// Read (as much as possible of) a chunk of binary log events starting the given startingCoordinates
func readBinlogEventsChunk(instanceKey *InstanceKey, startingCoordinates BinlogCoordinates) ([]BinlogEvent, error) {
	events := []BinlogEvent{}
	db, err := db.OpenTopology(instanceKey.Hostname, instanceKey.Port)
	if err != nil {
		return events, err
	}
	commandToken := math.TernaryString(startingCoordinates.Type == BinaryLog, "binlog", "relaylog")
	if startingCoordinates.LogFile == "" {
		return events, log.Errorf("readBinlogEventsChunk: empty binlog file name for %+v.", *instanceKey)
	}
	query := fmt.Sprintf("show %s events in '%s' FROM %d LIMIT %d", commandToken, startingCoordinates.LogFile, startingCoordinates.LogPos, config.Config.BinlogEventsChunkSize)
	err = sqlutils.QueryRowsMap(db, query, func(m sqlutils.RowMap) error {
		binlogEvent := BinlogEvent{}
		binlogEvent.Coordinates.LogFile = m.GetString("Log_name")
		binlogEvent.Coordinates.LogPos = m.GetInt64("Pos")
		binlogEvent.Coordinates.Type = startingCoordinates.Type
		binlogEvent.NextEventPos = m.GetInt64("End_log_pos")
		binlogEvent.EventType = m.GetString("Event_type")
		binlogEvent.Info = m.GetString("Info")

		events = append(events, binlogEvent)
		return nil
	})
	return events, err
}

// ScanInstanceRow executes a read-a-single-row query on a given MySQL topology instance
func ScanInstanceRow(instanceKey *InstanceKey, query string, dest ...interface{}) error {
	db, err := db.OpenTopology(instanceKey.Hostname, instanceKey.Port)
	if err != nil {
		return err
	}
	err = db.QueryRow(query).Scan(dest...)
	return err
}

// ExecInstanceNoPrepare executes a given query on the given MySQL topology instance, without using prepared statements
func ExecInstanceNoPrepare(instanceKey *InstanceKey, query string, args ...interface{}) (sql.Result, error) {
	db, err := db.OpenTopology(instanceKey.Hostname, instanceKey.Port)
	if err != nil {
		return nil, err
	}
	res, err := sqlutils.ExecNoPrepare(db, query, args...)
	return res, err
}

// Try and find the last position of a pseudo GTID query entry in the given binary log.
// Also return the full text of that entry.
// maxCoordinates is the position beyond which we should not read. This is relevant when reading relay logs; in particular,
// the last relay log. We must be careful not to scan for Pseudo-GTID entries past the position executed by the SQL thread.
// maxCoordinates == nil means no limit.
func getLastPseudoGTIDEntryInBinlog(instanceKey *InstanceKey, binlog string, binlogType BinlogType, maxCoordinates *BinlogCoordinates) (*BinlogCoordinates, string, error) {
	if binlog == "" {
		return nil, "", log.Errorf("getLastPseudoGTIDEntryInBinlog: empty binlog file name for %+v. maxCoordinates = %+v", *instanceKey, maxCoordinates)
	}
	binlogCoordinates := BinlogCoordinates{LogFile: binlog, LogPos: 0, Type: binlogType}
	db, err := db.OpenTopology(instanceKey.Hostname, instanceKey.Port)
	if err != nil {
		return nil, "", err
	}

	moreRowsExpected := true
	var nextPos int64 = 0
	step := 0

	entryText := ""
	for moreRowsExpected {
		query := ""
		if binlogCoordinates.Type == BinaryLog {
			query = fmt.Sprintf("show binlog events in '%s' FROM %d LIMIT %d", binlog, nextPos, config.Config.BinlogEventsChunkSize)
		} else {
			query = fmt.Sprintf("show relaylog events in '%s' LIMIT %d,%d", binlog, (step * config.Config.BinlogEventsChunkSize), config.Config.BinlogEventsChunkSize)
		}

		moreRowsExpected = false
		queryRowsFunc := sqlutils.QueryRowsMap
		if config.Config.BufferBinlogEvents {
			queryRowsFunc = sqlutils.QueryRowsMapBuffered
		}
		err = queryRowsFunc(db, query, func(m sqlutils.RowMap) error {
			moreRowsExpected = true
			nextPos = m.GetInt64("End_log_pos")
			binlogEntryInfo := m.GetString("Info")
			if matched, _ := regexp.MatchString(config.Config.PseudoGTIDPattern, binlogEntryInfo); matched {
				if maxCoordinates != nil && maxCoordinates.SmallerThan(&BinlogCoordinates{LogFile: binlog, LogPos: m.GetInt64("Pos")}) {
					// past the limitation
					moreRowsExpected = false
					return nil
				}
				binlogCoordinates.LogPos = m.GetInt64("Pos")
				entryText = binlogEntryInfo
				// Found a match. But we keep searching: we're interested in the LAST entry, and, alas,
				// we can only search in ASCENDING order...
			}
			return nil
		})
		if err != nil {
			return nil, "", err
		}
		step++
	}

	// Not found? return nil. an error is reserved to SQL problems.
	if binlogCoordinates.LogPos == 0 {
		return nil, "", nil
	}
	return &binlogCoordinates, entryText, err
}

// EmptyCommitInstance issues an empty COMMIT on a given instance
func EmptyCommitInstance(instanceKey *InstanceKey) error {
	db, err := db.OpenTopology(instanceKey.Hostname, instanceKey.Port)
	if err != nil {
		return err
	}
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	err = tx.Commit()
	if err != nil {
		return err
	}
	return err
}

// Given a binlog entry text (query), search it in the given binary log of a given instance
func SearchPseudoGTIDEntryInBinlog(instanceKey *InstanceKey, binlog string, entryText string, entriesMonotonic bool) (BinlogCoordinates, bool, error) {
	binlogCoordinates := BinlogCoordinates{LogFile: binlog, LogPos: 0, Type: BinaryLog}
	if binlog == "" {
		return binlogCoordinates, false, log.Errorf("SearchPseudoGTIDEntryInBinlog: empty binlog file name for %+v", *instanceKey)
	}

	db, err := db.OpenTopology(instanceKey.Hostname, instanceKey.Port)
	if err != nil {
		return binlogCoordinates, false, err
	}

	moreRowsExpected := true
	skipRestOfBinlog := false
	alreadyMatchedAscendingPseudoGTID := false
	var nextPos int64 = 0

	//	commandToken := math.TernaryString(binlogCoordinates.Type == BinaryLog, "binlog", "relaylog")
	for moreRowsExpected {
		query := fmt.Sprintf("show binlog events in '%s' FROM %d LIMIT %d", binlog, nextPos, config.Config.BinlogEventsChunkSize)

		// We don't know in advance when we will hit the end of the binlog. We will implicitly understand it when our
		// `show binlog events` query does not return any row.
		moreRowsExpected = false
		queryRowsFunc := sqlutils.QueryRowsMap
		if config.Config.BufferBinlogEvents {
			queryRowsFunc = sqlutils.QueryRowsMapBuffered
		}
		err = queryRowsFunc(db, query, func(m sqlutils.RowMap) error {
			if binlogCoordinates.LogPos != 0 {
				// Entry found!
				skipRestOfBinlog = true
				return nil
			}
			if skipRestOfBinlog {
				return nil
			}
			moreRowsExpected = true
			nextPos = m.GetInt64("End_log_pos")
			binlogEntryInfo := m.GetString("Info")
			//
			if binlogEntryInfo == entryText {
				// found it!
				binlogCoordinates.LogPos = m.GetInt64("Pos")
			} else if entriesMonotonic && !alreadyMatchedAscendingPseudoGTID {
				// More heavyweight computation here. Need to verify whether the binlog entry we have is a pseudo-gtid entry
				// We only want to check for ASCENDING once in the top of the binary log.
				// If we find the first entry to be higher than the searched one, clearly we are done.
				// If not, then by virtue of binary logs, we still have to full-scan the entrie binlog sequentially; we
				// do not check again for ASCENDING (no point), so we save up CPU energy wasted in regexp.
				if matched, _ := regexp.MatchString(config.Config.PseudoGTIDPattern, binlogEntryInfo); matched {
					alreadyMatchedAscendingPseudoGTID = true
					log.Debugf("Matched ascending Pseudo-GTID entry in %+v", binlog)
					if binlogEntryInfo > entryText {
						// Entries ascending, and current entry is larger than the one we are searching for.
						// There is no need to scan further on. We can skip the entire binlog
						log.Debugf(`Pseudo GTID entries are monotonic and we hit "%+v" > "%+v"; skipping binlog %+v`, m.GetString("Info"), entryText, binlogCoordinates.LogFile)
						skipRestOfBinlog = true
						return nil
					}
				}
			}
			return nil
		})
		if err != nil {
			return binlogCoordinates, (binlogCoordinates.LogPos != 0), err
		}
		if skipRestOfBinlog {
			return binlogCoordinates, (binlogCoordinates.LogPos != 0), err
		}
	}

	return binlogCoordinates, (binlogCoordinates.LogPos != 0), err
}