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 from the base region.</summary>
        public const float ExpeditionOffsetX = 1000f;

        /// <summary>World-space origin of <paramref name="region"/>, given the base center (BaseGridMath.PlotCenter).</summary>
        public static float3 RegionOrigin(byte region, float3 baseCenter)
        {
            return region == RegionId.Expedition
                ? baseCenter + new float3(ExpeditionOffsetX, 0f, 0f)
                : baseCenter;
        }
    }
}