using System;
using System.Collections.Generic;
using System.Linq;
using xCommons.Extensions;

namespace xDataService.Helpers {
    public partial class XCursorHelper {
        public static string ToCursor<T> (T id) {
            //
            // Check Numbers ...
            if (id.ToString ().IsDigits ()) {
                return Convert
                    .ToBase64String (BitConverter
                        .GetBytes (Convert.ToInt32 (id))
                    );
            } else
                //
                // Check Guid ...
                if (id.ToString ().IsGuid ()) {
                    return Convert
                        .ToBase64String (new Guid (id.ToString ())
                            .ToByteArray ());
                } else
            //
            // Assume as String ...
            {
                return Convert
                    .ToBase64String (id
                        .ToString ().ToBytes ());
            }
        }

        public static T FromCursor<T> (string cursor) {
            //
            // Check Numbers ...
            var returnType = typeof (T);
            if (returnType == typeof (int) ||
                returnType == typeof (long) ||
                returnType == typeof (decimal)) {
                return Convert.ChangeType ((BitConverter
                        .ToInt32 (Convert
                            .FromBase64String (cursor),
                            0
                        ))
                    .ToDynamicObject (), returnType);
            } else
                //
                // Check Guid ...
                if (returnType == typeof (Guid)) {
                    return Convert.ChangeType ((new Guid (
                            Convert.FromBase64String (cursor)
                        ))
                        .ToDynamicObject (), returnType);
                } else
            //
            // Assume as String ...
            {
                return Convert.ChangeType ((
                        Convert.FromBase64String (cursor)
                    )
                    .ToDynamicObject (), returnType);
            }
        }

        public static (string firstCursor, string lastCursor) GetFirstAndLastCursor<T> (IEnumerable<T> ids) {
            //
            if (ids?.Any () != true) {
                return (null, null);
            }

            //
            var firstCursor = ToCursor (ids.First ());
            var lastCursor = ToCursor (ids.Last ());

            //
            return (firstCursor, lastCursor);
        }
    }
}