using System;
using LibCpp2IL.BinaryStructures;
using LibCpp2IL.Metadata;
using LibCpp2IL.Reflection;

namespace LibCpp2IL;

public class MetadataUsage(MetadataUsageType type, ulong offset, uint value, LibCpp2IlContext context)
{
    public readonly MetadataUsageType Type = type;
    public readonly ulong Offset = offset;

    private string? _cachedName;

    private Il2CppType? _cachedType;

    private Il2CppMethodDefinition? _cachedMethod;

    private Il2CppFieldDefinition? _cachedField;

    private string? _cachedLiteral;

    private Cpp2IlMethodRef? _cachedGenericMethod;

    public uint RawValue => value;

    public object Value =>
        Type switch
        {
            MetadataUsageType.Type or MetadataUsageType.TypeInfo => AsType(),
            MetadataUsageType.MethodDef => AsMethod(),
            MetadataUsageType.FieldInfo => AsField(),
            MetadataUsageType.StringLiteral => AsLiteral(),
            MetadataUsageType.MethodRef => AsGenericMethodRef(),
            _ => throw new ArgumentOutOfRangeException()
        };

    public bool IsValid =>
        Type switch
        {
            MetadataUsageType.Type or MetadataUsageType.TypeInfo => value < context.Binary.NumTypes,
            MetadataUsageType.MethodDef => value < context.Metadata.MethodDefinitionCount,
            MetadataUsageType.FieldInfo => value < context.Metadata.fieldRefs.Length,
            MetadataUsageType.StringLiteral => value < context.Metadata.stringLiterals.Length,
            MetadataUsageType.MethodRef => value < context.Metadata.AllGenericMethodSpecs.Length,
            _ => false
        };

    public Il2CppType AsType()
    {
        if (_cachedType == null)
        {
            switch (Type)
            {
                case MetadataUsageType.Type:
                case MetadataUsageType.TypeInfo:
                    try
                    {
                        _cachedType = context.Binary.GetType(Il2CppVariableWidthIndex<Il2CppType>.MakeTemporaryForFixedWidthUsage((int) value)); //DynWidth: value is always masked out of 32-bits, ok for temp usage
                        _cachedName = _cachedType.ToString();
                    }
                    catch (Exception e)
                    {
                        throw new Exception($"Failed to convert this metadata usage to a type, but it is of type {Type}, with a value of {value} (0x{value:X}). There are {context.Binary.NumTypes} types", e);
                    }

                    break;
                default:
                    throw new Exception($"Cannot cast metadata usage of kind {Type} to a Type");
            }
        }

        return _cachedType!;
    }

    public Il2CppMethodDefinition AsMethod()
    {
        if (_cachedMethod == null)
        {
            switch (Type)
            {
                case MetadataUsageType.MethodDef:
                    _cachedMethod = context.Metadata.GetMethodDefinitionFromIndex(Il2CppVariableWidthIndex<Il2CppMethodDefinition>.MakeTemporaryForFixedWidthUsage((int)value)); //DynWidth: value is always masked out of 32-bits, ok for temp usage
                    _cachedName = _cachedMethod.GlobalKey;
                    break;
                default:
                    throw new Exception($"Cannot cast metadata usage of kind {Type} to a Method Def");
            }
        }

        return _cachedMethod!;
    }

    public Il2CppFieldDefinition AsField()
    {
        if (_cachedField == null)
        {
            switch (Type)
            {
                case MetadataUsageType.FieldInfo:
                    var fieldRef = context.Metadata.fieldRefs[value];
                    _cachedField = fieldRef.FieldDefinition;
                    _cachedName = fieldRef.DeclaringTypeDefinition!.FullName + "." + _cachedField!.Name;
                    break;
                default:
                    throw new Exception($"Cannot cast metadata usage of kind {Type} to a Field");
            }
        }

        return _cachedField;
    }

    public string AsLiteral()
    {
        if (_cachedLiteral == null)
        {
            switch (Type)
            {
                case MetadataUsageType.StringLiteral:
                    _cachedName = _cachedLiteral = context.Metadata.GetStringLiteralFromIndex(value);
                    break;
                default:
                    throw new Exception($"Cannot cast metadata usage of kind {Type} to a String Literal");
            }
        }

        return _cachedLiteral;
    }

    public Cpp2IlMethodRef AsGenericMethodRef()
    {
        if (_cachedGenericMethod == null)
        {
            switch (Type)
            {
                case MetadataUsageType.MethodRef:
                    var methodSpec = context.Metadata.GetMethodSpec((int)value);

                    _cachedGenericMethod = new Cpp2IlMethodRef(methodSpec);
                    _cachedName = _cachedGenericMethod.ToString();
                    break;
                default:
                    throw new Exception($"Cannot cast metadata usage of kind {Type} to a Generic Method Ref");
            }
        }

        return _cachedGenericMethod;
    }

    public override string ToString()
    {
        return $"Metadata Usage {{type={Type}, Value={Value}}}";
    }

    public static MetadataUsage? DecodeMetadataUsage(ulong encoded, ulong address, LibCpp2IlContext context)
    {
        var encodedType = encoded & 0xE000_0000;
        var type = (MetadataUsageType)(encodedType >> 29);
        if (context.Metadata.MetadataVersion > 106.1f && type > MetadataUsageType.TypeInfo)
            type += 1; //Type removed in v106.1
        
        if (type <= MetadataUsageType.MethodRef && type >= MetadataUsageType.TypeInfo)
        {
            var index = (uint)(encoded & 0x1FFF_FFFF);

            if (context.Metadata.MetadataVersion >= 27)
                index >>= 1;

            if (type is MetadataUsageType.Type or MetadataUsageType.TypeInfo && index > context.Binary.NumTypes)
                return null;

            if (type == MetadataUsageType.MethodDef && index > context.Metadata.MethodDefinitionCount)
                return null;


            return new MetadataUsage(type, address, index, context);
        }

        return null;
    }
}