using System.Reflection;
using System.Reflection.PortableExecutable;
using Iced.Intel;

// Find the il2cpp methods that reference a given string literal.
//
// Neither the bytes nor the index of a literal appear directly in the code: on
// metadata v27+ the code loads a pointer from a metadata-usage slot, and statically
// that slot holds the encoded usage token `(type << 29) | (index << 1) | 1` with
// type 5 for string literals. So the search is:
//   1. resolve the literal's index from its text,
//   2. scan the image for the 8-byte token  (this finds the slots),
//   3. scan the executable sections for instructions whose rip-relative operand
//      lands on one of those slots. The displacement is the tail of such an
//      instruction, so a cheap arithmetic pre-check narrows candidates and Iced
//      then confirms by decoding from the candidate's start.
internal static class LiteralFinder
{
    const ulong TokenBase = 5UL << 29;

    static object Prop(object o, string n) => o.GetType().GetProperty(n)!.GetValue(o)!;

    sealed class LineOutput : FormatterOutput
    {
        public string Value = "";
        public override void Write(string text, FormatterTextKind kind) => Value += text;
    }

    public static void Run(object main, object metadata, string binaryPath, string needle)
    {
        var defs = (System.Collections.IEnumerable)metadata.GetType().GetField("methodDefs")!.GetValue(metadata)!;
        var methods = new List<(object Method, ulong Address)>();
        foreach (var m in defs.Cast<object>())
        {
            var address = (ulong)Prop(m, "MethodPointer");
            if (address != 0) methods.Add((m, address));
        }
        methods.Sort((a, b) => a.Address.CompareTo(b.Address));

        var table = metadata.GetType().GetField("stringLiterals",
            BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public)!.GetValue(metadata) as Array;
        var getLiteralText = metadata.GetType().GetMethod("GetStringLiteralFromIndex")!;

        var tokens = new List<ulong>();
        for (int i = 0; i < (table?.Length ?? 0); i++)
        {
            var text = (string)getLiteralText.Invoke(metadata, new object[] { (uint)i })!;
            if (!text.Contains(needle, StringComparison.Ordinal)) continue;
            // Both low-bit spellings resolve to the same index downstream.
            tokens.Add(TokenBase | ((ulong)i << 1) | 1);
            tokens.Add(TokenBase | ((ulong)i << 1));
            Console.WriteLine($"  literal #{i} = \"{text}\"  token 0x{TokenBase | ((ulong)i << 1):X}");
        }
        if (tokens.Count == 0)
        {
            Console.WriteLine($"no literal contains \"{needle}\"");
            return;
        }

        var bytes = File.ReadAllBytes(binaryPath);
        using var pe = new PEReader(new MemoryStream(bytes));
        var imageBase = pe.PEHeaders.PEHeader!.ImageBase;

        // 1. slots: 8-byte tokens, so only probe 8-byte aligned positions.
        var slots = new List<(string Section, ulong Address, ulong Value)>();
        foreach (var section in pe.PEHeaders.SectionHeaders)
        {
            var size = Math.Min(section.SizeOfRawData, Math.Max(0, bytes.Length - section.PointerToRawData));
            for (int i = section.PointerToRawData; i < section.PointerToRawData + size - 8; i += 8)
            {
                var value = BitConverter.ToUInt64(bytes, i);
                if (!tokens.Contains(value)) continue;
                var slot = imageBase + (ulong)section.VirtualAddress + (ulong)(i - section.PointerToRawData);
                slots.Add((section.Name, slot, value));
                Console.WriteLine($"  slot 0x{slot:X} ({section.Name}, raw 0x{i:X}) = 0x{value:X}");
            }
        }
        if (slots.Count == 0)
        {
            Console.WriteLine("no metadata-usage slot found");
            return;
        }
        var slotSet = slots.Select(s => s.Address).ToHashSet();

        // 2. references: pre-check the displacement, confirm by decoding from the start.
        var formatter = new IntelFormatter();
        int hits = 0, candidates = 0;
        foreach (var section in pe.PEHeaders.SectionHeaders.Where(s => (s.SectionCharacteristics & SectionCharacteristics.MemExecute) != 0))
        {
            var rawToVa = (long)imageBase + section.VirtualAddress - section.PointerToRawData;
            var size = Math.Min(section.SizeOfRawData, Math.Max(0, bytes.Length - section.PointerToRawData));
            for (int i = section.PointerToRawData; i < section.PointerToRawData + size - 4; i++)
            {
                var disp = BitConverter.ToInt32(bytes, i);
                var target = (ulong)((long)i + 4 + rawToVa + disp);
                if (!slotSet.Contains(target)) continue;
                candidates++;
                for (int back = 0; back <= 7; back++)
                {
                    var candidateRaw = i - back;
                    if (candidateRaw < section.PointerToRawData) break;
                    var reader = new ByteArrayCodeReader(bytes, candidateRaw, Math.Min(16, bytes.Length - candidateRaw));
                    var decoder = Decoder.Create(64, reader);
                    decoder.IP = (ulong)((long)candidateRaw + rawToVa);
                    decoder.Decode(out var instruction);
                    if (instruction.IsInvalid || !instruction.IsIPRelativeMemoryOperand) continue;
                    if (instruction.IPRelativeMemoryAddress != target) continue;
                    hits++;
                    var method = Nearest(methods, instruction.IP);
                    var name = method == null
                        ? "<none>"
                        : Prop(Prop(method, "DeclaringType"), "Name") + "::" + Prop(method, "Name");
                    var offset = method == null ? 0 : instruction.IP - (ulong)Prop(method, "MethodPointer");
                    var output = new LineOutput();
                    formatter.Format(instruction, output);
                    Console.WriteLine($"  REF 0x{instruction.IP:X} -> slot 0x{target:X}   in {name} +0x{offset:X}   [{output.Value}]");
                    break;
                }
            }
        }
        Console.WriteLine($"slots {slots.Count}; displacement candidates {candidates}; confirmed references {hits}");
    }

    static object? Nearest(List<(object Method, ulong Address)> methods, ulong address)
    {
        object? best = null;
        foreach (var (method, addr) in methods)
        {
            if (addr > address) break;
            best = method;
        }
        return best;
    }
}