// Licensed to StellaOps under the AGPL-3.0-or-later license.

using System.Diagnostics;
using StellaOps.ReachGraph.Hashing;
using StellaOps.ReachGraph.Persistence;
using StellaOps.ReachGraph.WebService.Models;

namespace StellaOps.ReachGraph.WebService.Services;

/// <summary>
/// Service for verifying deterministic replay of reachability graphs.
/// </summary>
public sealed class ReachGraphReplayService : IReachGraphReplayService
{
    private readonly IReachGraphStoreService _storeService;
    private readonly IReachGraphRepository _repository;
    private readonly ReachGraphDigestComputer _digestComputer;
    private readonly ILogger<ReachGraphReplayService> _logger;

    public ReachGraphReplayService(
        IReachGraphStoreService storeService,
        IReachGraphRepository repository,
        ReachGraphDigestComputer digestComputer,
        ILogger<ReachGraphReplayService> logger)
    {
        _storeService = storeService ?? throw new ArgumentNullException(nameof(storeService));
        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
        _digestComputer = digestComputer ?? throw new ArgumentNullException(nameof(digestComputer));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    public async Task<ReplayResponse> ReplayAsync(
        ReplayRequest request,
        string tenantId,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(request);
        ArgumentException.ThrowIfNullOrEmpty(tenantId);

        var stopwatch = Stopwatch.StartNew();

        try
        {
            // Get the original graph to compare
            var original = await _storeService.GetByDigestAsync(
                request.ExpectedDigest, tenantId, cancellationToken);

            if (original is null)
            {
                stopwatch.Stop();
                return new ReplayResponse
                {
                    Match = false,
                    ComputedDigest = "N/A",
                    ExpectedDigest = request.ExpectedDigest,
                    DurationMs = (int)stopwatch.ElapsedMilliseconds,
                    Divergence = new Models.ReplayDivergence
                    {
                        NodesAdded = 0,
                        NodesRemoved = 0,
                        EdgesChanged = 0
                    }
                };
            }

            // Verify input digests match provenance
            var inputsVerified = VerifyInputs(request.Inputs, original.Provenance.Inputs);

            // Recompute digest from the stored graph (simulate replay)
            // In a full implementation, we would rebuild the graph from inputs
            var computedDigest = _digestComputer.ComputeDigest(original);

            stopwatch.Stop();

            var match = string.Equals(computedDigest, request.ExpectedDigest, StringComparison.Ordinal);

            // Log the replay attempt
            await _repository.RecordReplayAsync(new ReplayLogEntry
            {
                SubgraphDigest = request.ExpectedDigest,
                InputDigests = original.Provenance.Inputs,
                ComputedDigest = computedDigest,
                Matches = match,
                TenantId = tenantId,
                DurationMs = (int)stopwatch.ElapsedMilliseconds
            }, cancellationToken);

            _logger.LogInformation(
                "Replay verification {Result}: expected={Expected}, computed={Computed}, duration={Duration}ms",
                match ? "MATCH" : "MISMATCH",
                request.ExpectedDigest,
                computedDigest,
                stopwatch.ElapsedMilliseconds);

            return new ReplayResponse
            {
                Match = match,
                ComputedDigest = computedDigest,
                ExpectedDigest = request.ExpectedDigest,
                DurationMs = (int)stopwatch.ElapsedMilliseconds,
                InputsVerified = inputsVerified
            };
        }
        catch (Exception ex)
        {
            stopwatch.Stop();

            _logger.LogError(ex, "Replay verification failed for digest {Digest}", request.ExpectedDigest);

            return new ReplayResponse
            {
                Match = false,
                ComputedDigest = "ERROR",
                ExpectedDigest = request.ExpectedDigest,
                DurationMs = (int)stopwatch.ElapsedMilliseconds
            };
        }
    }

    private static ReplayInputsVerified VerifyInputs(
        ReplayInputs requested,
        Schema.ReachGraphInputs stored)
    {
        return new ReplayInputsVerified
        {
            Sbom = string.Equals(requested.Sbom, stored.Sbom, StringComparison.Ordinal),
            Vex = requested.Vex is not null && stored.Vex is not null
                ? string.Equals(requested.Vex, stored.Vex, StringComparison.Ordinal)
                : null,
            Callgraph = requested.Callgraph is not null && stored.Callgraph is not null
                ? string.Equals(requested.Callgraph, stored.Callgraph, StringComparison.Ordinal)
                : null,
            RuntimeFacts = requested.RuntimeFacts is not null && stored.RuntimeFacts is not null
                ? string.Equals(requested.RuntimeFacts, stored.RuntimeFacts, StringComparison.Ordinal)
                : null
        };
    }
}