// <copyright file="AiAttestationService.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under the AGPL-3.0-or-later.
// </copyright>

using System.Collections.Concurrent;
using System.Text.Json;
using Microsoft.Extensions.Logging;
using StellaOps.AdvisoryAI.Attestation.Models;

namespace StellaOps.AdvisoryAI.Attestation;

/// <summary>
/// In-memory implementation of AI attestation service.
/// Sprint: SPRINT_20260109_011_001 Task: AIAT-003
/// </summary>
/// <remarks>
/// This implementation stores attestations in memory. For production,
/// use a database-backed implementation with signing integration.
/// </remarks>
public sealed class AiAttestationService : IAiAttestationService
{
    private readonly TimeProvider _timeProvider;
    private readonly ILogger<AiAttestationService> _logger;
    private readonly ConcurrentDictionary<string, StoredAttestation> _runAttestations = new();
    private readonly ConcurrentDictionary<string, StoredAttestation> _claimAttestations = new();

    public AiAttestationService(
        TimeProvider timeProvider,
        ILogger<AiAttestationService> logger)
    {
        _timeProvider = timeProvider;
        _logger = logger;
    }

    /// <inheritdoc/>
    public Task<AiAttestationResult> CreateRunAttestationAsync(
        AiRunAttestation attestation,
        bool sign = true,
        CancellationToken ct = default)
    {
        var now = _timeProvider.GetUtcNow();
        var digest = attestation.ComputeDigest();
        var json = JsonSerializer.Serialize(attestation, AiAttestationJsonContext.Default.AiRunAttestation);

        // In production, this would call the signer service
        string? dsseEnvelope = null;
        if (sign)
        {
            // Placeholder - real implementation would use StellaOps.Signer
            dsseEnvelope = CreateMockDsseEnvelope(AiRunAttestation.PredicateType, json);
        }

        var stored = new StoredAttestation(
            attestation.RunId,
            AiRunAttestation.PredicateType,
            json,
            digest,
            dsseEnvelope,
            now);

        _runAttestations[attestation.RunId] = stored;

        _logger.LogInformation(
            "Created run attestation {RunId} with digest {Digest}, signed={Signed}",
            attestation.RunId,
            digest,
            sign);

        return Task.FromResult(new AiAttestationResult
        {
            AttestationId = attestation.RunId,
            Digest = digest,
            Signed = sign,
            DsseEnvelope = dsseEnvelope,
            StorageUri = $"stella://ai-attestation/run/{attestation.RunId}",
            CreatedAt = now
        });
    }

    /// <inheritdoc/>
    public Task<AiAttestationResult> CreateClaimAttestationAsync(
        AiClaimAttestation attestation,
        bool sign = true,
        CancellationToken ct = default)
    {
        var now = _timeProvider.GetUtcNow();
        var digest = attestation.ComputeDigest();
        var json = JsonSerializer.Serialize(attestation, AiAttestationJsonContext.Default.AiClaimAttestation);

        string? dsseEnvelope = null;
        if (sign)
        {
            dsseEnvelope = CreateMockDsseEnvelope(AiClaimAttestation.PredicateType, json);
        }

        var stored = new StoredAttestation(
            attestation.ClaimId,
            AiClaimAttestation.PredicateType,
            json,
            digest,
            dsseEnvelope,
            now);

        _claimAttestations[attestation.ClaimId] = stored;

        _logger.LogDebug(
            "Created claim attestation {ClaimId} for run {RunId}",
            attestation.ClaimId,
            attestation.RunId);

        return Task.FromResult(new AiAttestationResult
        {
            AttestationId = attestation.ClaimId,
            Digest = digest,
            Signed = sign,
            DsseEnvelope = dsseEnvelope,
            StorageUri = $"stella://ai-attestation/claim/{attestation.ClaimId}",
            CreatedAt = now
        });
    }

    /// <inheritdoc/>
    public Task<AiAttestationVerificationResult> VerifyRunAttestationAsync(
        string runId,
        CancellationToken ct = default)
    {
        var now = _timeProvider.GetUtcNow();

        if (!_runAttestations.TryGetValue(runId, out var stored))
        {
            return Task.FromResult(AiAttestationVerificationResult.Failure(
                now,
                $"Run attestation {runId} not found"));
        }

        // Verify digest
        var attestation = JsonSerializer.Deserialize(
            stored.Json,
            AiAttestationJsonContext.Default.AiRunAttestation);

        if (attestation == null)
        {
            return Task.FromResult(AiAttestationVerificationResult.Failure(
                now,
                "Failed to deserialize attestation"));
        }

        var computedDigest = attestation.ComputeDigest();
        if (computedDigest != stored.Digest)
        {
            return Task.FromResult(AiAttestationVerificationResult.Failure(
                now,
                "Digest mismatch",
                digestValid: false));
        }

        // In production, verify signature via signer service
        bool? signatureValid = stored.DsseEnvelope != null ? true : null;

        _logger.LogDebug("Verified run attestation {RunId}", runId);

        return Task.FromResult(AiAttestationVerificationResult.Success(
            now,
            stored.DsseEnvelope != null ? "ai-attestation-key" : null));
    }

    /// <inheritdoc/>
    public Task<AiAttestationVerificationResult> VerifyClaimAttestationAsync(
        string claimId,
        CancellationToken ct = default)
    {
        var now = _timeProvider.GetUtcNow();

        if (!_claimAttestations.TryGetValue(claimId, out var stored))
        {
            return Task.FromResult(AiAttestationVerificationResult.Failure(
                now,
                $"Claim attestation {claimId} not found"));
        }

        var attestation = JsonSerializer.Deserialize(
            stored.Json,
            AiAttestationJsonContext.Default.AiClaimAttestation);

        if (attestation == null)
        {
            return Task.FromResult(AiAttestationVerificationResult.Failure(
                now,
                "Failed to deserialize attestation"));
        }

        var computedDigest = attestation.ComputeDigest();
        if (computedDigest != stored.Digest)
        {
            return Task.FromResult(AiAttestationVerificationResult.Failure(
                now,
                "Digest mismatch",
                digestValid: false));
        }

        return Task.FromResult(AiAttestationVerificationResult.Success(
            now,
            stored.DsseEnvelope != null ? "ai-attestation-key" : null));
    }

    /// <inheritdoc/>
    public Task<AiRunAttestation?> GetRunAttestationAsync(
        string runId,
        CancellationToken ct = default)
    {
        if (!_runAttestations.TryGetValue(runId, out var stored))
        {
            return Task.FromResult<AiRunAttestation?>(null);
        }

        var attestation = JsonSerializer.Deserialize(
            stored.Json,
            AiAttestationJsonContext.Default.AiRunAttestation);

        return Task.FromResult(attestation);
    }

    /// <inheritdoc/>
    public Task<IReadOnlyList<AiClaimAttestation>> GetClaimAttestationsAsync(
        string runId,
        CancellationToken ct = default)
    {
        var claims = _claimAttestations.Values
            .Select(s => JsonSerializer.Deserialize(s.Json, AiAttestationJsonContext.Default.AiClaimAttestation))
            .Where(c => c != null && c.RunId == runId)
            .Cast<AiClaimAttestation>()
            .ToList();

        return Task.FromResult<IReadOnlyList<AiClaimAttestation>>(claims);
    }

    /// <inheritdoc/>
    public Task<IReadOnlyList<AiRunAttestation>> ListRecentAttestationsAsync(
        string tenantId,
        int limit = 100,
        CancellationToken ct = default)
    {
        var attestations = _runAttestations.Values
            .OrderByDescending(s => s.CreatedAt)
            .Select(s => JsonSerializer.Deserialize(s.Json, AiAttestationJsonContext.Default.AiRunAttestation))
            .Where(a => a != null && a.TenantId == tenantId)
            .Cast<AiRunAttestation>()
            .Take(limit)
            .ToList();

        return Task.FromResult<IReadOnlyList<AiRunAttestation>>(attestations);
    }

    private static string CreateMockDsseEnvelope(string predicateType, string payload)
    {
        // Mock DSSE envelope - real implementation would use StellaOps.Signer
        var payloadBase64 = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(payload));
        return $$"""
            {
                "payloadType": "{{predicateType}}",
                "payload": "{{payloadBase64}}",
                "signatures": [{"sig": "mock-signature"}]
            }
            """;
    }

    private sealed record StoredAttestation(
        string Id,
        string PredicateType,
        string Json,
        string Digest,
        string? DsseEnvelope,
        DateTimeOffset CreatedAt);
}