using FrameworkDAL.CustomCode.AuditQuery;
using FrameworkDAL.CustomCode.ChangeTracking;
using FrameworkDAL.DTO.AuditQuery;
using GB5Shared.DTO.Framework.Login;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;

namespace FrameworkBLL.AuditQuery
{
    /// <summary>
    /// Read-only service for querying audit history.
    ///
    /// Archive fan-out: when <see cref="AuditSearchCriteriaDTO.DateFrom"/> predates the
    /// current hot-table retention boundary (UtcNow - ArchiveSettings.RetentionMonths), results
    /// are retrieved from both TEVENTLOG and TEVENTLOG_ARCHIVE and merged.
    ///
    /// Change detail: for GetByEntity and GetByUser calls, the BLL loads the associated
    /// TEVENTLOGCHANGE rows for each result and attaches them to the DTO.
    /// For SearchAudit (potentially large result sets) changes are NOT loaded by default
    /// to avoid N+1 — callers that need changes should call GetByEntity for individual records.
    /// </summary>
    public sealed class AuditQueryBLL : IAuditQueryBLL
    {
        private readonly IAuditQueryDAL       _dal;
        private readonly IChangeTrackingDAL   _changeDal;
        private readonly IOptions<ArchiveSettings> _archiveSettings;
        private readonly ILogger<AuditQueryBLL>   _logger;

        public AuditQueryBLL(
            IAuditQueryDAL dal,
            IChangeTrackingDAL changeDal,
            IOptions<ArchiveSettings> archiveSettings,
            ILogger<AuditQueryBLL> logger)
        {
            _dal             = dal;
            _changeDal       = changeDal;
            _archiveSettings = archiveSettings;
            _logger          = logger;
        }

        public async Task<string> GetByEntityAsync(
            int entityType, int entityId, int pageOffset, int pageSize,
            LoginDTO login, CancellationToken ct = default)
        {
            var rows = await _dal.GetByEntityAsync(entityType, entityId, pageOffset, pageSize, login, ct)
                .ConfigureAwait(false);

            await EnrichWithChangesAsync(rows, login, ct).ConfigureAwait(false);

            return JsonSerializer.Serialize(rows);
        }

        public async Task<string> GetByUserAsync(
            AuditSearchCriteriaDTO criteria, LoginDTO login, CancellationToken ct = default)
        {
            var rows = await _dal.GetByUserAsync(criteria, login, ct).ConfigureAwait(false);

            if (ShouldQueryArchive(criteria.DateFrom))
            {
                var archiveRows = await _dal.GetByUserArchiveAsync(criteria, login, ct).ConfigureAwait(false);
                rows = MergeAndPage(rows, archiveRows, criteria.PageOffset, criteria.PageSize);
            }

            await EnrichWithChangesAsync(rows, login, ct).ConfigureAwait(false);

            return JsonSerializer.Serialize(rows);
        }

        public async Task<string> SearchAsync(
            AuditSearchCriteriaDTO criteria, LoginDTO login, CancellationToken ct = default)
        {
            var rows = await _dal.SearchAsync(criteria, login, ct).ConfigureAwait(false);

            if (ShouldQueryArchive(criteria.DateFrom))
            {
                var archiveRows = await _dal.SearchArchiveAsync(criteria, login, ct).ConfigureAwait(false);
                rows = MergeAndPage(rows, archiveRows, criteria.PageOffset, criteria.PageSize);
            }

            // Search results do not load per-row change detail — avoid N+1 on large result sets.
            // Callers needing changes should call GetByEntity for individual rows.
            return JsonSerializer.Serialize(rows);
        }

        // ── Helpers ───────────────────────────────────────────────────────────

        private bool ShouldQueryArchive(DateTime? dateFrom)
        {
            if (dateFrom is null) return false;
            var boundary = DateTime.UtcNow.AddMonths(-_archiveSettings.Value.RetentionMonths);
            return dateFrom.Value < boundary;
        }

        private static List<AuditEventDTO> MergeAndPage(
            List<AuditEventDTO> hot,
            List<AuditEventDTO> archive,
            int pageOffset,
            int pageSize)
        {
            return hot.Concat(archive)
                .OrderByDescending(e => e.Timestamp)
                .Skip(pageOffset)
                .Take(pageSize)
                .ToList();
        }

        private async Task EnrichWithChangesAsync(
            List<AuditEventDTO> rows, LoginDTO login, CancellationToken ct)
        {
            foreach (var row in rows)
            {
                try
                {
                    row.Changes = await _changeDal
                        .GetChangesByEventLogAsync(row.EventLogId, login, ct)
                        .ConfigureAwait(false);
                }
                catch (Exception ex)
                {
                    _logger.LogWarning(ex,
                        "AuditQueryBLL: failed to load changes for EventLogId={EventLogId}", row.EventLogId);
                    // Leave Changes as empty list — do not abort the whole query
                }
            }
        }
    }

    /// <summary>
    /// Configuration for the audit archive boundary.
    /// Bound from appsettings section "ArchiveSettings".
    /// </summary>
    public sealed class ArchiveSettings
    {
        public const string Section = "ArchiveSettings";
        /// <summary>How many months of events to keep in the hot TEVENTLOG table. Default: 6.</summary>
        public int RetentionMonths { get; set; } = 6;
    }
}