using dnlib.DotNet.Emit;
using dnlib.DotNet;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

/// 
/// To be honest, I don't even know where I got this class from. Just know it's cool :catThumbsUp: - body
///

namespace Pulsar.Server.Build.Obfuscator.Utils
{
    /// <summary>
	///     Provides methods to inject a <see cref="TypeDef" /> into another module.
	/// </summary>
	public static class InjectHelper
    {
        /// <summary>
        ///     Clones the specified origin TypeDef.
        /// </summary>
        /// <param name="origin">The origin TypeDef.</param>
        /// <returns>The cloned TypeDef.</returns>
        static TypeDefUser Clone(TypeDef origin)
        {
            var ret = new TypeDefUser(origin.Namespace, origin.Name);
            ret.Attributes = origin.Attributes;

            if (origin.ClassLayout != null)
                ret.ClassLayout = new ClassLayoutUser(origin.ClassLayout.PackingSize, origin.ClassSize);

            foreach (GenericParam genericParam in origin.GenericParameters)
                ret.GenericParameters.Add(new GenericParamUser(genericParam.Number, genericParam.Flags, "-"));

            return ret;
        }

        /// <summary>
        ///     Clones the specified origin MethodDef.
        /// </summary>
        /// <param name="origin">The origin MethodDef.</param>
        /// <returns>The cloned MethodDef.</returns>
        static MethodDefUser Clone(MethodDef origin)
        {
            var ret = new MethodDefUser(origin.Name, null, origin.ImplAttributes, origin.Attributes);

            foreach (GenericParam genericParam in origin.GenericParameters)
                ret.GenericParameters.Add(new GenericParamUser(genericParam.Number, genericParam.Flags, "-"));

            return ret;
        }

        /// <summary>
        ///     Clones the specified origin FieldDef.
        /// </summary>
        /// <param name="origin">The origin FieldDef.</param>
        /// <returns>The cloned FieldDef.</returns>
        static FieldDefUser Clone(FieldDef origin)
        {
            var ret = new FieldDefUser(origin.Name, null, origin.Attributes);
            return ret;
        }

        /// <summary>
        ///     Populates the context mappings.
        /// </summary>
        /// <param name="typeDef">The origin TypeDef.</param>
        /// <param name="ctx">The injection context.</param>
        /// <returns>The new TypeDef.</returns>
        static TypeDef PopulateContext(TypeDef typeDef, InjectContext ctx)
        {
            var ret = ctx.Map(typeDef)?.ResolveTypeDef();
            if (ret is null)
            {
                ret = Clone(typeDef);
                ctx.DefMap[typeDef] = ret;
            }

            foreach (TypeDef nestedType in typeDef.NestedTypes)
                ret.NestedTypes.Add(PopulateContext(nestedType, ctx));

            foreach (MethodDef method in typeDef.Methods)
                ret.Methods.Add((MethodDef)(ctx.DefMap[method] = Clone(method)));

            foreach (FieldDef field in typeDef.Fields)
                ret.Fields.Add((FieldDef)(ctx.DefMap[field] = Clone(field)));

            return ret;
        }

        /// <summary>
        ///     Copies the information from the origin type to injected type.
        /// </summary>
        /// <param name="typeDef">The origin TypeDef.</param>
        /// <param name="ctx">The injection context.</param>
        static void CopyTypeDef(TypeDef typeDef, InjectContext ctx)
        {
            var newTypeDef = ctx.Map(typeDef)?.ResolveTypeDefThrow();
            newTypeDef.BaseType = ctx.Importer.Import(typeDef.BaseType);

            foreach (InterfaceImpl iface in typeDef.Interfaces)
                newTypeDef.Interfaces.Add(new InterfaceImplUser(ctx.Importer.Import(iface.Interface)));
        }

        /// <summary>
        ///     Copies the information from the origin method to injected method.
        /// </summary>
        /// <param name="methodDef">The origin MethodDef.</param>
        /// <param name="ctx">The injection context.</param>
        static void CopyMethodDef(MethodDef methodDef, InjectContext ctx)
        {
            var newMethodDef = ctx.Map(methodDef)?.ResolveMethodDefThrow();

            newMethodDef.Signature = ctx.Importer.Import(methodDef.Signature);
            newMethodDef.Parameters.UpdateParameterTypes();

            foreach (var paramDef in methodDef.ParamDefs)
                newMethodDef.ParamDefs.Add(new ParamDefUser(paramDef.Name, paramDef.Sequence, paramDef.Attributes));

            if (methodDef.ImplMap != null)
                newMethodDef.ImplMap = new ImplMapUser(new ModuleRefUser(ctx.TargetModule, methodDef.ImplMap.Module.Name), methodDef.ImplMap.Name, methodDef.ImplMap.Attributes);

            foreach (CustomAttribute ca in methodDef.CustomAttributes)
                newMethodDef.CustomAttributes.Add(new CustomAttribute((ICustomAttributeType)ctx.Importer.Import(ca.Constructor)));

            if (methodDef.HasBody)
                CopyMethodBody(methodDef, ctx, newMethodDef);
        }

        static void CopyMethodBody(MethodDef methodDef, InjectContext ctx, MethodDef newMethodDef)
        {
            newMethodDef.Body = new CilBody(methodDef.Body.InitLocals, new List<Instruction>(),
                new List<ExceptionHandler>(), new List<Local>())
            { MaxStack = methodDef.Body.MaxStack };

            var bodyMap = new Dictionary<object, object>();

            foreach (Local local in methodDef.Body.Variables)
            {
                var newLocal = new Local(ctx.Importer.Import(local.Type));
                newMethodDef.Body.Variables.Add(newLocal);
                newLocal.Name = local.Name;

                bodyMap[local] = newLocal;
            }

            foreach (Instruction instr in methodDef.Body.Instructions)
            {
                var newInstr = new Instruction(instr.OpCode, instr.Operand)
                {
                    SequencePoint = instr.SequencePoint
                };

                switch (newInstr.Operand)
                {
                    case IType type:
                        newInstr.Operand = ctx.Importer.Import(type);
                        break;
                    case IMethod method:
                        newInstr.Operand = ctx.Importer.Import(method);
                        break;
                    case IField field:
                        newInstr.Operand = ctx.Importer.Import(field);
                        break;
                }

                newMethodDef.Body.Instructions.Add(newInstr);
                bodyMap[instr] = newInstr;
            }

            foreach (Instruction instr in newMethodDef.Body.Instructions)
            {
                if (instr.Operand != null && bodyMap.ContainsKey(instr.Operand))
                    instr.Operand = bodyMap[instr.Operand];
                else if (instr.Operand is Instruction[] instructions)
                    instr.Operand = instructions.Select(target => (Instruction)bodyMap[target]).ToArray();
            }

            foreach (ExceptionHandler eh in methodDef.Body.ExceptionHandlers)
                newMethodDef.Body.ExceptionHandlers.Add(new ExceptionHandler(eh.HandlerType)
                {
                    CatchType = eh.CatchType == null ? null : ctx.Importer.Import(eh.CatchType),
                    TryStart = (Instruction)bodyMap[eh.TryStart],
                    TryEnd = (Instruction)bodyMap[eh.TryEnd],
                    HandlerStart = (Instruction)bodyMap[eh.HandlerStart],
                    HandlerEnd = (Instruction)bodyMap[eh.HandlerEnd],
                    FilterStart = eh.FilterStart == null ? null : (Instruction)bodyMap[eh.FilterStart]
                });

            newMethodDef.Body.SimplifyMacros(newMethodDef.Parameters);
        }

        /// <summary>
        ///     Copies the information from the origin field to injected field.
        /// </summary>
        /// <param name="fieldDef">The origin FieldDef.</param>
        /// <param name="ctx">The injection context.</param>
        static void CopyFieldDef(FieldDef fieldDef, InjectContext ctx)
        {
            var newFieldDef = ctx.Map(fieldDef).ResolveFieldDefThrow();

            newFieldDef.Signature = ctx.Importer.Import(fieldDef.Signature);
        }

        /// <summary>
        ///     Copies the information to the injected definitions.
        /// </summary>
        /// <param name="typeDef">The origin TypeDef.</param>
        /// <param name="ctx">The injection context.</param>
        /// <param name="copySelf">if set to <c>true</c>, copy information of <paramref name="typeDef" />.</param>
        static void Copy(TypeDef typeDef, InjectContext ctx, bool copySelf)
        {
            if (copySelf)
                CopyTypeDef(typeDef, ctx);

            foreach (TypeDef nestedType in typeDef.NestedTypes)
                Copy(nestedType, ctx, true);

            foreach (MethodDef method in typeDef.Methods)
                CopyMethodDef(method, ctx);

            foreach (FieldDef field in typeDef.Fields)
                CopyFieldDef(field, ctx);
        }

        /// <summary>
        ///     Injects the specified TypeDef to another module.
        /// </summary>
        /// <param name="typeDef">The source TypeDef.</param>
        /// <param name="target">The target module.</param>
        /// <returns>The injected TypeDef.</returns>
        public static TypeDef Inject(TypeDef typeDef, ModuleDef target)
        {
            var ctx = new InjectContext(typeDef.Module, target);
            var result = PopulateContext(typeDef, ctx);
            Copy(typeDef, ctx, true);
            return result;
        }

        /// <summary>
        ///     Injects the specified MethodDef to another module.
        /// </summary>
        /// <param name="methodDef">The source MethodDef.</param>
        /// <param name="target">The target module.</param>
        /// <returns>The injected MethodDef.</returns>
        public static MethodDef Inject(MethodDef methodDef, ModuleDef target)
        {
            var ctx = new InjectContext(methodDef.Module, target);
            MethodDef result;
            ctx.DefMap[methodDef] = result = Clone(methodDef);
            CopyMethodDef(methodDef, ctx);
            return result;
        }

        /// <summary>
        ///     Injects the members of specified TypeDef to another module.
        /// </summary>
        /// <param name="typeDef">The source TypeDef.</param>
        /// <param name="newType">The new type.</param>
        /// <param name="target">The target module.</param>
        /// <returns>Injected members.</returns>
        public static IEnumerable<IDnlibDef> Inject(TypeDef typeDef, TypeDef newType, ModuleDef target)
        {
            var ctx = new InjectContext(typeDef.Module, target);
            ctx.DefMap[typeDef] = newType;
            PopulateContext(typeDef, ctx);
            Copy(typeDef, ctx, false);
            return ctx.DefMap.Values.Except(new[] { newType }).OfType<IDnlibDef>();
        }

        /// <summary>
        ///     Context of the injection process.
        /// </summary>
        class InjectContext : ImportMapper
        {
            /// <summary>
            ///     The mapping of origin definitions to injected definitions.
            /// </summary>
            public readonly Dictionary<IMemberRef, IMemberRef> DefMap = new Dictionary<IMemberRef, IMemberRef>();

            /// <summary>
            ///     The module which source type originated from.
            /// </summary>
            public readonly ModuleDef OriginModule;

            /// <summary>
            ///     The module which source type is being injected to.
            /// </summary>
            public readonly ModuleDef TargetModule;

            /// <summary>
            ///     Initializes a new instance of the <see cref="InjectContext" /> class.
            /// </summary>
            /// <param name="module">The origin module.</param>
            /// <param name="target">The target module.</param>
            public InjectContext(ModuleDef module, ModuleDef target)
            {
                OriginModule = module;
                TargetModule = target;
                Importer = new Importer(target, ImporterOptions.TryToUseTypeDefs, new GenericParamContext(), this);
            }

            /// <summary>
            ///     Gets the importer.
            /// </summary>
            /// <value>The importer.</value>
            public Importer Importer { get; }

            /// <inheritdoc />
            public override ITypeDefOrRef Map(ITypeDefOrRef source)
            {
                if (DefMap.TryGetValue(source, out var mappedRef))
                    return mappedRef as ITypeDefOrRef;

                // check if the assembly reference needs to be fixed.
                if (source is TypeRef sourceRef)
                {
                    var targetAssemblyRef = TargetModule.GetAssemblyRef(sourceRef.DefinitionAssembly.Name);
                    if (!(targetAssemblyRef is null) && !string.Equals(targetAssemblyRef.FullName, source.DefinitionAssembly.FullName, StringComparison.Ordinal))
                    {
                        // We got a matching assembly by the simple name, but not by the full name.
                        // This means the injected code uses a different assembly version than the target assembly.
                        // We'll fix the assembly reference, to avoid breaking anything.
                        var fixedTypeRef = new TypeRefUser(sourceRef.Module, sourceRef.Namespace, sourceRef.Name, targetAssemblyRef);
                        return Importer.Import(fixedTypeRef);
                    }
                }
                return null;
            }

            /// <inheritdoc />
            public override IMethod Map(MethodDef source)
            {
                if (DefMap.TryGetValue(source, out var mappedRef))
                    return mappedRef as IMethod;
                return null;
            }

            /// <inheritdoc />
            public override IField Map(FieldDef source)
            {
                if (DefMap.TryGetValue(source, out var mappedRef))
                    return mappedRef as IField;
                return null;
            }

            public override MemberRef Map(MemberRef source)
            {
                if (DefMap.TryGetValue(source, out var mappedRef))
                    return mappedRef as MemberRef;
                return null;
            }
        }
    }
}
