package maintenance

import (
	"fmt"
	"regexp"
	"strings"
)

const (
	DefaultBatchRows           = 10000
	MaxBatchRows               = 100000
	DefaultStatementTimeoutSec = 30
)

var (
	blockedTableNames = map[string]struct{}{
		"schema_migrations":               {},
		"tenant":                          {},
		"maintenance_policy":              {},
		"maintenance_policy_config_audit": {},
	}

	sqlForbidden = regexp.MustCompile(`(?i)(;|--|/\*|\b(drop|truncate|insert|update|alter|create|grant|revoke|copy)\b)`)
)

// ValidateTableName ensures table is a safe identifier and not blocked.
func ValidateTableName(name string) error {
	name = strings.TrimSpace(name)
	if name == "" || !isSafeIdent(name) {
		return fmt.Errorf("maintenance: invalid table name")
	}
	if _, blocked := blockedTableNames[strings.ToLower(name)]; blocked {
		return fmt.Errorf("maintenance: table %q is not allowed", name)
	}
	return nil
}

// ValidateCondition ensures the WHERE fragment is safe for parameterized cleanup.
func ValidateCondition(condition string) error {
	c := strings.TrimSpace(condition)
	if c == "" {
		return nil
	}
	if sqlForbidden.MatchString(c) {
		return fmt.Errorf("maintenance: unsafe condition")
	}
	return nil
}

// NormalizeBatchLimit clamps delete batch size.
func NormalizeBatchLimit(maxRows *int) int {
	if maxRows == nil || *maxRows <= 0 {
		return DefaultBatchRows
	}
	if *maxRows > MaxBatchRows {
		return MaxBatchRows
	}
	return *maxRows
}

func isSafeIdent(name string) bool {
	if name == "" {
		return false
	}
	for _, r := range name {
		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '_' {
			continue
		}
		return false
	}
	return true
}