use std::{collections::{HashMap, HashSet}, error::Error, os::unix::prelude::MetadataExt, path::PathBuf};

use clap::Parser;
use walkdir::WalkDir;

type StdError<T> = Result<T, Box<dyn Error>>;

#[derive(Parser)]
#[clap(author, version, about)]
struct Cli {
    /// Source directory
    #[clap(value_parser)]
    source: PathBuf,
    /// Destination directory
    #[clap(value_parser)]
    destination: PathBuf,
    // /// Be more verbose
    // #[clap(short, long, value_parser)]
    // verbose: bool,
}

// Map from (filesize, filename) to full file path relative to root
#[derive(Default)]
struct FileMap(HashMap<(u64, String), String>);

impl FileMap {
    fn new(path: &PathBuf) -> StdError<Self> {
        let mut fm = Self::default();
        for entry in WalkDir::new(path).into_iter().filter_entry(|e| {
            !e.file_name()
                .to_str()
                .map(|s| s.starts_with('.'))
                .unwrap_or(false)
        }) {
            let entry = entry?;
            let meta = &entry.metadata()?;
            if meta.is_dir() {
                continue;
            }
            let fname = entry.file_name().to_str().unwrap().to_owned();
            let fpath =  entry.path().to_str().unwrap().to_owned();
            if let Some(old) = fm.0.insert((meta.size(), fname.clone()), fpath.clone()) {
                return Err(format!("Duplicate filesize/filename detected: {}, clashes with {}!", old, fpath).into());
            }
        }
        Ok(fm)
    }
}

fn main() -> StdError<()> {
    let cli = Cli::parse();
    let source = FileMap::new(&cli.source)?;
    let source_set: HashSet<_> = source.0.keys().collect();
    eprintln!("{} files in source", source.0.len());
    let dest = FileMap::new(&cli.destination)?;
    let dest_set = dest.0.keys().collect();
    eprintln!("{} files in destination", dest.0.len());
    let mut diffs: Vec<_> = source_set.difference(&dest_set).map(|d| source.0[d].clone()).collect();
    diffs.sort();
    if !diffs.is_empty() {
        eprintln!("Files present in source but not dest:");
        for diff in diffs {
            eprintln!("{}", diff);
        }
    }

    Ok(())
}