package repository

import (
	"context"
	"database/sql"
	"fmt"
	"time"

	mysql "github.com/go-sql-driver/mysql"
)

const (
	defaultMaxOpenConns    = 40
	defaultMaxIdleConns    = 5
	defaultConnMaxLifetime = 5 * time.Minute
	defaultConnMaxIdleTime = 20 * time.Second
	defaultPingTimeout     = 3 * time.Second
)

func Open(dsn string) (*sql.DB, error) {
	if dsn == "" {
		return nil, fmt.Errorf("DATABASE_DSN is required")
	}
	normalizedDSN := normalizeDSN(dsn)

	db, err := sql.Open("mysql", normalizedDSN)
	if err != nil {
		return nil, err
	}
	db.SetMaxOpenConns(defaultMaxOpenConns)
	db.SetMaxIdleConns(defaultMaxIdleConns)
	db.SetConnMaxLifetime(defaultConnMaxLifetime)
	db.SetConnMaxIdleTime(defaultConnMaxIdleTime)

	if err := pingWithRetry(db, 3); err != nil {
		_ = db.Close()
		return nil, err
	}

	return db, nil
}

func pingWithRetry(db *sql.DB, attempts int) error {
	if attempts <= 0 {
		attempts = 1
	}
	var lastErr error
	for i := 0; i < attempts; i++ {
		ctx, cancel := context.WithTimeout(context.Background(), defaultPingTimeout)
		err := db.PingContext(ctx)
		cancel()
		if err == nil {
			return nil
		}
		lastErr = err
		time.Sleep(time.Duration(100*(i+1)) * time.Millisecond)
	}
	return lastErr
}

func normalizeDSN(dsn string) string {
	cfg, err := mysql.ParseDSN(dsn)
	if err != nil {
		return dsn
	}
	if cfg.Params == nil {
		cfg.Params = map[string]string{}
	}
	if _, ok := cfg.Params["parseTime"]; !ok {
		cfg.Params["parseTime"] = "true"
	}
	// Work around false-positive stale-connection detection observed on some
	// Docker Desktop + macOS setups that surface as "invalid connection".
	if _, ok := cfg.Params["checkConnLiveness"]; !ok {
		cfg.Params["checkConnLiveness"] = "false"
	}
	if cfg.Timeout == 0 {
		cfg.Timeout = 5 * time.Second
	}
	if cfg.ReadTimeout == 0 {
		cfg.ReadTimeout = 30 * time.Second
	}
	if cfg.WriteTimeout == 0 {
		cfg.WriteTimeout = 30 * time.Second
	}
	if cfg.Collation == "" {
		cfg.Collation = "utf8mb4_unicode_ci"
	}
	return cfg.FormatDSN()
}