using Unity.Entities;
using Unity.Mathematics;

namespace ProjectM.Simulation
{
    /// <summary>
    /// Identifies which world REGION an entity belongs to. M6 splits the single server world into two
    /// spatial regions at a large coordinate offset — the persistent home <see cref="RegionId.Base"/> and
    /// the procedurally-arranged <see cref="RegionId.Expedition"/> — and uses per-connection GhostRelevancy
    /// to replicate each region only to the connections whose player is currently in it. Server-side only
    /// (NOT a [GhostField]; the server makes all relevancy decisions). Added to players on spawn and to
    /// every region-scoped ghost the server spawns. Untagged ghosts are global (relevant to everyone).
    /// </summary>
    public struct RegionTag : IComponentData
    {
        /// <summary>Region id (see <see cref="RegionId"/>): 0 = base, 1 = expedition.</summary>
        public byte Region;
    }

    /// <summary>Region ids for <see cref="RegionTag.Region"/> (a byte, not an enum, to keep server/Burst code trivial).</summary>
    public static class RegionId
    {
        /// <summary>The persistent, shared home base.</summary>
        public const byte Base = 0;

        /// <summary>The procedural expedition field (offset far from the base on +X).</summary>
        public const byte Expedition = 1;
    }

    /// <summary>
    /// Deterministic mapping of a region id to its world-space origin. The base region keeps the existing
    /// home-base coordinates; the expedition region lives at a large +X offset so the two never overlap in
    /// the single shared PhysicsWorld. Pure (no RNG/wall-clock) — server-authoritative teleports and field
    /// spawners resolve region positions through here.
    /// </summary>
    public static class RegionMath
    {
        /// <summary>World-space X offset of the expedition region (room sub-slot 0) from the base region.</summary>
        public const float ExpeditionOffsetX = 1000f;

        /// <summary>X stride between the two ping-pong room sub-slots — kept >= any sweep/AI/aggro range so two
        /// transiently-coexisting arenas can never interact in the shared PhysicsWorld.</summary>
        public const float RoomStrideX = 500f;

        /// <summary>
        /// World-space origin of expedition room sub-slot <paramref name="subSlot"/> (0 or 1 — the run FSM
        /// ping-pongs consecutive rooms between two offsets so the next room spawns at the idle slot while the
        /// cleared one is torn down). THE single expedition coordinate authority: every expedition placement
        /// (field scatter, enemy ring, party teleport) resolves through here.
        /// </summary>
        public static float3 ExpeditionRoomOrigin(float3 baseCenter, byte subSlot)
        {
            return baseCenter + new float3(ExpeditionOffsetX + subSlot * RoomStrideX, 0f, 0f);
        }

        /// <summary>World-space origin of <paramref name="region"/>, given the base center (BaseGridMath.PlotCenter).
        /// The expedition resolves to room sub-slot 0 (legacy call sites; room-aware systems pass the ACTIVE
        /// sub-slot to <see cref="ExpeditionRoomOrigin"/> directly).</summary>
        public static float3 RegionOrigin(byte region, float3 baseCenter)
        {
            return region == RegionId.Expedition
                ? ExpeditionRoomOrigin(baseCenter, 0)
                : baseCenter;
        }
    }
}