// Package mysql wraps the github.com/go-sql-driver/mysql MySQL driver. See
// https://github.com/upper/db/adapter/mysql for documentation, particularities and usage
// examples.
package mysql

import (
	"reflect"
	"strings"

	"database/sql"

	"git.hexq.cn/tiglog/mydb"
	"git.hexq.cn/tiglog/mydb/internal/sqladapter"
	"git.hexq.cn/tiglog/mydb/internal/sqladapter/exql"
	_ "github.com/go-sql-driver/mysql" // MySQL driver.
)

// database is the actual implementation of Database
type database struct {
}

func (*database) Template() *exql.Template {
	return template
}

func (*database) OpenDSN(sess sqladapter.Session, dsn string) (*sql.DB, error) {
	return sql.Open("mysql", dsn)
}

func (*database) Collections(sess sqladapter.Session) (collections []string, err error) {
	q := sess.SQL().
		Select("table_name").
		From("information_schema.tables").
		Where("table_schema = ?", sess.Name())

	iter := q.Iterator()
	defer iter.Close()

	for iter.Next() {
		var tableName string
		if err := iter.Scan(&tableName); err != nil {
			return nil, err
		}
		collections = append(collections, tableName)
	}
	if err := iter.Err(); err != nil {
		return nil, err
	}

	return collections, nil
}

func (d *database) ConvertValue(in interface{}) interface{} {
	switch v := in.(type) {
	case *map[string]interface{}:
		return (*JSONMap)(v)

	case map[string]interface{}:
		return (*JSONMap)(&v)
	}

	dv := reflect.ValueOf(in)
	if dv.IsValid() {
		if dv.Type().Kind() == reflect.Ptr {
			dv = dv.Elem()
		}

		switch dv.Kind() {
		case reflect.Map:
			if reflect.TypeOf(in).Kind() == reflect.Ptr {
				w := reflect.ValueOf(in)
				z := reflect.New(w.Elem().Type())
				w.Elem().Set(z.Elem())
			}
			return &JSON{in}
		case reflect.Slice:
			return &JSON{in}
		}
	}

	return in
}

func (*database) Err(err error) error {
	if err != nil {
		// This error is not exported so we have to check it by its string value.
		s := err.Error()
		if strings.Contains(s, `many connections`) {
			return mydb.ErrTooManyClients
		}
	}
	return err
}

func (*database) NewCollection() sqladapter.CollectionAdapter {
	return &collectionAdapter{}
}

func (*database) LookupName(sess sqladapter.Session) (string, error) {
	q := sess.SQL().
		Select(mydb.Raw("DATABASE() AS name"))

	iter := q.Iterator()
	defer iter.Close()

	if iter.Next() {
		var name string
		if err := iter.Scan(&name); err != nil {
			return "", err
		}
		return name, nil
	}

	return "", iter.Err()
}

func (*database) TableExists(sess sqladapter.Session, name string) error {
	q := sess.SQL().
		Select("table_name").
		From("information_schema.tables").
		Where("table_schema = ? AND table_name = ?", sess.Name(), name)

	iter := q.Iterator()
	defer iter.Close()

	if iter.Next() {
		var name string
		if err := iter.Scan(&name); err != nil {
			return err
		}
		return nil
	}
	if err := iter.Err(); err != nil {
		return err
	}

	return mydb.ErrCollectionDoesNotExist
}

func (*database) PrimaryKeys(sess sqladapter.Session, tableName string) ([]string, error) {
	q := sess.SQL().
		Select("k.column_name").
		From("information_schema.key_column_usage AS k").
		Where(`
			k.constraint_name = 'PRIMARY'
			AND k.table_schema = ?
			AND k.table_name = ?
		`, sess.Name(), tableName).
		OrderBy("k.ordinal_position")

	iter := q.Iterator()
	defer iter.Close()

	pk := []string{}

	for iter.Next() {
		var k string
		if err := iter.Scan(&k); err != nil {
			return nil, err
		}
		pk = append(pk, k)
	}
	if err := iter.Err(); err != nil {
		return nil, err
	}

	return pk, nil
}