//! Shared state reading code.
//!
//! Used by [`StateService`] and [`ReadStateService`]
//! to read from the best [`Chain`] in the [`NonFinalizedState`],
//! and the database in the [`FinalizedState`].

use std::sync::Arc;

use zebra_chain::{
    block::Block,
    transaction::{self, Transaction},
};

use crate::{
    service::{finalized_state::ZebraDb, non_finalized_state::Chain},
    HashOrHeight,
};

/// Returns the [`Block`] with [`block::Hash`](zebra_chain::block::Hash) or
/// [`Height`](zebra_chain::block::Height),
/// if it exists in the non-finalized `chain` or finalized `db`.
pub(crate) fn block<C>(
    chain: Option<C>,
    db: &ZebraDb,
    hash_or_height: HashOrHeight,
) -> Option<Arc<Block>>
where
    C: AsRef<Chain>,
{
    // # Correctness
    //
    // The StateService commits blocks to the finalized state before updating the latest chain,
    // and it can commit additional blocks after we've cloned this `chain` variable.
    //
    // Since blocks are the same in the finalized and non-finalized state,
    // we check the most efficient alternative first.
    // (`chain` is always in memory, but `db` stores blocks on disk, with a memory cache.)
    chain
        .as_ref()
        .and_then(|chain| chain.as_ref().block(hash_or_height))
        .map(|contextual| contextual.block.clone())
        .or_else(|| db.block(hash_or_height))
}

/// Returns the [`Transaction`] with [`transaction::Hash`],
/// if it exists in the non-finalized `chain` or finalized `db`.
pub(crate) fn transaction<C>(
    chain: Option<C>,
    db: &ZebraDb,
    hash: transaction::Hash,
) -> Option<Arc<Transaction>>
where
    C: AsRef<Chain>,
{
    // # Correctness
    //
    // The StateService commits blocks to the finalized state before updating the latest chain,
    // and it can commit additional blocks after we've cloned this `chain` variable.
    //
    // Since transactions are the same in the finalized and non-finalized state,
    // we check the most efficient alternative first.
    // (`chain` is always in memory, but `db` stores transactions on disk, with a memory cache.)
    chain
        .as_ref()
        .and_then(|chain| chain.as_ref().transaction(hash).cloned())
        .or_else(|| db.transaction(hash))
}