using UnityEngine;
using UnityEngine.Events;
using FishNet.Object;
using FishNet.Object.Synchronizing;
using Ashwild.Inventory;
using Ashwild.Network;

namespace Ashwild.Player
{
    /// <summary>
    /// Owns the player's survival stats (health, hunger, thirst) and death state.
    /// Client-authoritative, exactly like PlayerInventory: the owning client simulates its own
    /// drain, damage and regen locally, then replicates a lightweight snapshot through SyncVars so
    /// other clients can observe this player (team-mate health bars, remote death). Only the owning
    /// client registers the Instance singleton and drives the static PlayerEvents bus; remote copies
    /// just mirror the replicated values.
    /// </summary>
    [DisallowMultipleComponent]
    public class PlayerStats : NetworkBehaviour
    {
        #region Singleton

        /// <summary>
        /// The local player's stats — set only on the owning client (mirrors PlayerInventory.Instance).
        /// </summary>
        public static PlayerStats Instance { get; private set; }

        #endregion

        #region Serialized Fields

        [Header("Health")]
        [SerializeField] private bool enableHealth = true;
        [SerializeField] private float maxHealth = 100f;
        [SerializeField] private float healthRegenRate = 0f;
        [SerializeField] private float healthRegenDelay = 5f;
        [SerializeField] private float healthRegenMinHunger = 30f;

        [Header("Hunger")]
        [SerializeField] private bool enableHunger = true;
        [SerializeField] private float maxHunger = 100f;
        [SerializeField] private float hungerDrainRate = 0.15f;
        [SerializeField] private float hungerSprintMultiplier = 2f;
        [SerializeField] private float starvationDamageRate = 2f;

        [Header("Thirst")]
        [SerializeField] private bool enableThirst = true;
        [SerializeField] private float maxThirst = 100f;
        [SerializeField] private float thirstDrainRate = 0.2f;
        [SerializeField] private float thirstSprintMultiplier = 2f;
        [SerializeField] private float dehydrationDamageRate = 3f;

        [Header("Fall Damage (drop-distance based)")]
        [SerializeField] private bool enableFallDamage = true;
        [SerializeField, Tooltip("Drop in meters under which no damage is applied. Forward jumps with small vertical drop stay safe.")]
        private float fallDamageSafeDrop = 3f;
        [SerializeField] private float fallDamageScale = 0.25f;
        [SerializeField] private float fallDamageExponent = 2f;

        [Header("Replication")]
        [SerializeField, Tooltip("Seconds between replicated stat snapshots sent to other clients. Discrete events (damage, death) replicate immediately regardless of this.")]
        private float replicationInterval = 0.2f;

        [Header("Events (consumed by UI)")]
        public UnityEvent<float> onHealthChanged;
        public UnityEvent<float> onHungerChanged;
        public UnityEvent<float> onThirstChanged;
        public UnityEvent onDeath;

        #endregion

        #region Networked State

        /// <summary>
        /// Replicated current health, written by the server from the owner's snapshot so other
        /// clients can read this player's health without simulating it.
        /// </summary>
        private readonly SyncVar<float> netHealth = new SyncVar<float>();

        /// <summary>
        /// Replicated current hunger (see netHealth).
        /// </summary>
        private readonly SyncVar<float> netHunger = new SyncVar<float>();

        /// <summary>
        /// Replicated current thirst (see netHealth).
        /// </summary>
        private readonly SyncVar<float> netThirst = new SyncVar<float>();

        /// <summary>
        /// Replicated death flag (see netHealth).
        /// </summary>
        private readonly SyncVar<bool> netDead = new SyncVar<bool>();

        #endregion

        #region Local State

        private float currentHealth;
        private float currentHunger;
        private float currentThirst;
        private float lastDamageTime;
        private float replicationTimer;
        private bool isDead;
        private bool isSprinting;

        public float Health => currentHealth;
        public float Hunger => currentHunger;
        public float Thirst => currentThirst;
        public float MaxHealth => maxHealth;
        public float MaxHunger => maxHunger;
        public float MaxThirst => maxThirst;
        public float HealthNormalized => currentHealth / maxHealth;
        public float HungerNormalized => currentHunger / maxHunger;
        public float ThirstNormalized => currentThirst / maxThirst;
        public bool IsDead => isDead;

        #endregion

        #region Unity Lifecycle

        /// <summary>
        /// Initialises local values to full so UI shows full bars before the network is up.
        /// No destructive singleton guard here — ownership decides the Instance in OnStartNetwork.
        /// </summary>
        private void Awake()
        {
            currentHealth = maxHealth;
            currentHunger = maxHunger;
            currentThirst = maxThirst;
        }

        /// <summary>
        /// Subscribes to the sprint state used to scale drain rates.
        /// </summary>
        private void OnEnable() { PlayerEvents.SprintChanged += OnSprintChanged; }

        /// <summary>
        /// Unsubscribes — mirrors OnEnable exactly.
        /// </summary>
        private void OnDisable() { PlayerEvents.SprintChanged -= OnSprintChanged; }

        /// <summary>
        /// Runs the survival simulation. Only the owning copy is enabled (PlayerNetworkController
        /// disables it on remote players), so this drives one player's stats locally.
        /// </summary>
        private void Update()
        {
            // Defense in depth: when networked, only the owner simulates (remotes mirror SyncVars).
            // When offline (no NetworkObject spawned), IsSpawned is false so single-scene tests still run.
            if (base.IsSpawned && !base.IsOwner) return;
            if (isDead) return;

            float dt = Time.deltaTime;
            float sprintMult = isSprinting ? 1f : 0f;

            if (enableHunger) DrainHunger(dt, sprintMult);
            if (enableThirst) DrainThirst(dt, sprintMult);
            if (enableHealth)
            {
                HandleStarvationAndDehydration(dt);
                HandleHealthRegen(dt);
            }

            ReplicateThrottled(dt);
        }

        #endregion

        #region Network Lifecycle

        /// <summary>
        /// Registers SyncVar hooks and claims the singleton on the owning client only.
        /// </summary>
        public override void OnStartNetwork()
        {
            base.OnStartNetwork();

            netHealth.OnChange += OnNetHealthChanged;
            netHunger.OnChange += OnNetHungerChanged;
            netThirst.OnChange += OnNetThirstChanged;
            netDead.OnChange += OnNetDeadChanged;

            if (base.Owner.IsLocalClient) Instance = this;
        }

        /// <summary>
        /// Seeds the authoritative snapshot to full so late joiners see correct bars immediately.
        /// </summary>
        public override void OnStartServer()
        {
            base.OnStartServer();
            netHealth.Value = maxHealth;
            netHunger.Value = maxHunger;
            netThirst.Value = maxThirst;
            netDead.Value = false;
        }

        /// <summary>
        /// Unregisters hooks and clears the singleton — mirrors OnStartNetwork exactly.
        /// </summary>
        public override void OnStopNetwork()
        {
            base.OnStopNetwork();

            netHealth.OnChange -= OnNetHealthChanged;
            netHunger.OnChange -= OnNetHungerChanged;
            netThirst.OnChange -= OnNetThirstChanged;
            netDead.OnChange -= OnNetDeadChanged;

            if (Instance == this) Instance = null;
        }

        #endregion

        #region Replication

        /// <summary>
        /// Pushes the current snapshot to other clients on a fixed cadence (owner only).
        /// </summary>
        private void ReplicateThrottled(float dt)
        {
            if (!base.IsOwner) return;
            replicationTimer += dt;
            if (replicationTimer >= replicationInterval) ReplicateNow();
        }

        /// <summary>
        /// Pushes the current snapshot immediately (owner only) — used for discrete events
        /// like damage, death and revive that should not wait for the throttle.
        /// </summary>
        private void ReplicateNow()
        {
            if (!base.IsOwner) return;
            replicationTimer = 0f;
            PushStatsServerRpc(currentHealth, currentHunger, currentThirst, isDead);
        }

        /// <summary>
        /// Server-side: stores the owner's snapshot into the SyncVars so all observers receive it.
        /// </summary>
        [ServerRpc]
        private void PushStatsServerRpc(float health, float hunger, float thirst, bool dead)
        {
            netHealth.Value = health;
            netHunger.Value = hunger;
            netThirst.Value = thirst;
            netDead.Value = dead;
        }

        /// <summary>
        /// On non-owning copies, mirrors replicated health into local state and fires the instance
        /// event (for team-mate UI). The static PlayerEvents bus is never touched here — it belongs
        /// to the local player only.
        /// </summary>
        private void OnNetHealthChanged(float prev, float next, bool asServer)
        {
            if (base.IsOwner) return;
            currentHealth = next;
            onHealthChanged?.Invoke(next);
        }

        /// <summary>
        /// On non-owning copies, mirrors replicated hunger into local state.
        /// </summary>
        private void OnNetHungerChanged(float prev, float next, bool asServer)
        {
            if (base.IsOwner) return;
            currentHunger = next;
            onHungerChanged?.Invoke(next);
        }

        /// <summary>
        /// On non-owning copies, mirrors replicated thirst into local state.
        /// </summary>
        private void OnNetThirstChanged(float prev, float next, bool asServer)
        {
            if (base.IsOwner) return;
            currentThirst = next;
            onThirstChanged?.Invoke(next);
        }

        /// <summary>
        /// On non-owning copies, mirrors replicated death state and fires the instance death event.
        /// </summary>
        private void OnNetDeadChanged(bool prev, bool next, bool asServer)
        {
            if (base.IsOwner) return;
            isDead = next;
            if (next) onDeath?.Invoke();
        }

        #endregion

        #region Event Handlers

        /// <summary>
        /// Caches the local player's sprint state to scale hunger/thirst drain.
        /// </summary>
        private void OnSprintChanged(bool sprinting) => isSprinting = sprinting;

        #endregion

        #region Simulation

        /// <summary>
        /// Drains hunger over time, faster while sprinting; broadcasts the new value.
        /// </summary>
        private void DrainHunger(float dt, float sprintMult)
        {
            float drain = hungerDrainRate + hungerDrainRate * sprintMult * hungerSprintMultiplier;
            currentHunger = Mathf.Max(0f, currentHunger - drain * dt);
            onHungerChanged?.Invoke(currentHunger);
            PlayerEvents.RaiseHungerChanged(currentHunger, maxHunger);
        }

        /// <summary>
        /// Drains thirst over time, faster while sprinting; broadcasts the new value.
        /// </summary>
        private void DrainThirst(float dt, float sprintMult)
        {
            float drain = thirstDrainRate + thirstDrainRate * sprintMult * thirstSprintMultiplier;
            currentThirst = Mathf.Max(0f, currentThirst - drain * dt);
            onThirstChanged?.Invoke(currentThirst);
            PlayerEvents.RaiseThirstChanged(currentThirst, maxThirst);
        }

        /// <summary>
        /// Applies starvation and dehydration damage when hunger or thirst hit zero.
        /// </summary>
        private void HandleStarvationAndDehydration(float dt)
        {
            if (currentHunger <= 0f)
            {
                float dmg = starvationDamageRate * dt;
                PlayerEvents.RaiseStarvationTick(dmg);
                TakeDamage(dmg, DamageType.Starvation);
            }
            if (currentThirst <= 0f)
            {
                float dmg = dehydrationDamageRate * dt;
                PlayerEvents.RaiseDehydrationTick(dmg);
                TakeDamage(dmg, DamageType.Dehydration);
            }
        }

        /// <summary>
        /// Regenerates health once enough time has passed since the last hit and hunger is high enough.
        /// </summary>
        private void HandleHealthRegen(float dt)
        {
            if (healthRegenRate <= 0f) return;
            if (Time.time - lastDamageTime < healthRegenDelay) return;
            if (currentHunger < healthRegenMinHunger) return;

            currentHealth = Mathf.Min(maxHealth, currentHealth + healthRegenRate * dt);
            onHealthChanged?.Invoke(currentHealth);
            PlayerEvents.RaiseHealthChanged(currentHealth, maxHealth);
        }

        #endregion

        #region Public API

        /// <summary>
        /// Applies generic damage to the local player.
        /// </summary>
        public void TakeDamage(float amount) => TakeDamage(amount, DamageType.Generic);

        /// <summary>
        /// Applies typed damage, broadcasts it, replicates the new state and triggers death at zero.
        /// </summary>
        private void TakeDamage(float amount, DamageType type)
        {
            if (isDead || amount <= 0f) return;

            currentHealth = Mathf.Max(0f, currentHealth - amount);
            lastDamageTime = Time.time;
            onHealthChanged?.Invoke(currentHealth);
            PlayerEvents.RaiseHealthChanged(currentHealth, maxHealth);
            PlayerEvents.RaiseDamaged(amount, type);

            if (currentHealth <= 0f) Die();
            else ReplicateNow();
        }

        /// <summary>
        /// Heals the local player, broadcasts the new value and replicates it.
        /// </summary>
        public void Heal(float amount)
        {
            if (isDead || amount <= 0f) return;
            currentHealth = Mathf.Min(maxHealth, currentHealth + amount);
            onHealthChanged?.Invoke(currentHealth);
            PlayerEvents.RaiseHealthChanged(currentHealth, maxHealth);
            ReplicateNow();
        }

        /// <summary>
        /// Restores hunger, broadcasts the new value and replicates it.
        /// </summary>
        public void Feed(float amount)
        {
            currentHunger = Mathf.Min(maxHunger, currentHunger + amount);
            onHungerChanged?.Invoke(currentHunger);
            PlayerEvents.RaiseHungerChanged(currentHunger, maxHunger);
            ReplicateNow();
        }

        /// <summary>
        /// Restores thirst, broadcasts the new value and replicates it.
        /// </summary>
        public void Drink(float amount)
        {
            currentThirst = Mathf.Min(maxThirst, currentThirst + amount);
            onThirstChanged?.Invoke(currentThirst);
            PlayerEvents.RaiseThirstChanged(currentThirst, maxThirst);
            ReplicateNow();
        }

        /// <summary>
        /// Computes and applies drop-distance fall damage; returns the damage dealt (0 if safe).
        /// </summary>
        public float ApplyFallDamage(float dropDistance)
        {
            if (!enableFallDamage) return 0f;
            if (dropDistance < fallDamageSafeDrop) return 0f;

            float excess = dropDistance - fallDamageSafeDrop;
            float damage = fallDamageScale * Mathf.Pow(excess, fallDamageExponent);
            TakeDamage(damage, DamageType.Fall);
            return damage;
        }

        /// <summary>
        /// Resets all stats to full, clears death and replicates the fresh state.
        /// </summary>
        public void Revive()
        {
            isDead = false;
            currentHealth = maxHealth;
            currentHunger = maxHunger;
            currentThirst = maxThirst;
            onHealthChanged?.Invoke(currentHealth);
            onHungerChanged?.Invoke(currentHunger);
            onThirstChanged?.Invoke(currentThirst);
            PlayerEvents.RaiseHealthChanged(currentHealth, maxHealth);
            PlayerEvents.RaiseHungerChanged(currentHunger, maxHunger);
            PlayerEvents.RaiseThirstChanged(currentThirst, maxThirst);
            PlayerEvents.RaiseRespawned();
            ReplicateNow();
        }

        #endregion

        #region Internal Helpers

        /// <summary>
        /// Marks the local player dead, fires events and replicates the death immediately.
        /// </summary>
        private void Die()
        {
            isDead = true;
            onDeath?.Invoke();
            PlayerEvents.RaiseDied();
            ReplicateNow();
        }

        #endregion
    }
}