using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Reflection;
using Godot;

public sealed class FormBinder<TViewModel> where TViewModel : INotifyPropertyChanged
{
    private readonly TViewModel _vm;
    private readonly Control _root;
    private readonly Dictionary<LineEdit, PropertyInfo> _lineToProp = new();
    private readonly Dictionary<string, LineEdit> _propNameToLine = new(StringComparer.OrdinalIgnoreCase);
    private bool _suppress;

    public FormBinder(TViewModel vm, Control root)
    {
        _vm = vm;
        _root = root;
    }

    public FormBinder<TViewModel> Bind()
    {
        Discover();
        _vm.PropertyChanged += OnPropertyChanged;
        foreach (var (line, prop) in _lineToProp)
        {
            line.TextChanged += (string text) =>
            {
                if (_suppress) return;
                if (prop.PropertyType == typeof(string) || prop.PropertyType == typeof(string))
                    prop.SetValue(_vm, text);
            };
        }
        // Initial sync UI <- VM
        PushAllFromVm();
        return this;
    }

    private void Discover()
    {
        var props = typeof(TViewModel).GetProperties(BindingFlags.Instance | BindingFlags.Public);
        var propMap = new Dictionary<string, PropertyInfo>(StringComparer.OrdinalIgnoreCase);
        foreach (var p in props) if (p.CanRead || p.CanWrite) propMap[p.Name] = p;

        void Walk(Node n)
        {
            if (n is LineEdit le)
            {
                // Prefer explicit metadata "vm_prop" to map to a property name; fallback to node name.
                string propName = le.HasMeta("vm_prop") ? (string)le.GetMeta("vm_prop") : StripSuffix(le.Name, "LineEdit");
                if (propMap.TryGetValue(propName, out var pi))
                {
                    _lineToProp[le] = pi;
                    _propNameToLine[propName] = le;
                }
            }
            foreach (var c in n.GetChildren())
                if (c is Node child) Walk(child);
        }

        Walk(_root);
    }

    private static string StripSuffix(string s, string suffix) =>
        s.EndsWith(suffix, StringComparison.Ordinal) ? s[..^suffix.Length] : s;

    private void OnPropertyChanged(object? sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == null) return;
        if (_propNameToLine.TryGetValue(e.PropertyName, out var le))
        {
            _suppress = true;
            try { le.Text = _lineToProp[le].GetValue(_vm)?.ToString() ?? string.Empty; }
            finally { _suppress = false; }
        }
    }

    public void PushAllFromVm()
    {
        _suppress = true;
        try
        {
            foreach (var (line, prop) in _lineToProp)
                line.Text = prop.GetValue(_vm)?.ToString() ?? string.Empty;
        }
        finally { _suppress = false; }
    }
}