// Copyright (c) 2020-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_WALLET_SQLITE_H

#define BITCOIN_WALLET_SQLITE_H

#include <sync.h>

#include <wallet/db.h>

#include <semaphore>

struct bilingual_str;

struct sqlite3_stmt;

struct sqlite3;

namespace wallet {

class SQLiteDatabase;

/** RAII class that provides a database cursor */

class SQLiteCursor : public DatabaseCursor

{

public:

    sqlite3_stmt* m_cursor_stmt{nullptr};

    // Copies of the prefix things for the prefix cursor.

    // Prevents SQLite from accessing temp variables for the prefix things.

    std::vector<std::byte> m_prefix_range_start;

    std::vector<std::byte> m_prefix_range_end;

    explicit SQLiteCursor() = default;

    explicit SQLiteCursor(std::vector<std::byte> start_range, std::vector<std::byte> end_range)

        : m_prefix_range_start(std::move(start_range)),

        m_prefix_range_end(std::move(end_range))

    {}

    ~SQLiteCursor() override;

    Status Next(DataStream& key, DataStream& value) override;

};

/** Class responsible for executing SQL statements in SQLite databases.

 *  Methods are virtual so they can be overridden by unit tests testing unusual database conditions. */

class SQliteExecHandler

{

public:

    virtual ~SQliteExecHandler() = default;

    virtual int Exec(SQLiteDatabase& database, const std::string& statement);

};

/** RAII class that provides access to a WalletDatabase */

class SQLiteBatch : public DatabaseBatch

{

private:

    SQLiteDatabase& m_database;

    std::unique_ptr<SQliteExecHandler> m_exec_handler{std::make_unique<SQliteExecHandler>()};

    sqlite3_stmt* m_read_stmt{nullptr};

    sqlite3_stmt* m_insert_stmt{nullptr};

    sqlite3_stmt* m_overwrite_stmt{nullptr};

    sqlite3_stmt* m_delete_stmt{nullptr};

    sqlite3_stmt* m_delete_prefix_stmt{nullptr};

    /** Whether this batch has started a database transaction and whether it owns SQLiteDatabase::m_write_semaphore.

     * If the batch starts a db tx, it acquires the semaphore and sets this to true, keeping the semaphore

     * until the transaction ends to prevent other batch objects from writing to the database.

     *

     * If this batch did not start a transaction, the semaphore is acquired transiently when writing and m_txn

     * is not set.

     *

     * m_txn is different from HasActiveTxn() as it is only true when this batch has started the transaction,

     * not just when any batch has started a transaction.

     */

    bool m_txn{false};

    void SetupSQLStatements();

    bool ExecStatement(sqlite3_stmt* stmt, std::span<const std::byte> blob);

protected:

    bool ReadKey(DataStream&& key, DataStream& value) override;

    bool WriteKey(DataStream&& key, DataStream&& value, bool overwrite = true) override;

    bool EraseKey(DataStream&& key) override;

    bool HasKey(DataStream&& key) override;

    bool ErasePrefix(std::span<const std::byte> prefix) override;

public:

    explicit SQLiteBatch(SQLiteDatabase& database);

    ~SQLiteBatch() override { Close(); }

    void SetExecHandler(std::unique_ptr<SQliteExecHandler>&& handler) { m_exec_handler = std::move(handler); }

    void Close() override;

    std::unique_ptr<DatabaseCursor> GetNewCursor() override;

    std::unique_ptr<DatabaseCursor> GetNewPrefixCursor(std::span<const std::byte> prefix) override;

    bool TxnBegin() override;

    bool TxnCommit() override;

    bool TxnAbort() override;

    bool HasActiveTxn() override { return m_txn; }

};

/** An instance of this class represents one SQLite3 database.

 **/

class SQLiteDatabase : public WalletDatabase

{

private:

    const fs::path m_dir_path;

    const std::string m_file_path;

    /**

     * This mutex protects SQLite initialization and shutdown.

     * sqlite3_config() and sqlite3_shutdown() are not thread-safe (sqlite3_initialize() is).

     * Concurrent threads that execute SQLiteDatabase::SQLiteDatabase() should have just one

     * of them do the init and the rest wait for it to complete before all can proceed.

     */

    static Mutex g_sqlite_mutex;

    static int g_sqlite_count GUARDED_BY(g_sqlite_mutex);

    void Cleanup() noexcept EXCLUSIVE_LOCKS_REQUIRED(!g_sqlite_mutex);

    void Open(int additional_flags);

protected:

    SQLiteDatabase(const fs::path& dir_path, const fs::path& file_path, const DatabaseOptions& options, int additional_flags);

public:

    SQLiteDatabase() = delete;

    /** Create DB handle to real database */

    SQLiteDatabase(const fs::path& dir_path, const fs::path& file_path, const DatabaseOptions& options);

    ~SQLiteDatabase();

    // Batches must acquire this semaphore on writing, and release when done writing.

    // This ensures that only one batch is modifying the database at a time.

    std::binary_semaphore m_write_semaphore;

    bool Verify(bilingual_str& error);

    /** Open the database if it is not already opened */

    void Open() override;

    /** Close the database */

    void Close() override;

    /** Rewrite the entire database on disk */

    bool Rewrite() override;

    /** Back up the entire database to a file.

     */

    bool Backup(const std::string& dest) const override;

    std::string Filename() override { return m_file_path; }

    /** Return paths to all database created files */

    std::vector<fs::path> Files() override

    {

        std::vector<fs::path> files;

        files.emplace_back(m_dir_path / fs::PathFromString(m_file_path));

        files.emplace_back(m_dir_path / fs::PathFromString(m_file_path + "-journal"));

        return files;

    }

    std::string Format() override { return "sqlite"; }

    /** Make a SQLiteBatch connected to this database */

    std::unique_ptr<DatabaseBatch> MakeBatch() override;

    /** Return true if there is an on-going txn in this connection */

    bool HasActiveTxn();

    sqlite3* m_db{nullptr};

    bool m_use_unsafe_sync;

};

std::unique_ptr<SQLiteDatabase> MakeSQLiteDatabase(const fs::path& path, const DatabaseOptions& options, DatabaseStatus& status, bilingual_str& error);

std::string SQLiteDatabaseVersion();

} // namespace wallet

#endif // BITCOIN_WALLET_SQLITE_H