//! Empty database implementation.
use crate::{DBErrorMarker, Database, DatabaseRef};
use core::error::Error;
use core::{convert::Infallible, fmt, marker::PhantomData};
use primitives::{keccak256, Address, FlaggedStorage, B256, U256};
use state::{AccountInfo, Bytecode};
use std::string::ToString;

/// An empty database that always returns default values when queried
pub type EmptyDB = EmptyDBTyped<Infallible>;

/// An empty database that always returns default values when queried
///
/// This is generic over a type which is used as the database error type.
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct EmptyDBTyped<E> {
    _phantom: PhantomData<E>,
}

// Don't derive traits, because the type parameter is unused.
impl<E> Clone for EmptyDBTyped<E> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<E> Copy for EmptyDBTyped<E> {}

impl<E> Default for EmptyDBTyped<E> {
    fn default() -> Self {
        Self::new()
    }
}

impl<E> fmt::Debug for EmptyDBTyped<E> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("EmptyDB").finish_non_exhaustive()
    }
}

impl<E> PartialEq for EmptyDBTyped<E> {
    fn eq(&self, _: &Self) -> bool {
        true
    }
}

impl<E> Eq for EmptyDBTyped<E> {}

impl<E> EmptyDBTyped<E> {
    /// Create a new empty database.
    pub fn new() -> Self {
        Self {
            _phantom: PhantomData,
        }
    }
}

impl<E: DBErrorMarker + Error> Database for EmptyDBTyped<E> {
    type Error = E;

    #[inline]
    fn basic(&mut self, address: Address) -> Result<Option<AccountInfo>, Self::Error> {
        <Self as DatabaseRef>::basic_ref(self, address)
    }

    #[inline]
    fn code_by_hash(&mut self, code_hash: B256) -> Result<Bytecode, Self::Error> {
        <Self as DatabaseRef>::code_by_hash_ref(self, code_hash)
    }

    #[inline]
    fn storage(&mut self, address: Address, index: U256) -> Result<FlaggedStorage, Self::Error> {
        <Self as DatabaseRef>::storage_ref(self, address, index)
    }

    #[inline]
    fn block_hash(&mut self, number: u64) -> Result<B256, Self::Error> {
        <Self as DatabaseRef>::block_hash_ref(self, number)
    }
}

impl<E: DBErrorMarker + Error> DatabaseRef for EmptyDBTyped<E> {
    type Error = E;

    #[inline]
    fn basic_ref(&self, _address: Address) -> Result<Option<AccountInfo>, Self::Error> {
        Ok(None)
    }

    #[inline]
    fn code_by_hash_ref(&self, _code_hash: B256) -> Result<Bytecode, Self::Error> {
        Ok(Bytecode::default())
    }

    #[inline]
    fn storage_ref(&self, _address: Address, _index: U256) -> Result<FlaggedStorage, Self::Error> {
        Ok(FlaggedStorage::default())
    }

    #[inline]
    fn block_hash_ref(&self, number: u64) -> Result<B256, Self::Error> {
        Ok(keccak256(number.to_string().as_bytes()))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use primitives::b256;

    #[test]
    fn conform_block_hash_calculation() {
        let db = EmptyDB::new();
        assert_eq!(
            db.block_hash_ref(0u64),
            Ok(b256!(
                "0x044852b2a670ade5407e78fb2863c51de9fcb96542a07186fe3aeda6bb8a116d"
            ))
        );

        assert_eq!(
            db.block_hash_ref(1u64),
            Ok(b256!(
                "0xc89efdaa54c0f20c7adf612882df0950f5a951637e0307cdcb4c672f298b8bc6"
            ))
        );

        assert_eq!(
            db.block_hash_ref(100u64),
            Ok(b256!(
                "0x8c18210df0d9514f2d2e5d8ca7c100978219ee80d3968ad850ab5ead208287b3"
            ))
        );
    }
}
