package db

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

	"go-dy/internal/config"

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

var (
    mu   sync.Mutex
    conn *sql.DB
)

func getDSN(cfg config.Config) string {
    if cfg.DBDsn != "" {
        return cfg.DBDsn
    }
    // sensible default for local dev
    return "root:password@tcp(127.0.0.1:3306)/go-dy?parseTime=true&charset=utf8mb4&loc=Local"
}

// Get returns a shared DB connection. It retries initialization if previous attempts failed.
func Get(cfg config.Config) (*sql.DB, error) {
    mu.Lock()
    defer mu.Unlock()
    if conn != nil {
        return conn, nil
    }
    dsn := getDSN(cfg)
    db, err := sql.Open("mysql", dsn)
    if err != nil {
        return nil, err
    }
    db.SetMaxOpenConns(20)
    db.SetMaxIdleConns(5)
    db.SetConnMaxLifetime(30 * time.Minute)

    // verify connection first
    if e := db.Ping(); e != nil {
        _ = db.Close()
        return nil, e
    }

    // init schema after successful ping
    if e := initSchema(db); e != nil {
        _ = db.Close()
        return nil, e
    }

    conn = db
    return conn, nil
}

func initSchema(db *sql.DB) error {
    // minimal users table
    _, err := db.Exec(`
CREATE TABLE IF NOT EXISTS users (
  id BIGINT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL UNIQUE,
  password_hash VARCHAR(255) NOT NULL,
  created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
);
`)
    if err != nil {
        return fmt.Errorf("init schema: %w", err)
    }
    return nil
}