFactDocument
                    {
                        SymbolId = fact.SymbolId,
                        CodeId = fact.CodeId,
                        LoaderBase = fact.LoaderBase,
                        ProcessId = fact.ProcessId,
                        ProcessName = fact.ProcessName,
                        SocketAddress = fact.SocketAddress,
                        ContainerId = fact.ContainerId,
                        EvidenceUri = fact.EvidenceUri,
                        HitCount = fact.HitCount,
                        Metadata = fact.Metadata is null
                            ? null
                            : new Dictionary<string, string?>(fact.Metadata, StringComparer.Ordinal)
                    };
                    continue;
                }

                existingFact.HitCount = Math.Clamp(existingFact.HitCount + fact.HitCount, 1, int.MaxValue);
                existingFact.ProcessId ??= fact.ProcessId;
                existingFact.ProcessName ??= fact.ProcessName;
                existingFact.SocketAddress ??= fact.SocketAddress;
                existingFact.ContainerId ??= fact.ContainerId;
                existingFact.EvidenceUri ??= fact.EvidenceUri;
                if (fact.Metadata != null && fact.Metadata.Count > 0)
                {
                    existingFact.Metadata ??= new Dictionary<string, string?>(StringComparer.Ordinal);
                    foreach (var (metaKey, metaValue) in fact.Metadata)
                    {
                        existingFact.Metadata[metaKey] = metaValue;
                    }
                }
            }
        }

        return map.Values
            .OrderBy(doc => doc.SymbolId, StringComparer.Ordinal)
            .ThenBy(doc => doc.CodeId, StringComparer.Ordinal)
            .ThenBy(doc => doc.LoaderBase, StringComparer.Ordinal)
            .ToList();
    }

    private static string? Normalize(string? value) =>
        string.IsNullOrWhiteSpace(value) ? null : value.Trim();

    private readonly record struct RuntimeFactKey(string SymbolId, string? CodeId, string? LoaderBase);

    private sealed class RuntimeFactKeyComparer : IEqualityComparer<RuntimeFactKey>
    {
        public static RuntimeFactKeyComparer Instance { get; } = new();

        public bool Equals(RuntimeFactKey x, RuntimeFactKey y) =>
            string.Equals(x.SymbolId, y.SymbolId, StringComparison.Ordinal) &&
            string.Equals(x.CodeId, y.CodeId, StringComparison.Ordinal) &&
            string.Equals(x.LoaderBase, y.LoaderBase, StringComparison.Ordinal);

        public int GetHashCode(RuntimeFactKey obj)
        {
            var hash = new HashCode();
            hash.Add(obj.SymbolId, StringComparer.Ordinal);
            if (obj.CodeId is not null)
            {
                hash.Add(obj.CodeId, StringComparer.Ordinal);
            }

            if (obj.LoaderBase is not null)
            {
                hash.Add(obj.LoaderBase, StringComparer.Ordinal);
            }

            return hash.ToHashCode();
        }
    }
}