// -----------------------------------------------------------------------------
// SurfaceQueryService.cs
// Sprint: SPRINT_3700_0004_0001_reachability_integration (REACH-002, REACH-003, REACH-007)
// Description: Implementation of vulnerability surface query service.
// -----------------------------------------------------------------------------


using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace StellaOps.Scanner.Reachability.Surfaces;

/// <summary>
/// Implementation of the vulnerability surface query service.
/// Queries the database for pre-computed vulnerability surfaces.
/// </summary>
public sealed class SurfaceQueryService : ISurfaceQueryService
{
    private readonly ISurfaceRepository _repository;
    private readonly IMemoryCache _cache;
    private readonly ILogger<SurfaceQueryService> _logger;
    private readonly SurfaceQueryOptions _options;

    private static readonly TimeSpan DefaultCacheDuration = TimeSpan.FromMinutes(15);

    public SurfaceQueryService(
        ISurfaceRepository repository,
        IMemoryCache cache,
        ILogger<SurfaceQueryService> logger,
        SurfaceQueryOptions? options = null)
    {
        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
        _cache = cache ?? throw new ArgumentNullException(nameof(cache));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _options = options ?? new SurfaceQueryOptions();
    }

    /// <inheritdoc />
    public async Task<SurfaceQueryResult> QueryAsync(
        SurfaceQueryRequest request,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(request);

        var cacheKey = $"surface:{request.QueryKey}";

        // Check cache first
        if (_options.EnableCaching && _cache.TryGetValue<SurfaceQueryResult>(cacheKey, out var cached))
        {
            SurfaceQueryMetrics.CacheHits.Add(1);
            return cached!;
        }

        SurfaceQueryMetrics.CacheMisses.Add(1);

        var sw = Stopwatch.StartNew();

        try
        {
            // Query repository
            var surface = await _repository.GetSurfaceAsync(
                request.CveId,
                request.Ecosystem,
                request.PackageName,
                request.Version,
                cancellationToken);

            SurfaceQueryResult result;

            if (surface is not null)
            {
                // Surface found - get triggers
                var triggers = await _repository.GetTriggersAsync(
                    surface.Id,
                    request.MaxTriggers,
                    cancellationToken);

                var sinks = await _repository.GetSinksAsync(surface.Id, cancellationToken);

                result = SurfaceQueryResult.Found(
                    surface.Id,
                    triggers,
                    sinks,
                    surface.ComputedAt);

                SurfaceQueryMetrics.SurfaceHits.Add(1);
                _logger.LogDebug(
                    "Surface found for {CveId}/{PackageName}: {TriggerCount} triggers, {SinkCount} sinks",
                    request.CveId, request.PackageName, triggers.Count, sinks.Count);
            }
            else
            {
                // Surface not found - apply fallback cascade
                result = ApplyFallbackCascade(request);
                SurfaceQueryMetrics.SurfaceMisses.Add(1);
            }

            sw.Stop();
            SurfaceQueryMetrics.QueryDurationMs.Record(sw.ElapsedMilliseconds);

            // Cache result
            if (_options.EnableCaching)
            {
                var cacheOptions = new MemoryCacheEntryOptions
                {
                    AbsoluteExpirationRelativeToNow = _options.CacheDuration ?? DefaultCacheDuration
                };
                _cache.Set(cacheKey, result, cacheOptions);
            }

            return result;
        }
        catch (Exception ex)
        {
            sw.Stop();
            SurfaceQueryMetrics.QueryErrors.Add(1);
            _logger.LogWarning(ex, "Failed to query surface for {CveId}/{PackageName}", request.CveId, request.PackageName);

            return SurfaceQueryResult.FallbackToPackageApi($"Query failed: {ex.Message}");
        }
    }

    /// <inheritdoc />
    public async Task<IReadOnlyDictionary<string, SurfaceQueryResult>> QueryBulkAsync(
        IEnumerable<SurfaceQueryRequest> requests,
        CancellationToken cancellationToken = default)
    {
        var requestList = requests.ToList();
        var results = new Dictionary<string, SurfaceQueryResult>(requestList.Count);

        // Split into cached and uncached
        var uncachedRequests = new List<SurfaceQueryRequest>();
        foreach (var request in requestList)
        {
            var cacheKey = $"surface:{request.QueryKey}";
            if (_options.EnableCaching && _cache.TryGetValue<SurfaceQueryResult>(cacheKey, out var cached))
            {
                results[request.QueryKey] = cached!;
                SurfaceQueryMetrics.CacheHits.Add(1);
            }
            else
            {
                uncachedRequests.Add(request);
                SurfaceQueryMetrics.CacheMisses.Add(1);
            }
        }

        // Query remaining in parallel batches
        if (uncachedRequests.Count > 0)
        {
            var batchSize = _options.BulkQueryBatchSize;
            var batches = uncachedRequests
                .Select((r, i) => new { Request = r, Index = i })
                .GroupBy(x => x.Index / batchSize)
                .Select(g => g.Select(x => x.Request).ToList());

            foreach (var batch in batches)
            {
                var tasks = batch.Select(r => QueryAsync(r, cancellationToken));
                var batchResults = await Task.WhenAll(tasks);

                for (var i = 0; i < batch.Count; i++)
                {
                    results[batch[i].QueryKey] = batchResults[i];
                }
            }
        }

        return results;
    }

    /// <inheritdoc />
    public async Task<bool> ExistsAsync(
        string cveId,
        string ecosystem,
        string packageName,
        string version,
        CancellationToken cancellationToken = default)
    {
        var cacheKey = $"surface_exists:{cveId}|{ecosystem}|{packageName}|{version}";

        if (_options.EnableCaching && _cache.TryGetValue<bool>(cacheKey, out var exists))
        {
            return exists;
        }

        var result = await _repository.ExistsAsync(cveId, ecosystem, packageName, version, cancellationToken);

        if (_options.EnableCaching)
        {
            _cache.Set(cacheKey, result, TimeSpan.FromMinutes(5));
        }

        return result;
    }

    private SurfaceQueryResult ApplyFallbackCascade(SurfaceQueryRequest request)
    {
        _logger.LogDebug(
            "No surface for {CveId}/{PackageName} v{Version}, applying fallback cascade",
            request.CveId, request.PackageName, request.Version);

        // Fallback cascade:
        // 1. If we have package API info, use that
        // 2. Otherwise, fall back to "all methods" mode

        // For now, return FallbackAll - in future we can add PackageApi lookup
        return SurfaceQueryResult.NotFound(request.CveId, request.PackageName);
    }
}

/// <summary>
/// Options for surface query service.
/// </summary>
public sealed record SurfaceQueryOptions
{
    /// <summary>
    /// Whether to enable in-memory caching.
    /// </summary>
    public bool EnableCaching { get; init; } = true;

    /// <summary>
    /// Cache duration for surface results.
    /// </summary>
    public TimeSpan? CacheDuration { get; init; }

    /// <summary>
    /// Batch size for bulk queries.
    /// </summary>
    public int BulkQueryBatchSize { get; init; } = 10;
}

/// <summary>
/// Metrics for surface query service.
/// </summary>
internal static class SurfaceQueryMetrics
{
    private static readonly string MeterName = "StellaOps.Scanner.Reachability.Surfaces";

    public static readonly System.Diagnostics.Metrics.Counter<long> CacheHits =
        new System.Diagnostics.Metrics.Meter(MeterName).CreateCounter<long>(
            "stellaops.surface_query.cache_hits",
            description: "Number of surface query cache hits");

    public static readonly System.Diagnostics.Metrics.Counter<long> CacheMisses =
        new System.Diagnostics.Metrics.Meter(MeterName).CreateCounter<long>(
            "stellaops.surface_query.cache_misses",
            description: "Number of surface query cache misses");

    public static readonly System.Diagnostics.Metrics.Counter<long> SurfaceHits =
        new System.Diagnostics.Metrics.Meter(MeterName).CreateCounter<long>(
            "stellaops.surface_query.surface_hits",
            description: "Number of surfaces found");

    public static readonly System.Diagnostics.Metrics.Counter<long> SurfaceMisses =
        new System.Diagnostics.Metrics.Meter(MeterName).CreateCounter<long>(
            "stellaops.surface_query.surface_misses",
            description: "Number of surfaces not found");

    public static readonly System.Diagnostics.Metrics.Counter<long> QueryErrors =
        new System.Diagnostics.Metrics.Meter(MeterName).CreateCounter<long>(
            "stellaops.surface_query.errors",
            description: "Number of query errors");

    public static readonly System.Diagnostics.Metrics.Histogram<long> QueryDurationMs =
        new System.Diagnostics.Metrics.Meter(MeterName).CreateHistogram<long>(
            "stellaops.surface_query.duration_ms",
            unit: "ms",
            description: "Surface query duration in milliseconds");
}