package bun

import (
	"bytes"
	"context"
	"database/sql"
	"errors"
	"fmt"
	"strconv"
	"strings"
	"sync"

	"github.com/uptrace/bun/dialect"

	"github.com/uptrace/bun/dialect/feature"
	"github.com/uptrace/bun/internal"
	"github.com/uptrace/bun/schema"
)

type union struct {
	expr  string
	query *SelectQuery
}

type SelectQuery struct {
	whereBaseQuery
	idxHintsQuery

	distinctOn []schema.QueryWithArgs
	joins      []joinQuery
	group      []schema.QueryWithArgs
	having     []schema.QueryWithArgs
	order      []schema.QueryWithArgs
	limit      int32
	offset     int32
	selFor     schema.QueryWithArgs

	union []union
}

var _ Query = (*SelectQuery)(nil)

func NewSelectQuery(db *DB) *SelectQuery {
	return &SelectQuery{
		whereBaseQuery: whereBaseQuery{
			baseQuery: baseQuery{
				db:   db,
				conn: db.DB,
			},
		},
	}
}

func (q *SelectQuery) Conn(db IConn) *SelectQuery {
	q.setConn(db)
	return q
}

func (q *SelectQuery) Model(model interface{}) *SelectQuery {
	q.setModel(model)
	return q
}

// Apply calls the fn passing the SelectQuery as an argument.
func (q *SelectQuery) Apply(fn func(*SelectQuery) *SelectQuery) *SelectQuery {
	return fn(q)
}

func (q *SelectQuery) With(name string, query schema.QueryAppender) *SelectQuery {
	q.addWith(name, query, false)
	return q
}

func (q *SelectQuery) WithRecursive(name string, query schema.QueryAppender) *SelectQuery {
	q.addWith(name, query, true)
	return q
}

func (q *SelectQuery) Distinct() *SelectQuery {
	q.distinctOn = make([]schema.QueryWithArgs, 0)
	return q
}

func (q *SelectQuery) DistinctOn(query string, args ...interface{}) *SelectQuery {
	q.distinctOn = append(q.distinctOn, schema.SafeQuery(query, args))
	return q
}

//------------------------------------------------------------------------------

func (q *SelectQuery) Table(tables ...string) *SelectQuery {
	for _, table := range tables {
		q.addTable(schema.UnsafeIdent(table))
	}
	return q
}

func (q *SelectQuery) TableExpr(query string, args ...interface{}) *SelectQuery {
	q.addTable(schema.SafeQuery(query, args))
	return q
}

func (q *SelectQuery) ModelTableExpr(query string, args ...interface{}) *SelectQuery {
	q.modelTableName = schema.SafeQuery(query, args)
	return q
}

//------------------------------------------------------------------------------

func (q *SelectQuery) Column(columns ...string) *SelectQuery {
	for _, column := range columns {
		q.addColumn(schema.UnsafeIdent(column))
	}
	return q
}

func (q *SelectQuery) ColumnExpr(query string, args ...interface{}) *SelectQuery {
	q.addColumn(schema.SafeQuery(query, args))
	return q
}

func (q *SelectQuery) ExcludeColumn(columns ...string) *SelectQuery {
	q.excludeColumn(columns)
	return q
}

//------------------------------------------------------------------------------

func (q *SelectQuery) WherePK(cols ...string) *SelectQuery {
	q.addWhereCols(cols)
	return q
}

func (q *SelectQuery) Where(query string, args ...interface{}) *SelectQuery {
	q.addWhere(schema.SafeQueryWithSep(query, args, " AND "))
	return q
}

func (q *SelectQuery) WhereOr(query string, args ...interface{}) *SelectQuery {
	q.addWhere(schema.SafeQueryWithSep(query, args, " OR "))
	return q
}

func (q *SelectQuery) WhereGroup(sep string, fn func(*SelectQuery) *SelectQuery) *SelectQuery {
	saved := q.where
	q.where = nil

	q = fn(q)

	where := q.where
	q.where = saved

	q.addWhereGroup(sep, where)

	return q
}

func (q *SelectQuery) WhereDeleted() *SelectQuery {
	q.whereDeleted()
	return q
}

func (q *SelectQuery) WhereAllWithDeleted() *SelectQuery {
	q.whereAllWithDeleted()
	return q
}

//------------------------------------------------------------------------------

func (q *SelectQuery) UseIndex(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addUseIndex(indexes...)
	}
	return q
}

func (q *SelectQuery) UseIndexForJoin(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addUseIndexForJoin(indexes...)
	}
	return q
}

func (q *SelectQuery) UseIndexForOrderBy(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addUseIndexForOrderBy(indexes...)
	}
	return q
}

func (q *SelectQuery) UseIndexForGroupBy(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addUseIndexForGroupBy(indexes...)
	}
	return q
}

func (q *SelectQuery) IgnoreIndex(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addIgnoreIndex(indexes...)
	}
	return q
}

func (q *SelectQuery) IgnoreIndexForJoin(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addIgnoreIndexForJoin(indexes...)
	}
	return q
}

func (q *SelectQuery) IgnoreIndexForOrderBy(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addIgnoreIndexForOrderBy(indexes...)
	}
	return q
}

func (q *SelectQuery) IgnoreIndexForGroupBy(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addIgnoreIndexForGroupBy(indexes...)
	}
	return q
}

func (q *SelectQuery) ForceIndex(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addForceIndex(indexes...)
	}
	return q
}

func (q *SelectQuery) ForceIndexForJoin(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addForceIndexForJoin(indexes...)
	}
	return q
}

func (q *SelectQuery) ForceIndexForOrderBy(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addForceIndexForOrderBy(indexes...)
	}
	return q
}

func (q *SelectQuery) ForceIndexForGroupBy(indexes ...string) *SelectQuery {
	if q.db.dialect.Name() == dialect.MySQL {
		q.addForceIndexForGroupBy(indexes...)
	}
	return q
}

//------------------------------------------------------------------------------

func (q *SelectQuery) Group(columns ...string) *SelectQuery {
	for _, column := range columns {
		q.group = append(q.group, schema.UnsafeIdent(column))
	}
	return q
}

func (q *SelectQuery) GroupExpr(group string, args ...interface{}) *SelectQuery {
	q.group = append(q.group, schema.SafeQuery(group, args))
	return q
}

func (q *SelectQuery) Having(having string, args ...interface{}) *SelectQuery {
	q.having = append(q.having, schema.SafeQuery(having, args))
	return q
}

func (q *SelectQuery) Order(orders ...string) *SelectQuery {
	for _, order := range orders {
		if order == "" {
			continue
		}

		index := strings.IndexByte(order, ' ')
		if index == -1 {
			q.order = append(q.order, schema.UnsafeIdent(order))
			continue
		}

		field := order[:index]
		sort := order[index+1:]

		switch strings.ToUpper(sort) {
		case "ASC", "DESC", "ASC NULLS FIRST", "DESC NULLS FIRST",
			"ASC NULLS LAST", "DESC NULLS LAST":
			q.order = append(q.order, schema.SafeQuery("? ?", []interface{}{
				Ident(field),
				Safe(sort),
			}))
		default:
			q.order = append(q.order, schema.UnsafeIdent(order))
		}
	}
	return q
}

func (q *SelectQuery) OrderExpr(query string, args ...interface{}) *SelectQuery {
	q.order = append(q.order, schema.SafeQuery(query, args))
	return q
}

func (q *SelectQuery) Limit(n int) *SelectQuery {
	q.limit = int32(n)
	return q
}

func (q *SelectQuery) Offset(n int) *SelectQuery {
	q.offset = int32(n)
	return q
}

func (q *SelectQuery) For(s string, args ...interface{}) *SelectQuery {
	q.selFor = schema.SafeQuery(s, args)
	return q
}

//------------------------------------------------------------------------------

func (q *SelectQuery) Union(other *SelectQuery) *SelectQuery {
	return q.addUnion(" UNION ", other)
}

func (q *SelectQuery) UnionAll(other *SelectQuery) *SelectQuery {
	return q.addUnion(" UNION ALL ", other)
}

func (q *SelectQuery) Intersect(other *SelectQuery) *SelectQuery {
	return q.addUnion(" INTERSECT ", other)
}

func (q *SelectQuery) IntersectAll(other *SelectQuery) *SelectQuery {
	return q.addUnion(" INTERSECT ALL ", other)
}

func (q *SelectQuery) Except(other *SelectQuery) *SelectQuery {
	return q.addUnion(" EXCEPT ", other)
}

func (q *SelectQuery) ExceptAll(other *SelectQuery) *SelectQuery {
	return q.addUnion(" EXCEPT ALL ", other)
}

func (q *SelectQuery) addUnion(expr string, other *SelectQuery) *SelectQuery {
	q.union = append(q.union, union{
		expr:  expr,
		query: other,
	})
	return q
}

//------------------------------------------------------------------------------

func (q *SelectQuery) Join(join string, args ...interface{}) *SelectQuery {
	q.joins = append(q.joins, joinQuery{
		join: schema.SafeQuery(join, args),
	})
	return q
}

func (q *SelectQuery) JoinOn(cond string, args ...interface{}) *SelectQuery {
	return q.joinOn(cond, args, " AND ")
}

func (q *SelectQuery) JoinOnOr(cond string, args ...interface{}) *SelectQuery {
	return q.joinOn(cond, args, " OR ")
}

func (q *SelectQuery) joinOn(cond string, args []interface{}, sep string) *SelectQuery {
	if len(q.joins) == 0 {
		q.err = errors.New("bun: query has no joins")
		return q
	}
	j := &q.joins[len(q.joins)-1]
	j.on = append(j.on, schema.SafeQueryWithSep(cond, args, sep))
	return q
}

//------------------------------------------------------------------------------

// Relation adds a relation to the query.
func (q *SelectQuery) Relation(name string, apply ...func(*SelectQuery) *SelectQuery) *SelectQuery {
	if len(apply) > 1 {
		panic("only one apply function is supported")
	}

	if q.tableModel == nil {
		q.setErr(errNilModel)
		return q
	}

	join := q.tableModel.join(name)
	if join == nil {
		q.setErr(fmt.Errorf("%s does not have relation=%q", q.table, name))
		return q
	}

	var apply1, apply2 func(*SelectQuery) *SelectQuery

	if len(join.Relation.Condition) > 0 {
		apply1 = func(q *SelectQuery) *SelectQuery {
			for _, opt := range join.Relation.Condition {
				q.addWhere(schema.SafeQueryWithSep(opt, nil, " AND "))
			}

			return q
		}
	}

	if len(apply) == 1 {
		apply2 = apply[0]
	}

	join.apply = func(q *SelectQuery) *SelectQuery {
		if apply1 != nil {
			q = apply1(q)
		}
		if apply2 != nil {
			q = apply2(q)
		}

		return q
	}

	return q
}

func (q *SelectQuery) forEachInlineRelJoin(fn func(*relationJoin) error) error {
	if q.tableModel == nil {
		return nil
	}
	return q._forEachInlineRelJoin(fn, q.tableModel.getJoins())
}

func (q *SelectQuery) _forEachInlineRelJoin(fn func(*relationJoin) error, joins []relationJoin) error {
	for i := range joins {
		j := &joins[i]
		switch j.Relation.Type {
		case schema.HasOneRelation, schema.BelongsToRelation:
			if err := fn(j); err != nil {
				return err
			}
			if err := q._forEachInlineRelJoin(fn, j.JoinModel.getJoins()); err != nil {
				return err
			}
		}
	}
	return nil
}

func (q *SelectQuery) selectJoins(ctx context.Context, joins []relationJoin) error {
	for i := range joins {
		j := &joins[i]

		var err error

		switch j.Relation.Type {
		case schema.HasOneRelation, schema.BelongsToRelation:
			err = q.selectJoins(ctx, j.JoinModel.getJoins())
		case schema.HasManyRelation:
			err = j.selectMany(ctx, q.db.NewSelect().Conn(q.conn))
		case schema.ManyToManyRelation:
			err = j.selectM2M(ctx, q.db.NewSelect().Conn(q.conn))
		default:
			panic("not reached")
		}

		if err != nil {
			return err
		}
	}
	return nil
}

//------------------------------------------------------------------------------

func (q *SelectQuery) Operation() string {
	return "SELECT"
}

func (q *SelectQuery) AppendQuery(fmter schema.Formatter, b []byte) (_ []byte, err error) {
	return q.appendQuery(fmter, b, false)
}

func (q *SelectQuery) appendQuery(
	fmter schema.Formatter, b []byte, count bool,
) (_ []byte, err error) {
	if q.err != nil {
		return nil, q.err
	}

	fmter = formatterWithModel(fmter, q)

	cteCount := count && (len(q.group) > 0 || q.distinctOn != nil)
	if cteCount {
		b = append(b, "WITH _count_wrapper AS ("...)
	}

	if len(q.union) > 0 {
		b = append(b, '(')
	}

	b, err = q.appendWith(fmter, b)
	if err != nil {
		return nil, err
	}

	b = append(b, "SELECT "...)

	if len(q.distinctOn) > 0 {
		b = append(b, "DISTINCT ON ("...)
		for i, app := range q.distinctOn {
			if i > 0 {
				b = append(b, ", "...)
			}
			b, err = app.AppendQuery(fmter, b)
			if err != nil {
				return nil, err
			}
		}
		b = append(b, ") "...)
	} else if q.distinctOn != nil {
		b = append(b, "DISTINCT "...)
	}

	if count && !cteCount {
		b = append(b, "count(*)"...)
	} else {
		b, err = q.appendColumns(fmter, b)
		if err != nil {
			return nil, err
		}
	}

	if q.hasTables() {
		b, err = q.appendTables(fmter, b)
		if err != nil {
			return nil, err
		}
	}

	if err := q.forEachInlineRelJoin(func(j *relationJoin) error {
		b = append(b, ' ')
		b, err = j.appendHasOneJoin(fmter, b, q)
		return err
	}); err != nil {
		return nil, err
	}

	for _, j := range q.joins {
		b, err = j.AppendQuery(fmter, b)
		if err != nil {
			return nil, err
		}
	}

	b, err = q.appendIndexHints(fmter, b)
	if err != nil {
		return nil, err
	}

	b, err = q.appendWhere(fmter, b, true)
	if err != nil {
		return nil, err
	}

	if len(q.group) > 0 {
		b = append(b, " GROUP BY "...)
		for i, f := range q.group {
			if i > 0 {
				b = append(b, ", "...)
			}
			b, err = f.AppendQuery(fmter, b)
			if err != nil {
				return nil, err
			}
		}
	}

	if len(q.having) > 0 {
		b = append(b, " HAVING "...)
		for i, f := range q.having {
			if i > 0 {
				b = append(b, " AND "...)
			}
			b = append(b, '(')
			b, err = f.AppendQuery(fmter, b)
			if err != nil {
				return nil, err
			}
			b = append(b, ')')
		}
	}

	if !count {
		b, err = q.appendOrder(fmter, b)
		if err != nil {
			return nil, err
		}

		if fmter.Dialect().Features().Has(feature.OffsetFetch) {
			if q.limit > 0 && q.offset > 0 {
				b = append(b, " OFFSET "...)
				b = strconv.AppendInt(b, int64(q.offset), 10)
				b = append(b, " ROWS"...)

				b = append(b, " FETCH NEXT "...)
				b = strconv.AppendInt(b, int64(q.limit), 10)
				b = append(b, " ROWS ONLY"...)
			} else if q.limit > 0 {
				b = append(b, " OFFSET 0 ROWS"...)

				b = append(b, " FETCH NEXT "...)
				b = strconv.AppendInt(b, int64(q.limit), 10)
				b = append(b, " ROWS ONLY"...)
			} else if q.offset > 0 {
				b = append(b, " OFFSET "...)
				b = strconv.AppendInt(b, int64(q.offset), 10)
				b = append(b, " ROWS"...)
			}
		} else {
			if q.limit > 0 {
				b = append(b, " LIMIT "...)
				b = strconv.AppendInt(b, int64(q.limit), 10)
			}
			if q.offset > 0 {
				b = append(b, " OFFSET "...)
				b = strconv.AppendInt(b, int64(q.offset), 10)
			}
		}

		if !q.selFor.IsZero() {
			b = append(b, " FOR "...)
			b, err = q.selFor.AppendQuery(fmter, b)
			if err != nil {
				return nil, err
			}
		}
	}

	if len(q.union) > 0 {
		b = append(b, ')')

		for _, u := range q.union {
			b = append(b, u.expr...)
			b = append(b, '(')
			b, err = u.query.AppendQuery(fmter, b)
			if err != nil {
				return nil, err
			}
			b = append(b, ')')
		}
	}

	if cteCount {
		b = append(b, ") SELECT count(*) FROM _count_wrapper"...)
	}

	return b, nil
}

func (q *SelectQuery) appendColumns(fmter schema.Formatter, b []byte) (_ []byte, err error) {
	start := len(b)

	switch {
	case q.columns != nil:
		for i, col := range q.columns {
			if i > 0 {
				b = append(b, ", "...)
			}

			if col.Args == nil && q.table != nil {
				if field, ok := q.table.FieldMap[col.Query]; ok {
					b = append(b, q.table.SQLAlias...)
					b = append(b, '.')
					b = append(b, field.SQLName...)
					continue
				}
			}

			b, err = col.AppendQuery(fmter, b)
			if err != nil {
				return nil, err
			}
		}
	case q.table != nil:
		if len(q.table.Fields) > 10 && fmter.IsNop() {
			b = append(b, q.table.SQLAlias...)
			b = append(b, '.')
			b = fmter.Dialect().AppendString(b, fmt.Sprintf("%d columns", len(q.table.Fields)))
		} else {
			b = appendColumns(b, q.table.SQLAlias, q.table.Fields)
		}
	default:
		b = append(b, '*')
	}

	if err := q.forEachInlineRelJoin(func(join *relationJoin) error {
		if len(b) != start {
			b = append(b, ", "...)
			start = len(b)
		}

		b, err = q.appendInlineRelColumns(fmter, b, join)
		if err != nil {
			return err
		}

		return nil
	}); err != nil {
		return nil, err
	}

	b = bytes.TrimSuffix(b, []byte(", "))

	return b, nil
}

func (q *SelectQuery) appendInlineRelColumns(
	fmter schema.Formatter, b []byte, join *relationJoin,
) (_ []byte, err error) {
	join.applyTo(q)

	if join.columns != nil {
		table := join.JoinModel.Table()
		for i, col := range join.columns {
			if i > 0 {
				b = append(b, ", "...)
			}

			if col.Args == nil {
				if field, ok := table.FieldMap[col.Query]; ok {
					b = join.appendAlias(fmter, b)
					b = append(b, '.')
					b = append(b, field.SQLName...)
					b = append(b, " AS "...)
					b = join.appendAliasColumn(fmter, b, field.Name)
					continue
				}
			}

			b, err = col.AppendQuery(fmter, b)
			if err != nil {
				return nil, err
			}
		}
		return b, nil
	}

	for i, field := range join.JoinModel.Table().Fields {
		if i > 0 {
			b = append(b, ", "...)
		}
		b = join.appendAlias(fmter, b)
		b = append(b, '.')
		b = append(b, field.SQLName...)
		b = append(b, " AS "...)
		b = join.appendAliasColumn(fmter, b, field.Name)
	}
	return b, nil
}

func (q *SelectQuery) appendTables(fmter schema.Formatter, b []byte) (_ []byte, err error) {
	b = append(b, " FROM "...)
	return q.appendTablesWithAlias(fmter, b)
}

func (q *SelectQuery) appendOrder(fmter schema.Formatter, b []byte) (_ []byte, err error) {
	if len(q.order) > 0 {
		b = append(b, " ORDER BY "...)

		for i, f := range q.order {
			if i > 0 {
				b = append(b, ", "...)
			}
			b, err = f.AppendQuery(fmter, b)
			if err != nil {
				return nil, err
			}
		}

		return b, nil
	}
	return b, nil
}

//------------------------------------------------------------------------------

func (q *SelectQuery) Rows(ctx context.Context) (*sql.Rows, error) {
	if q.err != nil {
		return nil, q.err
	}

	if err := q.beforeAppendModel(ctx, q); err != nil {
		return nil, err
	}

	queryBytes, err := q.AppendQuery(q.db.fmter, q.db.makeQueryBytes())
	if err != nil {
		return nil, err
	}

	query := internal.String(queryBytes)
	return q.conn.QueryContext(ctx, query)
}

func (q *SelectQuery) Exec(ctx context.Context, dest ...interface{}) (res sql.Result, err error) {
	if q.err != nil {
		return nil, q.err
	}
	if err := q.beforeAppendModel(ctx, q); err != nil {
		return nil, err
	}

	queryBytes, err := q.AppendQuery(q.db.fmter, q.db.makeQueryBytes())
	if err != nil {
		return nil, err
	}

	query := internal.String(queryBytes)

	if len(dest) > 0 {
		model, err := q.getModel(dest)
		if err != nil {
			return nil, err
		}

		res, err = q.scan(ctx, q, query, model, true)
		if err != nil {
			return nil, err
		}
	} else {
		res, err = q.exec(ctx, q, query)
		if err != nil {
			return nil, err
		}
	}

	return res, nil
}

func (q *SelectQuery) Scan(ctx context.Context, dest ...interface{}) error {
	if q.err != nil {
		return q.err
	}

	model, err := q.getModel(dest)
	if err != nil {
		return err
	}

	if q.table != nil {
		if err := q.beforeSelectHook(ctx); err != nil {
			return err
		}
	}

	if err := q.beforeAppendModel(ctx, q); err != nil {
		return err
	}

	queryBytes, err := q.AppendQuery(q.db.fmter, q.db.makeQueryBytes())
	if err != nil {
		return err
	}

	query := internal.String(queryBytes)

	res, err := q.scan(ctx, q, query, model, true)
	if err != nil {
		return err
	}

	if n, _ := res.RowsAffected(); n > 0 {
		if tableModel, ok := model.(TableModel); ok {
			if err := q.selectJoins(ctx, tableModel.getJoins()); err != nil {
				return err
			}
		}
	}

	if q.table != nil {
		if err := q.afterSelectHook(ctx); err != nil {
			return err
		}
	}

	return nil
}

func (q *SelectQuery) beforeSelectHook(ctx context.Context) error {
	if hook, ok := q.table.ZeroIface.(BeforeSelectHook); ok {
		if err := hook.BeforeSelect(ctx, q); err != nil {
			return err
		}
	}
	return nil
}

func (q *SelectQuery) afterSelectHook(ctx context.Context) error {
	if hook, ok := q.table.ZeroIface.(AfterSelectHook); ok {
		if err := hook.AfterSelect(ctx, q); err != nil {
			return err
		}
	}
	return nil
}

func (q *SelectQuery) Count(ctx context.Context) (int, error) {
	if q.err != nil {
		return 0, q.err
	}

	qq := countQuery{q}

	queryBytes, err := qq.AppendQuery(q.db.fmter, nil)
	if err != nil {
		return 0, err
	}

	query := internal.String(queryBytes)
	ctx, event := q.db.beforeQuery(ctx, qq, query, nil, query, q.model)

	var num int
	err = q.conn.QueryRowContext(ctx, query).Scan(&num)

	q.db.afterQuery(ctx, event, nil, err)

	return num, err
}

func (q *SelectQuery) ScanAndCount(ctx context.Context, dest ...interface{}) (int, error) {
	if _, ok := q.conn.(*DB); ok {
		return q.scanAndCountConc(ctx, dest...)
	}
	return q.scanAndCountSeq(ctx, dest...)
}

func (q *SelectQuery) scanAndCountConc(ctx context.Context, dest ...interface{}) (int, error) {
	var count int
	var wg sync.WaitGroup
	var mu sync.Mutex
	var firstErr error

	if q.limit >= 0 {
		wg.Add(1)
		go func() {
			defer wg.Done()

			if err := q.Scan(ctx, dest...); err != nil {
				mu.Lock()
				if firstErr == nil {
					firstErr = err
				}
				mu.Unlock()
			}
		}()
	}

	wg.Add(1)
	go func() {
		defer wg.Done()

		var err error
		count, err = q.Count(ctx)
		if err != nil {
			mu.Lock()
			if firstErr == nil {
				firstErr = err
			}
			mu.Unlock()
		}
	}()

	wg.Wait()
	return count, firstErr
}

func (q *SelectQuery) scanAndCountSeq(ctx context.Context, dest ...interface{}) (int, error) {
	var firstErr error

	if q.limit >= 0 {
		firstErr = q.Scan(ctx, dest...)
	}

	count, err := q.Count(ctx)
	if err != nil && firstErr == nil {
		firstErr = err
	}

	return count, firstErr
}

func (q *SelectQuery) Exists(ctx context.Context) (bool, error) {
	if q.err != nil {
		return false, q.err
	}

	if q.hasFeature(feature.SelectExists) {
		return q.selectExists(ctx)
	}
	return q.whereExists(ctx)
}

func (q *SelectQuery) selectExists(ctx context.Context) (bool, error) {
	qq := selectExistsQuery{q}

	queryBytes, err := qq.AppendQuery(q.db.fmter, nil)
	if err != nil {
		return false, err
	}

	query := internal.String(queryBytes)
	ctx, event := q.db.beforeQuery(ctx, qq, query, nil, query, q.model)

	var exists bool
	err = q.conn.QueryRowContext(ctx, query).Scan(&exists)

	q.db.afterQuery(ctx, event, nil, err)

	return exists, err
}

func (q *SelectQuery) whereExists(ctx context.Context) (bool, error) {
	qq := whereExistsQuery{q}

	queryBytes, err := qq.AppendQuery(q.db.fmter, nil)
	if err != nil {
		return false, err
	}

	query := internal.String(queryBytes)
	res, err := q.exec(ctx, qq, query)
	if err != nil {
		return false, err
	}

	n, err := res.RowsAffected()
	if err != nil {
		return false, err
	}

	return n == 1, nil
}

func (q *SelectQuery) String() string {
	buf, err := q.AppendQuery(q.db.Formatter(), nil)
	if err != nil {
		panic(err)
	}

	return string(buf)
}

//------------------------------------------------------------------------------

func (q *SelectQuery) QueryBuilder() QueryBuilder {
	return &selectQueryBuilder{q}
}

func (q *SelectQuery) ApplyQueryBuilder(fn func(QueryBuilder) QueryBuilder) *SelectQuery {
	return fn(q.QueryBuilder()).Unwrap().(*SelectQuery)
}

type selectQueryBuilder struct {
	*SelectQuery
}

func (q *selectQueryBuilder) WhereGroup(
	sep string, fn func(QueryBuilder) QueryBuilder,
) QueryBuilder {
	q.SelectQuery = q.SelectQuery.WhereGroup(sep, func(qs *SelectQuery) *SelectQuery {
		return fn(q).(*selectQueryBuilder).SelectQuery
	})
	return q
}

func (q *selectQueryBuilder) Where(query string, args ...interface{}) QueryBuilder {
	q.SelectQuery.Where(query, args...)
	return q
}

func (q *selectQueryBuilder) WhereOr(query string, args ...interface{}) QueryBuilder {
	q.SelectQuery.WhereOr(query, args...)
	return q
}

func (q *selectQueryBuilder) WhereDeleted() QueryBuilder {
	q.SelectQuery.WhereDeleted()
	return q
}

func (q *selectQueryBuilder) WhereAllWithDeleted() QueryBuilder {
	q.SelectQuery.WhereAllWithDeleted()
	return q
}

func (q *selectQueryBuilder) WherePK(cols ...string) QueryBuilder {
	q.SelectQuery.WherePK(cols...)
	return q
}

func (q *selectQueryBuilder) Unwrap() interface{} {
	return q.SelectQuery
}

//------------------------------------------------------------------------------

type joinQuery struct {
	join schema.QueryWithArgs
	on   []schema.QueryWithSep
}

func (j *joinQuery) AppendQuery(fmter schema.Formatter, b []byte) (_ []byte, err error) {
	b = append(b, ' ')

	b, err = j.join.AppendQuery(fmter, b)
	if err != nil {
		return nil, err
	}

	if len(j.on) > 0 {
		b = append(b, " ON "...)
		for i, on := range j.on {
			if i > 0 {
				b = append(b, on.Sep...)
			}

			b = append(b, '(')
			b, err = on.AppendQuery(fmter, b)
			if err != nil {
				return nil, err
			}
			b = append(b, ')')
		}
	}

	return b, nil
}

//------------------------------------------------------------------------------

type countQuery struct {
	*SelectQuery
}

func (q countQuery) AppendQuery(fmter schema.Formatter, b []byte) (_ []byte, err error) {
	if q.err != nil {
		return nil, q.err
	}
	return q.appendQuery(fmter, b, true)
}

//------------------------------------------------------------------------------

type selectExistsQuery struct {
	*SelectQuery
}

func (q selectExistsQuery) AppendQuery(fmter schema.Formatter, b []byte) (_ []byte, err error) {
	if q.err != nil {
		return nil, q.err
	}

	b = append(b, "SELECT EXISTS ("...)

	b, err = q.appendQuery(fmter, b, false)
	if err != nil {
		return nil, err
	}

	b = append(b, ")"...)

	return b, nil
}

//------------------------------------------------------------------------------

type whereExistsQuery struct {
	*SelectQuery
}

func (q whereExistsQuery) AppendQuery(fmter schema.Formatter, b []byte) (_ []byte, err error) {
	if q.err != nil {
		return nil, q.err
	}

	b = append(b, "SELECT 1 WHERE EXISTS ("...)

	b, err = q.appendQuery(fmter, b, false)
	if err != nil {
		return nil, err
	}

	b = append(b, ")"...)

	return b, nil
}