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// Copyright (c) Aptos
// SPDX-License-Identifier: Apache-2.0

use aptos_crypto::HashValue;
use aptos_types::{
    state_store::{state_key::StateKey, state_value::StateValue},
    transaction::Version,
};
use scratchpad::SparseMerkleTree;
use std::collections::HashMap;

/// This represents two state sparse merkle trees at their versions in memory with the updates
/// reflecting the difference of `current` on top of `base`.
///
/// The `base` is the state SMT that current is based on.
/// The `current` is the state SMT that results from applying udpates_since_base on top of `base`.
/// `updates_since_base` tracks all those key-value pairs that's changed since `base`, useful
///  when the next checkpoint is calculated.
#[derive(Clone, Debug)]
pub struct StateDelta {
    pub base: SparseMerkleTree<StateValue>,
    pub base_version: Option<Version>,
    pub current: SparseMerkleTree<StateValue>,
    pub current_version: Option<Version>,
    pub updates_since_base: HashMap<StateKey, StateValue>,
}

impl StateDelta {
    pub fn new(
        base: SparseMerkleTree<StateValue>,
        base_version: Option<Version>,
        current: SparseMerkleTree<StateValue>,
        current_version: Option<Version>,
        updates_since_base: HashMap<StateKey, StateValue>,
    ) -> Self {
        assert!(base_version.map_or(0, |v| v + 1) <= current_version.map_or(0, |v| v + 1));
        Self {
            base,
            base_version,
            current,
            current_version,
            updates_since_base,
        }
    }

    pub fn new_empty() -> Self {
        let smt = SparseMerkleTree::new_empty();
        Self::new(smt.clone(), None, smt, None, HashMap::new())
    }

    pub fn new_at_checkpoint(root_hash: HashValue, checkpoint_version: Option<Version>) -> Self {
        let smt = SparseMerkleTree::new(root_hash);
        Self::new(
            smt.clone(),
            checkpoint_version,
            smt,
            checkpoint_version,
            HashMap::new(),
        )
    }

    pub fn has_same_current_state(&self, other: &StateDelta) -> bool {
        self.current_version == other.current_version
            && self.current.has_same_root_hash(&other.current)
    }

    pub fn base_root_hash(&self) -> HashValue {
        self.base.root_hash()
    }

    pub fn root_hash(&self) -> HashValue {
        self.current.root_hash()
    }
}