use serde::{
    de::{SeqAccess, Visitor},
    ser::SerializeTuple,
    Deserializer, Serializer,
};
use serde::{Deserialize, Serialize};
use solana_sdk::{
    fee_calculator::FeeCalculator, hash::Hash, sysvar::recent_blockhashes, timing::timestamp,
};
use std::collections::HashMap;
use std::fmt;
use std::marker::PhantomData;

#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, AbiExample)]
struct HashAge {
    fee_calculator: FeeCalculator,
    hash_height: u64,
    timestamp: u64,
}

/// Low memory overhead, so can be cloned for every checkpoint
#[frozen_abi(digest = "J1fGiMHyiKEBcWE6mfm7grAEGJgYEaVLzcrNZvd37iA2")]
#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize, AbiExample)]
pub struct BlockhashQueue {
    /// updated whenever an hash is registered
    hash_height: u64,

    /// last hash to be registered
    last_hash: Option<Hash>,

    ages: HashMap<Hash, HashAge>,

    /// hashes older than `max_age` will be dropped from the queue
    max_age: usize,
}

impl BlockhashQueue {
    pub fn new(max_age: usize) -> Self {
        Self {
            ages: HashMap::new(),
            hash_height: 0,
            last_hash: None,
            max_age,
        }
    }

    #[allow(dead_code)]
    pub fn hash_height(&self) -> u64 {
        self.hash_height
    }

    pub fn last_hash(&self) -> Hash {
        self.last_hash.expect("no hash has been set")
    }

    pub fn get_fee_calculator(&self, hash: &Hash) -> Option<&FeeCalculator> {
        self.ages.get(hash).map(|hash_age| &hash_age.fee_calculator)
    }

    /// Check if the age of the hash is within the max_age
    /// return false for any hashes with an age above max_age
    /// return None for any hashes that were not found
    pub fn check_hash_age(&self, hash: &Hash, max_age: usize) -> Option<bool> {
        self.ages
            .get(hash)
            .map(|age| self.hash_height - age.hash_height <= max_age as u64)
    }

    pub fn get_hash_age(&self, hash: &Hash) -> Option<u64> {
        self.ages
            .get(hash)
            .map(|age| self.hash_height - age.hash_height)
    }

    /// check if hash is valid
    #[cfg(test)]
    pub fn check_hash(&self, hash: Hash) -> bool {
        self.ages.get(&hash).is_some()
    }

    pub fn genesis_hash(&mut self, hash: &Hash, fee_calculator: &FeeCalculator) {
        self.ages.insert(
            *hash,
            HashAge {
                fee_calculator: fee_calculator.clone(),
                hash_height: 0,
                timestamp: timestamp(),
            },
        );

        self.last_hash = Some(*hash);
    }

    fn check_age(hash_height: u64, max_age: usize, age: &HashAge) -> bool {
        hash_height - age.hash_height <= max_age as u64
    }

    pub fn register_hash(&mut self, hash: &Hash, fee_calculator: &FeeCalculator) {
        self.hash_height += 1;
        let hash_height = self.hash_height;

        // this clean up can be deferred until sigs gets larger
        //  because we verify age.nth every place we check for validity
        let max_age = self.max_age;
        if self.ages.len() >= max_age {
            self.ages
                .retain(|_, age| Self::check_age(hash_height, max_age, age));
        }
        self.ages.insert(
            *hash,
            HashAge {
                fee_calculator: fee_calculator.clone(),
                hash_height,
                timestamp: timestamp(),
            },
        );

        self.last_hash = Some(*hash);
    }

    /// Maps a hash height to a timestamp
    pub fn hash_height_to_timestamp(&self, hash_height: u64) -> Option<u64> {
        for age in self.ages.values() {
            if age.hash_height == hash_height {
                return Some(age.timestamp);
            }
        }
        None
    }

    pub fn get_recent_blockhashes(&self) -> impl Iterator<Item = recent_blockhashes::IterItem> {
        (&self.ages)
            .iter()
            .map(|(k, v)| recent_blockhashes::IterItem(v.hash_height, k, &v.fee_calculator))
    }

    pub fn len(&self) -> usize {
        self.max_age
    }
}

pub const MAX_EVM_BLOCKHASHES: usize = 256;
#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct BlockHashEvm {
    #[serde(with = "BlockHashEvm")]
    hashes: [evm_state::H256; MAX_EVM_BLOCKHASHES],
}

impl BlockHashEvm {
    pub fn new() -> BlockHashEvm {
        BlockHashEvm {
            hashes: [evm_state::H256::zero(); MAX_EVM_BLOCKHASHES],
        }
    }
    pub fn get_hashes(&self) -> &[evm_state::H256; MAX_EVM_BLOCKHASHES] {
        &self.hashes
    }

    pub fn insert_hash(&mut self, hash: evm_state::H256) {
        let new_hashes = self.hashes;
        self.hashes[0..MAX_EVM_BLOCKHASHES - 1]
            .copy_from_slice(&new_hashes[1..MAX_EVM_BLOCKHASHES]);
        self.hashes[MAX_EVM_BLOCKHASHES - 1] = hash
    }

    fn deserialize<'de, D>(
        deserializer: D,
    ) -> Result<[evm_state::H256; MAX_EVM_BLOCKHASHES], D::Error>
    where
        D: Deserializer<'de>,
    {
        struct ArrayVisitor<T> {
            element: PhantomData<T>,
        }
        impl<'de, T> Visitor<'de> for ArrayVisitor<T>
        where
            T: Default + Copy + Deserialize<'de>,
        {
            type Value = [T; MAX_EVM_BLOCKHASHES];

            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                formatter.write_str(concat!("an array of length ", 256))
            }

            fn visit_seq<A>(self, mut seq: A) -> Result<[T; MAX_EVM_BLOCKHASHES], A::Error>
            where
                A: SeqAccess<'de>,
            {
                let mut arr = [T::default(); MAX_EVM_BLOCKHASHES];
                for (i, item) in arr.iter_mut().enumerate().take(MAX_EVM_BLOCKHASHES) {
                    *item = seq
                        .next_element()?
                        .ok_or_else(|| serde::de::Error::invalid_length(i, &self))?;
                }
                Ok(arr)
            }
        }

        let visitor = ArrayVisitor {
            element: PhantomData,
        };
        deserializer.deserialize_tuple(MAX_EVM_BLOCKHASHES, visitor)
    }

    fn serialize<S>(
        data: &[evm_state::H256; MAX_EVM_BLOCKHASHES],
        serializer: S,
    ) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut seq = serializer.serialize_tuple(data.len())?;
        for elem in &data[..] {
            seq.serialize_element(elem)?;
        }
        seq.end()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use bincode::serialize;
    use evm_state::H256;
    use solana_sdk::{
        clock::MAX_RECENT_BLOCKHASHES, hash::hash, sysvar::recent_blockhashes::IterItem,
    };

    #[test]
    fn test_register_hash() {
        let last_hash = Hash::default();
        let mut hash_queue = BlockhashQueue::new(100);
        assert!(!hash_queue.check_hash(last_hash));
        hash_queue.register_hash(&last_hash, &FeeCalculator::default());
        assert!(hash_queue.check_hash(last_hash));
        assert_eq!(hash_queue.hash_height(), 1);
    }

    #[test]
    fn test_reject_old_last_hash() {
        let mut hash_queue = BlockhashQueue::new(100);
        let last_hash = hash(&serialize(&0).unwrap());
        for i in 0..102 {
            let last_hash = hash(&serialize(&i).unwrap());
            hash_queue.register_hash(&last_hash, &FeeCalculator::default());
        }
        // Assert we're no longer able to use the oldest hash.
        assert!(!hash_queue.check_hash(last_hash));
        assert_eq!(None, hash_queue.check_hash_age(&last_hash, 0));

        // Assert we are not able to use the oldest remaining hash.
        let last_valid_hash = hash(&serialize(&1).unwrap());
        assert!(hash_queue.check_hash(last_valid_hash));
        assert_eq!(Some(false), hash_queue.check_hash_age(&last_valid_hash, 0));
    }

    /// test that when max age is 0, that a valid last_hash still passes the age check
    #[test]
    fn test_queue_init_blockhash() {
        let last_hash = Hash::default();
        let mut hash_queue = BlockhashQueue::new(100);
        hash_queue.register_hash(&last_hash, &FeeCalculator::default());
        assert_eq!(last_hash, hash_queue.last_hash());
        assert_eq!(Some(true), hash_queue.check_hash_age(&last_hash, 0));
    }

    #[test]
    fn test_get_recent_blockhashes() {
        let mut blockhash_queue = BlockhashQueue::new(MAX_RECENT_BLOCKHASHES);
        let recent_blockhashes = blockhash_queue.get_recent_blockhashes();
        // Sanity-check an empty BlockhashQueue
        assert_eq!(recent_blockhashes.count(), 0);
        for i in 0..MAX_RECENT_BLOCKHASHES {
            let hash = hash(&serialize(&i).unwrap());
            blockhash_queue.register_hash(&hash, &FeeCalculator::default());
        }
        let recent_blockhashes = blockhash_queue.get_recent_blockhashes();
        // Verify that the returned hashes are most recent
        for IterItem(_slot, hash, _fee_calc) in recent_blockhashes {
            assert_eq!(
                Some(true),
                blockhash_queue.check_hash_age(hash, MAX_RECENT_BLOCKHASHES)
            );
        }
    }

    #[test]
    fn test_evm_blockhaheshes() {
        let mut blockhash_queue = BlockHashEvm::new();
        assert_eq!(
            blockhash_queue.get_hashes(),
            &[H256::zero(); MAX_EVM_BLOCKHASHES]
        );
        let hash1 = H256::repeat_byte(1);
        blockhash_queue.insert_hash(hash1);
        for hash in &blockhash_queue.get_hashes()[..MAX_EVM_BLOCKHASHES - 1] {
            assert_eq!(*hash, H256::zero())
        }
        assert_eq!(blockhash_queue.get_hashes()[MAX_EVM_BLOCKHASHES - 1], hash1);

        for i in 0..MAX_EVM_BLOCKHASHES {
            let hash1 = H256::repeat_byte(i as u8);
            blockhash_queue.insert_hash(hash1)
        }

        for (i, hash) in blockhash_queue.get_hashes()[..MAX_EVM_BLOCKHASHES]
            .iter()
            .enumerate()
        {
            let hash1 = H256::repeat_byte(i as u8);
            assert_eq!(*hash, hash1)
        }
    }
}