use std::fs;

use proc_macro::TokenStream;

/// Takes a path to the aoc year directory and generates module declarations
/// and argument parsing for each day found in that directory, each day
/// must begin with "day".
#[proc_macro]
pub fn gen_days(item: TokenStream) -> TokenStream {
    let path = format!("{item}");
    let mut days_in_dir: Vec<String> = Vec::new();
    for entry in fs::read_dir(&path).unwrap() {
        let entry = entry.unwrap();
        let path = entry.path();
        if let Some(file_stem) = path.file_stem() {
            let (day_prefix, day_number) = file_stem.to_str().unwrap().split_at(3);
            if day_prefix == "day" {
                // do template stuff for this day
                days_in_dir.push(day_number.to_string());
            }
        }
    }
    let mut module_imports = String::new();
    let mut day_checks = String::new();
    for day in days_in_dir {
        module_imports += &format!("mod day{day};\n");
        day_checks += &format!("
            if day == \"day{day}\" {{
                if part == \"1\" {{
                    println!(\"{{}}\", day{day}::part1());
                }} else if part == \"2\" {{
                    println!(\"{{}}\", day{day}::part2());
                }} else {{
                    panic!(\"expecting 1 or 2 for argument 2\")
                }}
            }}
        ");
    }
    format!("
        {module_imports} 

        fn main() {{
            let day = std::env::args().nth(1).expect(\"needs to specify day for first argument\");
            let part = std::env::args().nth(2).expect(\"needs to specify 1 or 2 for second argument\");

            {day_checks}
        }}
        ").parse().unwrap()
}