use std::env;
use std::path::PathBuf;
use std::process::Command;

/// Execute a shell command line and print output directly to stdout/stderr.
/// Returns the exit code.
pub fn execute(input: &str) -> i32 {
    let trimmed = input.trim();

    // Handle cd specially - it must affect our process
    if trimmed == "cd" || trimmed.starts_with("cd ") {
        return handle_cd(trimmed);
    }

    // Run everything else through sh -c for full shell semantics
    // (pipes, redirects, globs, etc.)
    let status = Command::new("sh")
        .arg("-c")
        .arg(trimmed)
        .status();

    match status {
        Ok(s) => s.code().unwrap_or(1),
        Err(e) => {
            eprintln!("aishell: {}", e);
            127
        }
    }
}

fn handle_cd(input: &str) -> i32 {
    let target = input.strip_prefix("cd").unwrap().trim();

    let dir: PathBuf = if target.is_empty() {
        // cd with no args → home directory
        match env::var("HOME") {
            Ok(home) => PathBuf::from(home),
            Err(_) => {
                eprintln!("aishell: cd: HOME not set");
                return 1;
            }
        }
    } else if target.starts_with('~') {
        // Expand ~ to HOME
        match env::var("HOME") {
            Ok(home) => PathBuf::from(target.replacen('~', &home, 1)),
            Err(_) => {
                eprintln!("aishell: cd: HOME not set");
                return 1;
            }
        }
    } else if target == "-" {
        // cd - → previous directory
        match env::var("OLDPWD") {
            Ok(old) => {
                println!("{}", old);
                PathBuf::from(old)
            }
            Err(_) => {
                eprintln!("aishell: cd: OLDPWD not set");
                return 1;
            }
        }
    } else {
        PathBuf::from(target)
    };

    // Save current dir as OLDPWD
    if let Ok(cwd) = env::current_dir() {
        env::set_var("OLDPWD", cwd);
    }

    match env::set_current_dir(&dir) {
        Ok(_) => 0,
        Err(e) => {
            eprintln!("aishell: cd: {}: {}", dir.display(), e);
            1
        }
    }
}