package dnscfg

import (
	"net"
	"os"
	"strings"
)

func ResolveDefaultSmartDNSAddr(addrEnvValue string, configPaths []string, fallback string) string {
	if v := strings.TrimSpace(addrEnvValue); v != "" {
		if addr := NormalizeSmartDNSAddr(v); addr != "" {
			return addr
		}
	}
	for _, path := range configPaths {
		if addr := SmartDNSAddrFromConfig(path); addr != "" {
			return addr
		}
	}
	return strings.TrimSpace(fallback)
}

func SmartDNSAddrFromConfig(path string) string {
	data, err := os.ReadFile(path)
	if err != nil {
		return ""
	}
	for _, ln := range strings.Split(string(data), "\n") {
		s := strings.TrimSpace(ln)
		if s == "" || strings.HasPrefix(s, "#") {
			continue
		}
		if !strings.HasPrefix(strings.ToLower(s), "bind ") {
			continue
		}
		parts := strings.Fields(s)
		if len(parts) < 2 {
			continue
		}
		if addr := NormalizeSmartDNSAddr(parts[1]); addr != "" {
			return addr
		}
	}
	return ""
}

func NormalizeDNSUpstream(raw string, defaultPort string) string {
	s := strings.TrimSpace(raw)
	if s == "" {
		return ""
	}

	s = strings.TrimPrefix(s, "udp://")
	s = strings.TrimPrefix(s, "tcp://")

	if strings.Contains(s, "#") {
		parts := strings.SplitN(s, "#", 2)
		host := strings.Trim(strings.TrimSpace(parts[0]), "[]")
		port := strings.TrimSpace(parts[1])
		if host == "" {
			return ""
		}
		if port == "" {
			port = defaultPort
		}
		return host + "#" + port
	}

	if host, port, err := net.SplitHostPort(s); err == nil {
		host = strings.Trim(strings.TrimSpace(host), "[]")
		port = strings.TrimSpace(port)
		if host == "" {
			return ""
		}
		if port == "" {
			port = defaultPort
		}
		return host + "#" + port
	}

	if strings.Count(s, ":") == 1 {
		parts := strings.SplitN(s, ":", 2)
		host := strings.TrimSpace(parts[0])
		port := strings.TrimSpace(parts[1])
		if host != "" && port != "" {
			return host + "#" + port
		}
	}

	return s
}

func NormalizeSmartDNSAddr(raw string) string {
	s := NormalizeDNSUpstream(raw, "6053")
	if s == "" {
		return ""
	}
	if strings.Contains(s, "#") {
		return s
	}
	return s + "#6053"
}