using System.Runtime.InteropServices;

namespace ChangeT50.Adapter;

/// <summary>
/// Native Change.dll ABI assumptions reconstructed from the supplied vendor document.
/// </summary>
public static class ChangeAbi
{
    public const ushort ImageFileMachineI386 = 0x014c;
    public const int NativePack = 8;

    public static readonly string[] RequiredExports =
    [
        "CapDBConnect",
        "CapDBDiscon",
        "CapDownBlacklist",
        "CapDownBlacklistCount",
        "CapDownCustomerInfo",
        "CapGetCustomerByNum",
        "CapGetCustomerCount",
        "CapGetCustomerList",
        "CapGetDepCount",
        "CapGetDepList",
        "CapGetNBCardInfo",
        "CapNBQueryCard",
        "CapSetNBCardInfo",
        "CapUpload",
        "CloseCom",
        "OpenCom"
    ];

    public static IReadOnlyList<string> ValidateManagedLayouts()
    {
        var errors = new List<string>();
        CheckSize<CustomerInfoNative>(68, errors);
        CheckSize<UploadInfoNative>(120, errors);
        CheckSize<DownInfoNative>(320, errors);
        CheckSize<DownDepartmentInfoNative>(268, errors);

        var psamIdOffset = Marshal.OffsetOf<UploadInfoNative>(nameof(UploadInfoNative.PsamId)).ToInt32();
        if (psamIdOffset != 96)
        {
            errors.Add($"UploadInfoNative.PsamId offset is {psamIdOffset}; expected 96.");
        }

        return errors;
    }

    public static void EnsureNativeLoadEnvironment()
    {
        if (!OperatingSystem.IsWindows())
        {
            throw new PlatformNotSupportedException(
                "Change.dll is a Windows PE32 library. Native loading must run on Windows.");
        }

        if (RuntimeInformation.ProcessArchitecture != Architecture.X86)
        {
            throw new BadImageFormatException(
                $"Change.dll requires an x86 process; current process is {RuntimeInformation.ProcessArchitecture}.");
        }

        var layoutErrors = ValidateManagedLayouts();
        if (layoutErrors.Count != 0)
        {
            throw new TypeLoadException(string.Join(" ", layoutErrors));
        }
    }

    private static void CheckSize<T>(int expected, ICollection<string> errors) where T : struct
    {
        var actual = Marshal.SizeOf<T>();
        if (actual != expected)
        {
            errors.Add($"{typeof(T).Name} size is {actual}; expected {expected}.");
        }
    }
}

[StructLayout(LayoutKind.Sequential, Pack = ChangeAbi.NativePack)]
public unsafe struct CustomerInfoNative
{
    public int CardClass;
    public int CustomerId;
    public int CardNumber;
    public int CardSerialNumber;
    public int Status;
    public int SubType;
    public int TotalAmountCents;
    public int MainWalletBalanceCents;
    public int MainWalletOperationCount;
    public int SubsidyWalletBalanceCents;
    public int SubsidyWalletOperationCount;
    public fixed byte CardAsn[24];
}

[StructLayout(LayoutKind.Sequential, Pack = ChangeAbi.NativePack)]
public unsafe struct UploadInfoNative
{
    public int TerminalId;
    public int CustomerId;
    public int CardNumber;
    public int CardSerialNumber;
    public int CardClass;
    public fixed byte CardAsn[24];
    public int TotalAmountCents;
    public int ManagementFeeCents;
    public int WalletNumber;
    public int OperationAmountCents;
    public int RemainingBalanceCents;
    public int OperationCount;
    public fixed byte TradeTime[24];
    public long PsamId;
    public int PsamTradeNumber;
    public int Tac;
    public int Result;
}

[StructLayout(LayoutKind.Sequential, Pack = ChangeAbi.NativePack)]
public unsafe struct DownInfoNative
{
    public fixed byte Department[200];
    public fixed byte StudentNumber[60];
    public fixed byte Name[40];
    public int Sex;
    public int CustomerId;
    public int CardNumber;
    public int Status;
    public int CardSerialNumber;
}

[StructLayout(LayoutKind.Sequential, Pack = ChangeAbi.NativePack)]
public unsafe struct DownDepartmentInfoNative
{
    public fixed byte DepartmentCode1[6];
    public fixed byte DepartmentCode2[6];
    public fixed byte DepartmentCode3[8];
    public fixed byte DepartmentCode4[8];
    public fixed byte DepartmentName1[60];
    public fixed byte DepartmentName2[60];
    public fixed byte DepartmentName3[60];
    public fixed byte DepartmentName4[60];
}