use {
    super::FileSum,
    crate::{
        app::*,
        path::*,
        task_sync::Dam,
    },
    crossbeam::channel,
    ahash::AHashMap,
    rayon::{ThreadPool, ThreadPoolBuilder},
    std::{
        convert::TryInto,
        fs,
        path::{Path, PathBuf},
        sync::{
            atomic::{AtomicIsize, Ordering},
            Arc,
        },
    },
};

#[cfg(unix)]
use {
    fnv::FnvHashSet,
    std::{
        os::unix::fs::MetadataExt,
        sync::Mutex,
    },
};

/// a node id, taking the device into account to be sure to discriminate
/// nodes with the same inode but on different devices
#[derive(Debug, Clone, Copy, PartialEq, Hash, Eq)]
struct NodeId {
    /// inode number
    inode: u64,
    /// device number
    dev: u64,
}

// threads used by one computation
const THREADS_COUNT: usize = 6;


#[inline(always)]
fn is_ignored(path: &Path, special_paths: &[SpecialPath]) -> bool {
    match special_paths.find(path) {
        SpecialHandling::NoEnter | SpecialHandling::Hide => true,
        SpecialHandling::None | SpecialHandling::Enter => false,
    }
}

/// compute the consolidated numbers for a directory, with implementation
/// varying depending on the OS:
/// On unix, the computation is done on blocks of 512 bytes
/// see https://doc.rust-lang.org/std/os/unix/fs/trait.MetadataExt.html#tymethod.blocks
pub fn compute_dir_sum(
    path: &Path,
    cache: &mut AHashMap<PathBuf, FileSum>,
    dam: &Dam,
    con: &AppContext,
) -> Option<FileSum> {
    //debug!("compute size of dir {:?} --------------- ", path);

    if is_ignored(path, &con.special_paths) {
        return Some(FileSum::zero());
    }

    lazy_static! {
        static ref THREAD_POOL: ThreadPool = ThreadPoolBuilder::new()
            .num_threads(THREADS_COUNT * 2)
            .build()
            .unwrap();
    }

    // to avoid counting twice a node, we store their id in a set
    #[cfg(unix)]
    let nodes = Arc::new(Mutex::new(FnvHashSet::<NodeId>::default()));

    // busy is the number of directories which are either being processed or queued
    // We use this count to determine when threads can stop waiting for tasks
    let mut busy = 0;
    let mut sum = compute_file_sum(path);

    // this MPMC channel contains the directory paths which must be handled.
    // A None means there's nothing left and the thread may send its result and stop
    let (dirs_sender, dirs_receiver) = channel::unbounded();

    let special_paths: Vec<SpecialPath> = con.special_paths.iter()
        .filter(|sp| sp.can_have_matches_in(path))
        .cloned()
        .collect();

    // the first level is managed a little differently: we look at the cache
    // before adding. This enables faster computations in two cases:
    // - for the root line (assuming it's computed after the content)
    // - when we navigate up the tree
    if let Ok(entries) = fs::read_dir(path) {
        for e in entries.flatten() {
            if let Ok(md) = e.metadata() {
                if md.is_dir() {
                    let entry_path = e.path();

                    if is_ignored(&entry_path, &special_paths) {
                        debug!("not summing special path {:?}", entry_path);
                        continue;
                    }

                    // we check the cache
                    if let Some(entry_sum) = cache.get(&entry_path) {
                        sum += *entry_sum;
                        continue;
                    }
                    // we add the directory to the channel of dirs needing
                    // processing
                    busy += 1;
                    dirs_sender.send(Some(entry_path)).unwrap();
                } else {

                    #[cfg(unix)]
                    if md.nlink() > 1 {
                        let mut nodes = nodes.lock().unwrap();
                        let node_id = NodeId {
                            inode: md.ino(),
                            dev: md.dev(),
                        };
                        if !nodes.insert(node_id) {
                            // it was already in the set
                            continue;
                        }
                    }

                }
                sum += md_sum(&md);
            }
        }
    }

    if busy == 0 {
        return Some(sum);
    }

    let busy = Arc::new(AtomicIsize::new(busy));

    // this MPMC channel is here for the threads to send their results
    // at end of computation
    let (thread_sum_sender, thread_sum_receiver) = channel::bounded(THREADS_COUNT);


    // Each  thread does a summation without merge and the data are merged
    // at the end (this avoids waiting for a mutex during computation)
    for _ in 0..THREADS_COUNT {
        let busy = Arc::clone(&busy);
        let (dirs_sender, dirs_receiver) = (dirs_sender.clone(), dirs_receiver.clone());

        #[cfg(unix)]
        let nodes = nodes.clone();

        let special_paths = special_paths.clone();

        let observer = dam.observer();
        let thread_sum_sender = thread_sum_sender.clone();
        THREAD_POOL.spawn(move || {
            let mut thread_sum = FileSum::zero();
            loop {
                let o = dirs_receiver.recv();
                if let Ok(Some(open_dir)) = o {
                    if let Ok(entries) = fs::read_dir(&open_dir) {
                        for e in entries.flatten() {
                            if let Ok(md) = e.metadata() {
                                if md.is_dir() {

                                    let path = e.path();

                                    if is_ignored(&path, &special_paths) {
                                        debug!("not summing (deep) special path {:?}", path);
                                        continue;
                                    }

                                    // we add the directory to the channel of dirs needing
                                    // processing
                                    busy.fetch_add(1, Ordering::Relaxed);
                                    dirs_sender.send(Some(path)).unwrap();
                                } else {

                                    #[cfg(unix)]
                                    if md.nlink() > 1 {
                                        let mut nodes = nodes.lock().unwrap();
                                        let node_id = NodeId {
                                            inode: md.ino(),
                                            dev: md.dev(),
                                        };
                                        if !nodes.insert(node_id) {
                                            // it was already in the set
                                            continue;
                                        }
                                    }

                                }
                                thread_sum += md_sum(&md);
                            } else {
                                // we can't measure much but we can count the file
                                thread_sum.incr();
                            }
                        }
                    }
                    busy.fetch_sub(1, Ordering::Relaxed);
                }
                if observer.has_event() {
                    dirs_sender.send(None).unwrap(); // to unlock the next waiting thread
                    break;
                }
                if busy.load(Ordering::Relaxed) < 1 {
                    dirs_sender.send(None).unwrap(); // to unlock the next waiting thread
                    break;
                }
            }
            thread_sum_sender.send(thread_sum).unwrap();
        });
    }
    // Wait for the threads to finish and consolidate their results
    for _ in 0..THREADS_COUNT {
        match thread_sum_receiver.recv() {
            Ok(thread_sum) => {
                sum += thread_sum;
            }
            Err(e) => {
                warn!("Error while recv summing thread result : {:?}", e);
            }
        }
    }
    if dam.has_event() {
        return None;
    }
    Some(sum)
}

/// compute the sum for a regular file (not a folder)
pub fn compute_file_sum(path: &Path) -> FileSum {
    match fs::symlink_metadata(path) {
        Ok(md) => {
            let seconds = extract_seconds(&md);

            #[cfg(unix)]
            {
                let nominal_size = md.size();
                let block_size = md.blocks() * 512;
                FileSum::new(
                    block_size.min(nominal_size),
                    block_size < nominal_size,
                    1,
                    seconds,
                )
            }

            #[cfg(not(unix))]
            FileSum::new(md.len(), false, 1, seconds)
        }
        Err(_) => FileSum::new(0, false, 1, 0),
    }
}

#[cfg(unix)]
#[inline(always)]
fn extract_seconds(md: &fs::Metadata) -> u32 {
    md.mtime().try_into().unwrap_or(0)
}

#[cfg(not(unix))]
#[inline(always)]
fn extract_seconds(md: &fs::Metadata) -> u32 {
    if let Ok(st) = md.modified() {
        if let Ok(d) = st.duration_since(std::time::UNIX_EPOCH) {
            if let Ok(secs) = d.as_secs().try_into() {
                return secs;
            }
        }
    }
    0
}


#[inline(always)]
fn md_sum(md: &fs::Metadata) -> FileSum {
    #[cfg(unix)]
    let size = md.blocks() * 512;

    #[cfg(not(unix))]
    let size = md.len();

    let seconds = extract_seconds(&md);
    FileSum::new(size, false, 1, seconds)
}