// SPDX-FileCopyrightText: Matteo Settenvini <matteo.settenvini@montecristosoftware.eu>
// SPDX-License-Identifier: EUPL-1.2

mod dso;
mod list;

use crate::{
    args::Args,
    decision::{Action, Decision},
};
use anyhow::Result;
use async_trait::async_trait;
use dso::DsoCleaner;
use list::ListCleaner;
use nix::libc::EXDEV;
use std::{
    collections::HashMap,
    io,
    path::{Path, PathBuf},
};
use tokio::{
    sync::{broadcast, mpsc},
    task::JoinSet,
};
use walkdir::{DirEntry, WalkDir};

#[async_trait]
pub trait Cleaner {
    async fn run(
        &mut self,
        mut files: broadcast::Receiver<PathBuf>,
        decisions: mpsc::Sender<Decision>,
    ) -> Result<()>;
}

type Cleaners = Vec<Box<dyn Cleaner + Send>>;
type RemovalFn = Box<dyn Fn(&Path) -> io::Result<()>>;

pub struct Runner {
    cleaners: Cleaners,
    removal_fn: RemovalFn,
}

const CHANNEL_SIZE: usize = 100;
const CHANNEL_MAX_LOAD: usize = CHANNEL_SIZE * 3 / 4;

impl Runner {
    pub fn new(args: Args) -> Self {
        let removal_fn = Self::new_removal_fn(&args);
        let mut cleaners: Cleaners = vec![];

        cleaners.push(Box::new(DsoCleaner::new(args.output_dotfile)));

        if let Some(wl) = args.allowlist {
            cleaners.push(Box::new(ListCleaner::new(Action::Keep, wl)));
        }

        if let Some(bl) = args.blocklist {
            cleaners.push(Box::new(ListCleaner::new(Action::Remove, bl)));
        }

        Self {
            cleaners,
            removal_fn,
        }
    }

    pub async fn run(self) -> Result<()> {
        let input_tx = broadcast::Sender::new(CHANNEL_SIZE);
        let (output_tx, output_rx) = mpsc::channel(CHANNEL_SIZE);
        let mut tasks = JoinSet::new();

        // Processors
        for mut cleaner in self.cleaners {
            let input_rx = input_tx.subscribe();
            let output_tx_clone = output_tx.clone();
            tasks.spawn(async move { cleaner.run(input_rx, output_tx_clone).await });
        }
        drop(output_tx);

        // Producer of inputs (note that this needs to happen
        // after all channels have been created)
        tasks.spawn(Self::input_producer(input_tx));

        // Output consumer
        Self::output_consumer(self.removal_fn, output_rx).await;

        while let Some(task) = tasks.join_next().await {
            if let Err(err) = task? {
                log::error!("{}", err);
            }
        }
        Ok(())
    }

    async fn input_producer(input_tx: broadcast::Sender<PathBuf>) -> Result<()> {
        let walker = WalkDir::new(".").follow_links(false);
        for entry in walker {
            match entry {
                Ok(e) if !Self::is_dir(&e) => {
                    if input_tx.len() >= CHANNEL_MAX_LOAD {
                        // TODO: FIXME: make this better, this is a quick hack
                        tokio::time::sleep(std::time::Duration::from_millis(50)).await;
                    }
                    input_tx.send(e.into_path())?;
                }
                Ok(_) => continue,
                Err(err) => log::warn!("unable to access path: {}", err),
            }
        }

        // we handle errors by warning the user, otherwise we always succeed
        Ok(())
    }

    fn is_dir(entry: &DirEntry) -> bool {
        let ty = entry.file_type();
        if ty.is_dir() {
            true
        } else if ty.is_file() {
            false
        } else {
            // it is a symlink
            match std::fs::metadata(entry.path()) {
                Ok(metadata) => metadata.is_dir(),
                Err(e) => {
                    log::debug!(
                        "unable to resolve symlink {}: {}",
                        entry.path().display(),
                        e
                    );
                    false
                }
            }
        }
    }

    async fn output_consumer(removal_fn: RemovalFn, mut output_rx: mpsc::Receiver<Decision>) {
        let mut to_remove = HashMap::new();
        while let Some(decision) = output_rx.recv().await {
            match to_remove.get_mut(&decision.path) {
                Some(prev_action) => {
                    if decision.action == Action::Keep {
                        *prev_action = Action::Keep;
                    }
                }
                None => {
                    to_remove.insert(decision.path, decision.action);
                }
            }
        }

        for (file, action) in to_remove {
            if action == Action::Remove {
                if let Err(err) = (removal_fn)(&file) {
                    log::error!("{}: {}", file.display(), err);
                }
            }
        }
    }

    fn new_removal_fn(args: &Args) -> RemovalFn {
        if let Some(dest) = args.split_to.clone() {
            if args.dry_run {
                Box::new(move |path| {
                    log::info!(
                        "(dry-run) would move {} to {}",
                        path.display(),
                        dest.display()
                    );
                    Ok(())
                })
            } else {
                Box::new(move |path| {
                    log::info!("moving {} to {}", path.display(), dest.display());
                    Self::move_preserve(&path, &dest)
                })
            }
        } else {
            if args.dry_run {
                Box::new(|path| {
                    let ty = if path.is_symlink() {
                        "symlink"
                    } else {
                        "regular file"
                    };
                    log::info!("(dry-run) would remove {} {}", ty, path.display());
                    Ok(())
                })
            } else {
                Box::new(move |path| {
                    log::info!("removing {}", path.display());
                    std::fs::remove_file(&path)
                })
            }
        }
    }

    fn move_preserve(src: &Path, dest: &Path) -> io::Result<()> {
        assert!(src.is_relative());
        let abs_dest = dest.join(src);
        if let Some(parent) = abs_dest.parent() {
            std::fs::create_dir_all(parent)?;
        }
        match std::fs::rename(&src, &abs_dest) {
            Err(err) if err.raw_os_error() == Some(EXDEV) => {
                log::trace!(
                    "different filesystems, falling back to copying {} to {}",
                    src.display(),
                    abs_dest.display()
                );
                std::fs::copy(src, abs_dest).and_then(|_| std::fs::remove_file(src))
            }
            other => other,
        }
    }
}