using System;
using System.DirectoryServices;
using System.Linq;
using DataModel.Models;
using NLog;
using SearchResult = System.DirectoryServices.SearchResult;

namespace WebInterface.Helpers
{
    /// <summary>
    /// LDAP server interface helper methods
    /// </summary>
    public class LDAPHelper
    {
        /// <summary>
        /// LDAP user lookup format
        /// </summary>
        private const string LDAP_LOOKUP_FORMAT = "(sAMAccountName={0})";

        /// <summary>
        /// Shared logger instance
        /// </summary>
        private static readonly Logger logger = LogManager.GetCurrentClassLogger();

        /// <summary>
        /// Authenticates the user's credentials against the given LDAP server
        /// </summary>
        /// <param name="username">LDAP username</param>
        /// <param name="password">LDAP password</param>
        /// <param name="serverURL">LDAP server URL</param>
        /// <param name="ldapGroup">LDAP group to filter for</param>
        /// <returns>Whether or not user's credentials are valid</returns>
        public static bool Authenticate(string username, string password, string serverURL, string ldapGroup = null)
        {
            bool result = false;

            try
            {
                //Form full LDAP URL
                string ldapURL = $"LDAP://{serverURL}";

                //Attempt to find entry
                DirectoryEntry entry = new DirectoryEntry(ldapURL, username, password);
                object val = entry.NativeObject;

                result = true;
            }
            catch (Exception error)
            {
                //Log but do not forward error
                logger.Error("Authenticate: failed to authenticate user '{0}' against LDAP server '{1}': {2}.", username, serverURL, error.Message);
            }

            return result;
        }

        /// <summary>
        /// Checks if user is in given group
        /// </summary>
        /// <param name="username">LDAP username</param>
        /// <param name="password">LDAP password</param>
        /// <param name="serverURL">LDAP server URL</param>
        /// <param name="ldapGroup">LDAP group to filter for</param>
        /// <param name="ldapFilter">LDAP search filter</param>
        /// <returns>Whether or not user belongs to given group</returns>
        public static bool IsInGroup(string username, string password, string serverURL, string ldapGroup, string ldapFilter = LDAP_LOOKUP_FORMAT)
        {
            try
            {
                //Form full LDAP URL
                string ldapURL = $"LDAP://{serverURL}";

                //Create a LDAP searcher
                DirectorySearcher searcher = new DirectorySearcher
                {
                    SearchRoot = new DirectoryEntry(ldapURL, username, password),
                    Filter = string.Format(ldapFilter, username)
                };

                foreach (SearchResult searchResult in searcher.FindAll())
                {
                    DirectoryEntry directoryEntry = searchResult.GetDirectoryEntry();
                    foreach (var groupName in directoryEntry.Properties["memberOf"])
                    {
                        if (string.Equals(groupName.ToString(), ldapGroup, StringComparison.CurrentCultureIgnoreCase))
                        {
                            return true;
                        }
                    }
                }
            }
            catch (Exception error)
            {
                //Log but do not forward error
                logger.Error("Authenticate: failed to authenticate user '{0}' against LDAP server '{1}': {2}.", username, serverURL, error.Message);
            }

            return false;
        }

        /// <summary>
        /// Searches LDAP server for matching entry
        /// </summary>
        /// <param name="serverURL">URL for LDAP server to search</param>
        /// <param name="username">LDAP server binding username</param>
        /// <param name="password">LDAP server binding password</param>
        /// <param name="ldapFilter">LDAP search filter</param>
        /// <returns>Collection of matching LDAP entries</returns>
        public static LDAPEntry LookupUser(string username, string password, string serverURL, string ldapFilter = LDAP_LOOKUP_FORMAT)
        {
            LDAPEntry result = null;

            //Form full LDAP URL
            string ldapURL = $"LDAP://{serverURL}";

            //Create a LDAP searcher
            DirectorySearcher searcher = new DirectorySearcher
            {
                SearchRoot = new DirectoryEntry(ldapURL, username, password),
                Filter = string.Format(ldapFilter, username)
            };

            //Loop through search results
            foreach (SearchResult searchResult in searcher.FindAll())
            {
                //Parse the entry's details
                result = new LDAPEntry()
                {
                    DN = ExtractProperty(searchResult, "distinguishedName"),
                    Username = username.ToLower(),
                    FirstName = ExtractProperty(searchResult, "givenName"),
                    LastName = ExtractProperty(searchResult, "sn"),
                    EmailAddress = ExtractProperty(searchResult, "mail"),
                    Title = ExtractProperty(searchResult, "title")
                };

                if (string.IsNullOrEmpty(result.FirstName) && !string.IsNullOrEmpty(result.DisplayName))
                {
                    result.FirstName = result.DisplayName;
                }

                if (string.IsNullOrEmpty(result.LastName) && !string.IsNullOrEmpty(result.DisplayName))
                {
                    result.LastName = result.DisplayName;
                }
            }

            return result;
        }

        /// <summary>
        /// Extracts the specified property from the LDAP search result
        /// </summary>
        /// <param name="result">LDAP search result to parse property from</param>
        /// <param name="key">Lookup key for property</param>
        /// <returns>Property value if it exists, empty string if it does not exist</returns>
        private static string ExtractProperty(SearchResult result, string key)
        {
            return result.Properties[key].Count > 0 ? (string)result.Properties[key][0] : string.Empty;
        }
    }
}