/*
    Copyright 2017 Perfare - https://github.com/Perfare/Il2CppDumper
    Copyright 2017-2019 Katy Coe - http://www.hearthcode.org - http://www.djkaty.com

    All rights reserved.
*/

using System;
using System.Linq;

namespace Il2CppInspector
{
    internal class Il2CppBinaryARM : Il2CppBinary
    {
        public Il2CppBinaryARM(IFileFormatReader stream) : base(stream) { }

        public Il2CppBinaryARM(IFileFormatReader stream, uint codeRegistration, uint metadataRegistration) : base(stream, codeRegistration, metadataRegistration) { }

        protected override (ulong, ulong) ConsiderCode(IFileFormatReader image, uint loc) {
            // Assembly bytes to search for at start of each function
            ulong metadataRegistration, codeRegistration;

            // ARMv7 based on ELF GOT
            // Il2CppCodeRegistration.cpp initializer
            image.Position = loc;

            var buff = image.ReadBytes(0xc);
            // LDR R0, [PC, #0x1C]; LDR R1, [PC, #0x1C]; LDR R2, [PC, #0x1C]
            if (new byte[] { 0x1c, 0x0, 0x9f, 0xe5, 0x1c, 0x10, 0x9f, 0xe5, 0x1c, 0x20, 0x9f, 0xe5 }.SequenceEqual(buff)) {

                // Get offset to all addresses
                var offset = image.ReadUInt32(loc + 0x24) + loc + 0xc + 8;

                // Get pointer to Il2CppCodegenRegistration(void)
                var pCgr = image.ReadUInt32(loc + 0x2C) + offset;

                // Read pointer table at end of function
                codeRegistration = image.ReadUInt32(pCgr + 0x28) + offset;
                var pMetadataRegistration = image.ReadUInt32(pCgr + 0x2C) + offset;
                metadataRegistration = image.ReadUInt32(pMetadataRegistration);
                return (codeRegistration, metadataRegistration);
            }

            // ARMv7
            // Il2CppCodeRegistration.cpp initializer
            image.Position = loc;

            buff = image.ReadBytes(0x18);
            // Check for ADD R0, PC, R0; ADD R1, PC, R1 near the end of the function
            if (new byte[] {0x00, 0x00, 0x8F, 0xE0, 0x01, 0x10, 0x8F, 0xE0}.SequenceEqual(buff.Skip(0x10))

                // Check for LDR R1, [PC, #x] where x is an offset to *Il2CppCodegenRegistration
                && new byte[] {0x10, 0x9F, 0xE5}.SequenceEqual(buff.Skip(0x9).Take(3))) {

                // Read offset in LDR operand plus pointer table at end of function to find pCgr
                var pCgr = buff[8] + loc + 0x10;
                image.Position = pCgr;
                pCgr = image.ReadUInt32() + loc + 0x1c;

                // void Il2CppCodegenRegistration()
                // Read pointer table at end of function
                image.Position = pCgr + 0x1C;
                var pMetadata = image.ReadUInt32() + pCgr + 0x14;
                codeRegistration = image.ReadUInt32() + pCgr + 0x18;

                image.Position = image.MapVATR(pMetadata);
                metadataRegistration = image.ReadUInt32();
                return (codeRegistration, metadataRegistration);
            }

            // ARMv7 Thumb (T1) metadata v23
            // void Il2CppCodeRegistration()
            image.Position = loc;

            // Check for ADD Rx, PC in relevant parts of function
            buff = image.ReadBytes(0x20);
            if (buff[0x0C] == 0x79 && buff[0x0D] == 0x44 && // ADD R1, PC
                buff[0x16] == 0x78 && buff[0x17] == 0x44 && // ADD R0, PC
                buff[0x1E] == 0x7A && buff[0x1F] == 0x44)   // ADD R2, PC
            {
                // Follow path to metadata pointer
                var ppMetadata = decodeMovImm32(buff) + loc + 0x10;
                image.Position = ppMetadata;
                metadataRegistration = image.ReadUInt32();

                // Follow path to code pointer
                var pCode = decodeMovImm32(buff.Skip(8).Take(4).Concat(buff.Skip(14).Take(4)).ToArray());
                codeRegistration = pCode + loc + 0x1A + image.GlobalOffset;

                return (codeRegistration, metadataRegistration);
            }

            // ARMv7 Thumb (T1)
            // http://liris.cnrs.fr/~mmrissa/lib/exe/fetch.php?media=armv7-a-r-manual.pdf - A8.8.106
            // http://armconverter.com/hextoarm/
            var bytes = new byte[] { 0x2d, 0xe9, 0x00, 0x48, 0xeb, 0x46 };
            image.Position = loc;
            buff = image.ReadBytes(6);
            if (!bytes.SequenceEqual(buff))
                return (0, 0);
            bytes = new byte[] { 0x00, 0x23, 0x00, 0x22, 0xbd, 0xe8, 0x00, 0x48 };
            image.Position += 0x10;
            buff = image.ReadBytes(8);
            if (!bytes.SequenceEqual(buff))
                return (0, 0);
            image.Position = loc + 6;
            image.Position = (image.MapVATR(decodeMovImm32(image.ReadBytes(8))) & 0xfffffffc) + 0x0e;
            metadataRegistration = decodeMovImm32(image.ReadBytes(8));
            codeRegistration = decodeMovImm32(image.ReadBytes(8));
            return (codeRegistration, metadataRegistration);
        }

        private uint decodeMovImm32(byte[] asm) {
            ushort low = (ushort) (asm[2] + ((asm[3] & 0x70) << 4) + ((asm[1] & 0x04) << 9) + ((asm[0] & 0x0f) << 12));
            ushort high = (ushort) (asm[6] + ((asm[7] & 0x70) << 4) + ((asm[5] & 0x04) << 9) + ((asm[4] & 0x0f) << 12));
            return (uint) ((high << 16) + low);
        }
    }
}