// Copyright (c) 2017-present The Bitcoin Core developers

// Distributed under the MIT software license, see the accompanying

// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_INDEX_BASE_H

#define BITCOIN_INDEX_BASE_H

#include <dbwrapper.h>

#include <interfaces/chain.h>

#include <interfaces/types.h>

#include <util/string.h>

#include <util/threadinterrupt.h>

#include <validationinterface.h>

#include <string>

class CBlock;

class CBlockIndex;

class Chainstate;

class ChainstateManager;

namespace interfaces {

class Chain;

} // namespace interfaces

struct IndexSummary {

    std::string name;

    bool synced{false};

    int best_block_height{0};

    uint256 best_block_hash;

};

/**

 * Base class for indices of blockchain data. This implements

 * CValidationInterface and ensures blocks are indexed sequentially according

 * to their position in the active chain.

 *

 * In the presence of multiple chainstates (i.e. if a UTXO snapshot is loaded),

 * only the background "IBD" chainstate will be indexed to avoid building the

 * index out of order. When the background chainstate completes validation, the

 * index will be reinitialized and indexing will continue.

 */

class BaseIndex : public CValidationInterface

{

protected:

    /**

     * The database stores a block locator of the chain the database is synced to

     * so that the index can efficiently determine the point it last stopped at.

     * A locator is used instead of a simple hash of the chain tip because blocks

     * and block index entries may not be flushed to disk until after this database

     * is updated.

    */

    class DB : public CDBWrapper

    {

    public:

        DB(const fs::path& path, size_t n_cache_size,

           bool f_memory = false, bool f_wipe = false, bool f_obfuscate = false);

        /// Read block locator of the chain that the index is in sync with.

        bool ReadBestBlock(CBlockLocator& locator) const;

        /// Write block locator of the chain that the index is in sync with.

        void WriteBestBlock(CDBBatch& batch, const CBlockLocator& locator);

    };

private:

    /// Whether the index has been initialized or not.

    std::atomic<bool> m_init{false};

    /// Whether the index is in sync with the main chain. The flag is flipped

    /// from false to true once, after which point this starts processing

    /// ValidationInterface notifications to stay in sync.

    ///

    /// Note that this will latch to true *immediately* upon startup if

    /// `m_chainstate->m_chain` is empty, which will be the case upon startup

    /// with an empty datadir if, e.g., `-txindex=1` is specified.

    std::atomic<bool> m_synced{false};

    /// The last block in the chain that the index is in sync with.

    std::atomic<const CBlockIndex*> m_best_block_index{nullptr};

    std::thread m_thread_sync;

    CThreadInterrupt m_interrupt;

    /// Write the current index state (eg. chain block locator and subclass-specific items) to disk.

    ///

    /// Recommendations for error handling:

    /// If called on a successor of the previous committed best block in the index, the index can

    /// continue processing without risk of corruption, though the index state will need to catch up

    /// from further behind on reboot. If the new state is not a successor of the previous state (due

    /// to a chain reorganization), the index must halt until Commit succeeds or else it could end up

    /// getting corrupted.

    bool Commit();

    /// Loop over disconnected blocks and call CustomRewind.

    bool Rewind(const CBlockIndex* current_tip, const CBlockIndex* new_tip);

    virtual bool AllowPrune() const = 0;

    template <typename... Args>

    void FatalErrorf(util::ConstevalFormatString<sizeof...(Args)> fmt, const Args&... args);

protected:

    std::unique_ptr<interfaces::Chain> m_chain;

    Chainstate* m_chainstate{nullptr};

    const std::string m_name;

    void BlockConnected(ChainstateRole role, const std::shared_ptr<const CBlock>& block, const CBlockIndex* pindex) override;

    void ChainStateFlushed(ChainstateRole role, const CBlockLocator& locator) override;

    /// Initialize internal state from the database and block index.

    [[nodiscard]] virtual bool CustomInit(const std::optional<interfaces::BlockRef>& block) { return true; }

    /// Write update index entries for a newly connected block.

    [[nodiscard]] virtual bool CustomAppend(const interfaces::BlockInfo& block) { return true; }

    /// Virtual method called internally by Commit that can be overridden to atomically

    /// commit more index state.

    virtual bool CustomCommit(CDBBatch& batch) { return true; }

    /// Rewind index to an earlier chain tip during a chain reorg. The tip must

    /// be an ancestor of the current best block.

    [[nodiscard]] virtual bool CustomRewind(const interfaces::BlockRef& current_tip, const interfaces::BlockRef& new_tip) { return true; }

    virtual DB& GetDB() const = 0;

    /// Update the internal best block index as well as the prune lock.

    void SetBestBlockIndex(const CBlockIndex* block);

public:

    BaseIndex(std::unique_ptr<interfaces::Chain> chain, std::string name);

    /// Destructor interrupts sync thread if running and blocks until it exits.

    virtual ~BaseIndex();

    /// Get the name of the index for display in logs.

    const std::string& GetName() const LIFETIMEBOUND { return m_name; }

    /// Blocks the current thread until the index is caught up to the current

    /// state of the block chain. This only blocks if the index has gotten in

    /// sync once and only needs to process blocks in the ValidationInterface

    /// queue. If the index is catching up from far behind, this method does

    /// not block and immediately returns false.

    bool BlockUntilSyncedToCurrentChain() const LOCKS_EXCLUDED(::cs_main);

    void Interrupt();

    /// Initializes the sync state and registers the instance to the

    /// validation interface so that it stays in sync with blockchain updates.

    [[nodiscard]] bool Init();

    /// Starts the initial sync process on a background thread.

    [[nodiscard]] bool StartBackgroundSync();

    /// Sync the index with the block index starting from the current best block.

    /// Intended to be run in its own thread, m_thread_sync, and can be

    /// interrupted with m_interrupt. Once the index gets in sync, the m_synced

    /// flag is set and the BlockConnected ValidationInterface callback takes

    /// over and the sync thread exits.

    void Sync();

    /// Stops the instance from staying in sync with blockchain updates.

    void Stop();

    /// Get a summary of the index and its state.

    IndexSummary GetSummary() const;

};

#endif // BITCOIN_INDEX_BASE_H