using ItWorx.KnowledgeHub.Application.Audit;
using ItWorx.KnowledgeHub.Application.Ingestion;
using ItWorx.KnowledgeHub.Application.Knowledge;
using ItWorx.KnowledgeHub.Application.Projects;
using ItWorx.KnowledgeHub.Domain.Attachments;

namespace ItWorx.KnowledgeHub.Application.Attachments.UseCases;

public enum UploadAttachmentStatus
{
    Success,
    PageNotFound,
    StagingSessionNotFound,
    IngestionProposalNotFound,
    ProjectNotFound,
    TooLarge,
    EmptyFile,
    InvalidFilename,
    Rejected
}

public enum AttachmentOwnerKind
{
    Page,
    StagingSession,
    IngestionProposal,
    Project
}

/// <summary>An attachment upload targets exactly one owner: either an existing,
/// already-published page, an open page-creation staging session, an ingestion
/// proposal awaiting review, or a project icon
/// (docs/adr/ADR-025-v2-r1-data-integrity-remediation.md). Both paths share the same
/// quarantine/hash/signature/dedup/commit pipeline below — only which
/// <see cref="AttachmentUsage"/> gets created differs.</summary>
public sealed record AttachmentOwner(AttachmentOwnerKind Kind, Guid Id)
{
    public static AttachmentOwner ForPage(Guid pageId) => new(AttachmentOwnerKind.Page, pageId);

    public static AttachmentOwner ForStagingSession(Guid stagingSessionId) => new(AttachmentOwnerKind.StagingSession, stagingSessionId);

    public static AttachmentOwner ForIngestionProposal(Guid proposalId) => new(AttachmentOwnerKind.IngestionProposal, proposalId);

    public static AttachmentOwner ForProject(Guid projectId) => new(AttachmentOwnerKind.Project, projectId);
}

public sealed record UploadAttachmentCommand(
    Guid WorkspaceId,
    AttachmentOwner Owner,
    string DeclaredFilename,
    string? DeclaredContentType,
    Stream Content,
    Guid ActorId,
    string? CorrelationId,
    bool DeferPersistence = false,
    long? MaximumUploadBytes = null,
    IReadOnlySet<string>? AllowedMediaTypes = null);

public sealed record UploadAttachmentResult(
    UploadAttachmentStatus Status,
    Guid? ReferenceId,
    string? StoredFilename,
    string? DetectedMediaType,
    AttachmentDeliveryPolicy? DeliveryPolicy,
    long? ByteLength,
    string? BlobSha256,
    bool NewBlobCommitted,
    string? Detail)
{
    public static UploadAttachmentResult Success(
        Guid referenceId, string storedFilename, string detectedMediaType, AttachmentDeliveryPolicy deliveryPolicy, long byteLength,
        string blobSha256, bool newBlobCommitted) =>
        new(UploadAttachmentStatus.Success, referenceId, storedFilename, detectedMediaType, deliveryPolicy, byteLength,
            blobSha256, newBlobCommitted, null);

    public static UploadAttachmentResult Failure(UploadAttachmentStatus status, string? detail = null) =>
        new(status, null, null, null, null, null, null, false, detail);
}

/// <summary>
/// The upload pipeline from docs/13-attachments.md: stream once to quarantine while
/// hashing, verify size, detect the real signature, apply delivery policy, then
/// atomically commit the blob before creating the logical reference and page usage in
/// one transaction. Every failure path discards the quarantined file
/// (docs/13-attachments.md — "remove quarantine data on every failure/cancellation").
/// </summary>
public sealed class UploadAttachmentUseCase(
    IPageRepository pages,
    IPageCreationSessionRepository stagingSessions,
    IIngestionProposalRepository ingestionProposals,
    IProjectRepository projects,
    IAttachmentRepository attachments,
    IAttachmentBlobStore blobStore,
    IContentSignatureDetector signatureDetector,
    IAuditEventRecorder auditEvents,
    AttachmentContentLock contentLock,
    TimeProvider timeProvider,
    long maximumUploadBytes = 100 * 1024 * 1024)
{
    public async Task<UploadAttachmentResult> ExecuteAsync(UploadAttachmentCommand command, CancellationToken cancellationToken)
    {
        if (command.Owner.Kind == AttachmentOwnerKind.Page)
        {
            var page = await pages.FindAsync(command.Owner.Id, cancellationToken);
            if (page is null)
            {
                return UploadAttachmentResult.Failure(UploadAttachmentStatus.PageNotFound);
            }
        }
        else if (command.Owner.Kind == AttachmentOwnerKind.StagingSession)
        {
            var now = timeProvider.GetUtcNow();
            var session = await stagingSessions.FindAsync(command.WorkspaceId, command.Owner.Id, cancellationToken);
            if (session is null || !session.IsOpen || session.IsExpired(now))
            {
                return UploadAttachmentResult.Failure(UploadAttachmentStatus.StagingSessionNotFound);
            }
        }
        else if (command.Owner.Kind == AttachmentOwnerKind.IngestionProposal)
        {
            var proposal = await ingestionProposals.FindAsync(command.WorkspaceId, command.Owner.Id, cancellationToken);
            if (proposal is null)
            {
                return UploadAttachmentResult.Failure(UploadAttachmentStatus.IngestionProposalNotFound);
            }
        }
        else
        {
            var project = await projects.FindAsync(command.Owner.Id, cancellationToken);
            if (project is null || project.WorkspaceId != command.WorkspaceId)
            {
                return UploadAttachmentResult.Failure(UploadAttachmentStatus.ProjectNotFound);
            }
        }

        SafeFilename filename;
        try
        {
            filename = SafeFilename.Create(command.DeclaredFilename);
        }
        catch (ArgumentException ex)
        {
            return UploadAttachmentResult.Failure(UploadAttachmentStatus.InvalidFilename, ex.Message);
        }

        var quarantined = await blobStore.WriteToQuarantineAsync(command.Content, cancellationToken);
        var committed = false;

        try
        {
            if (quarantined.ByteLength == 0)
            {
                return UploadAttachmentResult.Failure(UploadAttachmentStatus.EmptyFile);
            }

            var uploadLimit = Math.Min(maximumUploadBytes, command.MaximumUploadBytes ?? maximumUploadBytes);
            if (quarantined.ByteLength > uploadLimit)
            {
                return UploadAttachmentResult.Failure(
                    UploadAttachmentStatus.TooLarge,
                    $"Bestand is groter dan de toegestane {uploadLimit / (1024 * 1024)} MiB.");
            }

            var prefix = await blobStore.ReadQuarantinePrefixAsync(quarantined.QuarantineToken, 4096, cancellationToken);
            var signature = signatureDetector.Detect(prefix, command.DeclaredContentType, filename.LastExtension());

            if (signature.DeliveryPolicy == AttachmentDeliveryPolicy.Rejected)
            {
                return UploadAttachmentResult.Failure(
                    UploadAttachmentStatus.Rejected,
                    $"Bestandstype '{signature.DetectedMediaType}' wordt niet toegestaan als bijlage.");
            }

            if (command.AllowedMediaTypes is { } allowedMediaTypes && !allowedMediaTypes.Contains(signature.DetectedMediaType))
            {
                return UploadAttachmentResult.Failure(
                    UploadAttachmentStatus.Rejected,
                    $"Bestandstype '{signature.DetectedMediaType}' wordt voor dit gebruik niet toegestaan.");
            }

            // Deduplication spans both the filesystem commit and the database blob
            // row. Serialize that small critical section per content hash so two
            // concurrent requests cannot both observe "missing", race the atomic
            // rename and then race the attachment_blobs primary key. Unrelated hashes
            // remain fully concurrent; idle lock entries are removed safely.
            using var contentLease = await contentLock.AcquireAsync(quarantined.Sha256, cancellationToken);
            var now = timeProvider.GetUtcNow();
            var existingBlob = await attachments.FindBlobAsync(quarantined.Sha256, cancellationToken);

            if (existingBlob is null)
            {
                await blobStore.CommitAsync(quarantined.QuarantineToken, quarantined.Sha256, cancellationToken);
                committed = true;
                attachments.AddBlob(AttachmentBlob.Create(
                    quarantined.Sha256, quarantined.ByteLength, signature.DetectedMediaType, signature.DeliveryPolicy, now));
            }
            else
            {
                // Deduplication (docs/13-attachments.md): reuse the existing blob,
                // never store the same content twice — the quarantined duplicate is
                // discarded in the `finally` block below like any other non-committed
                // quarantine file.
            }

            var reference = AttachmentReference.Create(command.WorkspaceId, quarantined.Sha256, filename.Value, command.ActorId, now);
            attachments.AddReference(reference);
            attachments.AddUsage(command.Owner.Kind switch
            {
                AttachmentOwnerKind.Page => AttachmentUsage.ForPage(reference.Id, command.Owner.Id, now),
                AttachmentOwnerKind.StagingSession => AttachmentUsage.ForStagingSession(reference.Id, command.Owner.Id, now),
                AttachmentOwnerKind.IngestionProposal => AttachmentUsage.ForIngestionProposal(reference.Id, command.Owner.Id, now),
                AttachmentOwnerKind.Project => AttachmentUsage.ForProject(reference.Id, command.Owner.Id, now),
                _ => throw new ArgumentOutOfRangeException(nameof(command))
            });

            if (!command.DeferPersistence)
            {
                await attachments.SaveChangesAsync(cancellationToken);

                await auditEvents.RecordAsync(
                    new AuditEventRecord(
                        AuditActorKind.User,
                        command.ActorId,
                        Source: "web",
                        Action: "attachment.uploaded",
                        TargetType: "attachment_reference",
                        TargetId: reference.Id.ToString(),
                        Summary: $"Bijlage '{filename.Value}' geüpload ({quarantined.ByteLength} bytes).",
                        command.CorrelationId,
                        now),
                    cancellationToken);
            }

            return UploadAttachmentResult.Success(reference.Id, filename.Value, signature.DetectedMediaType, signature.DeliveryPolicy,
                quarantined.ByteLength, quarantined.Sha256, committed);
        }
        finally
        {
            if (!committed)
            {
                await blobStore.DiscardQuarantineAsync(quarantined.QuarantineToken, cancellationToken);
            }
        }
    }
}