package validation

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

// ValidateClientName validates the client name format
// Requirements: alphanumeric, hyphens, underscores only, max 64 characters
func ValidateClientName(name string) error {
	if name == "" {
		return fmt.Errorf("client name cannot be empty")
	}

	if len(name) > 64 {
		return fmt.Errorf("client name must be 64 characters or less (got %d)", len(name))
	}

	// Check for valid characters: a-z, A-Z, 0-9, hyphen, underscore
	matched, err := regexp.MatchString(`^[a-zA-Z0-9_-]+$`, name)
	if err != nil {
		return fmt.Errorf("failed to validate client name: %w", err)
	}

	if !matched {
		return fmt.Errorf("client name contains invalid characters (allowed: a-z, A-Z, 0-9, -, _)")
	}

	return nil
}

// ValidateIPAvailability checks if an IP address is already assigned to a client
// This function is meant to be called after getting next available IPs
func ValidateIPAvailability(ipv4, ipv6 string, existingIPs map[string]bool) error {
	if ipv4 != "" && existingIPs[ipv4] {
		return fmt.Errorf("IPv4 address %s is already assigned", ipv4)
	}

	if ipv6 != "" && existingIPs[ipv6] {
		return fmt.Errorf("IPv6 address %s is already assigned", ipv6)
	}

	return nil
}

// ValidateDNSServers validates DNS server addresses
// Requirements: comma-separated list of IPv4 addresses
func ValidateDNSServers(dns string) error {
	if dns == "" {
		return fmt.Errorf("DNS servers cannot be empty")
	}

	// Split by comma and trim whitespace
	servers := strings.Split(dns, ",")
	for _, server := range servers {
		server = strings.TrimSpace(server)
		if server == "" {
			continue
		}

		// Basic IPv4 validation (4 octets, each 0-255)
		matched, err := regexp.MatchString(`^(\d{1,3}\.){3}\d{1,3}$`, server)
		if err != nil {
			return fmt.Errorf("failed to validate DNS server: %w", err)
		}

		if !matched {
			return fmt.Errorf("invalid DNS server format: %s (expected IPv4 address)", server)
		}

		// Validate each octet is in range 0-255
		parts := strings.Split(server, ".")
		for _, part := range parts {
			var num int
			if _, err := fmt.Sscanf(part, "%d", &num); err != nil {
				return fmt.Errorf("invalid DNS server: %s", server)
			}
			if num < 0 || num > 255 {
				return fmt.Errorf("DNS server octet out of range (0-255) in: %s", server)
			}
		}
	}

	return nil
}