Database.h

// WARNING: Changes to this file must be contributed back to Sawyer or else they will
//          be clobbered by the next update from Sawyer.  The Sawyer repository is at
//          https://github.com/matzke1/sawyer.




#ifndef Sawyer_Database_H
#define Sawyer_Database_H

#if __cplusplus >= 201103L

#include <boost/iterator/iterator_facade.hpp>
#include <boost/lexical_cast.hpp>
#include <boost/numeric/conversion/cast.hpp>
#include <memory.h>
#include <Sawyer/Assert.h>
#include <Sawyer/Map.h>
#include <Sawyer/Optional.h>
#include <string>
#include <vector>

namespace Sawyer {

namespace Database {

class Connection;
class Statement;
class Row;
class Iterator;

namespace Detail {
    class ConnectionBase;
    class StatementBase;
}

class Exception: public std::runtime_error {
public:
    Exception(const std::string &what)
        : std::runtime_error(what) {}

    ~Exception() noexcept {}
};

// Connection

class Connection {
    friend class ::Sawyer::Database::Statement;
    friend class ::Sawyer::Database::Detail::ConnectionBase;

    std::shared_ptr<Detail::ConnectionBase> pimpl_;

public:
    Connection() {};

private:
    explicit Connection(const std::shared_ptr<Detail::ConnectionBase> &pimpl);

public:
    ~Connection() = default;

    bool isOpen() const;

    Connection& close();

    Statement stmt(const std::string &sql);

    Connection& run(const std::string &sql);

    template<typename T>
    Optional<T> get(const std::string &sql);

    std::string driverName() const;

    // Undocumented: Row number for the last SQL "insert" (do not use).
    //
    // This method is available only if the underlying database driver supports it and it has lots of caveats. In other words,
    // don't use this method. The most portable way to identify the rows that were just inserted is to insert a UUID as part of
    // the data.
    size_t lastInsert() const;

    // Set the pointer to implementation
    void pimpl(const std::shared_ptr<Detail::ConnectionBase> &p) {
        pimpl_ = p;
    }
};

// Statement

class Statement {
    friend class ::Sawyer::Database::Detail::ConnectionBase;

    std::shared_ptr<Detail::StatementBase> pimpl_;

public:
    enum State {
        UNBOUND,                                        
        READY,                                          
        EXECUTING,                                      
        FINISHED,                                       
        DEAD                                            
    };

public:
    Statement() {}

private:
    explicit Statement(const std::shared_ptr<Detail::StatementBase> &stmt)
        : pimpl_(stmt) {}

public:
    Connection connection() const;

    template<typename T>
    Statement& bind(const std::string &name, const T &value);

    template<typename T>
    Statement& rebind(const std::string &name, const T &value);

    Iterator begin();

    Iterator end();

    Statement& run();
    
    template<typename T>
    Optional<T> get();
};

// Row

class Row {
    friend class ::Sawyer::Database::Iterator;

    std::shared_ptr<Detail::StatementBase> stmt_;
    size_t sequence_;                                   // for checking validity

private:
    Row()
        : sequence_(0) {}

    explicit Row(const std::shared_ptr<Detail::StatementBase> &stmt);

public:
    template<typename T>
    Optional<T> get(size_t columnIdx) const;

    size_t rowNumber() const;
};

// Iterator

class Iterator: public boost::iterator_facade<Iterator, const Row, boost::forward_traversal_tag> {
    friend class ::Sawyer::Database::Detail::StatementBase;

    Row row_;

public:
    Iterator() {}

private:
    explicit Iterator(const std::shared_ptr<Detail::StatementBase> &stmt);

public:
    bool isEnd() const {
        return !row_.stmt_;
    }

    explicit operator bool() const {
        return !isEnd();
    }
    
private:
    friend class boost::iterator_core_access;
    const Row& dereference() const;
    bool equal(const Iterator&) const;
    void increment();
};


//
//                                  Only implementation details beyond this point.
//


namespace Detail {

// Base class for connection details. The individual drivers (SQLite3, PostgreSQL) will be derived from this class.
//
// Connection detail objects are reference counted. References come from only two places:
//   1. Each top-level Connection object that's in a connected state has a reference to this connection.
//   2. Each low-level Statement object that's in an "executing" state has a reference to this connection.
// Additionally, all low-level statement objects have a weak reference to a connection.
//
class ConnectionBase: public std::enable_shared_from_this<ConnectionBase> {
    friend class ::Sawyer::Database::Connection;

protected:
    ConnectionBase() {}

public:
    virtual ~ConnectionBase() {}

protected:
    // Close any low-level connection.
    virtual void close() = 0;

    // Create a prepared statement from the specified high-level SQL. By "high-level" we mean the binding syntax used by this
    // API such as "?name" (whereas low-level means the syntax passed to the driver such as "?").
    virtual Statement prepareStatement(const std::string &sql) = 0;

    // Row number for the last inserted row if supported by this driver.  It's better to use a table column that holds a value
    // generated from a sequence.
    virtual size_t lastInsert() const = 0;

    Statement makeStatement(const std::shared_ptr<Detail::StatementBase> &detail);

    virtual std::string driverName() const = 0;
};

// Describes the location of "?name" parameters in high-level SQL by associating them with one or more "?" parameters in
// low-level SQL. WARNIN: the low-level parameters are numbered starting at one instead of zero, which is inconsistent with how
// the low-level APIs index other things like query result columns (not to mention being surprising for C and C++ developers).
class Parameter {
    friend class ::Sawyer::Database::Detail::StatementBase;

    std::vector<size_t> indexes;                        // "?" indexes
    bool isBound = false;

    void append(size_t idx) {
        indexes.push_back(idx);
    }
};

template<typename T>
class ColumnReader {
    friend class ::Sawyer::Database::Detail::StatementBase;
    Optional<T> operator()(StatementBase *stmt, size_t idx);
};

//template<>
//class ColumnReader<std::vector<uint8_t>> {
//    friend class ::Sawyer::Database::Detail::StatementBase;
//    Optional<std::vector<uint8_t>> operator()(StatementBase *stmt, size_t idx);
//};

// Reference counted prepared statement details. Objects of this class are referenced from the high-level Statement objects and
// the query iterator rows.  This class is the base class for driver-specific statements.
class StatementBase: public std::enable_shared_from_this<StatementBase> {
    friend class ::Sawyer::Database::Iterator;
    friend class ::Sawyer::Database::Row;
    friend class ::Sawyer::Database::Statement;
    template<class T> friend class ::Sawyer::Database::Detail::ColumnReader;

    using Parameters = Container::Map<std::string, Parameter>;
    
    std::shared_ptr<ConnectionBase> connection_;        // non-null while statement is executing
    std::weak_ptr<ConnectionBase> weakConnection_;      // refers to the originating connection
    Parameters params_;                                 // mapping from param names to question marks
    Statement::State state_ = Statement::DEAD;          // don't set directly; use "state" member function
    size_t sequence_ = 0;                               // sequence number for invalidating row iterators
    size_t rowNumber_ = 0;                              // result row number

public:
    virtual ~StatementBase() {}

protected:
    explicit StatementBase(const std::shared_ptr<ConnectionBase> &connection)
        : weakConnection_(connection) {                 // save only a weak pointer, no shared pointer
        ASSERT_not_null(connection);
    }

    // Parse the high-level SQL (with "?name" parameters) into low-level SQL (with "?" parameters). Returns the low-level SQL
    // and the number of low-level "?" parameters and has the following side effects:
    //   1. Re-initializes this object's parameter list
    //   2. Sets this object's state to READY, UNBOUND, or DEAD.
    std::pair<std::string, size_t> parseParameters(const std::string &highSql) {
        params_.clear();
        std::string lowSql;
        bool inString = false;
        size_t nLowParams = 0;
        state(Statement::READY);                        // possibly reset below
        for (size_t i = 0; i < highSql.size(); ++i) {
            if ('\'' == highSql[i]) {
                inString = !inString;                   // works for "''" escape too
                lowSql += highSql[i];
            } else if ('?' == highSql[i] && !inString) {
                lowSql += '?';
                std::string paramName;
                while (i+1 < highSql.size() && (::isalnum(highSql[i+1]) || '_' == highSql[i+1]))
                    paramName += highSql[++i];
                if (paramName.empty())
                    throw Exception("invalid parameter name at character position " + boost::lexical_cast<std::string>(i));
                Parameter &param = params_.insertMaybeDefault(paramName);
                param.append(nLowParams++);             // 0-origin low-level parameter numbers
                state(Statement::UNBOUND);
            } else {
                lowSql += highSql[i];
            }
        }
        if (inString) {
            state(Statement::DEAD);
            throw Exception("mismatched quotes in SQL statement");
        }
        return std::make_pair(lowSql, nLowParams);
    }

    // Invalidate all iterators and their rows by incrementing this statements sequence number.
    void invalidateIteratorsAndRows() {
        ++sequence_;
    }

    // Sequence number used for checking iterator validity.
    size_t sequence() const {
        return sequence_;
    }
    
    // Cause this statement to lock the database connection by maintaining a shared pointer to the low-level
    // connection. Returns true if the connection could be locked, or false if unable.
    bool lockConnection() {
        return (connection_ = weakConnection_.lock()) != nullptr;
    }

    // Release the connection lock by throwing away the shared pointer to the connection. This statement will still maintain
    // a weak reference to the connection.
    void unlockConnection() {
        connection_.reset();
    }

    // Returns an indication of whether this statement holds a lock on the low-level connection, preventing the connection from
    // being destroyed.
    bool isConnectionLocked() const {
        return connection_ != nullptr;
    }

    // Returns the connection details associated with this statement.  The connection is not locked by querying this property.
    std::shared_ptr<ConnectionBase> connection() const {
        return weakConnection_.lock();
    }

    // Return the current statement state.
    Statement::State state() const {
        return state_;
    }

    // Change the statement state.  A statement in the EXECUTING state will lock the connection to prevent it from being
    // destroyed, but a statement in any other state will unlock the connection causing the last reference to destroy the
    // connection and will invalidate all iterators and rows.
    void state(Statement::State newState) {
        switch (newState) {
            case Statement::DEAD:
            case Statement::FINISHED:
            case Statement::UNBOUND:
            case Statement::READY:
                invalidateIteratorsAndRows();
                unlockConnection();
                break;
            case Statement::EXECUTING:
                ASSERT_require(isConnectionLocked());
                break;
        }
        state_ = newState;
    }

    // Returns true if this statement has parameters that have not been bound to a value.
    bool hasUnboundParameters() const {
        ASSERT_forbid(state() == Statement::DEAD);
        for (const Parameter &param: params_.values()) {
            if (!param.isBound)
                return true;
        }
        return false;
    }

    // Causes all parameters to become unbound and changes the state to either UNBOUND or READY (depending on whether there are
    // any parameters or not, respectively).
    virtual void unbindAllParams() {
        ASSERT_forbid(state() == Statement::DEAD);
        for (Parameter &param: params_.values())
            param.isBound = false;
        state(params_.isEmpty() ? Statement::READY : Statement::UNBOUND);
    }

    // Reset the statement by invalidating all iterators, unbinding all parameters, and changing the state to either UNBOUND or
    // READY depending on whether or not it has any parameters.
    virtual void reset(bool doUnbind) {
        ASSERT_forbid(state() == Statement::DEAD);
        invalidateIteratorsAndRows();
        if (doUnbind) {
            unbindAllParams();
        } else {
            state(hasUnboundParameters() ? Statement::UNBOUND : Statement::READY);
        }
    }

    // Bind a value to a parameter. If isRebind is set and the statement is in the EXECUTING state, then rewind back to the
    // READY state, preserve all previous bindings, and adjust only the specified binding.
    template<typename T>
    void bind(const std::string &name, const T &value, bool isRebind) {
        if (!connection())
            throw Exception("connection is closed");
        switch (state()) {
            case Statement::DEAD:
                throw Exception("statement is dead");
            case Statement::FINISHED:
            case Statement::EXECUTING:
                reset(!isRebind);
                // fall through
            case Statement::READY:
            case Statement::UNBOUND: {
                if (!params_.exists(name))
                    throw Exception("no such parameter \"" + name + "\" in statement");
                Parameter &param = params_[name];
                bool wasUnbound = !param.isBound;
                for (size_t idx: param.indexes) {
                    try {
                        bindLow(idx, value);
                    } catch (const Exception &e) {
                        if (param.indexes.size() > 1)
                            state(Statement::DEAD); // might be only partly bound now
                        throw e;
                    }
                }
                param.isBound = true;

                if (wasUnbound && !hasUnboundParameters())
                    state(Statement::READY); 
                break;
            }
        }
    }

    // Bind a value to an optional parameter.
    template<typename T>
    void bind(const std::string &name, const Sawyer::Optional<T> &value, bool isRebind) {
        if (value) {
            bind(name, *value, isRebind);
        } else {
            bind(name, Nothing(), isRebind);
        }
    }

    // Driver-specific part of binding by specifying the 0-origin low-level "?" number and the value.
    virtual void bindLow(size_t idx, int value) = 0;
    virtual void bindLow(size_t idx, int64_t value) = 0;
    virtual void bindLow(size_t idx, size_t value) = 0;
    virtual void bindLow(size_t idx, double value) = 0;
    virtual void bindLow(size_t idx, const std::string &value) = 0;
    virtual void bindLow(size_t idx, const char *cstring) = 0;
    virtual void bindLow(size_t idx, Nothing) = 0;
    virtual void bindLow(size_t idx, const std::vector<uint8_t> &data) = 0;

    Iterator makeIterator() {
        return Iterator(shared_from_this());
    }
    
    // Begin execution of a statement in the READY state. If the statement is in the FINISHED or EXECUTING state it will be
    // restarted.
    Iterator begin() {
        if (!connection())
            throw Exception("connection is closed");
        switch (state()) {
            case Statement::DEAD:
                throw Exception("statement is dead");
            case Statement::UNBOUND: {
                std::string s;
                for (Parameters::Node &param: params_.nodes()) {
                    if (!param.value().isBound)
                        s += (s.empty() ? "" : ", ") + param.key();
                }
                ASSERT_forbid(s.empty());
                throw Exception("unbound parameters: " + s);
            }
            case Statement::FINISHED:
            case Statement::EXECUTING:
                reset(false);
                // fall through
            case Statement::READY: {
                if (!lockConnection())
                    throw Exception("connection has been closed");
                state(Statement::EXECUTING);
                rowNumber_ = 0;
                Iterator iter = beginLow();
                rowNumber_ = 0;                         // in case beginLow changed it
                return iter;
            }
        }
        ASSERT_not_reachable("invalid state");
    }

    // The driver-specific component of "begin". The statement is guaranteed to be in the EXECUTING state when called,
    // but could be in some other state after returning.
    virtual Iterator beginLow() = 0;

    // Advance an executing statement to the next row
    Iterator next() {
        if (!connection())
            throw Exception("connection is closed");
        ASSERT_require(state() == Statement::EXECUTING); // no other way to get here
        invalidateIteratorsAndRows();
        ++rowNumber_;
        return nextLow();
    }

    // Current row number
    size_t rowNumber() const {
        return rowNumber_;
    }
    
    // The driver-specific component of "next". The statement is guaranteed to be in the EXECUTING state when called, but
    // could be in some other state after returning.
    virtual Iterator nextLow() = 0;

    // Get a column value from the current row of result
    template<typename T>
    Optional<T> get(size_t columnIdx) {
        if (!connection())
            throw Exception("connection is closed");
        ASSERT_require(state() == Statement::EXECUTING); // no other way to get here
        if (columnIdx >= nColumns())
            throw Exception("column index " + boost::lexical_cast<std::string>(columnIdx) + " is out of range");
        return ColumnReader<T>()(this, columnIdx);
    }

    // Number of columns returned by a query.
    virtual size_t nColumns() const = 0;

    // Get the value of a particular column of the current row.
    virtual Optional<std::string> getString(size_t idx) = 0;
    virtual Optional<std::vector<std::uint8_t>> getBlob(size_t idx) = 0;
};

template<typename T>
inline Optional<T>
ColumnReader<T>::operator()(StatementBase *stmt, size_t idx) {
    std::string str;
    if (!stmt->getString(idx).assignTo(str))
        return Nothing();
    return boost::lexical_cast<T>(str);
}

template<>
inline Optional<std::vector<uint8_t>>
ColumnReader<std::vector<uint8_t>>::operator()(StatementBase *stmt, size_t idx) {
    return stmt->getBlob(idx);
}

inline Statement
ConnectionBase::makeStatement(const std::shared_ptr<Detail::StatementBase> &detail) {
    return Statement(detail);
}

} // namespace

// Implementations Connection


inline Connection::Connection(const std::shared_ptr<Detail::ConnectionBase> &pimpl)
    : pimpl_(pimpl) {}

inline bool
Connection::isOpen() const {
    return pimpl_ != nullptr;
}

inline Connection&
Connection::close() {
    pimpl_ = nullptr;
    return *this;
}

inline std::string
Connection::driverName() const {
    if (pimpl_) {
        return pimpl_->driverName();
    } else {
        return "";
    }
}

inline Statement
Connection::stmt(const std::string &sql) {
    if (pimpl_) {
        return pimpl_->prepareStatement(sql);
    } else {
        throw Exception("no active database connection");
    }
}

inline Connection&
Connection::run(const std::string &sql) {
    stmt(sql).begin();
    return *this;
}

template<typename T>
inline Optional<T>
Connection::get(const std::string &sql) {
    for (auto row: stmt(sql))
        return row.get<T>(0);
    return Nothing();
}

inline size_t
Connection::lastInsert() const {
    if (pimpl_) {
        return pimpl_->lastInsert();
    } else {
        throw Exception("no active database connection");
    }
}

// Implementations for Statement

inline Connection
Statement::connection() const {
    if (pimpl_) {
        return Connection(pimpl_->connection());
    } else {
        return Connection();
    }
}

template<typename T>
inline Statement&
Statement::bind(const std::string &name, const T &value) {
    if (pimpl_) {
        pimpl_->bind(name, value, false);
    } else {
        throw Exception("no active database connection");
    }
    return *this;
}

template<typename T>
inline Statement&
Statement::rebind(const std::string &name, const T &value) {
    if (pimpl_) {
        pimpl_->bind(name, value, true);
    } else {
        throw Exception("no active database connection");
    }
    return *this;
}

inline Iterator
Statement::begin() {
    if (pimpl_) {
        return pimpl_->begin();
    } else {
        throw Exception("no active database connection");
    }
}

inline Iterator
Statement::end() {
    return Iterator();
}

inline Statement&
Statement::run() {
    begin();
    return *this;
}

template<typename T>
inline Optional<T>
Statement::get() {
    Iterator row = begin();
    if (row.isEnd())
        throw Exception("query did not return a row");
    return row->get<T>(0);
}

// Implementations for Iterator

inline
Iterator::Iterator(const std::shared_ptr<Detail::StatementBase> &stmt)
    : row_(stmt) {}

inline const Row&
Iterator::dereference() const {
    if (isEnd())
        throw Exception("dereferencing the end iterator");
    if (row_.sequence_ != row_.stmt_->sequence())
        throw Exception("iterator has been invalidated");
    return row_;
}

inline bool
Iterator::equal(const Iterator &other) const {
    return row_.stmt_ == other.row_.stmt_ && row_.sequence_ == other.row_.sequence_;
}

inline void
Iterator::increment() {
    if (isEnd())
        throw Exception("incrementing the end iterator");
    *this = row_.stmt_->next();
}

// Implementations for Row

inline
Row::Row(const std::shared_ptr<Detail::StatementBase> &stmt)
    : stmt_(stmt), sequence_(stmt ? stmt->sequence() : 0) {}

template<typename T>
inline Optional<T>
Row::get(size_t columnIdx) const {
    ASSERT_not_null(stmt_);
    if (sequence_ != stmt_->sequence())
        throw Exception("row has been invalidated");
    return stmt_->get<T>(columnIdx);
}

inline size_t
Row::rowNumber() const {
    ASSERT_not_null(stmt_);
    if (sequence_ != stmt_->sequence())
        throw Exception("row has been invalidated");
    return stmt_->rowNumber();
}

} // namespace
} // namespace

#endif
#endif