using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.Linq;

namespace gehGassi.Permissions
{
    /// <summary>
    /// Hilfsklasse zum Packen und entpacken der Permissions
    /// </summary>
    public static class PermissionPacker
    {
        public const char PackType = 'H';
        public const int PackedSize = 4;

        public static string FormDefaultPackPrefix()
        {
            return $"{PackType}{PackedSize:D1}-";
        }

        /// <summary>
        /// Liste von Permissions in String packen
        /// </summary>
        /// <param name="permissions">Liste Permissions</param>
        /// <returns>Rechte in String gepackt</returns>
        public static string PackPermissionsIntoString(this IEnumerable<Permission> permissions)
        {
            return permissions.Aggregate(FormDefaultPackPrefix(), (s, permission) => s + ((int)permission).ToString("X4"));
        }

        /// <summary>
        /// Entpacken der Permissions aus einem string in eine Liste von ints
        /// </summary>
        /// <param name="packedPermissions">Gepackte Liste mit Permissions</param>
        /// <returns>Liste Permissions als int</returns>
        [ExcludeFromCodeCoverage]
        public static IEnumerable<int> UnpackPermissionValuesFromString(this string packedPermissions)
        {
            var packPrefix = FormDefaultPackPrefix();
            if (packedPermissions == null)
            {
                throw new ArgumentNullException(nameof(packedPermissions));
            }

            if (!packedPermissions.StartsWith(packPrefix))
            {
                throw new InvalidOperationException("The format of the packed permissions is wrong" +
                                                    $" - should start with {packPrefix}");
            }

            int index = packPrefix.Length;
            while (index < packedPermissions.Length)
            {
                yield return int.Parse(packedPermissions.Substring(index, PackedSize), NumberStyles.HexNumber);
                index += PackedSize;
            }
        }

        /// <summary>
        /// Liste von Permissions aus String entpacken
        /// </summary>
        /// <param name="packedPermissions">Gepackte Liste mit Permissions</param>
        /// <returns>Liste Permissions</returns>
        public static IEnumerable<Permission> UnpackPermissionsFromString(this string packedPermissions)
        {
            return packedPermissions.UnpackPermissionValuesFromString().Select(x => ((Permission)x));
        }

        /// <summary>
        /// Sucht eine Permission im gepackten string
        /// </summary>
        /// <param name="permissionName">Name der gesuchten Permission</param>
        /// <returns>Permission wenn gefunden, null sonst</returns>
        public static Permission? FindPermissionViaName(this string permissionName)
        {
            return Enum.TryParse(permissionName, out Permission permission)
                ? (Permission?)permission
                : null;
        }
    }
}