// Assets/_Project/Scripts/Gameplay/TowerRegistry.cs
using System.Collections.Generic;
using UnityEngine;
using TD.Towers;

namespace TD.Gameplay
{
    /// <summary>
    /// Scene singleton that holds every <see cref="TowerDefinition"/> available in the
    /// current match and lets any code look one up by asset name.
    /// </summary>
    /// <remarks>
    /// <para><b>Why this exists.</b> <see cref="TowerInstance"/> replicates a tower's
    /// definition by name (a <c>FixedString64Bytes</c> over the network), then resolves
    /// the full ScriptableObject locally on every client. TowerRegistry is the lookup
    /// table that makes that resolution possible without hard-coding asset paths.</para>
    ///
    /// <para><b>Auto-discovery.</b> On Awake, all <see cref="TowerDefinition"/> assets
    /// under <c>Resources/TowerDefinitions/</c> are loaded automatically. No inspector
    /// drag-and-drop required — add a new asset to that folder and it is registered at
    /// runtime with no other changes needed. This scales cleanly to 100+ tower types.</para>
    ///
    /// <para><b>Path E upgrade path.</b> In Path E the registry will filter to only the
    /// definitions belonging to the active match's <c>RaceDefinition</c> rosters. For now
    /// all assets in the Resources folder are registered.</para>
    ///
    /// <para><b>Plain MonoBehaviour.</b> Not a NetworkBehaviour — the registry is
    /// identical on every peer (same assets, same names), so there is nothing to sync.</para>
    /// </remarks>
    public class TowerRegistry : MonoBehaviour
    {
        // ----- Singleton --------------------------------------------------

        /// <summary>
        /// The active TowerRegistry. Null before Awake or after the scene unloads.
        /// Always null-check before use.
        /// </summary>
        public static TowerRegistry Instance { get; private set; }

        // ----- Constants --------------------------------------------------

        /// <summary>
        /// Resources-relative folder path that TowerDefinition assets must live under
        /// to be auto-discovered. Create this folder if it doesn't exist.
        /// Full path: Assets/Resources/TowerDefinitions/
        /// </summary>
        private const string ResourcesFolder = "TowerDefinitions";

        // ----- Internal lookup table --------------------------------------

        // Keyed by TowerDefinition.name (the asset name, not DisplayName).
        private readonly Dictionary<string, TowerDefinition> byName
            = new Dictionary<string, TowerDefinition>();

        // ----- Lifecycle --------------------------------------------------

        private void Awake()
        {
            if (Instance != null && Instance != this)
            {
                Debug.LogError("[TowerRegistry] Multiple instances detected. " +
                               "Only one TowerRegistry should exist per scene.");
                return;
            }
            Instance = this;

            BuildLookupTable();
        }

        private void OnDestroy()
        {
            if (Instance == this) Instance = null;
        }

        // ----- Public API -------------------------------------------------

        /// <summary>
        /// Returns the <see cref="TowerDefinition"/> whose asset name equals
        /// <paramref name="assetName"/>, or null if no match is found.
        /// </summary>
        public TowerDefinition Get(string assetName)
        {
            byName.TryGetValue(assetName, out var def);
            return def;
        }

        /// <summary>
        /// Returns all registered tower definitions. Enumerates the internal
        /// dictionary values — do not modify the returned collection.
        /// </summary>
        public IEnumerable<TowerDefinition> All => byName.Values;

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

        private void BuildLookupTable()
        {
            byName.Clear();

            // Resources.LoadAll finds every TowerDefinition asset anywhere under
            // Assets/Resources/TowerDefinitions/ (including sub-folders).
            // No manual registration needed — drop an asset in the folder and it
            // is available on the next play session.
            var loaded = Resources.LoadAll<TowerDefinition>(ResourcesFolder);

            if (loaded.Length == 0)
            {
                Debug.LogWarning($"[TowerRegistry] No TowerDefinition assets found under " +
                                 $"Resources/{ResourcesFolder}/. " +
                                 $"Create the folder and add TowerDefinition assets to it.");
                return;
            }

            foreach (var def in loaded)
            {
                if (def == null) continue;

                if (byName.ContainsKey(def.name))
                {
                    Debug.LogWarning($"[TowerRegistry] Duplicate asset name '{def.name}'. " +
                                     $"Only the first entry will be used. Rename one of the assets.");
                    continue;
                }

                byName[def.name] = def;
            }

            Debug.Log($"[TowerRegistry] Auto-discovered and registered " +
                      $"{byName.Count} tower definition(s) from Resources/{ResourcesFolder}/.");
        }
    }
}