use clap::{CommandFactory, ValueEnum};
use clap_complete::{Shell, generate_to};
use std::{env, ffi::OsString, fs, io::Error, path::PathBuf};

include!("src/cli/mod.rs");

fn shell_name(shell: Shell) -> String {
    shell
        .to_possible_value()
        .map(|v| v.get_name().to_owned())
        .unwrap_or_default()
}

fn non_empty(name: &str) -> Option<OsString> {
    env::var_os(name).filter(|v| !v.is_empty())
}

fn install_dir(shell: Shell) -> Option<(PathBuf, bool)> {
    let per_shell = format!("SHELL_COMPLETIONS_DIR_{}", shell_name(shell).to_uppercase());

    if let Some(dir) = non_empty(&per_shell).or_else(|| non_empty("SHELL_COMPLETIONS_DIR")) {
        return Some((PathBuf::from(dir), true));
    }
    non_empty("OUT_DIR").map(|dir| (PathBuf::from(dir), false))
}

fn main() -> Result<(), Error> {
    // naming any rerun-if condition replaces cargo's default of re-running the
    // script whenever anything in the package changed, so everything that
    // shapes a completion script has to be named here. without them an
    // installed script goes stale against the binary it completes
    println!("cargo::rerun-if-changed=build.rs");
    println!("cargo::rerun-if-changed=src/cli");
    println!("cargo::rerun-if-changed=Cargo.toml");

    println!("cargo::rerun-if-env-changed=SHELL_COMPLETIONS_DIR");
    for shell in Shell::value_variants() {
        println!(
            "cargo::rerun-if-env-changed=SHELL_COMPLETIONS_DIR_{}",
            shell_name(*shell).to_uppercase()
        );
    }

    let mut cmd = ahab::Ahab::command();

    for shell in Shell::value_variants() {
        let Some((dir, requested)) = install_dir(*shell) else {
            continue;
        };

        // a build script's working directory is the package root, so a relative
        // dir would quietly install into the source tree and one holding `..`
        // somewhere else again. only a path that says where it means is taken
        if requested && !dir.is_absolute() {
            return Err(Error::other(format!(
                "the completions directory must be an absolute path, not {}",
                dir.display()
            )));
        }

        fs::create_dir_all(&dir)
            .map_err(|e| Error::other(format!("creating {}: {e}", dir.display())))?;
        let path = generate_to(*shell, &mut cmd, env!("CARGO_PKG_NAME"), &dir)?;

        if requested {
            println!(
                "cargo::warning=installed {} completion: {}",
                shell_name(*shell),
                path.display()
            );
        }
    }

    Ok(())
}