package bun

import (
	"context"
	"crypto/rand"
	"database/sql"
	"encoding/hex"
	"fmt"
	"reflect"
	"strings"
	"sync/atomic"
	"time"

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

const (
	discardUnknownColumns internal.Flag = 1 << iota
)

type DBStats struct {
	Queries uint32
	Errors  uint32
}

type DBOption func(db *DB)

func WithOptions(opts ...DBOption) DBOption {
	return func(db *DB) {
		for _, opt := range opts {
			opt(db)
		}
	}
}

func WithDiscardUnknownColumns() DBOption {
	return func(db *DB) {
		db.flags = db.flags.Set(discardUnknownColumns)
	}
}

func WithConnResolver(resolver ConnResolver) DBOption {
	return func(db *DB) {
		db.resolver = resolver
	}
}

type DB struct {
	// Must be a pointer so we copy the whole state, not individual fields.
	*noCopyState

	queryHooks []QueryHook

	fmter schema.Formatter
	stats DBStats
}

// noCopyState contains DB fields that must not be copied on clone(),
// for example, it is forbidden to copy atomic.Pointer.
type noCopyState struct {
	*sql.DB
	dialect  schema.Dialect
	resolver ConnResolver

	flags  internal.Flag
	closed atomic.Bool
}

func NewDB(sqldb *sql.DB, dialect schema.Dialect, opts ...DBOption) *DB {
	dialect.Init(sqldb)

	db := &DB{
		noCopyState: &noCopyState{
			DB:      sqldb,
			dialect: dialect,
		},
		fmter: schema.NewFormatter(dialect),
	}

	for _, opt := range opts {
		opt(db)
	}

	return db
}

func (db *DB) String() string {
	var b strings.Builder
	b.WriteString("DB<dialect=")
	b.WriteString(db.dialect.Name().String())
	b.WriteString(">")
	return b.String()
}

func (db *DB) Close() error {
	if db.closed.Swap(true) {
		return nil
	}

	firstErr := db.DB.Close()

	if db.resolver != nil {
		if err := db.resolver.Close(); err != nil && firstErr == nil {
			firstErr = err
		}
	}

	return firstErr
}

func (db *DB) DBStats() DBStats {
	return DBStats{
		Queries: atomic.LoadUint32(&db.stats.Queries),
		Errors:  atomic.LoadUint32(&db.stats.Errors),
	}
}

func (db *DB) NewValues(model interface{}) *ValuesQuery {
	return NewValuesQuery(db, model)
}

func (db *DB) NewMerge() *MergeQuery {
	return NewMergeQuery(db)
}

func (db *DB) NewSelect() *SelectQuery {
	return NewSelectQuery(db)
}

func (db *DB) NewInsert() *InsertQuery {
	return NewInsertQuery(db)
}

func (db *DB) NewUpdate() *UpdateQuery {
	return NewUpdateQuery(db)
}

func (db *DB) NewDelete() *DeleteQuery {
	return NewDeleteQuery(db)
}

func (db *DB) NewRaw(query string, args ...interface{}) *RawQuery {
	return NewRawQuery(db, query, args...)
}

func (db *DB) NewCreateTable() *CreateTableQuery {
	return NewCreateTableQuery(db)
}

func (db *DB) NewDropTable() *DropTableQuery {
	return NewDropTableQuery(db)
}

func (db *DB) NewCreateIndex() *CreateIndexQuery {
	return NewCreateIndexQuery(db)
}

func (db *DB) NewDropIndex() *DropIndexQuery {
	return NewDropIndexQuery(db)
}

func (db *DB) NewTruncateTable() *TruncateTableQuery {
	return NewTruncateTableQuery(db)
}

func (db *DB) NewAddColumn() *AddColumnQuery {
	return NewAddColumnQuery(db)
}

func (db *DB) NewDropColumn() *DropColumnQuery {
	return NewDropColumnQuery(db)
}

func (db *DB) ResetModel(ctx context.Context, models ...interface{}) error {
	for _, model := range models {
		if _, err := db.NewDropTable().Model(model).IfExists().Cascade().Exec(ctx); err != nil {
			return err
		}
		if _, err := db.NewCreateTable().Model(model).Exec(ctx); err != nil {
			return err
		}
	}
	return nil
}

func (db *DB) Dialect() schema.Dialect {
	return db.dialect
}

func (db *DB) ScanRows(ctx context.Context, rows *sql.Rows, dest ...interface{}) error {
	defer rows.Close()

	model, err := newModel(db, dest)
	if err != nil {
		return err
	}

	_, err = model.ScanRows(ctx, rows)
	if err != nil {
		return err
	}

	return rows.Err()
}

func (db *DB) ScanRow(ctx context.Context, rows *sql.Rows, dest ...interface{}) error {
	model, err := newModel(db, dest)
	if err != nil {
		return err
	}

	rs, ok := model.(rowScanner)
	if !ok {
		return fmt.Errorf("bun: %T does not support ScanRow", model)
	}

	return rs.ScanRow(ctx, rows)
}

type queryHookIniter interface {
	Init(db *DB)
}

func (db *DB) AddQueryHook(hook QueryHook) {
	if initer, ok := hook.(queryHookIniter); ok {
		initer.Init(db)
	}
	db.queryHooks = append(db.queryHooks, hook)
}

func (db *DB) Table(typ reflect.Type) *schema.Table {
	return db.dialect.Tables().Get(typ)
}

// RegisterModel registers models by name so they can be referenced in table relations
// and fixtures.
func (db *DB) RegisterModel(models ...interface{}) {
	db.dialect.Tables().Register(models...)
}

func (db *DB) clone() *DB {
	clone := *db

	l := len(clone.queryHooks)
	clone.queryHooks = clone.queryHooks[:l:l]

	return &clone
}

func (db *DB) WithNamedArg(name string, value interface{}) *DB {
	clone := db.clone()
	clone.fmter = clone.fmter.WithNamedArg(name, value)
	return clone
}

func (db *DB) Formatter() schema.Formatter {
	return db.fmter
}

// UpdateFQN returns a fully qualified column name. For MySQL, it returns the column name with
// the table alias. For other RDBMS, it returns just the column name.
func (db *DB) UpdateFQN(alias, column string) Ident {
	if db.HasFeature(feature.UpdateMultiTable) {
		return Ident(alias + "." + column)
	}
	return Ident(column)
}

// HasFeature uses feature package to report whether the underlying DBMS supports this feature.
func (db *DB) HasFeature(feat feature.Feature) bool {
	return db.dialect.Features().Has(feat)
}

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

func (db *DB) Exec(query string, args ...interface{}) (sql.Result, error) {
	return db.ExecContext(context.Background(), query, args...)
}

func (db *DB) ExecContext(
	ctx context.Context, query string, args ...interface{},
) (sql.Result, error) {
	formattedQuery := db.format(query, args)
	ctx, event := db.beforeQuery(ctx, nil, query, args, formattedQuery, nil)
	res, err := db.DB.ExecContext(ctx, formattedQuery)
	db.afterQuery(ctx, event, res, err)
	return res, err
}

func (db *DB) Query(query string, args ...interface{}) (*sql.Rows, error) {
	return db.QueryContext(context.Background(), query, args...)
}

func (db *DB) QueryContext(
	ctx context.Context, query string, args ...interface{},
) (*sql.Rows, error) {
	formattedQuery := db.format(query, args)
	ctx, event := db.beforeQuery(ctx, nil, query, args, formattedQuery, nil)
	rows, err := db.DB.QueryContext(ctx, formattedQuery)
	db.afterQuery(ctx, event, nil, err)
	return rows, err
}

func (db *DB) QueryRow(query string, args ...interface{}) *sql.Row {
	return db.QueryRowContext(context.Background(), query, args...)
}

func (db *DB) QueryRowContext(ctx context.Context, query string, args ...interface{}) *sql.Row {
	formattedQuery := db.format(query, args)
	ctx, event := db.beforeQuery(ctx, nil, query, args, formattedQuery, nil)
	row := db.DB.QueryRowContext(ctx, formattedQuery)
	db.afterQuery(ctx, event, nil, row.Err())
	return row
}

func (db *DB) format(query string, args []interface{}) string {
	return db.fmter.FormatQuery(query, args...)
}

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

type Conn struct {
	db *DB
	*sql.Conn
}

func (db *DB) Conn(ctx context.Context) (Conn, error) {
	conn, err := db.DB.Conn(ctx)
	if err != nil {
		return Conn{}, err
	}
	return Conn{
		db:   db,
		Conn: conn,
	}, nil
}

func (c Conn) ExecContext(
	ctx context.Context, query string, args ...interface{},
) (sql.Result, error) {
	formattedQuery := c.db.format(query, args)
	ctx, event := c.db.beforeQuery(ctx, nil, query, args, formattedQuery, nil)
	res, err := c.Conn.ExecContext(ctx, formattedQuery)
	c.db.afterQuery(ctx, event, res, err)
	return res, err
}

func (c Conn) QueryContext(
	ctx context.Context, query string, args ...interface{},
) (*sql.Rows, error) {
	formattedQuery := c.db.format(query, args)
	ctx, event := c.db.beforeQuery(ctx, nil, query, args, formattedQuery, nil)
	rows, err := c.Conn.QueryContext(ctx, formattedQuery)
	c.db.afterQuery(ctx, event, nil, err)
	return rows, err
}

func (c Conn) QueryRowContext(ctx context.Context, query string, args ...interface{}) *sql.Row {
	formattedQuery := c.db.format(query, args)
	ctx, event := c.db.beforeQuery(ctx, nil, query, args, formattedQuery, nil)
	row := c.Conn.QueryRowContext(ctx, formattedQuery)
	c.db.afterQuery(ctx, event, nil, row.Err())
	return row
}

func (c Conn) Dialect() schema.Dialect {
	return c.db.Dialect()
}

func (c Conn) NewValues(model interface{}) *ValuesQuery {
	return NewValuesQuery(c.db, model).Conn(c)
}

func (c Conn) NewMerge() *MergeQuery {
	return NewMergeQuery(c.db).Conn(c)
}

func (c Conn) NewSelect() *SelectQuery {
	return NewSelectQuery(c.db).Conn(c)
}

func (c Conn) NewInsert() *InsertQuery {
	return NewInsertQuery(c.db).Conn(c)
}

func (c Conn) NewUpdate() *UpdateQuery {
	return NewUpdateQuery(c.db).Conn(c)
}

func (c Conn) NewDelete() *DeleteQuery {
	return NewDeleteQuery(c.db).Conn(c)
}

func (c Conn) NewRaw(query string, args ...interface{}) *RawQuery {
	return NewRawQuery(c.db, query, args...).Conn(c)
}

func (c Conn) NewCreateTable() *CreateTableQuery {
	return NewCreateTableQuery(c.db).Conn(c)
}

func (c Conn) NewDropTable() *DropTableQuery {
	return NewDropTableQuery(c.db).Conn(c)
}

func (c Conn) NewCreateIndex() *CreateIndexQuery {
	return NewCreateIndexQuery(c.db).Conn(c)
}

func (c Conn) NewDropIndex() *DropIndexQuery {
	return NewDropIndexQuery(c.db).Conn(c)
}

func (c Conn) NewTruncateTable() *TruncateTableQuery {
	return NewTruncateTableQuery(c.db).Conn(c)
}

func (c Conn) NewAddColumn() *AddColumnQuery {
	return NewAddColumnQuery(c.db).Conn(c)
}

func (c Conn) NewDropColumn() *DropColumnQuery {
	return NewDropColumnQuery(c.db).Conn(c)
}

// RunInTx runs the function in a transaction. If the function returns an error,
// the transaction is rolled back. Otherwise, the transaction is committed.
func (c Conn) RunInTx(
	ctx context.Context, opts *sql.TxOptions, fn func(ctx context.Context, tx Tx) error,
) error {
	tx, err := c.BeginTx(ctx, opts)
	if err != nil {
		return err
	}

	var done bool

	defer func() {
		if !done {
			_ = tx.Rollback()
		}
	}()

	if err := fn(ctx, tx); err != nil {
		return err
	}

	done = true
	return tx.Commit()
}

func (c Conn) BeginTx(ctx context.Context, opts *sql.TxOptions) (Tx, error) {
	ctx, event := c.db.beforeQuery(ctx, nil, "BEGIN", nil, "BEGIN", nil)
	tx, err := c.Conn.BeginTx(ctx, opts)
	c.db.afterQuery(ctx, event, nil, err)
	if err != nil {
		return Tx{}, err
	}
	return Tx{
		ctx: ctx,
		db:  c.db,
		Tx:  tx,
	}, nil
}

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

type Stmt struct {
	*sql.Stmt
}

func (db *DB) Prepare(query string) (Stmt, error) {
	return db.PrepareContext(context.Background(), query)
}

func (db *DB) PrepareContext(ctx context.Context, query string) (Stmt, error) {
	stmt, err := db.DB.PrepareContext(ctx, query)
	if err != nil {
		return Stmt{}, err
	}
	return Stmt{Stmt: stmt}, nil
}

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

type Tx struct {
	ctx context.Context
	db  *DB
	// name is the name of a savepoint
	name string
	*sql.Tx
}

// RunInTx runs the function in a transaction. If the function returns an error,
// the transaction is rolled back. Otherwise, the transaction is committed.
func (db *DB) RunInTx(
	ctx context.Context, opts *sql.TxOptions, fn func(ctx context.Context, tx Tx) error,
) error {
	tx, err := db.BeginTx(ctx, opts)
	if err != nil {
		return err
	}

	var done bool

	defer func() {
		if !done {
			_ = tx.Rollback()
		}
	}()

	if err := fn(ctx, tx); err != nil {
		return err
	}

	done = true
	return tx.Commit()
}

func (db *DB) Begin() (Tx, error) {
	return db.BeginTx(context.Background(), nil)
}

func (db *DB) BeginTx(ctx context.Context, opts *sql.TxOptions) (Tx, error) {
	ctx, event := db.beforeQuery(ctx, nil, "BEGIN", nil, "BEGIN", nil)
	tx, err := db.DB.BeginTx(ctx, opts)
	db.afterQuery(ctx, event, nil, err)
	if err != nil {
		return Tx{}, err
	}
	return Tx{
		ctx: ctx,
		db:  db,
		Tx:  tx,
	}, nil
}

func (tx Tx) Commit() error {
	if tx.name == "" {
		return tx.commitTX()
	}
	return tx.commitSP()
}

func (tx Tx) commitTX() error {
	ctx, event := tx.db.beforeQuery(tx.ctx, nil, "COMMIT", nil, "COMMIT", nil)
	err := tx.Tx.Commit()
	tx.db.afterQuery(ctx, event, nil, err)
	return err
}

func (tx Tx) commitSP() error {
	if tx.db.HasFeature(feature.MSSavepoint) {
		return nil
	}
	query := "RELEASE SAVEPOINT " + tx.name
	_, err := tx.ExecContext(tx.ctx, query)
	return err
}

func (tx Tx) Rollback() error {
	if tx.name == "" {
		return tx.rollbackTX()
	}
	return tx.rollbackSP()
}

func (tx Tx) rollbackTX() error {
	ctx, event := tx.db.beforeQuery(tx.ctx, nil, "ROLLBACK", nil, "ROLLBACK", nil)
	err := tx.Tx.Rollback()
	tx.db.afterQuery(ctx, event, nil, err)
	return err
}

func (tx Tx) rollbackSP() error {
	query := "ROLLBACK TO SAVEPOINT " + tx.name
	if tx.db.HasFeature(feature.MSSavepoint) {
		query = "ROLLBACK TRANSACTION " + tx.name
	}
	_, err := tx.ExecContext(tx.ctx, query)
	return err
}

func (tx Tx) Exec(query string, args ...interface{}) (sql.Result, error) {
	return tx.ExecContext(context.TODO(), query, args...)
}

func (tx Tx) ExecContext(
	ctx context.Context, query string, args ...interface{},
) (sql.Result, error) {
	formattedQuery := tx.db.format(query, args)
	ctx, event := tx.db.beforeQuery(ctx, nil, query, args, formattedQuery, nil)
	res, err := tx.Tx.ExecContext(ctx, formattedQuery)
	tx.db.afterQuery(ctx, event, res, err)
	return res, err
}

func (tx Tx) Query(query string, args ...interface{}) (*sql.Rows, error) {
	return tx.QueryContext(context.TODO(), query, args...)
}

func (tx Tx) QueryContext(
	ctx context.Context, query string, args ...interface{},
) (*sql.Rows, error) {
	formattedQuery := tx.db.format(query, args)
	ctx, event := tx.db.beforeQuery(ctx, nil, query, args, formattedQuery, nil)
	rows, err := tx.Tx.QueryContext(ctx, formattedQuery)
	tx.db.afterQuery(ctx, event, nil, err)
	return rows, err
}

func (tx Tx) QueryRow(query string, args ...interface{}) *sql.Row {
	return tx.QueryRowContext(context.TODO(), query, args...)
}

func (tx Tx) QueryRowContext(ctx context.Context, query string, args ...interface{}) *sql.Row {
	formattedQuery := tx.db.format(query, args)
	ctx, event := tx.db.beforeQuery(ctx, nil, query, args, formattedQuery, nil)
	row := tx.Tx.QueryRowContext(ctx, formattedQuery)
	tx.db.afterQuery(ctx, event, nil, row.Err())
	return row
}

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

func (tx Tx) Begin() (Tx, error) {
	return tx.BeginTx(tx.ctx, nil)
}

// BeginTx will save a point in the running transaction.
func (tx Tx) BeginTx(ctx context.Context, _ *sql.TxOptions) (Tx, error) {
	// mssql savepoint names are limited to 32 characters
	sp := make([]byte, 14)
	_, err := rand.Read(sp)
	if err != nil {
		return Tx{}, err
	}

	qName := "SP_" + hex.EncodeToString(sp)
	query := "SAVEPOINT " + qName
	if tx.db.HasFeature(feature.MSSavepoint) {
		query = "SAVE TRANSACTION " + qName
	}
	_, err = tx.ExecContext(ctx, query)
	if err != nil {
		return Tx{}, err
	}
	return Tx{
		ctx:  ctx,
		db:   tx.db,
		Tx:   tx.Tx,
		name: qName,
	}, nil
}

func (tx Tx) RunInTx(
	ctx context.Context, _ *sql.TxOptions, fn func(ctx context.Context, tx Tx) error,
) error {
	sp, err := tx.BeginTx(ctx, nil)
	if err != nil {
		return err
	}

	var done bool

	defer func() {
		if !done {
			_ = sp.Rollback()
		}
	}()

	if err := fn(ctx, sp); err != nil {
		return err
	}

	done = true
	return sp.Commit()
}

func (tx Tx) Dialect() schema.Dialect {
	return tx.db.Dialect()
}

func (tx Tx) NewValues(model interface{}) *ValuesQuery {
	return NewValuesQuery(tx.db, model).Conn(tx)
}

func (tx Tx) NewMerge() *MergeQuery {
	return NewMergeQuery(tx.db).Conn(tx)
}

func (tx Tx) NewSelect() *SelectQuery {
	return NewSelectQuery(tx.db).Conn(tx)
}

func (tx Tx) NewInsert() *InsertQuery {
	return NewInsertQuery(tx.db).Conn(tx)
}

func (tx Tx) NewUpdate() *UpdateQuery {
	return NewUpdateQuery(tx.db).Conn(tx)
}

func (tx Tx) NewDelete() *DeleteQuery {
	return NewDeleteQuery(tx.db).Conn(tx)
}

func (tx Tx) NewRaw(query string, args ...interface{}) *RawQuery {
	return NewRawQuery(tx.db, query, args...).Conn(tx)
}

func (tx Tx) NewCreateTable() *CreateTableQuery {
	return NewCreateTableQuery(tx.db).Conn(tx)
}

func (tx Tx) NewDropTable() *DropTableQuery {
	return NewDropTableQuery(tx.db).Conn(tx)
}

func (tx Tx) NewCreateIndex() *CreateIndexQuery {
	return NewCreateIndexQuery(tx.db).Conn(tx)
}

func (tx Tx) NewDropIndex() *DropIndexQuery {
	return NewDropIndexQuery(tx.db).Conn(tx)
}

func (tx Tx) NewTruncateTable() *TruncateTableQuery {
	return NewTruncateTableQuery(tx.db).Conn(tx)
}

func (tx Tx) NewAddColumn() *AddColumnQuery {
	return NewAddColumnQuery(tx.db).Conn(tx)
}

func (tx Tx) NewDropColumn() *DropColumnQuery {
	return NewDropColumnQuery(tx.db).Conn(tx)
}

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

func (db *DB) makeQueryBytes() []byte {
	return internal.MakeQueryBytes()
}

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

// ConnResolver enables routing queries to multiple databases.
type ConnResolver interface {
	ResolveConn(query Query) IConn
	Close() error
}

// TODO:
//   - make monitoring interval configurable
//   - make ping timeout configutable
//   - allow adding read/write replicas for multi-master replication
type ReadWriteConnResolver struct {
	replicas        []*sql.DB // read-only replicas
	healthyReplicas atomic.Pointer[[]*sql.DB]
	nextReplica     atomic.Int64
	closed          atomic.Bool
}

func NewReadWriteConnResolver(opts ...ReadWriteConnResolverOption) *ReadWriteConnResolver {
	r := new(ReadWriteConnResolver)

	for _, opt := range opts {
		opt(r)
	}

	if len(r.replicas) > 0 {
		r.healthyReplicas.Store(&r.replicas)
		go r.monitor()
	}

	return r
}

type ReadWriteConnResolverOption func(r *ReadWriteConnResolver)

func WithReadOnlyReplica(dbs ...*sql.DB) ReadWriteConnResolverOption {
	return func(r *ReadWriteConnResolver) {
		r.replicas = append(r.replicas, dbs...)
	}
}

func (r *ReadWriteConnResolver) Close() error {
	if r.closed.Swap(true) {
		return nil
	}

	var firstErr error
	for _, db := range r.replicas {
		if err := db.Close(); err != nil && firstErr == nil {
			firstErr = err
		}
	}
	return firstErr
}

// healthyReplica returns a random healthy replica.
func (r *ReadWriteConnResolver) ResolveConn(query Query) IConn {
	if len(r.replicas) == 0 || !isReadOnlyQuery(query) {
		return nil
	}

	replicas := r.loadHealthyReplicas()
	if len(replicas) == 0 {
		return nil
	}
	if len(replicas) == 1 {
		return replicas[0]
	}
	i := r.nextReplica.Add(1)
	return replicas[int(i)%len(replicas)]
}

func isReadOnlyQuery(query Query) bool {
	sel, ok := query.(*SelectQuery)
	if !ok {
		return false
	}
	for _, el := range sel.with {
		if !isReadOnlyQuery(el.query) {
			return false
		}
	}
	return true
}

func (r *ReadWriteConnResolver) loadHealthyReplicas() []*sql.DB {
	if ptr := r.healthyReplicas.Load(); ptr != nil {
		return *ptr
	}
	return nil
}

func (r *ReadWriteConnResolver) monitor() {
	const interval = 5 * time.Second
	for !r.closed.Load() {
		healthy := make([]*sql.DB, 0, len(r.replicas))

		for _, replica := range r.replicas {
			ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
			err := replica.PingContext(ctx)
			cancel()

			if err == nil {
				healthy = append(healthy, replica)
			}
		}

		r.healthyReplicas.Store(&healthy)
		time.Sleep(interval)
	}
}