// Copyright 2021 PingCAP, Inc. Licensed under Apache-2.0.

package utils

import (
	"context"
	"database/sql"
	"strings"
	"sync"

	"github.com/pingcap/errors"
	"github.com/pingcap/log"
	"github.com/pingcap/tidb/kv"
	"github.com/pingcap/tidb/sessionctx"
	"github.com/pingcap/tidb/util/sqlexec"
	"go.uber.org/zap"
)

const (
	tidbNewCollationEnabled = "new_collation_enabled"
)

var (
	// check sql.DB and sql.Conn implement QueryExecutor and DBExecutor
	_ DBExecutor = &sql.DB{}
	_ DBExecutor = &sql.Conn{}

	LogBackupTaskMutex sync.Mutex
	logBackupTaskCount int
)

// QueryExecutor is a interface for exec query
type QueryExecutor interface {
	QueryContext(ctx context.Context, query string, args ...interface{}) (*sql.Rows, error)
	QueryRowContext(ctx context.Context, query string, args ...interface{}) *sql.Row
}

// StmtExecutor define both query and exec methods
type StmtExecutor interface {
	QueryExecutor
	ExecContext(ctx context.Context, query string, args ...interface{}) (sql.Result, error)
}

// DBExecutor is a interface for statements and txn
type DBExecutor interface {
	StmtExecutor
	BeginTx(ctx context.Context, opts *sql.TxOptions) (*sql.Tx, error)
}

// CheckLogBackupEnabled checks if LogBackup is enabled in cluster.
// this mainly used in three places.
// 1. GC worker resolve locks to scan more locks after safepoint. (every minute)
// 2. Add index skipping use lightning.(every add index ddl)
// 3. Telemetry of log backup feature usage (every 6 hours).
// NOTE: this result shouldn't be cached by caller. because it may change every time in one cluster.
func CheckLogBackupEnabled(ctx sessionctx.Context) bool {
	executor, ok := ctx.(sqlexec.RestrictedSQLExecutor)
	if !ok {
		// shouldn't happen
		log.Error("[backup] unable to translate executor from sessionctx")
		return false
	}
	enabled, err := IsLogBackupEnabled(executor)
	if err != nil {
		// if it failed by any reason. we can simply return true this time.
		// for GC worker it will scan more locks in one tick.
		// for Add index it will skip using lightning this time.
		// for Telemetry it will get a false positive usage count.
		log.Warn("[backup] check log backup config failed, ignore it", zap.Error(err))
		return true
	}
	return enabled
}

// IsLogBackupEnabled is used for br to check whether tikv has enabled log backup.
// we use `sqlexec.RestrictedSQLExecutor` as parameter because it's easy to mock.
// it should return error.
func IsLogBackupEnabled(ctx sqlexec.RestrictedSQLExecutor) (bool, error) {
	valStr := "show config where name = 'log-backup.enable' and type = 'tikv'"
	internalCtx := kv.WithInternalSourceType(context.Background(), kv.InternalTxnBR)
	rows, fields, errSQL := ctx.ExecRestrictedSQL(internalCtx, nil, valStr)
	if errSQL != nil {
		return false, errSQL
	}
	if len(rows) == 0 {
		// no rows mean not support log backup.
		return false, nil
	}
	for _, row := range rows {
		d := row.GetDatum(3, &fields[3].Column.FieldType)
		value, errField := d.ToString()
		if errField != nil {
			return false, errField
		}
		if strings.ToLower(value) == "false" {
			return false, nil
		}
	}
	return true, nil
}

func GetGcRatio(ctx sqlexec.RestrictedSQLExecutor) (string, error) {
	valStr := "show config where name = 'gc.ratio-threshold' and type = 'tikv'"
	rows, fields, errSQL := ctx.ExecRestrictedSQL(
		kv.WithInternalSourceType(context.Background(), kv.InternalTxnBR),
		nil,
		valStr,
	)
	if errSQL != nil {
		return "", errSQL
	}
	if len(rows) == 0 {
		// no rows mean not support log backup.
		return "", nil
	}

	d := rows[0].GetDatum(3, &fields[3].Column.FieldType)
	return d.ToString()
}

func SetGcRatio(ctx sqlexec.RestrictedSQLExecutor, ratio string) error {
	_, _, err := ctx.ExecRestrictedSQL(
		kv.WithInternalSourceType(context.Background(), kv.InternalTxnBR),
		nil,
		"set config tikv `gc.ratio-threshold`=%?",
		ratio,
	)
	if err != nil {
		return errors.Annotatef(err, "failed to set config `gc.ratio-threshold`=%s", ratio)
	}
	log.Warn("set config tikv gc.ratio-threshold", zap.String("ratio", ratio))
	return nil
}

// LogBackupTaskCountInc increases the count of log backup task.
func LogBackupTaskCountInc() {
	LogBackupTaskMutex.Lock()
	logBackupTaskCount++
	LogBackupTaskMutex.Unlock()
}

// LogBackupTaskCountDec decreases the count of log backup task.
func LogBackupTaskCountDec() {
	LogBackupTaskMutex.Lock()
	logBackupTaskCount--
	LogBackupTaskMutex.Unlock()
}

// CheckLogBackupTaskExist checks that whether log-backup is existed.
func CheckLogBackupTaskExist() bool {
	return logBackupTaskCount > 0
}

// IsLogBackupInUse checks the log backup task existed.
func IsLogBackupInUse(ctx sessionctx.Context) bool {
	return CheckLogBackupEnabled(ctx) && CheckLogBackupTaskExist()
}

// GetTidbNewCollationEnabled returns the variable name of NewCollationEnabled.
func GetTidbNewCollationEnabled() string {
	return tidbNewCollationEnabled
}