package postgres

import (
	"os"
	"strconv"
	"time"

	"gorm.io/driver/postgres"
	"gorm.io/gorm"
	"gorm.io/gorm/logger"
	"gorm.io/gorm/schema"
	"gorm.io/plugin/dbresolver"
)

var (
	_db *gorm.DB
)

// 创建实例
func newDB() (*gorm.DB, error) {
	if _db != nil {
		return _db, nil
	}

	dsn := os.Getenv("POSTGRES_DSN")
	if dsn == "" {
		dsn = "host=localhost user=postgres password=postgres dbname=postgres port=5432 sslmode=disable TimeZone=Asia/Shanghai"
	}
	maxLifetime := func() int {
		c := os.Getenv("MAXLIFETIME")
		cc, err := strconv.Atoi(c)
		if err != nil {
			return 1
		}

		if cc <= 0 {
			return 1
		}
		if cc >= 1000 {
			cc = 1000
		}
		return cc
	}()
	maxIdleConns := func() int {
		c := os.Getenv("MAXIDLECONNS")
		cc, err := strconv.Atoi(c)
		if err != nil {
			return 1
		}

		if cc < 0 {
			return 0
		}
		if cc >= 1000 {
			cc = 1000
		}
		return cc
	}()
	maxOpenConns := func() int {
		c := os.Getenv("MAXOPENCONNS")
		cc, err := strconv.Atoi(c)
		if err != nil {
			return 1
		}

		if cc < 0 {
			return 0
		}
		if cc >= 1000 {
			cc = 1000
		}
		return cc
	}()

	var err error
	_db, err = gorm.Open(postgres.Open(dsn), &gorm.Config{
		SkipDefaultTransaction: true,
		Logger:                 logger.Default.LogMode(logger.Silent),
		NamingStrategy: schema.NamingStrategy{
			SingularTable: true,
		},
	})
	if err != nil {
		return nil, err
	}
	_db.Use(
		dbresolver.Register(dbresolver.Config{
			Sources:  []gorm.Dialector{postgres.Open(dsn)},
			Replicas: []gorm.Dialector{postgres.Open(dsn)},
			Policy:   dbresolver.RandomPolicy{},
		}).SetConnMaxIdleTime(time.Hour).
			SetConnMaxLifetime(time.Duration(maxLifetime) * time.Hour).
			SetMaxIdleConns(maxIdleConns).
			SetMaxOpenConns(maxOpenConns))
	return _db, nil
}