// Package mysql owns SQL connections, explicit migrations and transaction boundaries.
package mysql

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

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

// Open configures UTC, bounded I/O and an explicit connection pool. It never
// applies migrations and never logs the DSN. TLS is chosen in the secret DSN.
func Open(ctx context.Context, dsn string, maxOpen, maxIdle int) (*sql.DB, error) {
	if maxOpen <= 0 || maxIdle < 0 || maxIdle > maxOpen {
		return nil, errors.New("invalid database pool configuration")
	}
	cfg, err := driver.ParseDSN(dsn)
	if err != nil {
		return nil, errors.New("invalid MySQL DSN")
	}
	if cfg.DBName == "" {
		return nil, errors.New("MySQL database name required")
	}
	cfg.ParseTime = true
	cfg.Loc = time.UTC
	cfg.MultiStatements = false
	cfg.InterpolateParams = false
	cfg.Timeout = 5 * time.Second
	cfg.ReadTimeout = 10 * time.Second
	cfg.WriteTimeout = 10 * time.Second
	if cfg.Params == nil {
		cfg.Params = map[string]string{}
	}
	cfg.Params["time_zone"] = "'+00:00'"
	cfg.Params["sql_mode"] = "'STRICT_ALL_TABLES,NO_ZERO_DATE,NO_ZERO_IN_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION'"
	connector, err := driver.NewConnector(cfg)
	if err != nil {
		return nil, errors.New("invalid MySQL connection configuration")
	}
	db := sql.OpenDB(connector)
	db.SetMaxOpenConns(maxOpen)
	db.SetMaxIdleConns(maxIdle)
	db.SetConnMaxLifetime(5 * time.Minute)
	db.SetConnMaxIdleTime(time.Minute)
	if err := db.PingContext(ctx); err != nil {
		db.Close()
		return nil, errors.New("MySQL connection failed; check endpoint, credentials and TLS configuration")
	}
	return db, nil
}

// WithTx does not replay callbacks: a failed commit may have succeeded remotely.
// Callers reconcile by stable operation identity before retrying an ambiguous write.
func WithTx(ctx context.Context, db *sql.DB, fn func(*sql.Tx) error) error {
	tx, err := db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelReadCommitted})
	if err != nil {
		return err
	}
	defer tx.Rollback()
	if err := fn(tx); err != nil {
		return err
	}
	return tx.Commit()
}