using System.Numerics;
using System.Runtime.CompilerServices;
using Robust.Shared.Serialization;

namespace Content.Shared.Atmos
{
    /// <summary>
    ///     The reason we use this over <see cref="Direction"/> is that we are going to do some heavy bitflag usage.
    /// </summary>
    [Flags, Serializable]
    [FlagsFor(typeof(AtmosDirectionFlags))]
    public enum AtmosDirection
    {
        Invalid = 0,                        // 0
        North   = 1 << 0,                   // 1
        South   = 1 << 1,                   // 2
        East    = 1 << 2,                   // 4
        West    = 1 << 3,                   // 8
        // If more directions are added, note that AtmosDirectionHelpers.ToOppositeIndex() expects opposite directions
        // to come in pairs

        NorthEast = North | East,           // 5
        SouthEast = South | East,           // 6
        NorthWest = North | West,           // 9
        SouthWest = South | West,           // 10

        All = North | South | East | West,  // 15
    }

    public static class AtmosDirectionHelpers
    {
        public static AtmosDirection GetOpposite(this AtmosDirection direction)
        {
            return direction switch
            {
                AtmosDirection.North => AtmosDirection.South,
                AtmosDirection.South => AtmosDirection.North,
                AtmosDirection.East => AtmosDirection.West,
                AtmosDirection.West => AtmosDirection.East,
                AtmosDirection.NorthEast => AtmosDirection.SouthWest,
                AtmosDirection.NorthWest => AtmosDirection.SouthEast,
                AtmosDirection.SouthEast => AtmosDirection.NorthWest,
                AtmosDirection.SouthWest => AtmosDirection.NorthEast,
                _ => throw new ArgumentOutOfRangeException(nameof(direction))
            };
        }

        /// <summary>
        /// This returns the index that corresponds to the opposite direction of some other direction index.
        /// I.e., <c>1&lt;&lt;OppositeIndex(i) == (1&lt;&lt;i).GetOpposite()</c>
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static int ToOppositeIndex(this int index)
        {
            return index ^ 1;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static AtmosDirection ToOppositeDir(this int index)
        {
            return (AtmosDirection) (1 << (index ^ 1));
        }

        public static Direction ToDirection(this AtmosDirection direction)
        {
            return direction switch
            {
                AtmosDirection.North => Direction.North,
                AtmosDirection.South => Direction.South,
                AtmosDirection.East => Direction.East,
                AtmosDirection.West => Direction.West,
                AtmosDirection.NorthEast => Direction.NorthEast,
                AtmosDirection.NorthWest => Direction.NorthWest,
                AtmosDirection.SouthEast => Direction.SouthEast,
                AtmosDirection.SouthWest => Direction.SouthWest,
                AtmosDirection.Invalid => Direction.Invalid,
                _ => throw new ArgumentOutOfRangeException(nameof(direction))
            };
        }

        public static AtmosDirection ToAtmosDirection(this Direction direction)
        {
            return direction switch
            {
                Direction.North => AtmosDirection.North,
                Direction.South => AtmosDirection.South,
                Direction.East => AtmosDirection.East,
                Direction.West => AtmosDirection.West,
                Direction.NorthEast => AtmosDirection.NorthEast,
                Direction.NorthWest => AtmosDirection.NorthWest,
                Direction.SouthEast => AtmosDirection.SouthEast,
                Direction.SouthWest => AtmosDirection.SouthWest,
                Direction.Invalid => AtmosDirection.Invalid,
                _ => throw new ArgumentOutOfRangeException(nameof(direction))
            };
        }

        /// <summary>
        /// Converts a direction to an angle, where angle is -PI to +PI.
        /// </summary>
        /// <param name="direction"></param>
        /// <returns></returns>
        public static Angle ToAngle(this AtmosDirection direction)
        {
            return direction switch
            {
                AtmosDirection.South => Angle.Zero,
                AtmosDirection.East => new Angle(MathHelper.PiOver2),
                AtmosDirection.North => new Angle(Math.PI),
                AtmosDirection.West => new Angle(-MathHelper.PiOver2),
                AtmosDirection.NorthEast => new Angle(Math.PI*3/4),
                AtmosDirection.NorthWest => new Angle(-Math.PI*3/4),
                AtmosDirection.SouthWest => new Angle(-MathHelper.PiOver4),
                AtmosDirection.SouthEast => new Angle(MathHelper.PiOver4),

                _ => throw new ArgumentOutOfRangeException(nameof(direction), $"It was {direction}."),
            };
        }

        /// <summary>
        /// Converts an angle to a cardinal AtmosDirection
        /// </summary>
        /// <param name="angle"></param>
        /// <returns></returns>
        public static AtmosDirection ToAtmosDirectionCardinal(this Angle angle)
        {
            return angle.GetCardinalDir().ToAtmosDirection();
        }

        /// <summary>
        /// Converts an angle to an AtmosDirection
        /// </summary>
        /// <param name="angle"></param>
        /// <returns></returns>
        public static AtmosDirection ToAtmosDirection(this Angle angle)
        {
            return angle.GetDir().ToAtmosDirection();
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static int ToIndex(this AtmosDirection direction)
        {
            // This will throw if you pass an invalid direction. Not this method's fault, but yours!
            return BitOperations.Log2((uint)direction);
        }

        public static AtmosDirection WithFlag(this AtmosDirection direction, AtmosDirection other)
        {
            return direction | other;
        }

        public static AtmosDirection WithoutFlag(this AtmosDirection direction, AtmosDirection other)
        {
            return direction & ~other;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static bool IsFlagSet(this AtmosDirection direction, AtmosDirection other)
        {
            return (direction & other) == other;
        }

        public static Vector2i CardinalToIntVec(this AtmosDirection dir)
        {
            switch (dir)
            {
                case AtmosDirection.North:
                    return new Vector2i(0, 1);
                case AtmosDirection.East:
                    return new Vector2i(1, 0);
                case AtmosDirection.South:
                    return new Vector2i(0, -1);
                case AtmosDirection.West:
                    return new Vector2i(-1, 0);
                default:
                    throw new ArgumentException($"Direction dir {dir} is not a cardinal direction", nameof(dir));
            }
        }

        public static Vector2i Offset(this Vector2i pos, AtmosDirection dir)
        {
            return pos + dir.CardinalToIntVec();
        }
    }

    public sealed class AtmosDirectionFlags { }
}