using CursorLang.Core.Models;
using CursorLang.Core.Services;
using CursorLang.Tests.Shared;
using Microsoft.Win32;

namespace CursorLang.Core.Tests.Services;

/// <summary>
/// Startup of a build unpacked into a folder: a value under the Run key. The tests
/// keep to a root of their own, so the startup list of the machine is untouched.
/// </summary>
public sealed class RegistryStartupTests
{
    private const string RunPath = @"Software\Microsoft\Windows\CurrentVersion\Run";

    private const string ApprovedPath =
        @"Software\Microsoft\Windows\CurrentVersion\Explorer\StartupApproved\Run";

    private const string ValueName = "CursorLang";

    private const string Command = @"""C:\Apps\CursorLang\CursorLang.exe""";

    [Fact]
    public void With_nothing_written_down_startup_is_off()
    {
        using var root = new TempRegistryKey();

        Assert.Equal(StartupState.Disabled, new RegistryStartup(root.Key, Command).GetState());
    }

    [Fact]
    public void Switching_startup_on_writes_the_path_of_the_app()
    {
        using var root = new TempRegistryKey();
        var startup = new RegistryStartup(root.Key, Command);

        Assert.Equal(StartupState.Enabled, startup.SetEnabled(true));
        Assert.Equal(Command, ReadRunValue(root));
    }

    [Fact]
    public void Switching_startup_off_takes_the_entry_away()
    {
        using var root = new TempRegistryKey();
        var startup = new RegistryStartup(root.Key, Command);

        startup.SetEnabled(true);

        Assert.Equal(StartupState.Disabled, startup.SetEnabled(false));
        Assert.Null(ReadRunValue(root));
    }

    // Switching off what is already off is what happens when Windows and the app
    // disagree about the state, and it is no reason to fail
    [Fact]
    public void Switching_off_startup_that_is_already_off_passes_quietly()
    {
        using var root = new TempRegistryKey();

        Assert.Equal(StartupState.Disabled, new RegistryStartup(root.Key, Command).SetEnabled(false));
    }

    [Fact]
    public void The_path_is_written_afresh_every_time()
    {
        using var root = new TempRegistryKey();

        new RegistryStartup(root.Key, @"""C:\Old\CursorLang.exe""").SetEnabled(true);
        new RegistryStartup(root.Key, Command).SetEnabled(true);

        Assert.Equal(Command, ReadRunValue(root));
    }

    [Fact]
    public void An_entry_the_user_has_banned_counts_as_off()
    {
        using var root = new TempRegistryKey();
        var startup = new RegistryStartup(root.Key, Command);

        startup.SetEnabled(true);
        Ban(root);

        Assert.Equal(StartupState.DisabledByUser, startup.GetState());
    }

    // The ban outlives the request: the entry is written, and Windows still ignores it
    [Fact]
    public void The_ban_of_the_user_survives_a_request_to_switch_startup_on()
    {
        using var root = new TempRegistryKey();
        var startup = new RegistryStartup(root.Key, Command);

        Ban(root);

        Assert.Equal(StartupState.DisabledByUser, startup.SetEnabled(true));
        Assert.Equal(Command, ReadRunValue(root));
    }

    [Fact]
    public void A_verdict_of_the_user_in_favour_leaves_startup_on()
    {
        using var root = new TempRegistryKey();
        var startup = new RegistryStartup(root.Key, Command);

        startup.SetEnabled(true);
        WriteVerdict(root, 0x02);

        Assert.Equal(StartupState.Enabled, startup.GetState());
    }

    // An empty blob is not a ban: Windows writes twelve bytes, but a value cut
    // short says nothing about the will of the user
    [Fact]
    public void A_verdict_with_no_bytes_in_it_is_no_ban()
    {
        using var root = new TempRegistryKey();
        var startup = new RegistryStartup(root.Key, Command);

        startup.SetEnabled(true);

        using RegistryKey approved = root.Key.CreateSubKey(ApprovedPath);
        approved.SetValue(ValueName, Array.Empty<byte>(), RegistryValueKind.Binary);

        Assert.Equal(StartupState.Enabled, startup.GetState());
    }

    [Fact]
    public void With_no_path_to_the_app_startup_is_unavailable()
    {
        using var root = new TempRegistryKey();
        var startup = new RegistryStartup(root.Key, command: null);

        Assert.Equal(StartupState.Unavailable, startup.GetState());
        Assert.Equal(StartupState.Unavailable, startup.SetEnabled(true));
        Assert.Equal(StartupState.Unavailable, startup.SetEnabled(false));
        Assert.Null(ReadRunValue(root));
    }

    private static string? ReadRunValue(TempRegistryKey root)
    {
        using RegistryKey? run = root.Key.OpenSubKey(RunPath);
        return run?.GetValue(ValueName) as string;
    }

    /// <summary>The mark Windows leaves after the user switches the entry off.</summary>
    private static void Ban(TempRegistryKey root) => WriteVerdict(root, 0x03);

    private static void WriteVerdict(TempRegistryKey root, byte first)
    {
        var verdict = new byte[12];
        verdict[0] = first;

        using RegistryKey approved = root.Key.CreateSubKey(ApprovedPath);
        approved.SetValue(ValueName, verdict, RegistryValueKind.Binary);
    }
}