use std::collections::HashSet;

use garage_util::crdt::{Crdt, Lww, LwwMap};
use garage_util::data::*;
use garage_util::encode::nonversioned_encode;
use garage_util::error::*;

use super::*;
use crate::layout::ComputationStat;
use crate::replication_mode::*;

impl LayoutHistory {
	pub fn new(replication_factor: ReplicationFactor) -> Self {
		let version = LayoutVersion::new(replication_factor);

		let staging = LayoutStaging {
			parameters: Lww::<LayoutParameters>::new(version.parameters),
			roles: LwwMap::new(),
		};

		LayoutHistory {
			versions: vec![version],
			old_versions: vec![],
			update_trackers: Default::default(),
			staging: Lww::raw(0, staging),
		}
	}

	// ------------------ who stores what now? ---------------

	/// Returns the layout version with the highest number
	pub fn current(&self) -> &LayoutVersion {
		self.versions.last().as_ref().unwrap()
	}

	/// Returns the version number of the oldest layout version still active
	pub fn min_stored(&self) -> u64 {
		self.versions.first().as_ref().unwrap().version
	}

	/// Calculate the set of all nodes that have a role (gateway or storage)
	/// in one of the currently active layout versions
	pub fn get_all_nodes(&self) -> Vec<Uuid> {
		if self.versions.len() == 1 {
			self.versions[0].all_nodes().to_vec()
		} else {
			let set = self
				.versions
				.iter()
				.flat_map(|x| x.all_nodes())
				.collect::<HashSet<_>>();
			set.into_iter().copied().collect::<Vec<_>>()
		}
	}

	/// Calculate the set of all nodes that are configured to store data
	/// in one of the currently active layout versions
	pub(crate) fn get_all_nongateway_nodes(&self) -> Vec<Uuid> {
		if self.versions.len() == 1 {
			self.versions[0].nongateway_nodes().to_vec()
		} else {
			let set = self
				.versions
				.iter()
				.flat_map(|x| x.nongateway_nodes())
				.collect::<HashSet<_>>();
			set.into_iter().copied().collect::<Vec<_>>()
		}
	}

	// ---- housekeeping (all invoked by LayoutHelper) ----

	pub(crate) fn keep_current_version_only(&mut self) {
		while self.versions.len() > 1 {
			let removed = self.versions.remove(0);
			self.old_versions.push(removed);
		}
	}

	pub(crate) fn cleanup_old_versions(&mut self) {
		// If there are invalid versions before valid versions, remove them
		if self.versions.len() > 1 && self.current().check().is_ok() {
			while self.versions.len() > 1 && self.versions.first().unwrap().check().is_err() {
				let removed = self.versions.remove(0);
				info!(
					"Layout history: pruning old invalid version {}",
					removed.version
				);
			}
		}

		// If there are old versions that no one is reading from anymore,
		// remove them (keep them in self.old_versions).
		// ASSUMPTION: we only care about where nodes in the current layout version
		// are reading from, as we assume older nodes are being discarded.
		let current_nodes = &self.current().node_id_vec;
		let min_version = self.min_stored();
		let sync_ack_map_min = self
			.update_trackers
			.sync_ack_map
			.min_among(current_nodes, min_version);
		while self.min_stored() < sync_ack_map_min {
			assert!(self.versions.len() > 1);
			let removed = self.versions.remove(0);
			info!(
				"Layout history: moving version {} to old_versions",
				removed.version
			);
			self.old_versions.push(removed);
		}

		while self.old_versions.len() > OLD_VERSION_COUNT {
			let removed = self.old_versions.remove(0);
			info!("Layout history: removing old_version {}", removed.version);
		}
	}

	pub(crate) fn clamp_update_trackers(&mut self, nodes: &[Uuid]) {
		let min_v = self.min_stored();
		for node in nodes {
			self.update_trackers.ack_map.set_max(*node, min_v);
			self.update_trackers.sync_map.set_max(*node, min_v);
			self.update_trackers.sync_ack_map.set_max(*node, min_v);
		}
	}

	/// This function calculates the minimum layout version from which
	/// it is safe to read if we want to maintain read-after-write consistency.
	pub(crate) fn calculate_sync_map_min_with_quorum(&self, all_nongateway_nodes: &[Uuid]) -> u64 {
		// In the general case the computation can be a bit expensive so
		// we try to optimize it in several ways.

		// If there is only one layout version, we know that's the one
		// we need to read from.
		if self.versions.len() == 1 {
			return self.current().version;
		}

		let min_version = self.min_stored();
		let global_min = self
			.update_trackers
			.sync_map
			.min_among(all_nongateway_nodes, min_version);

		// If the write quorums are equal to the total number of nodes,
		// i.e. no writes can succeed while they are not written to all nodes,
		// then we must in all case wait for all nodes to complete a sync.
		// This is represented by reading from the layout with version
		// number global_min, the smallest layout version for which all nodes
		// have completed a sync.
		//
		// While we currently do not support changing the replication factor
		// between layout versions, this calculation is future-proofing for the
		// case where this might be possible.
		if self
			.versions
			.iter()
			.filter(|v| v.version >= global_min)
			.all(|v| v.write_quorum(ConsistencyMode::Consistent) == v.replication_factor)
		{
			return global_min;
		}

		// In the general case, we need to look at all write sets for all partitions,
		// and find a safe layout version to read for that partition. We then
		// take the minimum value among all partition as the safe layout version
		// to read in all cases (the layout version to which all reads are directed).
		let mut current_min = self.current().version;
		let mut sets_done = HashSet::<Vec<Uuid>>::new();

		for (_, p_hash) in self.current().partitions() {
			for v in self.versions.iter() {
				if v.version == self.current().version {
					// We don't care about whether nodes in the latest layout version
					// have completed a sync or not, as the sync is push-only
					// and by definition nodes in the latest layout version do not
					// hold data that must be pushed to nodes in the latest layout
					// version, since that's the same version (any data that's
					// already in the latest version is assumed to have been written
					// by an operation that ensured a quorum of writes within
					// that version).
					continue;
				}

				// Determine set of nodes for partition p in layout version v.
				// Sort the node set to avoid duplicate computations.
				let mut set = v.nodes_of(&p_hash).collect::<Vec<Uuid>>();
				set.sort();

				// If this set was already processed, skip it.
				if sets_done.contains(&set) {
					continue;
				}

				// Find the value of the sync update trackers that is the
				// highest possible minimum within a quorum of nodes.
				let mut sync_values = set
					.iter()
					.map(|x| self.update_trackers.sync_map.get(x, min_version))
					.collect::<Vec<_>>();
				sync_values.sort();
				let set_min =
					sync_values[sync_values.len() - v.write_quorum(ConsistencyMode::Consistent)];
				if set_min < current_min {
					current_min = set_min;
				}
				// defavorable case, we know we are at the smallest possible version,
				// so we can stop early
				assert!(current_min >= global_min);
				if current_min == global_min {
					return current_min;
				}

				// Add set to already processed sets
				sets_done.insert(set);
			}
		}

		current_min
	}

	pub(crate) fn calculate_trackers_hash(&self) -> Hash {
		blake2sum(&nonversioned_encode(&self.update_trackers).unwrap()[..])
	}

	pub(crate) fn calculate_staging_hash(&self) -> Hash {
		blake2sum(&nonversioned_encode(&self.staging).unwrap()[..])
	}

	// ================== updates to layout, public interface ===================

	pub fn merge(&mut self, other: &LayoutHistory) -> bool {
		// If our current layout version is completely out-of-date,
		// forget everything we know and replace it by incoming layout data.
		if self.current().version < other.min_stored() {
			*self = other.clone();
			return true;
		}

		let mut changed = false;

		// Add any new versions to history
		for v2 in other.versions.iter() {
			if v2.version == self.current().version + 1 {
				// This is the next version, add it to our version list
				self.versions.push(v2.clone());
				changed = true;
			} else if let Some(v1) = self.versions.iter().find(|v| v.version == v2.version) {
				// Version is already present, check consistency
				if v1 != v2 {
					error!("Inconsistent layout histories: different layout compositions for version {}. Your cluster will be broken as long as this layout version is not replaced.", v2.version);
				}
			} else {
				// This is an older version
				assert!(v2.version < self.min_stored());
			}
		}

		// Merge trackers
		let c = self.update_trackers.merge(&other.update_trackers);
		changed = changed || c;

		// Merge staged layout changes
		if self.staging != other.staging {
			let prev_staging = self.staging.clone();
			self.staging.merge(&other.staging);
			changed = changed || self.staging != prev_staging;
		}

		changed
	}

	pub fn apply_staged_changes(mut self, version: u64) -> Result<(Self, ComputationStat), Error> {
		if version != self.current().version + 1 {
			return Err(Error::Message("Invalid new layout version".into()));
		}

		// Compute new version and add it to history
		let (new_version, stat) = self
			.current()
			.clone()
			.calculate_next_version(self.staging.get())?;

		self.versions.push(new_version);
		self.cleanup_old_versions();

		// Reset the staged layout changes
		self.staging.update(LayoutStaging {
			parameters: self.staging.get().parameters.clone(),
			roles: LwwMap::new(),
		});

		Ok((self, stat))
	}

	pub fn revert_staged_changes(mut self) -> Result<Self, Error> {
		self.staging.update(LayoutStaging {
			parameters: Lww::new(self.current().parameters),
			roles: LwwMap::new(),
		});

		Ok(self)
	}

	pub fn check(&self) -> Result<(), String> {
		// TODO: anything more ?
		self.current().check()
	}
}
