//! Handling store mutation
use super::*;
use std::borrow::Borrow;

impl Store
{
    /// Insert this entry into the data table, overwriting any identically hashed one and returning it.
    pub fn insert_overwrite(&mut self, ent: Entry) -> Option<Entry>
    {
	let old = self.remove(ent.hash());

	let hash_idx = self.data_hashes.insert(*ent.hash());
	for tag in ent.tags.iter() {
	    self.insert_tag_for_idx(tag, hash_idx);
	}
	self.data.insert(ent);
	old
    }

    /// Insert this entry then return a reference to it.
    pub fn insert<'a, 'b>(&'a mut self, ent: Entry) -> &'b Entry
	where 'a: 'b
    {
	let ffd = *ent.hash();
	self.insert_overwrite(ent);
	self.data.get(&ffd).unwrap()
    }

    /// Mutate this entry in place if it exists.
    ///
    /// See [`map_entry`].
    pub fn mutate_entry_in_place<T, F>(&mut self, ent_id: &EntryKey, f: F) -> Option<T>
    where F: FnOnce(&mut Entry) -> T
    {
	if let Some(mut ent) = self.data.take(ent_id) {
	    let update = ent.prepare_for_refresh();
	    
	    let out = f(&mut ent);
	    let new = ent;

	    self.refresh_for_entry(update, &new);
	    
	    self.data.insert(new);
	    Some(out)
	} else {
	    None
	}
    }

    /// Update an entry that may have been modified.
    ///
    /// The entries old hash and tags are passed, and it updates the store to reflect the new entry mutation.
    /// You must still insert the new entry after this.
    fn refresh_for_entry(&mut self, (ohash, otags): (impl Borrow<EntryKey>, impl AsRef<[String]>), new: &Entry)
    {
	let ohash = ohash.borrow();
	let iidx = if new.hash() != ohash {
	    // We need to update `data_hashes`.
	    for (_, hash) in self.data_hashes.iter_mut()
	    {
		if hash == ohash {
		    *hash = *new.hash();
		    break;
		}
	    }
	    self.reverse_index_lookup(new.hash()).unwrap()
	} else {
	    self.reverse_index_lookup(ohash).unwrap()
	};

	let otags =otags.as_ref();
	if &new.tags[..] != &otags[..] {
	    // We need to update tag mappings
	    
	    let ntags: HashSet<_> = new.tags.iter().collect();
	    let otags: HashSet<_> = otags.iter().collect();
	    // Find the ones that were removed and added in parallel.
	    for (t, u) in ntags.iter().zip(otags.iter())
	    {
		if !otags.contains(t) {
		    // It was added
		    self.insert_tag_for_idx(t, iidx);
		}
		if !ntags.contains(u) {
		    // It was removed
		    self.remove_tag_for_idx(t, iidx);
		}
	    }
	    
	}
    }
    
    /// Map the entry with this function, updating references to it if needed.
    ///
    /// If the hash of the entry if modified by this map, then the hashes indecies are updated to the new hash.
    pub fn map_entry<F>(&mut self, ent_id: &EntryKey, f: F)
    where F: FnOnce(Entry) -> Entry
    {
	if let Some(ent) = self.data.take(ent_id) {
	    let update = ent.prepare_for_refresh();
	    let new = f(ent);
	    
	    self.refresh_for_entry(update, &new);
	    
	    self.data.insert(new); 
	}
    }


    /// Remove this entry, and return it, if it was set.
    pub fn remove(&mut self, key: &EntryKey) -> Option<Entry>
    {
	if let Some(entry) = self.data.take(key) {
	    Some(self.cleanup_remove_entry(entry.with_no_cache()))
	} else {
	    None
	}
    }
    
    /// Preform cleanup on an entry *already removed* from `data`.
    fn cleanup_remove_entry(&mut self, ent: Entry) -> Entry
    {
	// Remove any unused tags
	if let Some(hash_idx) = self.reverse_index_lookup(ent.hash()) {   
	    for tag in ent.tags.iter()
	    {
		self.remove_tag_for_idx(tag, hash_idx);
	    }
	}
	
	// Remove from data hashes can be deferred
	self.purge_if_needed();
	ent
    }

    /// Remove dead mappings from `data_hashes` to `data`.
    #[inline] fn purge_data_hash_mappings(&mut self)
    {
	let data = &self.data;
	self.data_hashes.retain(move |_, hash| data.get(hash).is_some());
    }

    /// Purge the arena mapping if threshold of dead entries is reached, otherwise defer it.
    #[inline] fn purge_if_needed(&mut self)
    {
	if self.purge_track.should_purge() {
	    self.purge_data_hash_mappings();
	    self.purge_track.num_removals = 0;
	} else {
	    self.purge_track.num_removals += 1;
	}
    }
}

// Tag specific stuff
impl Store
{
    /// Remove a mapping for this tag string to this specific hash index, cleaning up the tag mappings if needed.
    #[inline] fn remove_tag_for_idx(&mut self, tag: impl AsRef<str>, hash_idx: ArenaIndex)
    {
	let tag = tag.as_ref();
	if let Some(&ti) = self.tags.get(tag) {
	    match self.tag_mappings.get_mut(ti).map(|x| {x.remove(&hash_idx); x.len()}) {
		Some(0) => no_op!(self.tag_mappings.remove(ti)), // there is only 1 mapping, remove it and then remove the tag (TODO: Should we keep the tag in the btree as cache? TODO: Add this to `PurgeTrack`)
		None => (), // there is no mapping, just remove the tag
		_ => return, //don't remove the tag, there's other references in the mapping
	    }
	    self.tags.remove(tag);
	}
    }
    /// Insert a mapping for this tag string to this single hash index, creating it if needed
    #[inline] fn insert_tag_for_idx(&mut self, tag: impl AsRef<str>, hash_idx: ArenaIndex)
    {
	let tag = tag.as_ref();
	if let Some(&ti) = self.tags.get(tag) {
	    // This tag has an entry already, append to it
	    self.tag_mappings.get_mut(ti).unwrap().insert(hash_idx);
	} else {
	    // This tag has no entry, create it
	    let ti = self.tag_mappings.insert(iter![hash_idx].collect());
	    self.tags.insert(tag.to_owned(), ti);
	}
    }
}