using UnityEngine;

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Runtime.CompilerServices;

public static class PathIndexer
{
    private sealed class NodeMeta
    {
        public object Parent;
        public string Segment; // 예: "production_system", "asrs[0]"
    }

    // 모델 클래스를 수정하지 않기 위해 외부 메타 테이블 사용
    private static readonly ConditionalWeakTable<object, NodeMeta> _meta = new();

    /// <summary>
    /// 루트부터 전체 그래프를 순회하며 (Parent, Segment) 메타를 구축합니다.
    /// 로직 데이터 로딩/디시리얼라이즈 직후 1회 호출을 권장합니다.
    /// </summary>
    public static void Build(object root)
    {
        if (root == null) throw new ArgumentNullException(nameof(root));
        var visited = new HashSet<object>(ReferenceEqualityComparer.Instance);
        Visit(root, parent: null, segment: null, visited);
    }

    /// <summary>
    /// 특정 객체 노드의 경로(노드까지)를 반환합니다. 예: "production_system.asrs[0]"
    /// </summary>
    public static string GetNodePath(object node, string rootPrefix = null)
    {
        if (node == null) throw new ArgumentNullException(nameof(node));

        var segments = new List<string>();
        var cur = node;

        while (cur != null && _meta.TryGetValue(cur, out var m))
        {
            if (!string.IsNullOrWhiteSpace(m.Segment))
                segments.Add(m.Segment);

            cur = m.Parent;
        }

        segments.Reverse();

        var path = string.Join(".", segments.Where(s => !string.IsNullOrWhiteSpace(s)));
        if (!string.IsNullOrWhiteSpace(rootPrefix))
        {
            // 서버가 production_system[0] 같은 추가 프리픽스를 요구하면 여기서 붙이세요.
            // 예: rootPrefix = "production_system[0]" 또는 "data" 등
            path = string.IsNullOrWhiteSpace(path) ? rootPrefix : $"{rootPrefix}.{path}";
        }

        return path;
    }

    /// <summary>
    /// (변경된 객체) + (변경된 프로퍼티명)으로 최종 patch path를 만듭니다.
    /// 예: GetPropertyPath(asrs0, "name") => "production_system.asrs[0].name"
    /// </summary>
    public static string GetPropertyPath(object node, string propertyName, string rootPrefix = null)
    {
        if (string.IsNullOrWhiteSpace(propertyName))
            throw new ArgumentException("propertyName is required.", nameof(propertyName));

        var basePath = GetNodePath(node, rootPrefix);
        return string.IsNullOrWhiteSpace(basePath) ? propertyName : $"{basePath}.{propertyName}";
    }

    // ----------------- 내부 구현 -----------------

    private static void Visit(object node, object parent, string segment, HashSet<object> visited)
    {
        if (node == null) return;

        var t = node.GetType();
        if (IsTerminalType(t)) return;
        if (!visited.Add(node)) return;

        AttachMeta(node, parent, segment);

        // 1) 프로퍼티 순회(기존)
        var props = t.GetProperties(BindingFlags.Public | BindingFlags.Instance)
                     .Where(p => p.CanRead && p.GetIndexParameters().Length == 0);

        foreach (var p in props)
        {
            object child;
            try { child = p.GetValue(node); }
            catch { continue; }

            VisitChild(node, p.Name, child, visited);
        }

        // 2) 필드 순회(추가)
        var fields = t.GetFields(BindingFlags.Public | BindingFlags.Instance)
                      .Where(f => !f.IsStatic);

        foreach (var f in fields)
        {
            object child;
            try { child = f.GetValue(node); }
            catch { continue; }

            VisitChild(node, f.Name, child, visited);
        }
    }

    private static void VisitChild(object parentNode, string memberName, object child, HashSet<object> visited)
    {
        if (child == null) return;

        var ct = child.GetType();
        if (IsTerminalType(ct)) return;

        // IList면 원소에 memberName[i] 형태로 세그먼트 부여
        if (child is IList list && child is not string)
        {
            for (int i = 0; i < list.Count; i++)
            {
                var elem = list[i];
                if (elem == null) continue;

                var et = elem.GetType();
                if (IsTerminalType(et)) continue;

                Visit(elem, parent: parentNode, segment: $"{memberName}[{i}]", visited);
            }
            return;
        }

        // 일반 객체
        Visit(child, parent: parentNode, segment: memberName, visited);
    }

    private static void AttachMeta(object node, object parent, string segment)
    {
        // ConditionalWeakTable은 같은 키 add가 안 되므로 교체
        _meta.Remove(node);
        _meta.Add(node, new NodeMeta { Parent = parent, Segment = segment });
    }

    private static bool IsTerminalType(Type t)
    {
        if (t.IsPrimitive || t.IsEnum) return true;
        if (t == typeof(string) || t == typeof(decimal)) return true;
        if (t == typeof(DateTime) || t == typeof(DateTimeOffset) || t == typeof(Guid) || t == typeof(TimeSpan)) return true;

        // Nullable<T> 처리
        var nt = Nullable.GetUnderlyingType(t);
        if (nt != null) return IsTerminalType(nt);

        return false;
    }

    private sealed class ReferenceEqualityComparer : IEqualityComparer<object>
    {
        public static readonly ReferenceEqualityComparer Instance = new();
        public new bool Equals(object x, object y) => ReferenceEquals(x, y);
        public int GetHashCode(object obj) => RuntimeHelpers.GetHashCode(obj);
    }
}