using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Reflection;

namespace Python.Runtime
{
 static partial class InternString
 {
 private static readonly Dictionary<string, PyString> _string2interns = new();
 private static readonly Dictionary<IntPtr, string> _intern2strings = new();
 const BindingFlags PyIdentifierFieldFlags = BindingFlags.Static | BindingFlags.NonPublic;

 static InternString()
 {
 var identifierNames = typeof(PyIdentifier).GetFields(PyIdentifierFieldFlags)
 .Select(fi => fi.Name.Substring(1));
 var validNames = new HashSet<string>(identifierNames);
 if (validNames.Count != _builtinNames.Length)
 {
 throw new InvalidOperationException("Identifiers args not matching");
 }
 foreach (var name in _builtinNames)
 {
 if (!validNames.Contains(name))
 {
 throw new InvalidOperationException($"{name} is not declared");
 }
 }
 }

 public static void Initialize()
 {
 Debug.Assert(_string2interns.Count == 0);

 Type type = typeof(PyIdentifier);
 foreach (string name in _builtinNames)
 {
 NewReference pyStr = Runtime.PyUnicode_InternFromString(name);
 var op = new PyString(pyStr.StealOrThrow());
 Debug.Assert(name == op.As<string>());
 SetIntern(name, op);
 var field = type.GetField("f" + name, PyIdentifierFieldFlags)!;
 field.SetValue(null, op.DangerousGetAddressOrNull());
 }
 }

 public static void Shutdown()
 {
 foreach (var entry in _string2interns)
 {
 var field = typeof(PyIdentifier).GetField("f" + entry.Value, PyIdentifierFieldFlags)!;
 entry.Value.Dispose();
 field.SetValue(null, IntPtr.Zero);
 }

 _string2interns.Clear();
 _intern2strings.Clear();
 }

 public static string? GetManagedString(BorrowedReference op)
 {
 if (TryGetInterned(op, out string s))
 {
 return s;
 }
 return Runtime.GetManagedString(op);
 }

 public static bool TryGetInterned(BorrowedReference op, out string s)
 {
 return _intern2strings.TryGetValue(op.DangerousGetAddress(), out s);
 }

 private static void SetIntern(string s, PyString op)
 {
 _string2interns.Add(s, op);
 _intern2strings.Add(op.Reference.DangerousGetAddress(), s);
 }
 }
}