package nmlite

import (
	"bytes"
	"fmt"
	"html/template"
	"net"
	"os"
	"strings"

	"github.com/jetkvm/kvm/internal/network/types"
	"github.com/rs/zerolog"
)

const (
	resolvConfPath     = "/etc/resolv.conf"
	resolvConfFileMode = 0644
	resolvConfTemplate = `# the resolv.conf file is managed by the jetkvm network manager
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

{{ if .searchList }}
search {{ join .searchList " " }} # {{ .iface }}
{{- end -}}
{{ if .domain }}
domain {{ .domain }} # {{ .iface }}
{{- end -}}
{{ range .nameservers }}
nameserver {{ printf "%s" . }} # {{ $.iface }}
{{- end }}
`
)

var (
	tplFuncMap = template.FuncMap{
		"join": strings.Join,
	}
)

// ResolvConfManager manages the resolv.conf file
type ResolvConfManager struct {
	logger *zerolog.Logger
}

// NewResolvConfManager creates a new resolv.conf manager
func NewResolvConfManager(logger *zerolog.Logger) *ResolvConfManager {
	if logger == nil {
		// Create a no-op logger if none provided
		logger = &zerolog.Logger{}
	}

	return &ResolvConfManager{
		logger: logger,
	}
}

// UpdateFromLease updates resolv.conf from a DHCP lease
func (rcm *ResolvConfManager) UpdateFromLease(lease *types.DHCPLease) error {
	if lease == nil {
		return fmt.Errorf("lease cannot be nil")
	}

	rcm.logger.Info().
		Str("interface", lease.InterfaceName).
		Msg("updating resolv.conf from DHCP lease")

	return rcm.Update(lease.InterfaceName, lease.DNS, lease.SearchList, lease.Domain)
}

// UpdateFromStaticConfig updates resolv.conf from static configuration
func (rcm *ResolvConfManager) UpdateFromStaticConfig(iface string, dns []string) error {
	if len(dns) == 0 {
		rcm.logger.Debug().Str("interface", iface).Msg("no DNS servers in static config")
		return nil
	}

	// Parse DNS servers
	var dnsIPs []net.IP
	for _, dnsStr := range dns {
		dnsIP := net.ParseIP(dnsStr)
		if dnsIP == nil {
			rcm.logger.Warn().Str("dns", dnsStr).Msg("invalid DNS server, skipping")
			continue
		}
		dnsIPs = append(dnsIPs, dnsIP)
	}

	if len(dnsIPs) == 0 {
		rcm.logger.Debug().Str("interface", iface).Msg("no valid DNS servers in static config")
		return nil
	}

	rcm.logger.Info().
		Str("interface", iface).
		Interface("dns", dnsIPs).
		Msg("updating resolv.conf from static config")

	return rcm.Update(iface, dnsIPs, nil, "")
}

// Update updates the resolv.conf file
func (rcm *ResolvConfManager) Update(iface string, nameservers []net.IP, searchList []string, domain string) error {
	rcm.logger.Debug().
		Str("interface", iface).
		Interface("nameservers", nameservers).
		Interface("searchList", searchList).
		Str("domain", domain).
		Msg("updating resolv.conf")

	// Generate resolv.conf content
	content, err := rcm.generateResolvConf(iface, nameservers, searchList, domain)
	if err != nil {
		return fmt.Errorf("failed to generate resolv.conf: %w", err)
	}

	// Write to file
	if err := os.WriteFile(resolvConfPath, content, resolvConfFileMode); err != nil {
		return fmt.Errorf("failed to write resolv.conf: %w", err)
	}

	rcm.logger.Info().
		Str("interface", iface).
		Int("nameservers", len(nameservers)).
		Msg("resolv.conf updated successfully")

	return nil
}

// generateResolvConf generates resolv.conf content
func (rcm *ResolvConfManager) generateResolvConf(iface string, nameservers []net.IP, searchList []string, domain string) ([]byte, error) {
	tmpl, err := template.New("resolv.conf").Funcs(tplFuncMap).Parse(resolvConfTemplate)
	if err != nil {
		return nil, fmt.Errorf("failed to parse template: %w", err)
	}

	var buf bytes.Buffer
	if err := tmpl.Execute(&buf, map[string]interface{}{
		"iface":       iface,
		"nameservers": nameservers,
		"searchList":  searchList,
		"domain":      domain,
	}); err != nil {
		return nil, fmt.Errorf("failed to execute template: %w", err)
	}

	return buf.Bytes(), nil
}

// Clear clears the resolv.conf file (removes all entries)
func (rcm *ResolvConfManager) Clear() error {
	rcm.logger.Info().Msg("clearing resolv.conf")

	content := []byte("# the resolv.conf file is managed by the jetkvm network manager\n# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN\n")

	if err := os.WriteFile(resolvConfPath, content, resolvConfFileMode); err != nil {
		return fmt.Errorf("failed to clear resolv.conf: %w", err)
	}

	rcm.logger.Info().Msg("resolv.conf cleared")
	return nil
}

// GetCurrentContent returns the current content of resolv.conf
func (rcm *ResolvConfManager) GetCurrentContent() ([]byte, error) {
	return os.ReadFile(resolvConfPath)
}

// Backup creates a backup of the current resolv.conf
func (rcm *ResolvConfManager) Backup() error {
	content, err := rcm.GetCurrentContent()
	if err != nil {
		return fmt.Errorf("failed to read current resolv.conf: %w", err)
	}

	backupPath := resolvConfPath + ".backup"
	if err := os.WriteFile(backupPath, content, resolvConfFileMode); err != nil {
		return fmt.Errorf("failed to create backup: %w", err)
	}

	rcm.logger.Info().Str("backup", backupPath).Msg("resolv.conf backed up")
	return nil
}

// Restore restores resolv.conf from backup
func (rcm *ResolvConfManager) Restore() error {
	backupPath := resolvConfPath + ".backup"
	content, err := os.ReadFile(backupPath)
	if err != nil {
		return fmt.Errorf("failed to read backup: %w", err)
	}

	if err := os.WriteFile(resolvConfPath, content, resolvConfFileMode); err != nil {
		return fmt.Errorf("failed to restore resolv.conf: %w", err)
	}

	rcm.logger.Info().Str("backup", backupPath).Msg("resolv.conf restored from backup")
	return nil
}