use std::num::NonZeroU32;
use std::sync::Arc;
use std::time::{Duration, Instant};

use collection::config::ShardingMethod;
use collection::operations::verification::VerificationPass;
use common::counter::hardware_accumulator::HwMeasurementAcc;
use common::defaults::CONSENSUS_META_OP_WAIT;
use segment::types::default_shard_number_per_node_const;

use crate::content_manager::collection_meta_ops::AliasOperations;
use crate::content_manager::shard_distribution::ShardDistributionProposal;
use crate::rbac::Access;
use crate::{
    ClusterStatus, CollectionMetaOperations, ConsensusOperations, ConsensusStateRef, StorageError,
    TableOfContent,
};

#[derive(Clone)]
pub struct Dispatcher {
    toc: Arc<TableOfContent>,
    consensus_state: Option<ConsensusStateRef>,
}

impl Dispatcher {
    pub fn new(toc: Arc<TableOfContent>) -> Self {
        Self {
            toc,
            consensus_state: None,
        }
    }

    pub fn with_consensus(self, state_ref: ConsensusStateRef) -> Self {
        Self {
            consensus_state: Some(state_ref),
            ..self
        }
    }

    /// Get the table of content.
    /// The `_access` and `_verification_pass` parameter are not used, but it's required to verify caller's possession
    /// of both objects.
    pub fn toc(
        &self,
        _access: &Access,
        _verification_pass: &VerificationPass,
    ) -> &Arc<TableOfContent> {
        &self.toc
    }

    pub fn consensus_state(&self) -> Option<&ConsensusStateRef> {
        self.consensus_state.as_ref()
    }

    /// If `wait_timeout` is not supplied - then default duration will be used.
    /// This function needs to be called from a runtime with timers enabled.
    pub async fn submit_collection_meta_op(
        &self,
        operation: CollectionMetaOperations,
        access: Access,
        wait_timeout: Option<Duration>,
    ) -> Result<bool, StorageError> {
        access.check_collection_meta_operation(&operation)?;

        // if distributed deployment is enabled
        if let Some(state) = self.consensus_state.as_ref() {
            let start = Instant::now();

            // List of operations to await for collection to be operational
            let mut expect_operations: Vec<ConsensusOperations> = vec![];

            let op = match operation {
                CollectionMetaOperations::CreateCollection(mut op) => {
                    self.toc.check_write_lock()?;
                    if !op.is_distribution_set() {
                        match op.create_collection.sharding_method.unwrap_or_default() {
                            ShardingMethod::Auto => {
                                // Suggest even distribution of shards across nodes
                                let number_of_peers = state.0.peer_count();

                                let shard_nr_per_node = self
                                    .toc
                                    .storage_config
                                    .collection
                                    .as_ref()
                                    .map(|i| i.shard_number_per_node)
                                    .unwrap_or(default_shard_number_per_node_const());

                                let suggested_shard_nr = number_of_peers as u32 * shard_nr_per_node;

                                let shard_distribution = self.toc.suggest_shard_distribution(
                                    &op,
                                    NonZeroU32::new(suggested_shard_nr)
                                        .expect("Peer count should be always >= 1"),
                                );

                                // Expect all replicas to become active eventually
                                for (shard_id, peer_ids) in &shard_distribution.distribution {
                                    for peer_id in peer_ids {
                                        expect_operations.push(
                                            ConsensusOperations::initialize_replica(
                                                op.collection_name.clone(),
                                                *shard_id,
                                                *peer_id,
                                            ),
                                        );
                                    }
                                }

                                op.set_distribution(shard_distribution);
                            }
                            ShardingMethod::Custom => {
                                // If custom sharding is used - we don't create any shards in advance
                                let empty_distribution = ShardDistributionProposal::empty();
                                op.set_distribution(empty_distribution);
                            }
                        }
                    }

                    if let Some(uuid) = &op.create_collection.uuid {
                        log::warn!(
                            "Collection UUID {uuid} explicitly specified, \
                             when proposing create collection {} operation, \
                             new random UUID will be generated instead",
                            op.collection_name,
                        );
                    }

                    op.create_collection.uuid = Some(uuid::Uuid::new_v4());

                    CollectionMetaOperations::CreateCollection(op)
                }
                CollectionMetaOperations::CreateShardKey(op) => {
                    self.toc.check_write_lock()?;
                    CollectionMetaOperations::CreateShardKey(op)
                }

                op => op,
            };

            let operation_awaiter =
                // If explicit timeout is set - then we need to wait for all expected operations.
                // E.g. in case of `CreateCollection` we will explicitly wait for all replicas to be activated.
                // We need to register receivers(by calling the function) before submitting the operation.
                if !expect_operations.is_empty() {
                    Some(state.await_for_multiple_operations(expect_operations, wait_timeout))
                } else {
                    None
                };

            let do_sync_nodes = match &op {
                // Sync nodes after collection or shard key creation
                CollectionMetaOperations::CreateCollection(_)
                | CollectionMetaOperations::CreateShardKey(_) => true,

                // Sync nodes when creating or renaming collection aliases
                CollectionMetaOperations::ChangeAliases(changes) => {
                    changes.actions.iter().any(|change| match change {
                        AliasOperations::CreateAlias(_) | AliasOperations::RenameAlias(_) => true,
                        AliasOperations::DeleteAlias(_) => false,
                    })
                }

                // TODO(resharding): Do we need/want to synchronize `Resharding` operations?
                CollectionMetaOperations::Resharding(_, _) => false,

                // No need to sync nodes for other operations
                CollectionMetaOperations::UpdateCollection(_)
                | CollectionMetaOperations::DeleteCollection(_)
                | CollectionMetaOperations::TransferShard(_, _)
                | CollectionMetaOperations::SetShardReplicaState(_)
                | CollectionMetaOperations::DropShardKey(_)
                | CollectionMetaOperations::CreatePayloadIndex(_)
                | CollectionMetaOperations::DropPayloadIndex(_)
                | CollectionMetaOperations::Nop { .. } => false,
            };

            let res = state
                .propose_consensus_op_with_await(
                    ConsensusOperations::CollectionMeta(Box::new(op)),
                    wait_timeout,
                )
                .await?;

            if let Some(operation_awaiter) = operation_awaiter {
                // Actually await for expected operations to complete on the consensus
                match operation_awaiter.await {
                    Ok(Ok(())) => {} // all good
                    Ok(Err(err)) => {
                        log::warn!("Not all expected operations were completed: {}", err)
                    }
                    Err(err) => log::warn!("Awaiting for expected operations timed out: {}", err),
                }
            }

            // On some operations, synchronize all nodes to ensure all are ready for point operations
            if do_sync_nodes {
                let remaining_timeout =
                    wait_timeout.map(|timeout| timeout.saturating_sub(start.elapsed()));
                if let Err(err) = self.await_consensus_sync(remaining_timeout).await {
                    log::warn!("Failed to synchronize all nodes after collection operation in time, some nodes may not be ready: {err}");
                }
            }

            Ok(res)
        } else {
            if let CollectionMetaOperations::CreateCollection(_) = &operation {
                self.toc.check_write_lock()?;
            }
            self.toc.perform_collection_meta_op(operation).await
        }
    }

    pub fn cluster_status(&self) -> ClusterStatus {
        match self.consensus_state.as_ref() {
            Some(state) => state.cluster_status(),
            None => ClusterStatus::Disabled,
        }
    }

    pub async fn await_consensus_sync(
        &self,
        timeout: Option<Duration>,
    ) -> Result<(), StorageError> {
        let timeout = timeout.unwrap_or(CONSENSUS_META_OP_WAIT);

        if let Some(state) = self.consensus_state.as_ref() {
            let state = state.hard_state();
            let term = state.term;
            let commit = state.commit;
            let channel_service = self.toc.get_channel_service();
            let this_peer_id = self.toc.this_peer_id;

            channel_service
                .await_commit_on_all_peers(this_peer_id, commit, term, timeout)
                .await?;

            log::debug!(
                "Consensus is synchronized with term: {}, commit: {}",
                term,
                commit
            );

            Ok(())
        } else {
            Ok(())
        }
    }

    #[must_use]
    pub fn get_collection_hw_metrics(&self, collection: String) -> Arc<HwMeasurementAcc> {
        self.toc.get_collection_hw_metrics(collection)
    }
}