using System.Runtime.InteropServices;

namespace Flyshot.Native.Planning;

/// <summary>
/// 声明 Rust 原生规划库导出的稳定 C ABI 方法。
/// </summary>
internal static partial class NativeIcspMethods
{
    /// <summary>
    /// 保护原生库句柄首次初始化，避免并发规划重复加载。
    /// </summary>
    private static readonly object LibraryLoadLock = new();

    /// <summary>
    /// 保存已加载原生库句柄，使 P/Invoke 生命周期覆盖整个进程。
    /// </summary>
    private static nint _libraryHandle;

    /// <summary>
    /// 保存当前进程已绑定到 P/Invoke 逻辑名称的实际库路径。
    /// </summary>
    private static string? _loadedLibraryPath;

    /// <summary>
    /// 初始化程序集级 DllImport 解析器，把逻辑库名绑定到显式加载句柄。
    /// </summary>
    static NativeIcspMethods()
    {
        NativeLibrary.SetDllImportResolver(
            typeof(NativeIcspMethods).Assembly,
            ResolveImportedLibrary);
    }

    /// <summary>
    /// 使用指定解析器确保原生规划库已加载。
    /// </summary>
    /// <param name="resolver">负责生成平台路径并加载原生库的解析器。</param>
    internal static void EnsureLibraryLoaded(NativePlanningLibraryResolver resolver)
    {
        ArgumentNullException.ThrowIfNull(resolver);
        string requestedPath = resolver.ResolveLibraryPath();

        lock (LibraryLoadLock)
        {
            if (_libraryHandle != nint.Zero)
            {
                StringComparison comparison = OperatingSystem.IsWindows()
                    ? StringComparison.OrdinalIgnoreCase
                    : StringComparison.Ordinal;
                if (!string.Equals(_loadedLibraryPath, requestedPath, comparison))
                {
                    throw new NativePlanningException(
                        $"Rust 原生规划库已绑定到“{_loadedLibraryPath}”，不能在同一进程中改为“{requestedPath}”。",
                        errorCode: -1008);
                }

                return;
            }

            _libraryHandle = resolver.LoadLibrary();
            _loadedLibraryPath = requestedPath;
        }
    }

    /// <summary>
    /// 调用 Rust ICSP 入口并返回错误码和结果指针。
    /// </summary>
    /// <param name="waypoints">行优先连续路点数组。</param>
    /// <param name="waypointCount">路点数量。</param>
    /// <param name="degreesOfFreedom">每个路点的关节自由度。</param>
    /// <param name="velocityLimits">逐关节速度上限。</param>
    /// <param name="accelerationLimits">逐关节加速度上限。</param>
    /// <param name="jerkLimits">逐关节 jerk 上限。</param>
    /// <param name="options">与 Rust C ABI 对齐的规划选项。</param>
    /// <param name="result">接收 Rust 分配的结果指针。</param>
    /// <returns>零表示成功，非零表示固定类别的原生错误。</returns>
    [LibraryImport(
        NativePlanningLibraryResolver.LogicalLibraryName,
        EntryPoint = "flyshot_icsp_plan")]
    internal static unsafe partial int FlyshotIcspPlan(
        double* waypoints,
        int waypointCount,
        int degreesOfFreedom,
        double* velocityLimits,
        double* accelerationLimits,
        double* jerkLimits,
        NativeIcspOptions* options,
        out nint result);

    /// <summary>
    /// 释放由 Rust 分配的 ICSP 结果对象。
    /// </summary>
    /// <param name="result">Rust 返回的结果对象指针；允许为空指针。</param>
    [LibraryImport(
        NativePlanningLibraryResolver.LogicalLibraryName,
        EntryPoint = "flyshot_icsp_result_free")]
    internal static partial void FlyshotIcspResultFree(nint result);

    /// <summary>
    /// 获取当前线程最近一次 Rust 调用保存的 UTF-8 错误文本。
    /// </summary>
    /// <returns>指向线程局部 C 字符串的只读指针。</returns>
    [LibraryImport(
        NativePlanningLibraryResolver.LogicalLibraryName,
        EntryPoint = "flyshot_last_error_message")]
    internal static partial nint FlyshotLastErrorMessage();

    /// <summary>
    /// 将固定逻辑库名解析为已经显式加载的系统句柄。
    /// </summary>
    /// <param name="libraryName">P/Invoke 请求的逻辑库名。</param>
    /// <param name="assembly">发起请求的托管程序集。</param>
    /// <param name="searchPath">调用方提供的可选搜索路径。</param>
    /// <returns>逻辑名称匹配时返回已加载句柄，否则返回零交给系统继续解析。</returns>
    private static nint ResolveImportedLibrary(
        string libraryName,
        System.Reflection.Assembly assembly,
        DllImportSearchPath? searchPath)
    {
        _ = assembly;
        _ = searchPath;
        return string.Equals(
            libraryName,
            NativePlanningLibraryResolver.LogicalLibraryName,
            StringComparison.Ordinal)
            ? _libraryHandle
            : nint.Zero;
    }
}