package configreader

import (
	"bufio"
	"fmt"
	"net"
	"os"
	"os/exec"
	"path/filepath"
	"strings"

	"networktool/internal/model"

	"gopkg.in/yaml.v3"
)

type Service struct{}

type configuredInterfaceValues struct {
	DHCP4   bool
	IP      string
	Prefix  int
	Gateway string
	DNS     []string
}

func New() *Service { return &Service{} }

func (s *Service) Read(interfaceName string) (model.InterfaceConfig, error) {
	iface, err := net.InterfaceByName(interfaceName)
	if err != nil {
		return model.InterfaceConfig{}, err
	}

	config := model.InterfaceConfig{Interface: interfaceName, DNS: []string{}}
	configured := readConfiguredInterfaceValues(interfaceName)
	config.Dhcp4 = configured.DHCP4
	config.IP = configured.IP
	config.Prefix = configured.Prefix
	config.Gateway = configured.Gateway
	if configured.DNS != nil {
		config.DNS = configured.DNS
	}
	if config.Dhcp4 || config.IP == "" {
		ip, prefix := readInterfaceIPv4(iface)
		if ip != "" {
			config.IP = ip
			config.Prefix = prefix
		}
	}
	if config.Dhcp4 || config.Gateway == "" {
		config.Gateway = readGateway(interfaceName)
	}
	if config.Dhcp4 || len(config.DNS) == 0 {
		config.DNS = readDNS()
	}
	return config, nil
}

func readInterfaceIPv4(iface *net.Interface) (string, int) {
	addrs, err := iface.Addrs()
	if err != nil {
		return "", 0
	}
	for _, addr := range addrs {
		ipNet, ok := addr.(*net.IPNet)
		if !ok || ipNet.IP.To4() == nil {
			continue
		}
		prefix, _ := ipNet.Mask.Size()
		return ipNet.IP.String(), prefix
	}
	return "", 0
}

func readGateway(interfaceName string) string {
	cmd := exec.Command("ip", "route", "show", "dev", interfaceName)
	output, err := cmd.Output()
	if err != nil {
		return ""
	}
	for _, line := range strings.Split(string(output), "\n") {
		line = strings.TrimSpace(line)
		if !strings.HasPrefix(line, "default via ") {
			continue
		}
		parts := strings.Fields(line)
		if len(parts) >= 3 {
			return parts[2]
		}
	}
	return ""
}

func readDNS() []string {
	file, err := os.Open("/etc/resolv.conf")
	if err != nil {
		return []string{}
	}
	defer file.Close()

	result := make([]string, 0, 2)
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if !strings.HasPrefix(line, "nameserver ") {
			continue
		}
		parts := strings.Fields(line)
		if len(parts) >= 2 {
			result = append(result, parts[1])
		}
	}
	return result
}

func readConfiguredInterfaceValues(interfaceName string) configuredInterfaceValues {
	files, err := filepath.Glob("/etc/netplan/*.yaml")
	if err != nil || len(files) == 0 {
		return configuredInterfaceValues{}
	}
	for _, filePath := range files {
		data, err := os.ReadFile(filePath)
		if err != nil {
			continue
		}
		var raw map[string]any
		if err := yaml.Unmarshal(data, &raw); err != nil {
			continue
		}
		values, ok := findInterfaceValues(raw, interfaceName)
		if ok {
			return values
		}
	}
	return configuredInterfaceValues{}
}

func findInterfaceValues(raw map[string]any, interfaceName string) (configuredInterfaceValues, bool) {
	network, ok := raw["network"].(map[string]any)
	if !ok {
		return configuredInterfaceValues{}, false
	}
	ethernets, ok := network["ethernets"].(map[string]any)
	if !ok {
		return configuredInterfaceValues{}, false
	}
	entry, ok := ethernets[interfaceName].(map[string]any)
	if !ok {
		return configuredInterfaceValues{}, false
	}
	values := configuredInterfaceValues{}
	if dhcp4, ok := entry["dhcp4"].(bool); ok {
		values.DHCP4 = dhcp4
	}
	addresses, ok := entry["addresses"].([]any)
	if ok {
		for _, item := range addresses {
			text, ok := item.(string)
			if !ok || strings.TrimSpace(text) == "" {
				continue
			}
			ip, ipNet, err := net.ParseCIDR(text)
			if err != nil || ip == nil || ip.To4() == nil {
				continue
			}
			prefix, _ := ipNet.Mask.Size()
			values.IP = ip.String()
			values.Prefix = prefix
			break
		}
	}
	if nameservers, ok := entry["nameservers"].(map[string]any); ok {
		values.DNS = anyToStringSlice(nameservers["addresses"])
	}
	if routes, ok := entry["routes"].([]any); ok {
		for _, item := range routes {
			route, ok := item.(map[string]any)
			if !ok {
				continue
			}
			to, _ := route["to"].(string)
			via, _ := route["via"].(string)
			if strings.TrimSpace(to) == "default" && strings.TrimSpace(via) != "" {
				values.Gateway = strings.TrimSpace(via)
				break
			}
		}
	}
	if values.Gateway == "" {
		if gateway4, ok := entry["gateway4"].(string); ok {
			values.Gateway = strings.TrimSpace(gateway4)
		}
	}
	return values, values.DHCP4 || values.IP != "" || values.Gateway != "" || len(values.DNS) > 0
}

func anyToStringSlice(value any) []string {
	switch typed := value.(type) {
	case []string:
		return append([]string(nil), typed...)
	case []any:
		result := make([]string, 0, len(typed))
		for _, item := range typed {
			text, ok := item.(string)
			if ok && strings.TrimSpace(text) != "" {
				result = append(result, text)
			}
		}
		return result
	default:
		return []string{}
	}
}

func MustRead(interfaceName string) model.InterfaceConfig {
	config, err := New().Read(interfaceName)
	if err != nil {
		panic(fmt.Sprintf("read interface config failed: %v", err))
	}
	return config
}