using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using StellaOps.Messaging;
using StellaOps.Messaging.Abstractions;
using StellaOps.Policy.Engine.Options;
using StellaOps.Policy.Engine.Telemetry;

namespace StellaOps.Policy.Engine.EffectiveDecisionMap;

/// <summary>
/// Transport-agnostic effective decision map using StellaOps.Messaging abstractions.
/// Works with any configured transport (Valkey, PostgreSQL, InMemory).
/// </summary>
internal sealed class MessagingEffectiveDecisionMap : IEffectiveDecisionMap
{
    private readonly IDistributedCache<string, EffectiveDecisionEntry> _entryCache;
    private readonly ISortedIndex<string, string> _assetIndex;
    private readonly IDistributedCache<string, long> _versionCache;
    private readonly ILogger<MessagingEffectiveDecisionMap> _logger;
    private readonly EffectiveDecisionMapOptions _options;
    private readonly TimeProvider _timeProvider;

    private const string EntryKeyPrefix = "edm:entry";
    private const string IndexKeyPrefix = "edm:index";
    private const string VersionKeyPrefix = "edm:version";

    public MessagingEffectiveDecisionMap(
        IDistributedCacheFactory cacheFactory,
        ISortedIndexFactory sortedIndexFactory,
        ILogger<MessagingEffectiveDecisionMap> logger,
        IOptions<PolicyEngineOptions> options,
        TimeProvider timeProvider)
    {
        ArgumentNullException.ThrowIfNull(cacheFactory);
        ArgumentNullException.ThrowIfNull(sortedIndexFactory);

        _entryCache = cacheFactory.Create<string, EffectiveDecisionEntry>(new CacheOptions { KeyPrefix = "edm:entries" });
        _assetIndex = sortedIndexFactory.Create<string, string>("edm-asset-index");
        _versionCache = cacheFactory.Create<string, long>(new CacheOptions { KeyPrefix = "edm:versions" });
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _options = options?.Value.EffectiveDecisionMap ?? new EffectiveDecisionMapOptions();
        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
    }

    public async Task SetAsync(
        string tenantId,
        string snapshotId,
        EffectiveDecisionEntry entry,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(entry);

        var entryKey = GetEntryKey(tenantId, snapshotId, entry.AssetId);
        var indexKey = GetIndexKey(tenantId, snapshotId);
        var now = _timeProvider.GetUtcNow();

        var ttl = entry.ExpiresAt - now;
        if (ttl <= TimeSpan.Zero)
        {
            ttl = TimeSpan.FromMinutes(_options.DefaultTtlMinutes);
        }

        var cacheOptions = new CacheEntryOptions { TimeToLive = ttl };

        // Store entry with TTL
        await _entryCache.SetAsync(entryKey, entry, cacheOptions, cancellationToken).ConfigureAwait(false);

        // Add to sorted index by evaluated_at timestamp
        var score = entry.EvaluatedAt.ToUnixTimeMilliseconds();
        await _assetIndex.AddAsync(indexKey, entry.AssetId, score, cancellationToken).ConfigureAwait(false);

        // Set TTL on index (slightly longer than entries)
        await _assetIndex.SetExpirationAsync(indexKey, ttl.Add(TimeSpan.FromMinutes(5)), cancellationToken).ConfigureAwait(false);

        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(1,
            new KeyValuePair<string, object?>("operation", "set"),
            new KeyValuePair<string, object?>("tenant_id", tenantId));
    }

    public async Task SetBatchAsync(
        string tenantId,
        string snapshotId,
        IEnumerable<EffectiveDecisionEntry> entries,
        CancellationToken cancellationToken = default)
    {
        var now = _timeProvider.GetUtcNow();
        var indexKey = GetIndexKey(tenantId, snapshotId);
        var count = 0;
        var maxTtl = TimeSpan.Zero;

        var indexElements = new List<ScoredElement<string>>();

        foreach (var entry in entries)
        {
            var entryKey = GetEntryKey(tenantId, snapshotId, entry.AssetId);
            var ttl = entry.ExpiresAt - now;
            if (ttl <= TimeSpan.Zero)
            {
                ttl = TimeSpan.FromMinutes(_options.DefaultTtlMinutes);
            }

            if (ttl > maxTtl) maxTtl = ttl;

            var cacheOptions = new CacheEntryOptions { TimeToLive = ttl };
            await _entryCache.SetAsync(entryKey, entry, cacheOptions, cancellationToken).ConfigureAwait(false);

            indexElements.Add(new ScoredElement<string>(entry.AssetId, entry.EvaluatedAt.ToUnixTimeMilliseconds()));
            count++;
        }

        if (indexElements.Count > 0)
        {
            await _assetIndex.AddRangeAsync(indexKey, indexElements, cancellationToken).ConfigureAwait(false);
            await _assetIndex.SetExpirationAsync(indexKey, maxTtl.Add(TimeSpan.FromMinutes(5)), cancellationToken).ConfigureAwait(false);
        }

        // Increment version after batch write
        await IncrementVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);

        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(count,
            new KeyValuePair<string, object?>("operation", "set_batch"),
            new KeyValuePair<string, object?>("tenant_id", tenantId));

        _logger.LogDebug("Set {Count} effective decisions for snapshot {SnapshotId}", count, snapshotId);
    }

    public async Task<EffectiveDecisionEntry?> GetAsync(
        string tenantId,
        string snapshotId,
        string assetId,
        CancellationToken cancellationToken = default)
    {
        var entryKey = GetEntryKey(tenantId, snapshotId, assetId);
        var result = await _entryCache.GetAsync(entryKey, cancellationToken).ConfigureAwait(false);

        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(1,
            new KeyValuePair<string, object?>("operation", "get"),
            new KeyValuePair<string, object?>("tenant_id", tenantId),
            new KeyValuePair<string, object?>("cache_hit", result.HasValue));

        return result.HasValue ? result.Value : null;
    }

    public async Task<EffectiveDecisionQueryResult> GetBatchAsync(
        string tenantId,
        string snapshotId,
        IReadOnlyList<string> assetIds,
        CancellationToken cancellationToken = default)
    {
        var entries = new Dictionary<string, EffectiveDecisionEntry>();
        var notFound = new List<string>();

        foreach (var assetId in assetIds)
        {
            var entryKey = GetEntryKey(tenantId, snapshotId, assetId);
            var result = await _entryCache.GetAsync(entryKey, cancellationToken).ConfigureAwait(false);

            if (result.HasValue && result.Value is not null)
            {
                entries[assetId] = result.Value;
            }
            else
            {
                notFound.Add(assetId);
            }
        }

        var version = await GetVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);

        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(assetIds.Count,
            new KeyValuePair<string, object?>("operation", "get_batch"),
            new KeyValuePair<string, object?>("tenant_id", tenantId));

        return new EffectiveDecisionQueryResult
        {
            Entries = entries,
            NotFound = notFound,
            MapVersion = version,
            FromCache = true,
        };
    }

    public async Task<IReadOnlyList<EffectiveDecisionEntry>> GetAllForSnapshotAsync(
        string tenantId,
        string snapshotId,
        EffectiveDecisionFilter? filter = null,
        CancellationToken cancellationToken = default)
    {
        var indexKey = GetIndexKey(tenantId, snapshotId);

        // Get all asset IDs from index, ordered by score (evaluated_at) descending
        var assetElements = await _assetIndex.GetByRankAsync(
            indexKey, 0, -1, SortOrder.Descending, cancellationToken).ConfigureAwait(false);

        if (assetElements.Count == 0)
        {
            return Array.Empty<EffectiveDecisionEntry>();
        }

        var entries = new List<EffectiveDecisionEntry>();

        foreach (var element in assetElements)
        {
            var entryKey = GetEntryKey(tenantId, snapshotId, element.Element);
            var result = await _entryCache.GetAsync(entryKey, cancellationToken).ConfigureAwait(false);

            if (!result.HasValue || result.Value is null) continue;

            var entry = result.Value;

            // Apply filters
            if (filter != null)
            {
                if (filter.Statuses?.Count > 0 &&
                    !filter.Statuses.Contains(entry.Status, StringComparer.OrdinalIgnoreCase))
                {
                    continue;
                }

                if (filter.Severities?.Count > 0 &&
                    (entry.Severity is null || !filter.Severities.Contains(entry.Severity, StringComparer.OrdinalIgnoreCase)))
                {
                    continue;
                }

                if (filter.HasException == true && entry.ExceptionId is null)
                {
                    continue;
                }

                if (filter.HasException == false && entry.ExceptionId is not null)
                {
                    continue;
                }

                if (filter.MinAdvisoryCount.HasValue && entry.AdvisoryCount < filter.MinAdvisoryCount)
                {
                    continue;
                }

                if (filter.MinHighSeverityCount.HasValue && entry.HighSeverityCount < filter.MinHighSeverityCount)
                {
                    continue;
                }
            }

            entries.Add(entry);

            // Apply limit (accounting for offset)
            if (filter?.Limit > 0 && entries.Count >= filter.Limit + (filter?.Offset ?? 0))
            {
                break;
            }
        }

        // Apply offset
        if (filter?.Offset > 0)
        {
            entries = entries.Skip(filter.Offset).ToList();
        }

        // Apply final limit
        if (filter?.Limit > 0)
        {
            entries = entries.Take(filter.Limit).ToList();
        }

        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(1,
            new KeyValuePair<string, object?>("operation", "get_all"),
            new KeyValuePair<string, object?>("tenant_id", tenantId));

        return entries;
    }

    public async Task<EffectiveDecisionSummary> GetSummaryAsync(
        string tenantId,
        string snapshotId,
        CancellationToken cancellationToken = default)
    {
        var entries = await GetAllForSnapshotAsync(tenantId, snapshotId, null, cancellationToken)
            .ConfigureAwait(false);

        var statusCounts = entries
            .GroupBy(e => e.Status, StringComparer.OrdinalIgnoreCase)
            .ToDictionary(g => g.Key, g => g.Count(), StringComparer.OrdinalIgnoreCase);

        var severityCounts = entries
            .Where(e => e.Severity is not null)
            .GroupBy(e => e.Severity!, StringComparer.OrdinalIgnoreCase)
            .ToDictionary(g => g.Key, g => g.Count(), StringComparer.OrdinalIgnoreCase);

        var version = await GetVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);

        return new EffectiveDecisionSummary
        {
            SnapshotId = snapshotId,
            TotalAssets = entries.Count,
            StatusCounts = statusCounts,
            SeverityCounts = severityCounts,
            ExceptionCount = entries.Count(e => e.ExceptionId is not null),
            MapVersion = version,
            ComputedAt = _timeProvider.GetUtcNow(),
        };
    }

    public async Task InvalidateAsync(
        string tenantId,
        string snapshotId,
        string assetId,
        CancellationToken cancellationToken = default)
    {
        var entryKey = GetEntryKey(tenantId, snapshotId, assetId);
        var indexKey = GetIndexKey(tenantId, snapshotId);

        await _entryCache.InvalidateAsync(entryKey, cancellationToken).ConfigureAwait(false);
        await _assetIndex.RemoveAsync(indexKey, assetId, cancellationToken).ConfigureAwait(false);

        await IncrementVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);

        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(1,
            new KeyValuePair<string, object?>("operation", "invalidate"),
            new KeyValuePair<string, object?>("tenant_id", tenantId));
    }

    public async Task InvalidateSnapshotAsync(
        string tenantId,
        string snapshotId,
        CancellationToken cancellationToken = default)
    {
        var indexKey = GetIndexKey(tenantId, snapshotId);

        // Get all asset IDs from the index
        var assetElements = await _assetIndex.GetByRankAsync(indexKey, 0, -1, cancellationToken: cancellationToken).ConfigureAwait(false);
        var count = assetElements.Count;

        foreach (var element in assetElements)
        {
            var entryKey = GetEntryKey(tenantId, snapshotId, element.Element);
            await _entryCache.InvalidateAsync(entryKey, cancellationToken).ConfigureAwait(false);
        }

        // Delete the index
        await _assetIndex.DeleteAsync(indexKey, cancellationToken).ConfigureAwait(false);

        // Delete the version
        var versionKey = GetVersionKey(tenantId, snapshotId);
        await _versionCache.InvalidateAsync(versionKey, cancellationToken).ConfigureAwait(false);

        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(count,
            new KeyValuePair<string, object?>("operation", "invalidate_snapshot"),
            new KeyValuePair<string, object?>("tenant_id", tenantId));

        _logger.LogInformation("Invalidated {Count} entries for snapshot {SnapshotId}", count, snapshotId);
    }

    public async Task InvalidateTenantAsync(
        string tenantId,
        CancellationToken cancellationToken = default)
    {
        // Invalidate all entries and indexes for the tenant using pattern matching
        var pattern = $"{EntryKeyPrefix}:{tenantId}:*";
        var entryCount = await _entryCache.InvalidateByPatternAsync(pattern, cancellationToken).ConfigureAwait(false);

        // Note: ISortedIndex doesn't have pattern-based deletion, so we can't easily clean up indexes
        // This is a limitation of the abstraction - the Redis implementation handled this with KEYS scan

        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(entryCount,
            new KeyValuePair<string, object?>("operation", "invalidate_tenant"),
            new KeyValuePair<string, object?>("tenant_id", tenantId));

        _logger.LogInformation("Invalidated {Count} entries for tenant {TenantId}", entryCount, tenantId);
    }

    public async Task<long> GetVersionAsync(
        string tenantId,
        string snapshotId,
        CancellationToken cancellationToken = default)
    {
        var versionKey = GetVersionKey(tenantId, snapshotId);
        var result = await _versionCache.GetAsync(versionKey, cancellationToken).ConfigureAwait(false);
        return result.HasValue ? result.Value : 0;
    }

    public async Task<long> IncrementVersionAsync(
        string tenantId,
        string snapshotId,
        CancellationToken cancellationToken = default)
    {
        var versionKey = GetVersionKey(tenantId, snapshotId);
        var current = await GetVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);
        var newVersion = current + 1;

        var cacheOptions = new CacheEntryOptions
        {
            TimeToLive = TimeSpan.FromMinutes(_options.DefaultTtlMinutes + 10)
        };

        await _versionCache.SetAsync(versionKey, newVersion, cacheOptions, cancellationToken).ConfigureAwait(false);

        return newVersion;
    }

    public Task<EffectiveDecisionMapStats> GetStatsAsync(
        string? tenantId = null,
        CancellationToken cancellationToken = default)
    {
        // Stats require implementation-specific queries that aren't available through abstractions
        // Return placeholder stats - a complete implementation would need transport-specific code
        return Task.FromResult(new EffectiveDecisionMapStats
        {
            TotalEntries = 0,
            TotalSnapshots = 0,
            MemoryUsedBytes = null,
            ExpiringWithinHour = 0,
            LastEvictionAt = null,
            LastEvictionCount = 0,
        });
    }

    private static string GetEntryKey(string tenantId, string snapshotId, string assetId) =>
        $"{EntryKeyPrefix}:{tenantId}:{snapshotId}:{assetId}";

    private static string GetIndexKey(string tenantId, string snapshotId) =>
        $"{IndexKeyPrefix}:{tenantId}:{snapshotId}";

    private static string GetVersionKey(string tenantId, string snapshotId) =>
        $"{VersionKeyPrefix}:{tenantId}:{snapshotId}";
}