using System.Collections.Concurrent;
using System.ComponentModel.DataAnnotations;

namespace StellaOps.Scheduler.WebService.VulnerabilityResolverJobs;

/// <summary>
/// Lightweight in-memory resolver job service to satisfy API contract and rate-limit callers.
/// Suitable for stub/air-gap scenarios; replace with Mongo-backed implementation when ready.
/// </summary>
public sealed class InMemoryResolverJobService : IResolverJobService
{
    private readonly ConcurrentDictionary<string, ResolverJobResponse> _store = new(StringComparer.OrdinalIgnoreCase);
    private readonly ConcurrentDictionary<string, List<DateTimeOffset>> _tenantCreates = new(StringComparer.OrdinalIgnoreCase);
    private readonly TimeProvider _timeProvider;
    private const int MaxJobsPerMinute = 60;

    public InMemoryResolverJobService(TimeProvider? timeProvider = null)
    {
        _timeProvider = timeProvider ?? TimeProvider.System;
    }

    public Task<ResolverJobResponse> CreateAsync(string tenantId, ResolverJobRequest request, CancellationToken cancellationToken)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(tenantId);
        ArgumentNullException.ThrowIfNull(request);
        ValidateRequest(request);

        EnforceRateLimit(tenantId);

        var id = GenerateId(tenantId, request.ArtifactId, request.PolicyId);
        var created = _timeProvider.GetUtcNow();

        var response = new ResolverJobResponse(
            id,
            request.ArtifactId.Trim(),
            request.PolicyId.Trim(),
            "queued",
            created,
            CompletedAt: null,
            request.CorrelationId,
            request.Metadata ?? new Dictionary<string, string>());

        _store[id] = response;
        TrackCreate(tenantId, created);
        return Task.FromResult(response);
    }

    public Task<ResolverJobResponse?> GetAsync(string tenantId, string jobId, CancellationToken cancellationToken)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(tenantId);
        ArgumentException.ThrowIfNullOrWhiteSpace(jobId);

        _store.TryGetValue(jobId, out var response);
        return Task.FromResult(response);
    }

    public ResolverBacklogMetricsResponse ComputeMetrics(string tenantId)
    {
        var now = _timeProvider.GetUtcNow();
        var pending = new List<ResolverJobResponse>();
        var completed = new List<ResolverJobResponse>();

        foreach (var job in _store.Values)
        {
            if (string.Equals(job.Status, "completed", StringComparison.OrdinalIgnoreCase))
            {
                completed.Add(job);
            }
            else
            {
                pending.Add(job);
            }
        }

        var lagEntries = completed
            .Where(j => j.CompletedAt is not null)
            .Select(j => new ResolverLagEntry(
                j.Id,
                j.CompletedAt!.Value,
                Math.Max((j.CompletedAt!.Value - j.CreatedAt).TotalSeconds, 0d),
                j.CorrelationId,
                j.ArtifactId,
                j.PolicyId))
            .OrderByDescending(e => e.CompletedAt)
            .ToList();

        return new ResolverBacklogMetricsResponse(
            tenantId,
            Pending: pending.Count,
            Running: 0,
            Completed: completed.Count,
            Failed: 0,
            MinLagSeconds: lagEntries.Count == 0 ? null : lagEntries.Min(e => (double?)e.LagSeconds),
            MaxLagSeconds: lagEntries.Count == 0 ? null : lagEntries.Max(e => (double?)e.LagSeconds),
            AverageLagSeconds: lagEntries.Count == 0 ? null : lagEntries.Average(e => e.LagSeconds),
            RecentCompleted: lagEntries.Take(5).ToList());
    }

    private static void ValidateRequest(ResolverJobRequest request)
    {
        if (string.IsNullOrWhiteSpace(request.ArtifactId))
        {
            throw new ValidationException("artifactId is required.");
        }

        if (string.IsNullOrWhiteSpace(request.PolicyId))
        {
            throw new ValidationException("policyId is required.");
        }
    }

    private static string GenerateId(string tenantId, string artifactId, string policyId)
    {
        var raw = $"{tenantId}:{artifactId}:{policyId}:{Guid.NewGuid():N}";
        return "resolver-" + Convert.ToHexString(System.Security.Cryptography.SHA256.HashData(System.Text.Encoding.UTF8.GetBytes(raw))).ToLowerInvariant();
    }

    private void EnforceRateLimit(string tenantId)
    {
        var now = _timeProvider.GetUtcNow();
        var cutoff = now.AddMinutes(-1);
        var list = _tenantCreates.GetOrAdd(tenantId, static _ => new List<DateTimeOffset>());
        lock (list)
        {
            list.RemoveAll(ts => ts < cutoff);
            if (list.Count >= MaxJobsPerMinute)
            {
                throw new InvalidOperationException("resolver job rate limit exceeded");
            }
        }
    }

    private void TrackCreate(string tenantId, DateTimeOffset timestamp)
    {
        var list = _tenantCreates.GetOrAdd(tenantId, static _ => new List<DateTimeOffset>());
        lock (list)
        {
            list.Add(timestamp);
        }
    }
}