namespace DSInternals.DataStore
{
    using DSInternals.Common;
    using DSInternals.Common.Data;
    using Microsoft.Database.Isam;
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Security.Principal;

    /// <summary>
    /// The DomainController class represents a domain controller in an Active Directory domain.
    /// </summary>
    public class DomainController : IDisposable, IDomainController
    {
        public const long UsnMinValue = 1;
        public const long UsnMaxValue = long.MaxValue;
        public const long EpochMinValue = 1;
        public const long EpochMaxValue = int.MaxValue;

        // List of columns in the hiddentable:
        private const string ntdsSettingsCol = "dsa_col";
        private const string osVersionMinorCol = "osminorversion_col";
        private const string osVersionMajorCol = "osmajorversion_col";
        private const string highestCommitedUsnCol = "usn_col";
        private const string backupExpirationCol = "backupexpiration_col";
        private const string backupUsnCol = "backupusn_col";
        private const string usnAtIfmCol = "usnatrifm_col";
        private const string stateCol = "state_col";
        private const string epochCol = "epoch_col";
        private const string flagsCol = "flags_col";
        
        private Cursor systemTableCursor;
        private long highestUSNCache;
        private int? epochCache;

        public DomainController(DirectoryContext context)
        {
            // TODO: Split to different methods.

            // Open the hiddentable
            this.systemTableCursor = context.OpenSystemTable();
            // Go to the first and only record in the hiddentable:
            this.systemTableCursor.MoveToFirst();
            // Load attributes from the hiddentable:
            this.NTDSSettingsDNT = this.systemTableCursor.RetrieveColumnAsInt(ntdsSettingsCol).Value;
            if(this.systemTableCursor.TableDefinition.Columns.Contains(osVersionMajorCol))
            {
                // Some databases like the initial adamntds.dit or ntds.dit on Windows Server 2003 do not contain the OS Version
                this.OSVersionMinor = this.systemTableCursor.RetrieveColumnAsUInt(osVersionMinorCol);
                this.OSVersionMajor = this.systemTableCursor.RetrieveColumnAsUInt(osVersionMajorCol);
            }
            if (this.systemTableCursor.TableDefinition.Columns.Contains(epochCol))
            {
                // This is a new feature since Windows Server 2008
                this.epochCache = this.systemTableCursor.RetrieveColumnAsInt(epochCol);
            }
            if (this.systemTableCursor.TableDefinition.Columns.Contains(usnAtIfmCol))
            {
                this.UsnAtIfm = this.systemTableCursor.RetrieveColumnAsLong(usnAtIfmCol);
            }
            this.BackupExpiration = this.systemTableCursor.RetrieveColumnAsGeneralizedTime(backupExpirationCol);
            this.BackupUsn = this.systemTableCursor.RetrieveColumnAsLong(backupUsnCol);
            this.State = (DatabaseState) this.systemTableCursor.RetrieveColumnAsInt(stateCol).Value;
            byte[] binaryFlags = this.systemTableCursor.RetrieveColumnAsByteArray(flagsCol);
            var databaseFlags = new DatabaseFlags(binaryFlags);
            this.IsADAM = databaseFlags.ADAMDatabase;
            // TODO: Export other database flags, not just IsADAM.
            // TODO: Load database health
            this.highestUSNCache = this.systemTableCursor.RetrieveColumnAsLong(highestCommitedUsnCol).Value;
            
            // Now we can load the Invocation ID and other information from the datatable:
            using (var dataTableCursor = context.OpenDataTable())
            {
                // Goto NTDS Settings object:
                DirectorySchema schema = context.Schema;
                dataTableCursor.CurrentIndex = schema.FindIndexName(CommonDirectoryAttributes.DNTag);
                bool ntdsFound = dataTableCursor.GotoKey(Key.Compose(this.NTDSSettingsDNT));
                // Load data from the NTDS Settings object
                this.InvocationId = dataTableCursor.RetrieveColumnAsGuid(schema.FindColumnId(CommonDirectoryAttributes.InvocationId)).Value;
                this.DsaGuid = dataTableCursor.RetrieveColumnAsGuid(schema.FindColumnId(CommonDirectoryAttributes.ObjectGUID)).Value;
                this.Options = dataTableCursor.RetrieveColumnAsDomainControllerOptions(schema.FindColumnId(CommonDirectoryAttributes.Options));
                string ntdsName = dataTableCursor.RetrieveColumnAsString(schema.FindColumnId(CommonDirectoryAttributes.CommonName));

                // Retrieve Configuration Naming Context
                this.ConfigurationNamingContextDNT = dataTableCursor.RetrieveColumnAsDNTag(schema.FindColumnId(CommonDirectoryAttributes.NamingContextDNTag)).Value;
                this.ConfigurationNamingContext = context.DistinguishedNameResolver.Resolve(this.ConfigurationNamingContextDNT);

                // Retrieve Schema Naming Context
                this.SchemaNamingContextDNT = dataTableCursor.RetrieveColumnAsDNTag(schema.FindColumnId(CommonDirectoryAttributes.SchemaLocation)).Value;
                this.SchemaNamingContext = context.DistinguishedNameResolver.Resolve(this.SchemaNamingContextDNT);

                // Goto DC object (parent of NTDS):
                bool dcFound = dataTableCursor.GotoToParentObject(schema);
                // Load data from the DC object
                // Load DC name:
                string dcName = dataTableCursor.RetrieveColumnAsString(schema.FindColumnId(CommonDirectoryAttributes.CommonName));
                // DC name is null in the initial database, so use NTDS Settings object's CN instead
                this.Name = dcName ?? ntdsName;

                // Load DNS Host Name
                this.DNSHostName = dataTableCursor.RetrieveColumnAsString(schema.FindColumnId(CommonDirectoryAttributes.DNSHostName));

                // Load server reference to domain partition:
                int dcDNTag = dataTableCursor.RetrieveColumnAsDNTag(schema.FindColumnId(CommonDirectoryAttributes.DNTag)).Value;
                this.ServerReferenceDNT = context.LinkResolver.GetLinkedDNTag(dcDNTag, CommonDirectoryAttributes.ServerReference);

                // Goto Servers object (parent of DC):
                bool serversFound = dataTableCursor.GotoToParentObject(schema);
                // Goto Site object (parent of servers):
                bool siteFound = dataTableCursor.GotoToParentObject(schema);
                // Load data from the Site object
                if(siteFound)
                {
                    this.SiteName = dataTableCursor.RetrieveColumnAsString(schema.FindColumnId(CommonDirectoryAttributes.CommonName));
                }

                // Load partitions (linked multivalue attribute)
                // TODO: Does not return PAS partitions on RODCs
                IEnumerable<int> partitionDNTags = context.LinkResolver.GetLinkedDNTags(this.NTDSSettingsDNT, CommonDirectoryAttributes.MasterNamingContexts);
                this.WritablePartitions = context.DistinguishedNameResolver.Resolve(partitionDNTags).Select(dn => dn.ToString()).ToArray();

                // Load domain (linked multivalue attribute)
                // TODO: Test this against a GC and RODC:
                this.DomainNamingContextDNT = context.LinkResolver.GetLinkedDNTag(this.NTDSSettingsDNT, CommonDirectoryAttributes.DomainNamingContexts);
                if (this.DomainNamingContextDNT.HasValue)
                {
                    // Move cursor to domain:
                    bool domainObjectFound = dataTableCursor.GotoKey(Key.Compose(this.DomainNamingContextDNT.Value));

                    // Load domain SID
                    this.DomainSid = dataTableCursor.RetrieveColumnAsSid(schema.FindColumnId(CommonDirectoryAttributes.ObjectSid));

                    // Load domain naming context:
                    this.DomainNamingContext = context.DistinguishedNameResolver.Resolve(this.DomainNamingContextDNT.Value);
                }

                // Goto server object in domain partition
                if (this.ServerReferenceDNT.HasValue)
                {
                    bool serverFound = dataTableCursor.GotoKey(Key.Compose(this.ServerReferenceDNT.Value));
                    this.OSName = dataTableCursor.RetrieveColumnAsString(schema.FindColumnId(CommonDirectoryAttributes.OperatingSystemName));
                    this.ServerReference = context.DistinguishedNameResolver.Resolve(this.ServerReferenceDNT.Value);
                }
            }
        }

        public int NTDSSettingsDNT
        {
            get;
            private set;
        }

        public int SchemaNamingContextDNT
        {
            get;
            private set;
        }

        public int ConfigurationNamingContextDNT
        {
            get;
            private set;
        }

        /// <summary>
        /// Gets the operating system version of this domain controller.
        /// </summary>
        public string OSVersion
        {
            get
            {
                if(this.OSVersionMajor == null)
                {
                    return null;
                }
                return String.Format("{0}.{1}", this.OSVersionMajor, this.OSVersionMinor);
            }
        }
        public uint? OSVersionMajor
        {
            get;
            private set;
        }
        public uint? OSVersionMinor
        {
            get;
            private set;
        }
        /// <summary>
        /// Gets the domain that this domain controller is a member of.
        /// </summary>
        public string Domain
        {
            get
            {
                // DomainNamingContext in ADAM DB might be null.
                return (this.DomainNamingContext != null) ? this.DomainNamingContext.GetDnsName() : null;
            }
        }

        /// <summary>
        /// Gets the SID of the domain.
        /// </summary>
        public SecurityIdentifier DomainSid
        {
            get;
            private set;
        }

        /// <summary>
        /// DSA Database Epoch
        /// </summary>
        public int? Epoch
        {
            get
            {
                return this.epochCache;
            }
            set
            {
                if(this.epochCache == null)
                {
                    // This is a legacy DB without the epoch_col, so we cannot change it.
                    // TODO: Extract as a resource.
                    throw new InvalidOperationException("Current database does not support epoch information.");
                }
                // Update table
                this.systemTableCursor.BeginEditForUpdate();
                this.systemTableCursor.EditRecord[epochCol] = value;
                this.systemTableCursor.AcceptChanges();
                // Cache the value
                this.epochCache = value;
            }
        }

        // TODO: Nullable InvocationId?
        public Guid InvocationId
        {
            get;
            private set;
        }

        public Guid DsaGuid
        {
            get;
            private set;
        }
        /// <summary>
        /// Gets the name of the directory server.
        /// </summary>
        public string Name
        {
            get;
            private set;
        }

        public string DNSHostName
        {
            get;
            private set;
        }

        public DistinguishedName ServerReference
        {
            get;
            private set;
        }

        public DateTime? BackupExpiration
        {
            get;
            private set;
        }

        /// <summary>
        /// Gets the wtitable partitions on this directory server.
        /// </summary>
        public string[] WritablePartitions
        {
            get;
            private set;
        }

        /// <summary>
        /// Gets the name of the site that this domain controller belongs to.
        /// </summary>
        public string SiteName
        {
            get;
            private set;
        }

        public DatabaseState State
        {
            get;
            private set;
        }

        public long? BackupUsn
        {
            get;
            private set;
        }

        public long? UsnAtIfm
        {
            get;
            private set;
        }

        public DomainControllerOptions Options
        {
            get;
            private set;
        }
        /// <summary>
        /// Determines if this domain controller is a global catalog server.
        /// </summary>
        public bool IsGlobalCatalog
        {
            get
            {
                return this.Options.HasFlag(DomainControllerOptions.GlobalCatalog);
            }
        }

        /// <summary>
        /// Gets or sets the highest update sequence number that has been committed to this domain controller.
        /// </summary>
        public long HighestCommittedUsn
        {
            get
            {
                return this.highestUSNCache;
            }
            set
            {
                // Update table
                this.systemTableCursor.BeginEditForUpdate();
                this.systemTableCursor.EditRecord[highestCommitedUsnCol] = value;
                this.systemTableCursor.AcceptChanges();
                // Cache the value
                this.highestUSNCache = value;
            }
        }

        /// <summary>
        /// Releases unmanaged and - optionally - managed resources.
        /// </summary>
        /// <param name="disposing"><c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged resources.</param>
        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                if (this.systemTableCursor != null)
                {
                    this.systemTableCursor.Dispose();
                    this.systemTableCursor = null;
                }
            }
        }

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        public int? DomainNamingContextDNT
        {
            get;
            private set;
        }

        public DistinguishedName DomainNamingContext
        {
            get;
            private set;
        }

        public DistinguishedName ConfigurationNamingContext
        {
            get;
            private set;
        }

        public DistinguishedName SchemaNamingContext
        {
            get;
            private set;
        }

        public int? ServerReferenceDNT
        {
            get;
            private set;
        }

        public string OSName
        {
            get;
            private set;
        }

        public bool IsADAM {
            get;
            private set;
        }
    }
}