using Microsoft.EntityFrameworkCore;
using ZB.MOM.WW.OtOpcUa.Admin.Services;
using ZB.MOM.WW.OtOpcUa.Configuration;
using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
using ZB.MOM.WW.OtOpcUa.Configuration.Enums;

namespace ZB.MOM.WW.OtOpcUa.Admin.Services;

/// <summary>
///     Staged-import orchestrator per Phase 6.4 Stream B.2-B.4. Covers the four operator
///     actions: CreateBatch → StageRows (chunked) → FinaliseBatch (atomic apply into
///     <see cref="Equipment"/>) → DropBatch (rollback of pre-finalise state).
/// </summary>
/// <remarks>
///     <para>FinaliseBatch runs inside one EF transaction + bulk-inserts accepted rows into
///     <see cref="Equipment"/>. Rejected rows stay behind as audit evidence; the batch row
///     gains <see cref="EquipmentImportBatch.FinalisedAtUtc"/> so future writes know it's
///     archived. DropBatch removes the batch + its cascaded rows.</para>
///
///     <para>Idempotence: calling FinaliseBatch twice throws <see cref="ImportBatchAlreadyFinalisedException"/>
///     rather than double-inserting. Operator refreshes the admin page to see the first
///     finalise completed.</para>
///
///     <para>ExternalIdReservation merging (ZTag + SAPID uniqueness) is NOT done here — a
///     narrower follow-up wires it once the concurrent-insert test matrix is green.</para>
/// </remarks>
public sealed class EquipmentImportBatchService(OtOpcUaConfigDbContext db)
{
    /// <summary>Create a new empty batch header. Returns the row with Id populated.</summary>
    public async Task<EquipmentImportBatch> CreateBatchAsync(string clusterId, string createdBy, CancellationToken ct)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(clusterId);
        ArgumentException.ThrowIfNullOrWhiteSpace(createdBy);

        var batch = new EquipmentImportBatch
        {
            Id = Guid.NewGuid(),
            ClusterId = clusterId,
            CreatedBy = createdBy,
            CreatedAtUtc = DateTime.UtcNow,
        };
        db.EquipmentImportBatches.Add(batch);
        await db.SaveChangesAsync(ct).ConfigureAwait(false);
        return batch;
    }

    /// <summary>
    ///     Stage one chunk of rows into the batch. Caller usually feeds
    ///     <see cref="EquipmentCsvImporter.Parse"/> output here — each
    ///     <see cref="EquipmentCsvRow"/> becomes one accepted <see cref="EquipmentImportRow"/>,
    ///     each rejected parser error becomes one row with <see cref="EquipmentImportRow.IsAccepted"/> false.
    /// </summary>
    public async Task StageRowsAsync(
        Guid batchId,
        IReadOnlyList<EquipmentCsvRow> acceptedRows,
        IReadOnlyList<EquipmentCsvRowError> rejectedRows,
        CancellationToken ct)
    {
        var batch = await db.EquipmentImportBatches.FirstOrDefaultAsync(b => b.Id == batchId, ct).ConfigureAwait(false)
                    ?? throw new ImportBatchNotFoundException($"Batch {batchId} not found.");

        if (batch.FinalisedAtUtc is not null)
            throw new ImportBatchAlreadyFinalisedException(
                $"Batch {batchId} finalised at {batch.FinalisedAtUtc:o}; no more rows can be staged.");

        foreach (var row in acceptedRows)
        {
            db.EquipmentImportRows.Add(new EquipmentImportRow
            {
                Id = Guid.NewGuid(),
                BatchId = batchId,
                IsAccepted = true,
                ZTag = row.ZTag,
                MachineCode = row.MachineCode,
                SAPID = row.SAPID,
                EquipmentId = row.EquipmentId,
                EquipmentUuid = row.EquipmentUuid,
                Name = row.Name,
                UnsAreaName = row.UnsAreaName,
                UnsLineName = row.UnsLineName,
                Manufacturer = row.Manufacturer,
                Model = row.Model,
                SerialNumber = row.SerialNumber,
                HardwareRevision = row.HardwareRevision,
                SoftwareRevision = row.SoftwareRevision,
                YearOfConstruction = row.YearOfConstruction,
                AssetLocation = row.AssetLocation,
                ManufacturerUri = row.ManufacturerUri,
                DeviceManualUri = row.DeviceManualUri,
            });
        }

        foreach (var error in rejectedRows)
        {
            db.EquipmentImportRows.Add(new EquipmentImportRow
            {
                Id = Guid.NewGuid(),
                BatchId = batchId,
                IsAccepted = false,
                RejectReason = error.Reason,
                LineNumberInFile = error.LineNumber,
                // Required columns need values for EF; reject rows use sentinel placeholders.
                ZTag = "", MachineCode = "", SAPID = "", EquipmentId = "", EquipmentUuid = "",
                Name = "", UnsAreaName = "", UnsLineName = "",
            });
        }

        batch.RowsStaged += acceptedRows.Count + rejectedRows.Count;
        batch.RowsAccepted += acceptedRows.Count;
        batch.RowsRejected += rejectedRows.Count;

        await db.SaveChangesAsync(ct).ConfigureAwait(false);
    }

    /// <summary>Drop the batch (pre-finalise rollback). Cascaded row delete removes staged rows.</summary>
    public async Task DropBatchAsync(Guid batchId, CancellationToken ct)
    {
        var batch = await db.EquipmentImportBatches.FirstOrDefaultAsync(b => b.Id == batchId, ct).ConfigureAwait(false);
        if (batch is null) return;
        if (batch.FinalisedAtUtc is not null)
            throw new ImportBatchAlreadyFinalisedException(
                $"Batch {batchId} already finalised at {batch.FinalisedAtUtc:o}; cannot drop.");

        db.EquipmentImportBatches.Remove(batch);
        await db.SaveChangesAsync(ct).ConfigureAwait(false);
    }

    /// <summary>
    ///     Atomic finalise. Inserts every accepted row into the live
    ///     <see cref="Equipment"/> table under the target generation + stamps
    ///     <see cref="EquipmentImportBatch.FinalisedAtUtc"/>. Failure rolls the whole tx
    ///     back — <see cref="Equipment"/> never partially mutates.
    /// </summary>
    public async Task FinaliseBatchAsync(
        Guid batchId, long generationId, string driverInstanceIdForRows, string unsLineIdForRows, CancellationToken ct)
    {
        var batch = await db.EquipmentImportBatches
            .Include(b => b.Rows)
            .FirstOrDefaultAsync(b => b.Id == batchId, ct)
            .ConfigureAwait(false)
            ?? throw new ImportBatchNotFoundException($"Batch {batchId} not found.");

        if (batch.FinalisedAtUtc is not null)
            throw new ImportBatchAlreadyFinalisedException(
                $"Batch {batchId} already finalised at {batch.FinalisedAtUtc:o}.");

        // EF InMemory provider doesn't honour BeginTransaction; SQL Server provider does.
        // Tests run the happy path under in-memory; production SQL Server runs the atomic tx.
        var supportsTx = db.Database.IsRelational();
        Microsoft.EntityFrameworkCore.Storage.IDbContextTransaction? tx = null;
        if (supportsTx)
            tx = await db.Database.BeginTransactionAsync(ct).ConfigureAwait(false);

        try
        {
            // Snapshot active reservations that overlap this batch's ZTag + SAPID set — one
            // round-trip instead of N. Released rows (ReleasedAt IS NOT NULL) are ignored so
            // an explicitly-released value can be reused.
            var accepted = batch.Rows.Where(r => r.IsAccepted).ToList();
            var zTags = accepted.Where(r => !string.IsNullOrWhiteSpace(r.ZTag))
                .Select(r => r.ZTag).Distinct(StringComparer.OrdinalIgnoreCase).ToList();
            var sapIds = accepted.Where(r => !string.IsNullOrWhiteSpace(r.SAPID))
                .Select(r => r.SAPID).Distinct(StringComparer.OrdinalIgnoreCase).ToList();

            var existingReservations = await db.ExternalIdReservations
                .Where(r => r.ReleasedAt == null &&
                    ((r.Kind == ReservationKind.ZTag && zTags.Contains(r.Value)) ||
                     (r.Kind == ReservationKind.SAPID && sapIds.Contains(r.Value))))
                .ToListAsync(ct).ConfigureAwait(false);
            var resByKey = existingReservations.ToDictionary(
                r => (r.Kind, r.Value.ToLowerInvariant()),
                r => r);

            var nowUtc = DateTime.UtcNow;
            var firstPublishedBy = batch.CreatedBy;

            foreach (var row in accepted)
            {
                var equipmentUuid = Guid.TryParse(row.EquipmentUuid, out var u) ? u : Guid.NewGuid();

                db.Equipment.Add(new Equipment
                {
                    EquipmentRowId = Guid.NewGuid(),
                    GenerationId = generationId,
                    EquipmentId = row.EquipmentId,
                    EquipmentUuid = equipmentUuid,
                    DriverInstanceId = driverInstanceIdForRows,
                    UnsLineId = unsLineIdForRows,
                    Name = row.Name,
                    MachineCode = row.MachineCode,
                    ZTag = row.ZTag,
                    SAPID = row.SAPID,
                    Manufacturer = row.Manufacturer,
                    Model = row.Model,
                    SerialNumber = row.SerialNumber,
                    HardwareRevision = row.HardwareRevision,
                    SoftwareRevision = row.SoftwareRevision,
                    YearOfConstruction = short.TryParse(row.YearOfConstruction, out var y) ? y : null,
                    AssetLocation = row.AssetLocation,
                    ManufacturerUri = row.ManufacturerUri,
                    DeviceManualUri = row.DeviceManualUri,
                });

                MergeReservation(row.ZTag, ReservationKind.ZTag, equipmentUuid, batch.ClusterId,
                    firstPublishedBy, nowUtc, resByKey);
                MergeReservation(row.SAPID, ReservationKind.SAPID, equipmentUuid, batch.ClusterId,
                    firstPublishedBy, nowUtc, resByKey);
            }

            batch.FinalisedAtUtc = nowUtc;
            try
            {
                await db.SaveChangesAsync(ct).ConfigureAwait(false);
            }
            catch (DbUpdateException ex) when (IsReservationUniquenessViolation(ex))
            {
                throw new ExternalIdReservationConflictException(
                    "Finalise rejected: one or more ZTag/SAPID values were reserved by another operator " +
                    "between batch preview and commit. Inspect active reservations + retry after resolving the conflict.",
                    ex);
            }
            if (tx is not null) await tx.CommitAsync(ct).ConfigureAwait(false);
        }
        catch
        {
            if (tx is not null) await tx.RollbackAsync(ct).ConfigureAwait(false);
            throw;
        }
        finally
        {
            if (tx is not null) await tx.DisposeAsync().ConfigureAwait(false);
        }
    }

    /// <summary>
    ///     Merge one external-ID reservation for an equipment row. Three outcomes:
    ///     (1) value is empty → skip; (2) reservation exists for same <paramref name="equipmentUuid"/>
    ///     → bump <c>LastPublishedAt</c>; (3) reservation exists for a different EquipmentUuid
    ///     → throw <see cref="ExternalIdReservationConflictException"/> with the conflicting UUID
    ///     so the caller sees which equipment already owns the value; (4) no reservation → create new.
    /// </summary>
    private void MergeReservation(
        string? value,
        ReservationKind kind,
        Guid equipmentUuid,
        string clusterId,
        string firstPublishedBy,
        DateTime nowUtc,
        Dictionary<(ReservationKind, string), ExternalIdReservation> cache)
    {
        if (string.IsNullOrWhiteSpace(value)) return;

        var key = (kind, value.ToLowerInvariant());
        if (cache.TryGetValue(key, out var existing))
        {
            if (existing.EquipmentUuid != equipmentUuid)
                throw new ExternalIdReservationConflictException(
                    $"{kind} '{value}' is already reserved by EquipmentUuid {existing.EquipmentUuid} " +
                    $"(first published {existing.FirstPublishedAt:u} on cluster '{existing.ClusterId}'). " +
                    $"Refusing to re-assign to {equipmentUuid}.");

            existing.LastPublishedAt = nowUtc;
            return;
        }

        var fresh = new ExternalIdReservation
        {
            ReservationId = Guid.NewGuid(),
            Kind = kind,
            Value = value,
            EquipmentUuid = equipmentUuid,
            ClusterId = clusterId,
            FirstPublishedAt = nowUtc,
            FirstPublishedBy = firstPublishedBy,
            LastPublishedAt = nowUtc,
        };
        db.ExternalIdReservations.Add(fresh);
        cache[key] = fresh;
    }

    /// <summary>
    ///     True when the <see cref="DbUpdateException"/> root-cause was the filtered-unique
    ///     index <c>UX_ExternalIdReservation_KindValue_Active</c> — i.e. another transaction
    ///     won the race between our cache-load + commit. SQL Server surfaces this as 2601 / 2627.
    /// </summary>
    private static bool IsReservationUniquenessViolation(DbUpdateException ex)
    {
        for (Exception? inner = ex; inner is not null; inner = inner.InnerException)
        {
            if (inner is Microsoft.Data.SqlClient.SqlException sql &&
                (sql.Number == 2601 || sql.Number == 2627) &&
                sql.Message.Contains("UX_ExternalIdReservation_KindValue_Active", StringComparison.OrdinalIgnoreCase))
            {
                return true;
            }
        }
        return false;
    }

    /// <summary>List batches created by the given user. Finalised batches are archived; include them on demand.</summary>
    public async Task<IReadOnlyList<EquipmentImportBatch>> ListByUserAsync(string createdBy, bool includeFinalised, CancellationToken ct)
    {
        var query = db.EquipmentImportBatches.AsNoTracking().Where(b => b.CreatedBy == createdBy);
        if (!includeFinalised)
            query = query.Where(b => b.FinalisedAtUtc == null);
        return await query.OrderByDescending(b => b.CreatedAtUtc).ToListAsync(ct).ConfigureAwait(false);
    }
}

public sealed class ImportBatchNotFoundException(string message) : Exception(message);
public sealed class ImportBatchAlreadyFinalisedException(string message) : Exception(message);

/// <summary>
///     Thrown when a <c>FinaliseBatchAsync</c> call detects that one of its ZTag/SAPID values is
///     already reserved by a different EquipmentUuid — either from a prior published generation
///     or a concurrent finalise that won the race. The operator sees the message + the conflicting
///     equipment ownership so they can resolve the conflict (pick a new ZTag, release the existing
///     reservation via <c>sp_ReleaseExternalIdReservation</c>, etc.) and retry the finalise.
/// </summary>
public sealed class ExternalIdReservationConflictException : Exception
{
    public ExternalIdReservationConflictException(string message) : base(message) { }
    public ExternalIdReservationConflictException(string message, Exception inner) : base(message, inner) { }
}