using System;
using System.Collections.Generic;

namespace Oni.Metadata
{
    internal class LinkVisitor : MetaTypeVisitor
    {
        private readonly List<int> links = new List<int>();
        private readonly BinaryReader reader;

        public LinkVisitor(BinaryReader reader)
        {
            this.reader = reader;
        }

        public ICollection<int> Links => links;

        public override void VisitByte(MetaByte type) => reader.Position += type.Size;
        public override void VisitInt16(MetaInt16 type) => reader.Position += type.Size;
        public override void VisitUInt16(MetaUInt16 type) => reader.Position += type.Size;
        public override void VisitInt32(MetaInt32 type) => reader.Position += type.Size;
        public override void VisitUInt32(MetaUInt32 type) => reader.Position += type.Size;
        public override void VisitInt64(MetaInt64 type) => reader.Position += type.Size;
        public override void VisitUInt64(MetaUInt64 type) => reader.Position += type.Size;
        public override void VisitFloat(MetaFloat type) => reader.Position += type.Size;
        public override void VisitColor(MetaColor type) => reader.Position += type.Size;
        public override void VisitRawOffset(MetaRawOffset type) => reader.Position += type.Size;
        public override void VisitSepOffset(MetaSepOffset type) => reader.Position += type.Size;

        public override void VisitPointer(MetaPointer type)
        {
            int id = reader.ReadInt32();

            if (id != 0)
                links.Add(id);
        }

        public override void VisitString(MetaString type) => reader.Position += type.Size;
        public override void VisitPadding(MetaPadding type) => reader.Position += type.Size;

        public override void VisitStruct(MetaStruct type)
        {
            foreach (Field field in type.Fields)
                field.Type.Accept(this);
        }

        public override void VisitArray(MetaArray type) => VisitArray(type.ElementType, type.Count);

        public override void VisitVarArray(MetaVarArray type)
        {
            int count;

            if (type.CountField.Type == MetaType.Int16)
                count = reader.ReadUInt16();
            else
                count = reader.ReadInt32();

            VisitArray(type.ElementType, count);
        }

        private void VisitArray(MetaType elementType, int count)
        {
            if (elementType is MetaPointer || elementType is MetaStruct)
            {
                for (int i = 0; i < count; i++)
                    elementType.Accept(this);
            }
            else
            {
                reader.Position += elementType.Size * count;
            }
        }
    }
}