package proxy

import (
	"errors"
	"fmt"
	"net"
	"strings"
)

// diagnosticHint returns a user-friendly suggestion for a validation failure.
func diagnosticHint(step string, err error) string {
	if err == nil {
		return ""
	}

	switch step {
	case StepDNS:
		return "Domain cannot be resolved. Check DNS settings or use an IP address."

	case StepTCP:
		return tcpHintFromError(err)

	case StepHTTP:
		return httpHint(err.Error())

	default:
		return "Validation failed: " + err.Error()
	}
}

// tcpHintFromError returns a specific hint based on the TCP error type.
func tcpHintFromError(err error) string {
	if err == nil {
		return ""
	}

	var opErr *net.OpError
	if errors.As(err, &opErr) {
		lower := strings.ToLower(opErr.Err.Error())
		switch {
		case strings.Contains(lower, "connection refused"):
			return "Port is not accepting connections. Check if the service is running and the port is correct."
		case strings.Contains(lower, "i/o timeout") || strings.Contains(lower, "timeout"):
			return "Connection timed out. Possible firewall blocking. Check network/firewall rules."
		case strings.Contains(lower, "no route to host") || strings.Contains(lower, "host is unreachable"):
			return "Host is not reachable. Verify the IP address and network connectivity."
		}
	}

	msg := err.Error()
	lower := strings.ToLower(msg)
	switch {
	case strings.Contains(lower, "connection refused"):
		return "Port is not accepting connections. Check if the service is running and the port is correct."
	case strings.Contains(lower, "timeout"):
		return "Connection timed out. Possible firewall blocking. Check network/firewall rules."
	default:
		return fmt.Sprintf("TCP connection failed: %s", msg)
	}
}

// httpHint returns a specific hint based on the HTTP probe result.
func httpHint(msg string) string {
	lower := strings.ToLower(msg)

	switch {
	case strings.Contains(lower, "status"):
		return msg // Already formatted by the caller with the status code.
	case strings.Contains(lower, "timeout"):
		return "HTTP health probe timed out. The service may be slow or unresponsive."
	default:
		return "HTTP health probe failed: " + msg
	}
}