use crate::{
    account::Account,
    hash::{hash, Hash},
    sysvar::Sysvar,
};
use bincode::serialize;
use std::collections::BinaryHeap;
use std::iter::FromIterator;
use std::ops::Deref;

const MAX_ENTRIES: usize = 32;

crate::declare_sysvar_id!(
    "SysvarRecentB1ockHashes11111111111111111111",
    RecentBlockhashes
);

#[repr(C)]
#[derive(Serialize, Deserialize, Debug, PartialEq)]
pub struct RecentBlockhashes(Vec<Hash>);

impl Default for RecentBlockhashes {
    fn default() -> Self {
        Self(Vec::with_capacity(MAX_ENTRIES))
    }
}

impl<'a> FromIterator<&'a Hash> for RecentBlockhashes {
    fn from_iter<I>(iter: I) -> Self
    where
        I: IntoIterator<Item = &'a Hash>,
    {
        let mut new = Self::default();
        for i in iter {
            new.0.push(*i)
        }
        new
    }
}

impl Sysvar for RecentBlockhashes {
    fn size_of() -> usize {
        // hard-coded so that we don't have to construct an empty
        1032 // golden, update if MAX_ENTRIES changes
    }
}

impl Deref for RecentBlockhashes {
    type Target = Vec<Hash>;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

pub fn create_account(lamports: u64) -> Account {
    RecentBlockhashes::default().create_account(lamports)
}

pub fn update_account<'a, I>(account: &mut Account, recent_blockhash_iter: I) -> Option<()>
where
    I: IntoIterator<Item = (u64, &'a Hash)>,
{
    let sorted = BinaryHeap::from_iter(recent_blockhash_iter);
    let recent_blockhash_iter = sorted.into_iter().take(MAX_ENTRIES).map(|(_, hash)| hash);
    let recent_blockhashes = RecentBlockhashes::from_iter(recent_blockhash_iter);
    recent_blockhashes.to_account(account)
}

pub fn create_account_with_data<'a, I>(lamports: u64, recent_blockhash_iter: I) -> Account
where
    I: IntoIterator<Item = (u64, &'a Hash)>,
{
    let mut account = create_account(lamports);
    update_account(&mut account, recent_blockhash_iter).unwrap();
    account
}

pub fn create_test_recent_blockhashes(start: usize) -> RecentBlockhashes {
    let bhq: Vec<_> = (start..start + (MAX_ENTRIES - 1))
        .map(|i| hash(&serialize(&i).unwrap()))
        .collect();
    RecentBlockhashes::from_iter(bhq.iter())
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::hash::Hash;

    #[test]
    fn test_size_of() {
        assert_eq!(
            bincode::serialized_size(&RecentBlockhashes(vec![Hash::default(); MAX_ENTRIES]))
                .unwrap() as usize,
            RecentBlockhashes::size_of()
        );
    }

    #[test]
    fn test_create_account_empty() {
        let account = create_account_with_data(42, vec![].into_iter());
        let recent_blockhashes = RecentBlockhashes::from_account(&account).unwrap();
        assert_eq!(recent_blockhashes, RecentBlockhashes::default());
    }

    #[test]
    fn test_create_account_full() {
        let def_hash = Hash::default();
        let account =
            create_account_with_data(42, vec![(0u64, &def_hash); MAX_ENTRIES].into_iter());
        let recent_blockhashes = RecentBlockhashes::from_account(&account).unwrap();
        assert_eq!(recent_blockhashes.len(), MAX_ENTRIES);
    }

    #[test]
    fn test_create_account_truncate() {
        let def_hash = Hash::default();
        let account =
            create_account_with_data(42, vec![(0u64, &def_hash); MAX_ENTRIES + 1].into_iter());
        let recent_blockhashes = RecentBlockhashes::from_account(&account).unwrap();
        assert_eq!(recent_blockhashes.len(), MAX_ENTRIES);
    }
}