using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Threading.Tasks;

using C4IT.FASD.Base;
using C4IT.Logging;

using update4u.SPS.DataLayer;

using static C4IT.Logging.cLogManager;

namespace C4IT.F4SD
{
    public partial class F4SDHelperService
    {
        private sealed class WorkspaceRoleCacheEntry
        {
            public DateTime ExpiresAtUtc { get; set; }
            public List<Guid> RoleIds { get; set; }
        }

        private static readonly object workspaceRoleCacheLock = new object();
        private static readonly Dictionary<string, WorkspaceRoleCacheEntry> workspaceRoleCache =
            new Dictionary<string, WorkspaceRoleCacheEntry>(StringComparer.OrdinalIgnoreCase);

        internal async Task<string> ApplyTicketFiltersAsync(string baseFilter, cTicketFilterPolicy policy)
        {
            var result = await TicketFilterCompiler.CompileAsync(policy, ResolveWorkspaceRolesAsync);
            if (!result.Success)
            {
                LogEntry($"Ticket filter rejected (fail closed): {result.Error}", LogLevels.Error);
                return null;
            }

            return string.IsNullOrWhiteSpace(result.Clause)
                ? baseFilter
                : $"({baseFilter}) AND ({result.Clause})";
        }

        internal cTicketFilterCapabilities GetTicketFilterCapabilities()
        {
            var capabilities = new cTicketFilterCapabilities
            {
                Provider = TicketFilterCompiler.ProviderName,
                CommonFields = new List<string> { TicketFilterCompiler.AssignmentGroupField },
                ProviderFields = new List<string> { TicketFilterCompiler.QueueField }
            };

            if (SPSDataEngineSchemaReader.ClassGetIDFromName("ESMWorkspaceClassBase") != Guid.Empty)
                capabilities.ProviderFields.Add(TicketFilterCompiler.WorkspaceField);

            return capabilities;
        }

        private async Task<TicketFilterResolution> ResolveWorkspaceRolesAsync(cTicketFilter filter)
        {
            await Task.Delay(0);
            var workspaceClassId = SPSDataEngineSchemaReader.ClassGetIDFromName("ESMWorkspaceClassBase");
            if (workspaceClassId == Guid.Empty)
                return WorkspaceFailure("ESMWorkspaceClassBase is not available.");

            var roleIds = new HashSet<Guid>();
            foreach (var value in filter?.Values ?? new List<cTicketFilterValue>())
            {
                var key = !string.IsNullOrWhiteSpace(value?.ID)
                    ? "id:" + value.ID.Trim()
                    : "name:" + value?.Name?.Trim();
                if (string.IsNullOrWhiteSpace(key) || key.EndsWith(":", StringComparison.Ordinal))
                    return WorkspaceFailure("A Workspace filter value has neither ID nor Name.");

                if (TryGetCachedWorkspaceRoles(key, out var cached))
                {
                    roleIds.UnionWith(cached);
                    continue;
                }

                DataTable table;
                try
                {
                    table = LoadWorkspaceRoles(
                        workspaceClassId,
                        !string.IsNullOrWhiteSpace(value.ID)
                            ? $"ID = '{Escape(value.ID.Trim())}'"
                            : $"Title = '{Escape(value.Name.Trim())}'");

                    // IDs are stable and therefore preferred. The name is kept as a
                    // portable fallback for configurations imported into another ESM.
                    if ((table?.Rows == null || table.Rows.Count == 0)
                        && !string.IsNullOrWhiteSpace(value.ID)
                        && !string.IsNullOrWhiteSpace(value.Name))
                    {
                        table = LoadWorkspaceRoles(
                            workspaceClassId,
                            $"Title = '{Escape(value.Name.Trim())}'");
                    }
                }
                catch (Exception exception)
                {
                    LogException(exception);
                    return WorkspaceFailure($"Workspace relation ESMWorkspaceClassBase.Roles could not be loaded for '{key}'.");
                }

                if (table?.Rows == null || table.Rows.Count == 0)
                    return WorkspaceFailure($"Workspace '{key}' was not found or has no resolvable Roles relation.");

                var workspaceIds = table.Rows.Cast<DataRow>()
                    .Select(row => getGuidFromObject(row["WorkspaceID"]))
                    .Where(id => id != Guid.Empty)
                    .Distinct()
                    .ToList();
                if (workspaceIds.Count != 1)
                    return WorkspaceFailure($"Workspace '{key}' is not unique.");

                var resolved = table.Rows.Cast<DataRow>()
                    .Select(row => getGuidFromObject(row["RoleID"]))
                    .Where(id => id != Guid.Empty)
                    .Distinct()
                    .ToList();
                if (resolved.Count == 0)
                    return WorkspaceFailure($"Workspace '{key}' contains no roles.");

                SetCachedWorkspaceRoles(key, resolved);
                roleIds.UnionWith(resolved);
            }

            return new TicketFilterResolution
            {
                Success = true,
                RoleIds = roleIds.ToList()
            };
        }

        private static DataTable LoadWorkspaceRoles(Guid workspaceClassId, string where)
        {
            return FragmentRequestBase.SimpleLoad(
                workspaceClassId,
                "ID as WorkspaceID, Title as WorkspaceTitle, Roles.T(SPSSecurityClassRole).ID as RoleID",
                where);
        }

        private static bool TryGetCachedWorkspaceRoles(string key, out List<Guid> roleIds)
        {
            lock (workspaceRoleCacheLock)
            {
                if (workspaceRoleCache.TryGetValue(key, out var entry) && entry.ExpiresAtUtc > DateTime.UtcNow)
                {
                    roleIds = new List<Guid>(entry.RoleIds);
                    return true;
                }
            }

            roleIds = null;
            return false;
        }

        private static void SetCachedWorkspaceRoles(string key, List<Guid> roleIds)
        {
            lock (workspaceRoleCacheLock)
            {
                workspaceRoleCache[key] = new WorkspaceRoleCacheEntry
                {
                    ExpiresAtUtc = DateTime.UtcNow.AddMinutes(5),
                    RoleIds = new List<Guid>(roleIds)
                };
            }
        }

        private static TicketFilterResolution WorkspaceFailure(string error)
        {
            return new TicketFilterResolution
            {
                Success = false,
                Error = error
            };
        }
    }
}