using System;
using System.Reflection;
using ProtoBuf.Compiler;

namespace ProtoBuf.Serializers;

internal sealed class FieldDecorator : ProtoDecoratorBase
{
	private readonly FieldInfo field;

	private readonly Type forType;

	public override Type ExpectedType => forType;

	public override bool RequiresOldValue => true;

	public override bool ReturnsValue => false;

	public FieldDecorator(Type forType, FieldInfo field, IProtoSerializer tail)
		: base(tail)
	{
		this.forType = forType;
		this.field = field;
	}

	public override void Write(object value, ProtoWriter dest)
	{
		value = field.GetValue(value);
		if (value != null)
		{
			Tail.Write(value, dest);
		}
	}

	public override object Read(object value, ProtoReader source)
	{
		object obj = Tail.Read(Tail.RequiresOldValue ? field.GetValue(value) : null, source);
		if (obj != null)
		{
			field.SetValue(value, obj);
		}
		return null;
	}

	protected override void EmitWrite(CompilerContext ctx, Local valueFrom)
	{
		ctx.LoadAddress(valueFrom, ExpectedType);
		ctx.LoadValue(field);
		ctx.WriteNullCheckedTail(field.FieldType, Tail, null);
	}

	protected override void EmitRead(CompilerContext ctx, Local valueFrom)
	{
		using Local local = ctx.GetLocalWithValue(ExpectedType, valueFrom);
		if (Tail.RequiresOldValue)
		{
			ctx.LoadAddress(local, ExpectedType);
			ctx.LoadValue(field);
		}
		ctx.ReadNullCheckedTail(field.FieldType, Tail, null);
		MemberInfo member = field;
		ctx.CheckAccessibility(ref member);
		if (member is FieldInfo)
		{
			if (!Tail.ReturnsValue)
			{
				return;
			}
			using Local local2 = new Local(ctx, field.FieldType);
			ctx.StoreValue(local2);
			if (Helpers.IsValueType(field.FieldType))
			{
				ctx.LoadAddress(local, ExpectedType);
				ctx.LoadValue(local2);
				ctx.StoreValue(field);
				return;
			}
			CodeLabel label = ctx.DefineLabel();
			ctx.LoadValue(local2);
			ctx.BranchIfFalse(label, @short: true);
			ctx.LoadAddress(local, ExpectedType);
			ctx.LoadValue(local2);
			ctx.StoreValue(field);
			ctx.MarkLabel(label);
			return;
		}
		if (Tail.ReturnsValue)
		{
			ctx.DiscardValue();
		}
	}
}