//! Handle deletion
//!
//! # Handling paths
//! Deletion of single files is trivial, deletion of directories is not as trivial.
//! Other types of filesystem object are ignored.
//!
//! ## Directories
//! With directories the deletion processes all files containing recursively.
//! See `restore` for restoration of directories
use super::*;
use std::{
    path::{
	Path,
    },
};
use tokio::{
    fs,
};
use futures::{
    prelude::*,
    future::BoxFuture,
};

/// Process a single file.
///
/// `path` is known to be a file at this point.
async fn process_single(state: Arc<state::State>, path: impl AsRef<Path>) -> eyre::Result<()>
{
    let path = path.as_ref();
    #[cfg(debug_assertions)] {
	if !path.is_file() {
	    panic!("process_single() expected a file, but {:?} is not one.", path);
	}
    }
    let _g = state.lock().await;
    debug!("{:?} Processing", path);
    Ok(())
}

fn walk_dir<'a, T, F, P, Fut>(path: P, mut output: F) -> BoxFuture<'static, eyre::Result<Vec<T>>>
where F: FnMut(fs::DirEntry) -> Fut + Clone + 'static + Send + Sync,
      P: AsRef<Path> + Send + Sync + 'static,
      T: Send + 'static,
      Fut: Future<Output= T> + Send + Sync,
{
    #[cfg(debug_assertions)] {
	let path = path.as_ref();
	if !path.is_dir() {
	    panic!("walk_dir() expected a directory, but {:?} is not one.", path);
	}
    }
    trace!("{:?} Spawning children", path.as_ref());
    async move {
	let se_path = || format!("{:?}", path.as_ref()).header("Path was");
	let mut dir = fs::read_dir(&path).await
	    .wrap_err(eyre!("Failed to read directory contents"))
	    .with_section(se_path)?;
	let mut voutput: Vec<T> = util::alloc_stream_hint(&dir);
	let mut workers: Vec<_> = util::alloc_stream_hint(&dir);
	while let Some(entry) = dir.next_entry().await
	    .wrap_err(eyre!("Failed to read entry from directory contents"))
	    .with_section(se_path)?
	{
	    let path = entry.path();
	    if path.is_dir() {
		
		workers.push(tokio::spawn(walk_dir(path, output.clone())));
	    } else if path.is_file() {
		voutput.push(output(entry).await);
	    }
	}
	voutput.extend(future::join_all(workers)
		       .map(|x| x.into_iter()
			    .filter_map(Result::ok).flatten())
		       .await.into_iter()
		       .flatten());
	Ok(voutput)
    }.boxed()
}

/// Process this path
///
/// This will not return until all its children finish too (if any)
pub async fn process(state: Arc<state::State>, path: impl AsRef<Path>) -> eyre::Result<()>
{
    let path = path.as_ref();
    let se_path = || format!("{:?}", path).header("Path was");
    if path.is_dir() {
	for res in  walk_dir(path.to_owned(), move |file| process_single(Arc::clone(&state), file.path())).await?
	    .into_iter()
	    .filter_map(Result::err)
	{
	    error!("{:?} Failed to process child: {}", path, res);
	    return Err(res)
		.wrap_err(eyre!("Failed to process child"))
		.with_section(se_path);
	}
	Ok(())
    } else if path.is_file() {
	process_single(state, path).await
	    .wrap_err(eyre!("Processing file failed"))
	    .with_section(se_path)
    } else {
	error!("{:?} is not a recognised FS object", path);
	return Err(eyre!("Unsupported FS object"))
	    .with_section(se_path)
    }
}