use std::io::{self, Write};

use anyhow::{Context, Result};
use clap::CommandFactory;
use clap_complete::{Shell, generate};

use crate::cli::Ahab;

pub fn completions(shell: Shell) -> Result<()> {
    let script = script(shell);

    let mut stdout = io::stdout().lock();
    match stdout.write_all(&script).and_then(|()| stdout.flush()) {
        Err(e) if e.kind() == io::ErrorKind::BrokenPipe => Ok(()),
        result => result.context("writing the completion script"),
    }
}

fn script(shell: Shell) -> Vec<u8> {
    let mut cmd = Ahab::command();
    let name = cmd.get_name().to_string();

    let mut script = Vec::new();
    generate(shell, &mut cmd, name, &mut script);
    script
}

#[cfg(test)]
mod tests {
    use super::{Ahab, Shell, script};
    use clap::{CommandFactory, ValueEnum};

    #[test]
    fn every_shell_gets_a_script_covering_the_subcommands() {
        // asked of the parser rather than listed here, which is a list that
        // silently stops covering the newest command
        let subcommands: Vec<String> = Ahab::command()
            .get_subcommands()
            .map(|sub| sub.get_name().to_string())
            .collect();

        assert!(subcommands.len() > 1, "{subcommands:?}");

        for shell in Shell::value_variants() {
            let out = String::from_utf8(script(*shell)).expect("script is utf8");

            for subcommand in &subcommands {
                assert!(
                    out.contains(subcommand),
                    "{shell:?} script never mentions {subcommand}"
                );
            }
        }
    }
}