use memmap2::Mmap;
use once_cell::sync::Lazy;
use rayon::prelude::*;
use regex::Regex;
use serde_json::json;
use std::{
    collections::BTreeMap,
    env, fs,
    fs::File,
    path::{Path, PathBuf},
};
use walkdir::WalkDir;
use xxhash_rust::xxh3::xxh3_64;

static RE: Lazy<Regex> = Lazy::new(|| {
    Regex::new(r"(metin2\.exe|granny2\.dll|SpeedTreeRT\.dll|BGM[/\\].*|lib[/\\].*|pack[/\\].*)")
        .unwrap()
});

fn hash_file(path: &Path, base_path: &String) -> (String, String) {
    let file = File::open(path).expect("Failed to open file");
    let mmap = unsafe { Mmap::map(&file).expect("Failed to mmap file") };
    let hash = xxh3_64(&mmap);
    let hash_str = hash.to_string();

    let filename = path.to_str().unwrap().to_string().replace(base_path, "");
    (filename, hash_str)
}

fn collect_files(folder: &Path) -> Vec<PathBuf> {
    WalkDir::new(folder)
        .into_iter()
        .filter_map(|e| e.ok())
        .filter(|e| e.path().is_file() && RE.is_match(e.path().to_str().unwrap()))
        .map(|e| e.path().to_path_buf())
        .collect()
}

fn main() -> std::io::Result<()> {
    use std::time::Instant;
    let now = Instant::now();

    let args: Vec<String> = env::args().collect();
    if args.len() != 2 {
        eprintln!("Usage: {} <folder>", args[0]);
        std::process::exit(1);
    }

    let folder = Path::new(&args[1]);
    if !folder.is_dir() {
        eprintln!("Error: '{}' is not a directory", folder.display());
        std::process::exit(1);
    }

    let files = collect_files(folder);

    let results: BTreeMap<String, String> =
        files.par_iter().map(|f| hash_file(f, &args[1])).collect();

    let json_output = json!({ "checksums": results });

    fs::write("checksum.json", serde_json::to_string_pretty(&json_output)?)?;
    let elapsed = now.elapsed();
    println!("Generated 'checksum', elapsed {:.2?}", elapsed);
    Ok(())
}