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use std::collections::HashMap;

use automerge::ActorId;

use crate::{Persister, StoredSizes};

/// **For Testing** An in-memory persister.
///
/// As this provides no actual persistence it should not be used for any real application, it
/// actually reduces performance of the plain backend slightly due to tracking the changes itself.
#[derive(Debug, Default)]
pub struct MemoryPersister {
    changes: HashMap<(ActorId, u64), Vec<u8>>,
    document: Option<Vec<u8>>,
    sync_states: HashMap<Vec<u8>, Vec<u8>>,
    sizes: StoredSizes,
}

impl Persister for MemoryPersister {
    type Error = std::convert::Infallible;

    /// Get the changes out of the map.
    fn get_changes(&self) -> Result<Vec<Vec<u8>>, Self::Error> {
        Ok(self.changes.values().cloned().collect())
    }

    /// Insert changes into the map.
    fn insert_changes(&mut self, changes: Vec<(ActorId, u64, Vec<u8>)>) -> Result<(), Self::Error> {
        for (a, u, c) in changes {
            self.sizes.changes += c.len() as u64;
            if let Some(old) = self.changes.insert((a, u), c) {
                self.sizes.changes -= old.len() as u64;
            }
        }
        Ok(())
    }

    /// Remove changes from the map.
    fn remove_changes(&mut self, changes: Vec<(&ActorId, u64)>) -> Result<(), Self::Error> {
        for (a, u) in changes {
            if let Some(old) = self.changes.remove(&(a.clone(), u)) {
                self.sizes.changes -= old.len() as u64;
            }
        }
        Ok(())
    }

    /// Get the document.
    fn get_document(&self) -> Result<Option<Vec<u8>>, Self::Error> {
        Ok(self.document.clone())
    }

    /// Set the document.
    fn set_document(&mut self, data: Vec<u8>) -> Result<(), Self::Error> {
        self.sizes.document = data.len() as u64;
        self.document = Some(data);
        Ok(())
    }

    fn get_sync_state(&self, peer_id: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
        Ok(self.sync_states.get(peer_id).cloned())
    }

    fn set_sync_state(&mut self, peer_id: Vec<u8>, sync_state: Vec<u8>) -> Result<(), Self::Error> {
        self.sizes.sync_states += sync_state.len() as u64;
        if let Some(old) = self.sync_states.insert(peer_id, sync_state) {
            self.sizes.sync_states -= old.len() as u64;
        }
        Ok(())
    }

    fn remove_sync_states(&mut self, peer_ids: &[&[u8]]) -> Result<(), Self::Error> {
        for id in peer_ids {
            if let Some(old) = self.sync_states.remove(*id) {
                self.sizes.sync_states -= old.len() as u64;
            }
        }
        Ok(())
    }

    fn get_peer_ids(&self) -> Result<Vec<Vec<u8>>, Self::Error> {
        Ok(self.sync_states.keys().cloned().collect())
    }

    fn sizes(&self) -> StoredSizes {
        self.sizes.clone()
    }

    fn flush(&mut self) -> Result<usize, Self::Error> {
        Ok(0)
    }
}