using System.Diagnostics;

namespace DodoSSH.Client.App.Platform;

/// <summary>
/// Opens a local copy of a remote file for editing, without running it.
/// </summary>
/// <remarks>
/// <para>
/// One of the two halves of editing a remote file in place, and both are this platform's rather than the
/// shell's: what opens a <c>.conf</c> is a registry association, a desktop entry or a Launch Services binding
/// depending on which desktop this is. The shell decides <em>when</em>; see
/// <c>TransfersViewModel.EditRemoteAsync</c>.
/// </para>
/// <para>
/// ◆ <b>"Open" is not "edit", and for a file somebody else named the difference is code execution.</b> The
/// file comes from a host, and whoever can write to that host chooses its name. Handing <c>deploy.bat</c>,
/// <c>notes.hta</c> or <c>run.command</c> to the desktop's default action runs it, on this machine, as this
/// user — so a file whose default action is to run is opened with an editor instead. On Windows that is the
/// type's own <c>edit</c> verb where it has one (Notepad, for <c>.bat</c>, <c>.cmd</c>, <c>.js</c>,
/// <c>.vbs</c>, <c>.ps1</c> and <c>.reg</c>) and Notepad where it has not; on macOS it is <c>open -t</c>,
/// which is the default text editor whatever the type. Everything else still goes to its association, which
/// is the point of the feature — an <c>nginx.conf</c> should open in whatever this person edits configs with.
/// </para>
/// <para>
/// Linux is the exception: there is no portable "the text editor", so a <c>.desktop</c> entry — the one type
/// <c>xdg-open</c> may launch rather than open — is refused with a sentence instead. A shell script is opened
/// by every mainstream desktop's file associations in an editor, not run.
/// </para>
/// <para>
/// The process is not waited on and is deliberately not kept: an editor may hand off to an already-open
/// instance and exit at once, so its lifetime says nothing about whether the file is still being edited.
/// What ends an edit session is the user saying so — see the file browser's STOP EDITING.
/// </para>
/// </remarks>
internal static class LocalEditor
{
    /// <summary>
    /// Extensions Windows runs rather than opens, beyond whatever <c>PATHEXT</c> lists on this machine.
    /// </summary>
    /// <remarks>
    /// <c>PATHEXT</c> covers the console's notion of executable (<c>.exe</c>, <c>.bat</c>, <c>.js</c>,
    /// <c>.vbs</c>…) and is read as well, because an interpreter's installer may add its own. These are the
    /// ones Explorer acts on that are not in it: shortcuts, installers, HTML applications, control panel
    /// items, and the script hosts that installers do not register there.
    /// </remarks>
    private static readonly string[] WindowsRunsThese =
    [
        ".application", ".appref-ms", ".bat", ".chm", ".cmd", ".com", ".cpl", ".diagcab", ".exe", ".hta",
        ".inf", ".jar", ".js", ".jse", ".library-ms", ".lnk", ".msc", ".msi", ".msp", ".pif", ".ps1",
        ".psm1", ".py", ".pyw", ".reg", ".scf", ".scr", ".search-ms", ".settingcontent-ms", ".url",
        ".vbe", ".vbs", ".website", ".ws", ".wsc", ".wsf", ".wsh", ".xll",
    ];

    /// <summary>Extensions Launch Services runs, or installs, rather than opens.</summary>
    private static readonly string[] MacRunsThese =
    [
        ".app", ".command", ".dmg", ".fileloc", ".inetloc", ".jar", ".mpkg", ".pkg", ".scpt", ".terminal",
        ".tool", ".webloc", ".workflow",
    ];

    /// <summary>Opens <paramref name="path"/> for editing.</summary>
    /// <exception cref="InvalidOperationException">
    /// This desktop would run the file and has no editor to offer in its place.
    /// </exception>
    internal static Task OpenAsync(string path)
    {
        ArgumentNullException.ThrowIfNull(path);

        using var opened = Process.Start(StartInfoFor(path));

        return Task.CompletedTask;
    }

    /// <summary>What to start so that <paramref name="path"/> opens in an editor.</summary>
    internal static ProcessStartInfo StartInfoFor(string path)
    {
        if (OperatingSystem.IsWindows() && WouldRunOnWindows(path))
        {
            var edit = new ProcessStartInfo(path) { UseShellExecute = true, Verb = "edit" };

            if (edit.Verbs.Contains("edit", StringComparer.OrdinalIgnoreCase))
            {
                return edit;
            }

            return new ProcessStartInfo("notepad.exe") { UseShellExecute = false, ArgumentList = { path } };
        }

        if (OperatingSystem.IsMacOS() && HasExtension(path, MacRunsThese))
        {
            return new ProcessStartInfo("open") { UseShellExecute = false, ArgumentList = { "-t", path } };
        }

        if (OperatingSystem.IsLinux() && HasExtension(path, [".desktop"]))
        {
            throw new InvalidOperationException(
                $"{Path.GetFileName(path)} is a launcher, which this desktop would run rather than open. "
                + "Download it and open it in an editor instead.");
        }

        return new ProcessStartInfo(path) { UseShellExecute = true };
    }

    /// <summary>Whether Windows' default action for this file is to run it.</summary>
    internal static bool WouldRunOnWindows(string path, string? pathExt = null)
    {
        var listed = (pathExt ?? Environment.GetEnvironmentVariable("PATHEXT") ?? string.Empty)
            .Split(';', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);

        return HasExtension(path, WindowsRunsThese) || HasExtension(path, listed);
    }

    /// <summary>Whether the file's last extension is one of these, ignoring case.</summary>
    /// <remarks>
    /// Trailing dots and spaces are dropped first, because Windows drops them too: <c>run.bat.</c> is
    /// <c>run.bat</c> by the time anything acts on it.
    /// </remarks>
    private static bool HasExtension(string path, IEnumerable<string> extensions)
    {
        var extension = Path.GetExtension(Path.GetFileName(path).TrimEnd('.', ' '));

        return extension.Length > 0
            && extensions.Contains(extension, StringComparer.OrdinalIgnoreCase);
    }
}