//! helpers for squashing append vecs into ancient append vecs
//! an ancient append vec is:
//! 1. a slot that is older than an epoch old
//! 2. multiple 'slots' squashed into a single older (ie. ancient) slot for convenience and performance
//! Otherwise, an ancient append vec is the same as any other append vec
use {
    crate::append_vec::{AppendVec, StoredAccountMeta},
    solana_sdk::clock::Slot,
};

/// a set of accounts need to be stored.
/// If there are too many to fit in 'Primary', the rest are put in 'Overflow'
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum StorageSelector {
    Primary,
    Overflow,
}

/// reference a set of accounts to store
/// The accounts may have to be split between 2 storages (primary and overflow) if there is not enough room in the primary storage.
/// The 'store' functions need data stored in a slice of specific type.
/// We need 1-2 of these slices constructed based on available bytes and individual account sizes.
/// The slice arithmetic accross both hashes and account data gets messy. So, this struct abstracts that.
pub struct AccountsToStore<'a> {
    accounts: &'a [&'a StoredAccountMeta<'a>],
    /// if 'accounts' contains more items than can be contained in the primary storage, then we have to split these accounts.
    /// 'index_first_item_overflow' specifies the index of the first item in 'accounts' that will go into the overflow storage
    index_first_item_overflow: usize,
    pub slot: Slot,
}

impl<'a> AccountsToStore<'a> {
    /// break 'stored_accounts' into primary and overflow
    /// available_bytes: how many bytes remain in the primary storage. Excess accounts will be directed to an overflow storage
    pub fn new(
        mut available_bytes: u64,
        accounts: &'a [&'a StoredAccountMeta<'a>],
        alive_total_bytes: usize,
        slot: Slot,
    ) -> Self {
        let num_accounts = accounts.len();
        // index of the first account that doesn't fit in the current append vec
        let mut index_first_item_overflow = num_accounts; // assume all fit
        if alive_total_bytes > available_bytes as usize {
            // not all the alive bytes fit, so we have to find how many accounts fit within available_bytes
            for (i, account) in accounts.iter().enumerate() {
                let account_size = account.stored_size as u64;
                if available_bytes >= account_size {
                    available_bytes = available_bytes.saturating_sub(account_size);
                } else if index_first_item_overflow == num_accounts {
                    // the # of accounts we have so far seen is the most that will fit in the current ancient append vec
                    index_first_item_overflow = i;
                    break;
                }
            }
        }
        Self {
            accounts,
            index_first_item_overflow,
            slot,
        }
    }

    /// true if a request to 'get' 'Overflow' would return accounts & hashes
    pub fn has_overflow(&self) -> bool {
        self.index_first_item_overflow < self.accounts.len()
    }

    /// get the accounts to store in the given 'storage'
    pub fn get(&self, storage: StorageSelector) -> &[&'a StoredAccountMeta<'a>] {
        let range = match storage {
            StorageSelector::Primary => 0..self.index_first_item_overflow,
            StorageSelector::Overflow => self.index_first_item_overflow..self.accounts.len(),
        };
        &self.accounts[range]
    }
}

/// capacity of an ancient append vec
pub fn get_ancient_append_vec_capacity() -> u64 {
    use crate::append_vec::MAXIMUM_APPEND_VEC_FILE_SIZE;
    // smaller than max by a bit just in case
    // some functions add slop on allocation
    // temporarily smaller to force ancient append vec operations to occur more often to flush out any bugs
    MAXIMUM_APPEND_VEC_FILE_SIZE / 10 - 2048
}

/// is this a max-size append vec designed to be used as an ancient append vec?
pub fn is_ancient(storage: &AppendVec) -> bool {
    storage.capacity() >= get_ancient_append_vec_capacity()
}

#[cfg(test)]
pub mod tests {
    use {
        super::*,
        crate::{
            accounts_db::get_temp_accounts_paths,
            append_vec::{AccountMeta, StoredAccountMeta, StoredMeta},
        },
        solana_sdk::{
            account::{AccountSharedData, ReadableAccount},
            hash::Hash,
            pubkey::Pubkey,
        },
    };

    #[test]
    fn test_accounts_to_store_simple() {
        let map = vec![];
        let slot = 1;
        let accounts_to_store = AccountsToStore::new(0, &map, 0, slot);
        for selector in [StorageSelector::Primary, StorageSelector::Overflow] {
            let accounts = accounts_to_store.get(selector);
            assert!(accounts.is_empty());
        }
        assert!(!accounts_to_store.has_overflow());
    }

    #[test]
    fn test_accounts_to_store_more() {
        let pubkey = Pubkey::from([1; 32]);
        let account_size = 3;

        let account = AccountSharedData::default();

        let account_meta = AccountMeta {
            lamports: 1,
            owner: Pubkey::from([2; 32]),
            executable: false,
            rent_epoch: 0,
        };
        let offset = 3;
        let hash = Hash::new(&[2; 32]);
        let stored_meta = StoredMeta {
            /// global write version
            write_version_obsolete: 0,
            /// key for the account
            pubkey,
            data_len: 43,
        };
        let account = StoredAccountMeta {
            meta: &stored_meta,
            /// account data
            account_meta: &account_meta,
            data: account.data(),
            offset,
            stored_size: account_size,
            hash: &hash,
        };
        let map = vec![&account];
        for (selector, available_bytes) in [
            (StorageSelector::Primary, account_size),
            (StorageSelector::Overflow, account_size - 1),
        ] {
            let slot = 1;
            let alive_total_bytes = account_size;
            let accounts_to_store =
                AccountsToStore::new(available_bytes as u64, &map, alive_total_bytes, slot);
            let accounts = accounts_to_store.get(selector);
            assert_eq!(
                accounts.iter().collect::<Vec<_>>(),
                map.iter().collect::<Vec<_>>(),
                "mismatch"
            );
            let accounts = accounts_to_store.get(get_opposite(&selector));
            assert_eq!(
                selector == StorageSelector::Overflow,
                accounts_to_store.has_overflow()
            );
            assert!(accounts.is_empty());
        }
    }
    fn get_opposite(selector: &StorageSelector) -> StorageSelector {
        match selector {
            StorageSelector::Overflow => StorageSelector::Primary,
            StorageSelector::Primary => StorageSelector::Overflow,
        }
    }

    #[test]
    fn test_get_ancient_append_vec_capacity() {
        assert_eq!(
            get_ancient_append_vec_capacity(),
            crate::append_vec::MAXIMUM_APPEND_VEC_FILE_SIZE / 10 - 2048
        );
    }

    #[test]
    fn test_is_ancient() {
        for (size, expected_ancient) in [
            (get_ancient_append_vec_capacity() + 1, true),
            (get_ancient_append_vec_capacity(), true),
            (get_ancient_append_vec_capacity() - 1, false),
        ] {
            let tf = crate::append_vec::test_utils::get_append_vec_path("test_is_ancient");
            let (_temp_dirs, _paths) = get_temp_accounts_paths(1).unwrap();
            let av = AppendVec::new(&tf.path, true, size as usize);

            assert_eq!(expected_ancient, is_ancient(&av));
        }
    }
}