//! Keep track of the blockchain as seen by a Web3Rpcs.
use super::consensus::ConsensusFinder;
use super::many::Web3Rpcs;
use super::one::Web3Rpc;
use super::transactions::TxStatus;
use crate::config::BlockAndRpc;
use crate::errors::{Web3ProxyError, Web3ProxyErrorContext, Web3ProxyResult};
use crate::frontend::authorization::Authorization;
use derive_more::From;
use ethers::prelude::{Block, TxHash, H256, U64};
use log::{debug, trace, warn};
use moka::future::Cache;
use serde::ser::SerializeStruct;
use serde::Serialize;
use serde_json::json;
use std::hash::Hash;
use std::{cmp::Ordering, fmt::Display, sync::Arc};
use tokio::sync::broadcast;

// TODO: type for Hydrated Blocks with their full transactions?
pub type ArcBlock = Arc<Block<TxHash>>;

pub type BlocksByHashCache = Cache<H256, Web3ProxyBlock>;
pub type BlocksByNumberCache = Cache<U64, H256>;

/// A block and its age.
#[derive(Clone, Debug, Default, From)]
pub struct Web3ProxyBlock {
    pub block: ArcBlock,
    /// number of seconds this block was behind the current time when received
    /// this is only set if the block is from a subscription
    pub received_age: Option<u64>,
}

impl Serialize for Web3ProxyBlock {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        // TODO: i'm not sure about this name
        let mut state = serializer.serialize_struct("saved_block", 2)?;

        state.serialize_field("age", &self.age())?;

        let block = json!({
            "hash": self.block.hash,
            "parent_hash": self.block.parent_hash,
            "number": self.block.number,
            "timestamp": self.block.timestamp,
        });

        state.serialize_field("block", &block)?;

        state.end()
    }
}

impl PartialEq for Web3ProxyBlock {
    fn eq(&self, other: &Self) -> bool {
        match (self.block.hash, other.block.hash) {
            (None, None) => true,
            (Some(_), None) => false,
            (None, Some(_)) => false,
            (Some(s), Some(o)) => s == o,
        }
    }
}

impl Eq for Web3ProxyBlock {}

impl Hash for Web3ProxyBlock {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.block.hash.hash(state);
    }
}

impl Web3ProxyBlock {
    /// A new block has arrived over a subscription
    pub fn try_new(block: ArcBlock) -> Option<Self> {
        if block.number.is_none() || block.hash.is_none() {
            return None;
        }

        let mut x = Self {
            block,
            received_age: None,
        };

        // no need to recalulate lag every time
        // if the head block gets too old, a health check restarts this connection
        // TODO: emit a stat for received_age
        x.received_age = Some(x.age());

        Some(x)
    }

    pub fn age(&self) -> u64 {
        let now = chrono::Utc::now().timestamp();

        let block_timestamp = self.block.timestamp.as_u32() as i64;

        if block_timestamp < now {
            // this server is still syncing from too far away to serve requests
            // u64 is safe because we checked equality above
            (now - block_timestamp) as u64
        } else {
            0
        }
    }

    #[inline(always)]
    pub fn parent_hash(&self) -> &H256 {
        &self.block.parent_hash
    }

    #[inline(always)]
    pub fn hash(&self) -> &H256 {
        self.block
            .hash
            .as_ref()
            .expect("saved blocks must have a hash")
    }

    #[inline(always)]
    pub fn number(&self) -> &U64 {
        self.block
            .number
            .as_ref()
            .expect("saved blocks must have a number")
    }

    pub fn uncles(&self) -> &[H256] {
        &self.block.uncles
    }
}

impl TryFrom<ArcBlock> for Web3ProxyBlock {
    type Error = Web3ProxyError;

    fn try_from(x: ArcBlock) -> Result<Self, Self::Error> {
        if x.number.is_none() || x.hash.is_none() {
            return Err(Web3ProxyError::NoBlockNumberOrHash);
        }

        let b = Web3ProxyBlock {
            block: x,
            received_age: None,
        };

        Ok(b)
    }
}

impl Display for Web3ProxyBlock {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "{} ({}, {}s old)",
            self.number(),
            self.hash(),
            self.age()
        )
    }
}

impl Web3Rpcs {
    /// add a block to our mappings and track the heaviest chain
    pub async fn try_cache_block(
        &self,
        block: Web3ProxyBlock,
        consensus_head: bool,
    ) -> Web3ProxyResult<Web3ProxyBlock> {
        let block_hash = *block.hash();

        // TODO: i think we can rearrange this function to make it faster on the hot path
        if block_hash.is_zero() {
            debug!("Skipping block without hash!");
            return Ok(block);
        }

        // this block is very likely already in block_hashes

        if consensus_head {
            let block_num = block.number();

            // TODO: if there is an existing entry with a different block_hash,
            // TODO: use entry api to handle changing existing entries
            self.blocks_by_number.insert(*block_num, block_hash).await;

            for uncle in block.uncles() {
                self.blocks_by_hash.invalidate(uncle).await;
                // TODO: save uncles somewhere?
            }

            // loop to make sure parent hashes match our caches
            // set the first ancestor to the blocks' parent hash. but keep going up the chain
            if let Some(parent_num) = block.number().checked_sub(1.into()) {
                struct Ancestor {
                    num: U64,
                    hash: H256,
                }
                let mut ancestor = Ancestor {
                    num: parent_num,
                    hash: *block.parent_hash(),
                };
                loop {
                    let ancestor_number_to_hash_entry = self
                        .blocks_by_number
                        .entry_by_ref(&ancestor.num)
                        .or_insert(ancestor.hash)
                        .await;

                    if *ancestor_number_to_hash_entry.value() == ancestor.hash {
                        // the existing number entry matches. all good
                        break;
                    }

                    // oh no! ancestor_number_to_hash_entry is different

                    // remove the uncled entry in blocks_by_hash
                    // we will look it up later if necessary
                    self.blocks_by_hash
                        .invalidate(ancestor_number_to_hash_entry.value())
                        .await;

                    // TODO: delete any cached entries for eth_getBlockByHash or eth_getBlockByNumber

                    // TODO: race on this drop and insert?
                    drop(ancestor_number_to_hash_entry);

                    // update the entry in blocks_by_number
                    self.blocks_by_number
                        .insert(ancestor.num, ancestor.hash)
                        .await;

                    // try to check the parent of this ancestor
                    if let Some(ancestor_block) = self.blocks_by_hash.get(&ancestor.hash) {
                        match ancestor_block.number().checked_sub(1.into()) {
                            None => break,
                            Some(ancestor_parent_num) => {
                                ancestor = Ancestor {
                                    num: ancestor_parent_num,
                                    hash: *ancestor_block.parent_hash(),
                                }
                            }
                        }
                    } else {
                        break;
                    }
                }
            }
        }

        let block = self
            .blocks_by_hash
            .get_with_by_ref(&block_hash, async move { block })
            .await;

        Ok(block)
    }

    /// Get a block from caches with fallback.
    /// Will query a specific node or the best available.
    pub async fn block(
        &self,
        authorization: &Arc<Authorization>,
        hash: &H256,
        rpc: Option<&Arc<Web3Rpc>>,
    ) -> Web3ProxyResult<Web3ProxyBlock> {
        // first, try to get the hash from our cache
        // the cache is set last, so if its here, its everywhere
        // TODO: use try_get_with
        if let Some(block) = self.blocks_by_hash.get(hash) {
            // double check that it matches the blocks_by_number cache
            let cached_hash = self
                .blocks_by_number
                .get_with_by_ref(block.number(), async { *hash })
                .await;

            if cached_hash == *hash {
                return Ok(block);
            }

            // hashes don't match! this block must be in the middle of being uncled
            // TODO: check known uncles
        }

        // block not in cache. we need to ask an rpc for it
        let get_block_params = (*hash, false);

        let block: Option<ArcBlock> = if let Some(rpc) = rpc {
            // ask a specific rpc
            // TODO: request_with_metadata would probably be better than authorized_request
            rpc.authorized_request::<_, Option<ArcBlock>>(
                "eth_getBlockByHash",
                &get_block_params,
                authorization,
                None,
            )
            .await?
        } else {
            // ask any rpc
            // TODO: request_with_metadata instead of internal_request
            self.internal_request::<_, Option<ArcBlock>>("eth_getBlockByHash", &get_block_params)
                .await?
        };

        match block {
            Some(block) => {
                let block = self.try_cache_block(block.try_into()?, false).await?;
                Ok(block)
            }
            // TODO: better error. some blocks are known, just not this one
            None => Err(Web3ProxyError::NoBlocksKnown),
        }
    }

    /// Convenience method to get the cannonical block at a given block height.
    pub async fn block_hash(
        &self,
        authorization: &Arc<Authorization>,
        num: &U64,
    ) -> Web3ProxyResult<(H256, u64)> {
        let (block, block_depth) = self.cannonical_block(authorization, num).await?;

        let hash = *block.hash();

        Ok((hash, block_depth))
    }

    /// Get the heaviest chain's block from cache or backend rpc
    /// Caution! If a future block is requested, this might wait forever. Be sure to have a timeout outside of this!
    pub async fn cannonical_block(
        &self,
        authorization: &Arc<Authorization>,
        num: &U64,
    ) -> Web3ProxyResult<(Web3ProxyBlock, u64)> {
        // we only have blocks by hash now
        // maybe save them during save_block in a blocks_by_number Cache<U64, Vec<ArcBlock>>
        // if theres multiple, use petgraph to find the one on the main chain (and remove the others if they have enough confirmations)

        let mut consensus_head_receiver = self
            .watch_consensus_head_sender
            .as_ref()
            .web3_context("need new head subscriptions to fetch cannonical_block")?
            .subscribe();

        // be sure the requested block num exists
        // TODO: is this okay? what if we aren't synced?!
        let mut head_block_num = *consensus_head_receiver
            .borrow_and_update()
            .as_ref()
            .web3_context("no consensus head block")?
            .number();

        loop {
            if num <= &head_block_num {
                break;
            }

            trace!("waiting for future block {} > {}", num, head_block_num);
            consensus_head_receiver.changed().await?;

            if let Some(head) = consensus_head_receiver.borrow_and_update().as_ref() {
                head_block_num = *head.number();
            }
        }

        let block_depth = (head_block_num - num).as_u64();

        // try to get the hash from our cache
        // deref to not keep the lock open
        if let Some(block_hash) = self.blocks_by_number.get(num) {
            // TODO: sometimes this needs to fetch the block. why? i thought block_numbers would only be set if the block hash was set
            // TODO: pass authorization through here?
            let block = self.block(authorization, &block_hash, None).await?;

            return Ok((block, block_depth));
        }

        // block number not in cache. we need to ask an rpc for it
        // TODO: this error is too broad
        let response = self
            .internal_request::<_, Option<ArcBlock>>("eth_getBlockByNumber", &(*num, false))
            .await?
            .ok_or(Web3ProxyError::NoBlocksKnown)?;

        let block = Web3ProxyBlock::try_from(response)?;

        // the block was fetched using eth_getBlockByNumber, so it should have all fields and be on the heaviest chain
        let block = self.try_cache_block(block, true).await?;

        Ok((block, block_depth))
    }

    pub(super) async fn process_incoming_blocks(
        &self,
        authorization: &Arc<Authorization>,
        block_receiver: flume::Receiver<BlockAndRpc>,
        // TODO: document that this is a watch sender and not a broadcast! if things get busy, blocks might get missed
        // Geth's subscriptions have the same potential for skipping blocks.
        pending_tx_sender: Option<broadcast::Sender<TxStatus>>,
    ) -> Web3ProxyResult<()> {
        let mut connection_heads = ConsensusFinder::new(self.max_block_age, self.max_block_lag);

        loop {
            match block_receiver.recv_async().await {
                Ok((new_block, rpc)) => {
                    let rpc_name = rpc.name.clone();

                    if let Err(err) = self
                        .process_block_from_rpc(
                            authorization,
                            &mut connection_heads,
                            new_block,
                            rpc,
                            &pending_tx_sender,
                        )
                        .await
                    {
                        warn!(
                            "error while processing block from rpc {}: {:#?}",
                            rpc_name, err
                        );
                    }
                }
                Err(err) => {
                    warn!("block_receiver exited! {:#?}", err);
                    return Err(err.into());
                }
            }
        }
    }

    /// `connection_heads` is a mapping of rpc_names to head block hashes.
    /// self.blockchain_map is a mapping of hashes to the complete ArcBlock.
    /// TODO: return something?
    pub(crate) async fn process_block_from_rpc(
        &self,
        authorization: &Arc<Authorization>,
        consensus_finder: &mut ConsensusFinder,
        new_block: Option<Web3ProxyBlock>,
        rpc: Arc<Web3Rpc>,
        _pending_tx_sender: &Option<broadcast::Sender<TxStatus>>,
    ) -> Web3ProxyResult<()> {
        // TODO: how should we handle an error here?
        if !consensus_finder
            .update_rpc(new_block.clone(), rpc.clone(), self)
            .await
            .web3_context("failed to update rpc")?
        {
            // nothing changed. no need to scan for a new consensus head
            return Ok(());
        }

        let new_consensus_rpcs = match consensus_finder
            .find_consensus_connections(authorization, self)
            .await
        {
            Err(err) => {
                return Err(err).web3_context("error while finding consensus head block!");
            }
            Ok(None) => {
                return Err(Web3ProxyError::NoConsensusHeadBlock);
            }
            Ok(Some(x)) => x,
        };

        trace!("new_synced_connections: {:#?}", new_consensus_rpcs);

        let watch_consensus_head_sender = self.watch_consensus_head_sender.as_ref().unwrap();
        let consensus_tier = new_consensus_rpcs.tier;
        // TODO: think more about the default for total_tiers
        let total_tiers = consensus_finder.worst_tier().unwrap_or_default();
        let backups_needed = new_consensus_rpcs.backups_needed;
        let consensus_head_block = new_consensus_rpcs.head_block.clone();
        let num_consensus_rpcs = new_consensus_rpcs.num_consensus_rpcs();
        let num_active_rpcs = consensus_finder.len();
        let total_rpcs = self.len();

        let new_consensus_rpcs = Arc::new(new_consensus_rpcs);

        let old_consensus_head_connections = self
            .watch_consensus_rpcs_sender
            .send_replace(Some(new_consensus_rpcs.clone()));

        let backups_voted_str = if backups_needed { "B " } else { "" };

        match old_consensus_head_connections.as_ref() {
            None => {
                debug!(
                    "first {}/{} {}{}/{}/{} block={}, rpc={}",
                    consensus_tier,
                    total_tiers,
                    backups_voted_str,
                    num_consensus_rpcs,
                    num_active_rpcs,
                    total_rpcs,
                    consensus_head_block,
                    rpc,
                );

                if backups_needed {
                    // TODO: what else should be in this error?
                    warn!("Backup RPCs are in use!");
                }

                // this should already be cached
                let consensus_head_block = self.try_cache_block(consensus_head_block, true).await?;

                watch_consensus_head_sender
                    .send(Some(consensus_head_block))
                    .or(Err(Web3ProxyError::WatchSendError))
                    .web3_context(
                        "watch_consensus_head_sender failed sending first consensus_head_block",
                    )?;
            }
            Some(old_consensus_connections) => {
                let old_head_block = &old_consensus_connections.head_block;

                // TODO: do this log item better
                let rpc_head_str = new_block
                    .map(|x| x.to_string())
                    .unwrap_or_else(|| "None".to_string());

                match consensus_head_block.number().cmp(old_head_block.number()) {
                    Ordering::Equal => {
                        // multiple blocks with the same fork!
                        if consensus_head_block.hash() == old_head_block.hash() {
                            // no change in hash. no need to use watch_consensus_head_sender
                            // TODO: trace level if rpc is backup
                            debug!(
                                "con {}/{} {}{}/{}/{} con={} rpc={}@{}",
                                consensus_tier,
                                total_tiers,
                                backups_voted_str,
                                num_consensus_rpcs,
                                num_active_rpcs,
                                total_rpcs,
                                consensus_head_block,
                                rpc,
                                rpc_head_str,
                            )
                        } else {
                            // hash changed

                            debug!(
                                "unc {}/{} {}{}/{}/{} con={} old={} rpc={}@{}",
                                consensus_tier,
                                total_tiers,
                                backups_voted_str,
                                num_consensus_rpcs,
                                num_active_rpcs,
                                total_rpcs,
                                consensus_head_block,
                                old_head_block,
                                rpc,
                                rpc_head_str,
                            );

                            let consensus_head_block = self
                                .try_cache_block(consensus_head_block, true)
                                .await
                                .web3_context("save consensus_head_block as heaviest chain")?;

                            watch_consensus_head_sender
                                .send(Some(consensus_head_block))
                                .or(Err(Web3ProxyError::WatchSendError))
                                .web3_context("watch_consensus_head_sender failed sending uncled consensus_head_block")?;
                        }
                    }
                    Ordering::Less => {
                        // this is unlikely but possible
                        // TODO: better log that includes all the votes
                        warn!(
                            "chain rolled back {}/{} {}{}/{}/{} con={} old={} rpc={}@{}",
                            consensus_tier,
                            total_tiers,
                            backups_voted_str,
                            num_consensus_rpcs,
                            num_active_rpcs,
                            total_rpcs,
                            consensus_head_block,
                            old_head_block,
                            rpc,
                            rpc_head_str,
                        );

                        if backups_needed {
                            // TODO: what else should be in this error?
                            warn!("Backup RPCs are in use!");
                        }

                        // TODO: tell save_block to remove any higher block numbers from the cache. not needed because we have other checks on requested blocks being > head, but still seems like a good idea
                        let consensus_head_block = self
                            .try_cache_block(consensus_head_block, true)
                            .await
                            .web3_context(
                                "save_block sending consensus_head_block as heaviest chain",
                            )?;

                        watch_consensus_head_sender
                            .send(Some(consensus_head_block))
                            .or(Err(Web3ProxyError::WatchSendError))
                            .web3_context("watch_consensus_head_sender failed sending rollback consensus_head_block")?;
                    }
                    Ordering::Greater => {
                        debug!(
                            "new {}/{} {}{}/{}/{} con={} rpc={}@{}",
                            consensus_tier,
                            total_tiers,
                            backups_voted_str,
                            num_consensus_rpcs,
                            num_active_rpcs,
                            total_rpcs,
                            consensus_head_block,
                            rpc,
                            rpc_head_str,
                        );

                        if backups_needed {
                            // TODO: what else should be in this error?
                            warn!("Backup RPCs are in use!");
                        }

                        let consensus_head_block =
                            self.try_cache_block(consensus_head_block, true).await?;

                        watch_consensus_head_sender.send(Some(consensus_head_block))
                            .or(Err(Web3ProxyError::WatchSendError))
                            .web3_context("watch_consensus_head_sender failed sending new consensus_head_block")?;
                    }
                }
            }
        }

        Ok(())
    }
}