// Assets/_Project/Scripts/Gameplay/EnemyHealth.cs
using Unity.Netcode;
using UnityEngine;
using TD.Core;

namespace TD.Gameplay
{
    /// <summary>
    /// Per-enemy HP component. Single point through which all damage flows so
    /// resistance lookups (Phase 1.5+) and kill attribution remain in one place.
    /// </summary>
    /// <remarks>
    /// <b>Initialization:</b> Call <see cref="InitializeServer"/> on the server
    /// immediately after <c>Instantiate</c> and before <c>NetworkObject.Spawn()</c>,
    /// following the same pattern as <c>TowerInstance.InitializeServer</c>.
    ///
    /// <b>Kill attribution:</b> <see cref="LastHitOwner"/> tracks the
    /// <see cref="PlayerSlot"/> of the tower that most recently dealt direct damage.
    /// DoT ticks from <c>EnemyStatus</c> also carry an owner so the credit
    /// follows the source tower, not the DoT applicator.
    ///
    /// <b>Death flow (server-only):</b> <see cref="TakeDamage"/> clamps HP to 0,
    /// fires <see cref="OnDied"/>, then calls <c>NetworkObject.Despawn</c>.
    /// Subscribers must not touch the NetworkObject after <see cref="OnDied"/> returns.
    /// </remarks>
    [RequireComponent(typeof(NetworkObject))]
    public class EnemyHealth : NetworkBehaviour
    {
        // ----- Pre-spawn init (server-local) ----------------------------------

        private float     pendingMaxHp    = 100f;
        private int       pendingGoldReward;
        private int       pendingLivesCost = 1;
        private bool      pendingIsFlying;
        private bool      hasPendingInit;

        // ----- Server-local runtime state -------------------------------------

        /// <summary>Gold awarded to the killing player when this enemy dies.</summary>
        public int GoldReward { get; private set; }

        /// <summary>Lives deducted from the shared pool when this enemy reaches the goal.</summary>
        public int LivesCost { get; private set; } = 1;

        /// <summary>
        /// The <see cref="PlayerSlot"/> of the tower that last dealt direct damage.
        /// Used by <c>WaveManager</c> to award kill gold to the correct player.
        /// Updated on every <see cref="TakeDamage"/> call, including DoT ticks whose
        /// source owner is tracked on <see cref="EnemyStatus.StatusEffect"/>.
        /// </summary>
        public PlayerSlot LastHitOwner { get; private set; } = PlayerSlot.None;

        // ----- Networked state ------------------------------------------------

        private readonly NetworkVariable<float> hp = new NetworkVariable<float>(
            0f,
            NetworkVariableReadPermission.Everyone,
            NetworkVariableWritePermission.Server);

        private readonly NetworkVariable<bool> isFlying = new NetworkVariable<bool>(
            false,
            NetworkVariableReadPermission.Everyone,
            NetworkVariableWritePermission.Server);

        // ----- Public state ---------------------------------------------------

        public float CurrentHp => hp.Value;
        public float MaxHp     { get; private set; } = 100f;
        public bool  IsDead    => hp.Value <= 0f;

        /// <summary>
        /// True if this enemy flies over tower footprints.
        /// Replicated so client visuals can adjust altitude.
        /// Grounded towers with GroundedOnly=true will not target flying enemies.
        /// </summary>
        public bool IsFlying => isFlying.Value;

        // ----- Events ---------------------------------------------------------

        /// <summary>
        /// Fired on the server immediately before the enemy NetworkObject is despawned.
        /// <c>WaveManager</c> subscribes to credit kill gold and decrement wave count.
        /// Do not access the NetworkObject after this event returns.
        /// </summary>
        public event System.Action<EnemyHealth> OnDied;

        // ----- Server-only pre-spawn init -------------------------------------

        /// <summary>
        /// Called by <c>WaveManager</c> on the server after <c>Instantiate</c>
        /// and before <c>NetworkObject.Spawn()</c>. Mirrors the
        /// <c>TowerInstance.InitializeServer</c> pattern.
        /// </summary>
        public void InitializeServer(float maxHp, int goldReward, int livesCost, bool flying)
        {
            pendingMaxHp      = maxHp;
            pendingGoldReward = goldReward;
            pendingLivesCost  = livesCost;
            pendingIsFlying   = flying;
            hasPendingInit    = true;

            // Cache locally on the server immediately — clients resolve via NV.
            MaxHp      = maxHp;
            GoldReward = goldReward;
            LivesCost  = livesCost;
        }

        // ----- NGO lifecycle --------------------------------------------------

        public override void OnNetworkSpawn()
        {
            if (IsServer && hasPendingInit)
            {
                hp.Value       = pendingMaxHp;
                isFlying.Value = pendingIsFlying;
                hasPendingInit = false;
            }

            // Non-server clients resolve MaxHp from the replicated hp initial value.
            if (!IsServer)
                MaxHp = hp.Value;
        }

        // ----- Server API -----------------------------------------------------

        /// <summary>
        /// Applies damage to this enemy. Server-only; silently no-ops on clients.
        /// <paramref name="type"/> is accepted for future resistance lookups (Phase 1.5+).
        /// <paramref name="attackerSlot"/> identifies the tower owner for kill attribution.
        /// </summary>
        public void TakeDamage(float damage, DamageType type, PlayerSlot attackerSlot)
        {
            if (!IsServer) return;
            if (IsDead)    return;

            // STUB — resistance table slot:
            // float modified = ResistanceTable.Apply(damage, type, this);
            float modified = damage;

            LastHitOwner = attackerSlot;
            hp.Value     = Mathf.Max(0f, hp.Value - modified);

            if (hp.Value <= 0f)
                HandleDeath();
        }

        // ----- Private --------------------------------------------------------

        private void HandleDeath()
        {
            OnDied?.Invoke(this);
            NetworkObject.Despawn();
        }
    }
}