using System.Runtime.InteropServices;
using Sms.Environment;

namespace Sms.Environment.Windows;

public sealed class WindowsEnvironmentVariableStore : IEnvironmentVariableStore
{
    private const int HWND_BROADCAST = 0xffff;
    private const int WM_SETTINGCHANGE = 0x001A;

    public string? Get(string name) =>
        System.Environment.GetEnvironmentVariable(name, EnvironmentVariableTarget.User)
        ?? System.Environment.GetEnvironmentVariable(name, EnvironmentVariableTarget.Process);

    public void Set(string name, string value)
    {
        System.Environment.SetEnvironmentVariable(name, value, EnvironmentVariableTarget.User);
        System.Environment.SetEnvironmentVariable(name, value, EnvironmentVariableTarget.Process);
        BroadcastEnvironmentChange();
    }

    public bool Exists(string name) => Get(name) is not null;

    public IReadOnlyDictionary<string, string> GetAll(IEnumerable<string> names)
    {
        var result = new Dictionary<string, string>(StringComparer.Ordinal);
        foreach (var name in names)
        {
            var value = Get(name);
            if (value is not null)
            {
                result[name] = value;
            }
        }

        return result;
    }

    public IReadOnlyDictionary<string, string> GetProcessEnvironment() =>
        ToDictionary(System.Environment.GetEnvironmentVariables(EnvironmentVariableTarget.Process));

    public IReadOnlyDictionary<string, string> GetUserPersistedEnvironment() =>
        ToDictionary(System.Environment.GetEnvironmentVariables(EnvironmentVariableTarget.User));

    public bool IsPersistedInUserStore(string name) =>
        System.Environment.GetEnvironmentVariable(name, EnvironmentVariableTarget.User) is not null;

    public void RemoveFromUserStore(string name)
    {
        System.Environment.SetEnvironmentVariable(name, null, EnvironmentVariableTarget.User);
        System.Environment.SetEnvironmentVariable(name, null, EnvironmentVariableTarget.Process);
        BroadcastEnvironmentChange();
    }

    private static Dictionary<string, string> ToDictionary(System.Collections.IDictionary source)
    {
        var result = new Dictionary<string, string>(StringComparer.Ordinal);
        foreach (string key in source.Keys)
        {
            result[key] = source[key]?.ToString() ?? string.Empty;
        }

        return result;
    }

    private static void BroadcastEnvironmentChange()
    {
        try
        {
            _ = NativeMethods.SendMessageTimeout(
                HWND_BROADCAST,
                WM_SETTINGCHANGE,
                IntPtr.Zero,
                "Environment",
                0,
                1000,
                out _);
        }
        catch
        {
            // Non-critical: new processes still see updated registry values.
        }
    }

    private static class NativeMethods
    {
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern IntPtr SendMessageTimeout(
            int hWnd,
            int msg,
            IntPtr wParam,
            string lParam,
            int fuFlags,
            int uTimeout,
            out IntPtr lpdwResult);
    }
}