/*
    Copyright 2017 Katy Coe - http://www.hearthcode.org - http://www.djkaty.com

    All rights reserved.
*/

using System.Linq;

namespace Il2CppInspector
{
    internal class Il2CppBinaryX86 : Il2CppBinary
    {
        public Il2CppBinaryX86(IFileFormatReader stream) : base(stream) { }
        public Il2CppBinaryX86(IFileFormatReader stream, uint codeRegistration, uint metadataRegistration) : base(stream, codeRegistration, metadataRegistration) { }

        protected override (ulong, ulong) ConsiderCode(uint loc, ulong globalOffset) {
            ulong metadata, code;
            long funcPtr;
            ushort opcode;

            // Variant 1

            // Assembly bytes to search for at start of each function
            var bytes = new byte[] {0x6A, 0x00, 0x6A, 0x00, 0x68};
            Image.Position = loc;
            var buff = Image.ReadBytes(5);
            if (bytes.SequenceEqual(buff)) {
                // Next 4 bytes are the function pointer being pushed onto the stack
                funcPtr = Image.ReadUInt32();

                // Start of next instruction
                if (Image.ReadByte() != 0xB9)
                    return (0, 0);

                // Jump to Il2CppCodegenRegistration
                Image.Position = Image.MapVATR((ulong) funcPtr + 6);
                metadata = Image.ReadUInt32();
                Image.Position = Image.MapVATR((ulong) funcPtr + 11);
                code = Image.ReadUInt32();
                return (code, metadata);
            }

            // Variant 2
            bytes = new byte[]
                {0x55, 0x89, 0xE5, 0x53, 0x83, 0xE4, 0xF0, 0x83, 0xEC, 0x20, 0xE8, 0x00, 0x00, 0x00, 0x00, 0x5B};
            Image.Position = loc;
            buff = Image.ReadBytes(16);
            if (!bytes.SequenceEqual(buff))
                return (0, 0);

            Image.Position += 8;
            funcPtr = Image.MapVATR(Image.ReadUInt32() + globalOffset);
            if (funcPtr > Image.Stream.BaseStream.Length)
                return (0, 0);

            // Extract Metadata pointer
            // An 0x838D opcode indicates LEA (no indirection)
            Image.Position = funcPtr + 0x20;
            opcode = Image.ReadUInt16();
            metadata = Image.ReadUInt32() + globalOffset;

            // An 8x838B opcode indicates MOV (pointer indirection)
            if (opcode == 0x838B) {
                Image.Position = Image.MapVATR(metadata);
                metadata = Image.ReadUInt32();

                // Repeat the same logic for extracting the Code pointer
                Image.Position = funcPtr + 0x2A;
                opcode = Image.ReadUInt16();
                code = Image.ReadUInt32() + globalOffset;

                if (opcode == 0x838B) {
                    Image.Position = Image.MapVATR(code);
                    code = Image.ReadUInt32();

                    return (code, metadata);
                }
            }
            return (0, 0);
        }
    }
}