// Copyright (c) 2017-2018 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_TXINDEX_H
#define BITCOIN_INDEX_TXINDEX_H

#include <primitives/block.h>
#include <primitives/transaction.h>
#include <threadinterrupt.h>
#include <txdb.h>
#include <uint256.h>
#include <validationinterface.h>

class CBlockIndex;

/**
 * TxIndex is used to look up transactions included in the blockchain by hash.
 * The index is written to a LevelDB database and records the filesystem
 * location of each transaction by transaction hash.
 */
class TxIndex final : public CValidationInterface
{
private:
    const std::unique_ptr<TxIndexDB> m_db;

    /// 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.
    std::atomic<bool> m_synced;

    /// The last block in the chain that the TxIndex is in sync with.
    std::atomic<const CBlockIndex*> m_best_block_index;

    std::thread m_thread_sync;
    CThreadInterrupt m_interrupt;

    /// Initialize internal state from the database and block index.
    bool Init();

    /// Sync the tx 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 txindex gets in sync, the
    /// m_synced flag is set and the BlockConnected ValidationInterface callback
    /// takes over and the sync thread exits.
    void ThreadSync();

    /// Write update index entries for a newly connected block.
    bool WriteBlock(const CBlock& block, const CBlockIndex* pindex);

    /// Write the current chain block locator to the DB.
    bool WriteBestBlock(const CBlockIndex* block_index);

protected:
    void BlockConnected(const std::shared_ptr<const CBlock>& block, const CBlockIndex* pindex,
                        const std::vector<CTransactionRef>& txn_conflicted) override;

    void SetBestChain(const CBlockLocator& locator) override;

public:
    /// Constructs the TxIndex, which becomes available to be queried.
    explicit TxIndex(std::unique_ptr<TxIndexDB> db);

    /// Destructor interrupts sync thread if running and blocks until it exits.
    ~TxIndex();

    /// Blocks the current thread until the transaction 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();

    /// Look up a transaction by hash.
    ///
    /// @param[in]   tx_hash  The hash of the transaction to be returned.
    /// @param[out]  block_hash  The hash of the block the transaction is found in.
    /// @param[out]  tx  The transaction itself.
    /// @return  true if transaction is found, false otherwise
    bool FindTx(const uint256& tx_hash, uint256& block_hash, CTransactionRef& tx) const;

    void Interrupt();

    /// Start initializes the sync state and registers the instance as a
    /// ValidationInterface so that it stays in sync with blockchain updates.
    void Start();

    /// Stops the instance from staying in sync with blockchain updates.
    void Stop();
};

/// The global transaction index, used in GetTransaction. May be null.
extern std::unique_ptr<TxIndex> g_txindex;

#endif // BITCOIN_INDEX_TXINDEX_H