use std::{ffi::OsString, path::Path};

use clap::Command;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RequestedApplet {
    Client,
    Tui,
    Server,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum AppletDispatch {
    Run {
        applet: RequestedApplet,
        argv: Vec<OsString>,
    },
    Help(String),
}

pub fn detect_applet_from_argv0(argv0: &str) -> Option<RequestedApplet> {
    match applet_basename(argv0) {
        "irtt-client" => Some(RequestedApplet::Client),
        "irtt-tui" => Some(RequestedApplet::Tui),
        "irtt-server" => Some(RequestedApplet::Server),
        "irtt-rs" => None,
        _ => None,
    }
}

pub fn dispatch_from_argv(argv: Vec<OsString>) -> Result<AppletDispatch, String> {
    let argv0 = argv
        .first()
        .and_then(|arg| arg.to_str())
        .unwrap_or("irtt-rs");

    if let Some(applet) = detect_applet_from_argv0(argv0) {
        return Ok(AppletDispatch::Run { applet, argv });
    }

    let basename = applet_basename(argv0);
    if basename.starts_with("irtt-") && basename != "irtt-rs" {
        return Err(format!(
            "unknown applet name '{basename}'. Known applet names: {}",
            known_applet_binary_names()
        ));
    }

    let Some(command) = argv.get(1).and_then(|arg| arg.to_str()) else {
        return Err(format!(
            "choose an applet: {}\n\n{}",
            applet_command_names(),
            dispatcher_help()
        ));
    };

    match command {
        "-h" | "--help" => Ok(AppletDispatch::Help(dispatcher_help())),
        "client" => Ok(AppletDispatch::Run {
            applet: RequestedApplet::Client,
            argv: applet_argv("irtt-client", &argv[2..]),
        }),
        "tui" => Ok(AppletDispatch::Run {
            applet: RequestedApplet::Tui,
            argv: applet_argv("irtt-tui", &argv[2..]),
        }),
        "server" => Ok(AppletDispatch::Run {
            applet: RequestedApplet::Server,
            argv: applet_argv("irtt-server", &argv[2..]),
        }),
        _ => Err(format!(
            "unknown applet '{command}'. Choose one of: {}\n\n{}",
            applet_command_names(),
            dispatcher_help()
        )),
    }
}

pub fn dispatcher_help() -> String {
    let mut command = Command::new("irtt-rs")
        .about("IRTT-compatible multi-applet dispatcher")
        .subcommand(Command::new("client").about(client_applet_about()))
        .subcommand(Command::new("tui").about(tui_applet_about()))
        .subcommand(Command::new("server").about(server_applet_about()))
        .after_help(dispatcher_after_help());
    command.render_help().to_string()
}

fn client_applet_about() -> &'static str {
    if cfg!(feature = "client") {
        "Run the stream client applet"
    } else {
        "Stream client applet is not available in this build"
    }
}

fn tui_applet_about() -> &'static str {
    if cfg!(feature = "tui") {
        "Run the terminal UI applet"
    } else {
        "Terminal UI applet is not available in this build"
    }
}

fn server_applet_about() -> &'static str {
    if cfg!(feature = "server") {
        "Run the UDP server applet"
    } else {
        "UDP server applet is not available in this build"
    }
}

fn known_applet_binary_names() -> &'static str {
    "irtt-rs, irtt-client, irtt-tui, irtt-server"
}

fn applet_command_names() -> &'static str {
    "client, tui, or server"
}

fn dispatcher_after_help() -> String {
    let mut help = "Recognized applet binary names: irtt-client, irtt-tui, irtt-server".to_owned();

    let mut missing = Vec::new();
    if !cfg!(feature = "client") {
        missing.push("irtt-client requires the client feature");
    }
    if !cfg!(feature = "server") {
        missing.push("irtt-server requires the server feature");
    }
    if !cfg!(feature = "tui") {
        missing.push("irtt-tui requires the tui feature");
    }

    match missing.len() {
        0 => {}
        1 => help.push_str(&format!("\nOptional applet: {}", missing[0])),
        _ => help.push_str(&format!("\nOptional applets: {}", missing.join("; "))),
    }
    help
}

fn applet_basename(argv0: &str) -> &str {
    let name = Path::new(argv0)
        .file_name()
        .and_then(|name| name.to_str())
        .unwrap_or(argv0);
    strip_suffix_ignoring_case(name, std::env::consts::EXE_SUFFIX)
}

/// Removes the platform executable suffix from a file name.
///
/// The suffix is part of the file name on Windows and empty everywhere else, so
/// this is a no-op on Unix. Without it, every applet name — including the
/// `irtt-rs` dispatcher itself — reaches argv0 detection as `<name>.exe` and is
/// rejected as an unknown applet. The applet names themselves are still matched
/// exactly; only this platform artifact is case-insensitive, because it is not
/// a name the user chose.
///
/// The suffix is a parameter so that Windows behavior is assertable from any
/// host, not only where `EXE_SUFFIX` happens to be non-empty.
fn strip_suffix_ignoring_case<'a>(name: &'a str, suffix: &str) -> &'a str {
    if suffix.is_empty() || name.len() <= suffix.len() {
        return name;
    }
    let split = name.len() - suffix.len();
    let (Some(stem), Some(tail)) = (name.get(..split), name.get(split..)) else {
        return name;
    };
    if tail.eq_ignore_ascii_case(suffix) {
        stem
    } else {
        name
    }
}

fn applet_argv(applet_name: &str, args: &[OsString]) -> Vec<OsString> {
    let mut argv = Vec::with_capacity(args.len() + 1);
    argv.push(OsString::from(applet_name));
    argv.extend(args.iter().cloned());
    argv
}