using System.Text.Json.Nodes;
using Microsoft.Extensions.Logging;
using StellaOps.Findings.Ledger.Domain;
using StellaOps.Findings.Ledger.Hashing;
using StellaOps.Findings.Ledger.Infrastructure;

namespace StellaOps.Findings.Ledger.Services;

public interface ILedgerEventWriteService
{
    Task<LedgerWriteResult> AppendAsync(LedgerEventDraft draft, CancellationToken cancellationToken);
}

public sealed class LedgerEventWriteService : ILedgerEventWriteService
{
    private readonly ILedgerEventRepository _repository;
    private readonly IMerkleAnchorScheduler _merkleAnchorScheduler;
    private readonly ILogger<LedgerEventWriteService> _logger;

    public LedgerEventWriteService(
        ILedgerEventRepository repository,
        IMerkleAnchorScheduler merkleAnchorScheduler,
        ILogger<LedgerEventWriteService> logger)
    {
        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
        _merkleAnchorScheduler = merkleAnchorScheduler ?? throw new ArgumentNullException(nameof(merkleAnchorScheduler));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    public async Task<LedgerWriteResult> AppendAsync(LedgerEventDraft draft, CancellationToken cancellationToken)
    {
        var validationErrors = ValidateDraft(draft);
        if (validationErrors.Count > 0)
        {
            return LedgerWriteResult.ValidationFailed([.. validationErrors]);
        }

        var existing = await _repository.GetByEventIdAsync(draft.TenantId, draft.EventId, cancellationToken).ConfigureAwait(false);
        if (existing is not null)
        {
            var canonicalJson = LedgerCanonicalJsonSerializer.Serialize(draft.CanonicalEnvelope);
            if (!string.Equals(existing.CanonicalJson, canonicalJson, StringComparison.Ordinal))
            {
                return LedgerWriteResult.Conflict(
                    "event_id_conflict",
                    $"Event '{draft.EventId}' already exists with a different payload.");
            }

            return LedgerWriteResult.Idempotent(existing);
        }

        var chainHead = await _repository.GetChainHeadAsync(draft.TenantId, draft.ChainId, cancellationToken).ConfigureAwait(false);

        var expectedSequence = chainHead is null ? 1 : chainHead.SequenceNumber + 1;
        if (draft.SequenceNumber != expectedSequence)
        {
            return LedgerWriteResult.Conflict(
                "sequence_mismatch",
                $"Sequence number '{draft.SequenceNumber}' does not match expected '{expectedSequence}'.");
        }

        var previousHash = chainHead?.EventHash ?? LedgerEventConstants.EmptyHash;
        if (draft.ProvidedPreviousHash is not null && !string.Equals(draft.ProvidedPreviousHash, previousHash, StringComparison.OrdinalIgnoreCase))
        {
            return LedgerWriteResult.Conflict(
                "previous_hash_mismatch",
                $"Provided previous hash '{draft.ProvidedPreviousHash}' does not match chain head hash '{previousHash}'.");
        }

        var canonicalEnvelope = LedgerCanonicalJsonSerializer.Canonicalize(draft.CanonicalEnvelope);
        var hashResult = LedgerHashing.ComputeHashes(canonicalEnvelope, draft.SequenceNumber);

        var eventBody = (JsonObject)canonicalEnvelope.DeepClone();
        var record = new LedgerEventRecord(
            draft.TenantId,
            draft.ChainId,
            draft.SequenceNumber,
            draft.EventId,
            draft.EventType,
            draft.PolicyVersion,
            draft.FindingId,
            draft.ArtifactId,
            draft.SourceRunId,
            draft.ActorId,
            draft.ActorType,
            draft.OccurredAt,
            draft.RecordedAt,
            eventBody,
            hashResult.EventHash,
            previousHash,
            hashResult.MerkleLeafHash,
            hashResult.CanonicalJson);

        try
        {
            await _repository.AppendAsync(record, cancellationToken).ConfigureAwait(false);
            await _merkleAnchorScheduler.EnqueueAsync(record, cancellationToken).ConfigureAwait(false);
        }
        catch (Exception ex) when (IsDuplicateKeyException(ex))
        {
            _logger.LogWarning(ex, "Ledger append detected concurrent duplicate for {EventId}", draft.EventId);
            var persisted = await _repository.GetByEventIdAsync(draft.TenantId, draft.EventId, cancellationToken).ConfigureAwait(false);
            if (persisted is null)
            {
                return LedgerWriteResult.Conflict("append_failed", "Ledger append failed due to concurrent write.");
            }

            if (!string.Equals(persisted.CanonicalJson, record.CanonicalJson, StringComparison.Ordinal))
            {
                return LedgerWriteResult.Conflict("event_id_conflict", "Ledger append raced with conflicting payload.");
            }

            return LedgerWriteResult.Idempotent(persisted);
        }

        return LedgerWriteResult.Success(record);
    }

    private static bool IsDuplicateKeyException(Exception exception)
    {
        if (exception is null)
        {
            return false;
        }

        if (exception is LedgerDuplicateEventException)
        {
            return true;
        }

        if (exception.GetType().Name.Contains("Unique", StringComparison.OrdinalIgnoreCase))
        {
            return true;
        }

        if (exception.InnerException is not null)
        {
            return IsDuplicateKeyException(exception.InnerException);
        }

        return false;
    }

    private static List<string> ValidateDraft(LedgerEventDraft draft)
    {
        var errors = new List<string>();
        if (draft is null)
        {
            errors.Add("draft_required");
            return errors;
        }

        if (string.IsNullOrWhiteSpace(draft.TenantId))
        {
            errors.Add("tenant_id_required");
        }

        if (draft.SequenceNumber < 1)
        {
            errors.Add("sequence_must_be_positive");
        }

        if (draft.EventId == Guid.Empty)
        {
            errors.Add("event_id_required");
        }

        if (draft.ChainId == Guid.Empty)
        {
            errors.Add("chain_id_required");
        }

        if (!LedgerEventConstants.SupportedEventTypes.Contains(draft.EventType))
        {
            errors.Add($"event_type_invalid:{draft.EventType}");
        }

        if (!LedgerEventConstants.SupportedActorTypes.Contains(draft.ActorType))
        {
            errors.Add($"actor_type_invalid:{draft.ActorType}");
        }

        if (string.IsNullOrWhiteSpace(draft.PolicyVersion))
        {
            errors.Add("policy_version_required");
        }

        if (string.IsNullOrWhiteSpace(draft.FindingId))
        {
            errors.Add("finding_id_required");
        }

        if (string.IsNullOrWhiteSpace(draft.ArtifactId))
        {
            errors.Add("artifact_id_required");
        }

        if (draft.Payload is null)
        {
            errors.Add("payload_required");
        }

        if (draft.CanonicalEnvelope is null)
        {
            errors.Add("canonical_envelope_required");
        }

        return errors;
    }
}