using WhiteMagic.Discovery;
using Process = System.Diagnostics.Process;
using ProcessModule = System.Diagnostics.ProcessModule;

namespace WhiteMagic;

/// <summary>
/// A module (loaded DLL/EXE image) in the target process, obtained by indexing the
/// facade with a module name (e.g. <c>magic["user32"]</c>). Exposes the module's base
/// address and resolves exported functions by name.
/// </summary>
public sealed class RemoteModule
{
    private readonly Magic _magic;

    /// <summary>The module's file name as reported by the OS (e.g. <c>user32.dll</c>).</summary>
    public string Name { get; }

    /// <summary>The module's load address in the target process.</summary>
    public IntPtr BaseAddress { get; }

    internal RemoteModule(Magic magic, string moduleName)
    {
        ArgumentNullException.ThrowIfNull(magic);
        ArgumentException.ThrowIfNullOrEmpty(moduleName);

        _magic = magic;

        (string name, IntPtr baseAddress) = FindModule(magic.Memory.ProcessId, moduleName);
        Name = name;
        BaseAddress = baseAddress;
    }

    /// <summary>
    /// Resolves an exported function by name and returns a <see cref="RemoteFunction"/>
    /// bound to its address. Export forwarders are followed.
    /// </summary>
    public RemoteFunction this[string functionName]
    {
        get
        {
            IntPtr address = GetExportAddress(functionName);
            return new RemoteFunction(_magic, functionName, address);
        }
    }

    /// <summary>Resolves the absolute address of an exported function by name.</summary>
    public IntPtr GetExportAddress(string functionName)
    {
        ArgumentException.ThrowIfNullOrEmpty(functionName);
        var parser = new PeHeaderParser(_magic.Memory, BaseAddress);
        return parser.GetExportAddress(functionName);
    }

    private static (string Name, IntPtr BaseAddress) FindModule(int processId, string moduleName)
    {
        using Process process = Process.GetProcessById(processId);
        foreach (ProcessModule module in process.Modules)
        {
            if (NameMatches(module.ModuleName, moduleName))
                return (module.ModuleName, module.BaseAddress);
        }

        throw new DllNotFoundException(
            $"Module '{moduleName}' is not loaded in process {processId}.");
    }

    /// <summary>
    /// Resolves a module's base address by name within a target process, returning
    /// <see cref="IntPtr.Zero"/> if it is not loaded. Used by export-forwarder resolution.
    /// </summary>
    internal static IntPtr ResolveBase(int processId, string moduleName)
    {
        using Process process = Process.GetProcessById(processId);
        foreach (ProcessModule module in process.Modules)
        {
            if (NameMatches(module.ModuleName, moduleName))
                return module.BaseAddress;
        }

        return IntPtr.Zero;
    }

    /// <summary>
    /// Matches a loaded module's file name against a requested name, tolerating a missing
    /// or present <c>.dll</c> extension and ignoring case (e.g. <c>KERNEL32</c> matches
    /// <c>kernel32.dll</c>).
    /// </summary>
    private static bool NameMatches(string actual, string requested)
    {
        if (string.Equals(actual, requested, StringComparison.OrdinalIgnoreCase))
            return true;

        string actualNoExt = Path.GetFileNameWithoutExtension(actual);
        string requestedNoExt = requested.EndsWith(".dll", StringComparison.OrdinalIgnoreCase)
            ? requested[..^4]
            : requested;

        return string.Equals(actualNoExt, requestedNoExt, StringComparison.OrdinalIgnoreCase);
    }
}