package node

import (
	"context"
	"fmt"
	"net"
	"os"
	"strings"

	"k8s.io/klog/v2"
	system "undecided.project/monok8s/pkg/system"
)

type NetworkConfig struct {
	MgmtIface        string
	MgmtAddress      string
	MgmtGateway      string
	DNSNameservers   []string
	DNSSearchDomains []string
}

func ConfigureMgmtInterface(cfg NetworkConfig) Step {
	return func(ctx context.Context, nctx *NodeContext) error {
		if strings.TrimSpace(cfg.MgmtIface) == "" {
			return fmt.Errorf("mgmt interface is required")
		}
		if strings.TrimSpace(cfg.MgmtAddress) == "" {
			return fmt.Errorf("mgmt address is required")
		}

		ip, ipNet, err := net.ParseCIDR(strings.TrimSpace(cfg.MgmtAddress))
		if err != nil {
			return fmt.Errorf("invalid mgmt address %q: %w", cfg.MgmtAddress, err)
		}

		ip4 := ip.To4()
		if ip4 == nil {
			return fmt.Errorf("mgmt address must be IPv4: %q", cfg.MgmtAddress)
		}

		wantIP := ip4.String()
		wantCIDR := fmt.Sprintf("%s/%d", wantIP, maskSize(ipNet.Mask))

		if gw := strings.TrimSpace(cfg.MgmtGateway); gw != "" {
			gwIP := net.ParseIP(gw)
			if gwIP == nil || gwIP.To4() == nil {
				return fmt.Errorf("invalid mgmt gateway %q", gw)
			}
		}

		if _, err := nctx.System.Run(ctx, "ip", "link", "show", "dev", cfg.MgmtIface); err != nil {
			return fmt.Errorf("interface not found: %s: %w", cfg.MgmtIface, err)
		}

		if _, err := nctx.System.Run(ctx, "ip", "link", "set", "dev", cfg.MgmtIface, "up"); err != nil {
			return fmt.Errorf("failed to bring up interface %s: %w", cfg.MgmtIface, err)
		}

		hasAddr, err := interfaceHasIPv4(ctx, nctx, cfg.MgmtIface, wantIP)
		if err != nil {
			return fmt.Errorf("failed checking existing address on %s: %w", cfg.MgmtIface, err)
		}

		if hasAddr {
			klog.Infof("address already present on %s: %s", cfg.MgmtIface, wantCIDR)
		} else {
			if _, err := nctx.System.Run(ctx, "ip", "addr", "add", wantCIDR, "dev", cfg.MgmtIface); err != nil {
				return fmt.Errorf("failed assigning %s to %s: %w", wantCIDR, cfg.MgmtIface, err)
			}
		}

		if gw := strings.TrimSpace(cfg.MgmtGateway); gw != "" {
			if _, err := nctx.System.Run(ctx, "ip", "route", "replace", "default", "via", gw, "dev", cfg.MgmtIface); err != nil {
				return fmt.Errorf("failed setting default route via %s dev %s: %w", gw, cfg.MgmtIface, err)
			}
		}

		return nil
	}
}

func maskSize(m net.IPMask) int {
	ones, _ := m.Size()
	return ones
}

func EnsureIPForward(ctx context.Context, n *NodeContext) error {
	return system.EnsureSysctl(ctx, n.System, "net.ipv4.ip_forward", "1")
}

func ConfigureDNS(cfg NetworkConfig) Step {
	return func(context.Context, *NodeContext) error {

		if len(cfg.DNSNameservers) == 0 {
			return nil
		}

		var nameservers []string
		for _, ns := range cfg.DNSNameservers {
			ns = strings.TrimSpace(ns)
			if ns == "" {
				continue
			}
			if ip := net.ParseIP(ns); ip == nil {
				return fmt.Errorf("invalid DNS nameserver %q", ns)
			}
			nameservers = append(nameservers, ns)
		}
		if len(nameservers) == 0 {
			return fmt.Errorf("DNSNameservers is set but no valid nameservers were parsed")
		}

		var searchDomains []string
		for _, d := range cfg.DNSSearchDomains {
			d = strings.TrimSpace(d)
			if d == "" {
				continue
			}
			searchDomains = append(searchDomains, d)
		}

		var b strings.Builder
		if len(searchDomains) > 0 {
			b.WriteString("search ")
			b.WriteString(strings.Join(searchDomains, " "))
			b.WriteByte('\n')
		}
		for _, ns := range nameservers {
			b.WriteString("nameserver ")
			b.WriteString(ns)
			b.WriteByte('\n')
		}
		b.WriteString("options timeout:2 attempts:3\n")

		const (
			resolvDir  = "/etc"
			tmpPath    = "/etc/resolv.conf.monok8s.tmp"
			resolvPath = "/etc/resolv.conf"
		)

		if err := os.MkdirAll(resolvDir, 0o755); err != nil {
			klog.Warningf("failed to create %s for DNS config: %v; leaving %s unchanged", resolvDir, err, resolvPath)
			return nil
		}

		if err := os.WriteFile(tmpPath, []byte(b.String()), 0o644); err != nil {
			klog.Warningf("failed to write temporary DNS config %s: %v; leaving %s unchanged", tmpPath, err, resolvPath)
			return nil
		}

		if err := os.Rename(tmpPath, resolvPath); err != nil {
			_ = os.Remove(tmpPath)
			klog.Warningf("failed to install DNS config at %s: %v; leaving existing DNS config unchanged", resolvPath, err)
			return nil
		}

		return nil
	}
}

func interfaceHasIPv4(ctx context.Context, nctx *NodeContext, iface, wantIP string) (bool, error) {
	res, err := nctx.System.Run(ctx, "ip", "-o", "-4", "addr", "show", "dev", iface)
	if err != nil {
		return false, err
	}
	for _, line := range strings.Split(res.Stdout, "\n") {
		fields := strings.Fields(strings.TrimSpace(line))
		for i := 0; i < len(fields)-1; i++ {
			if fields[i] != "inet" {
				continue
			}
			ip, _, err := net.ParseCIDR(fields[i+1])
			if err == nil && ip.String() == wantIP {
				return true, nil
			}
		}
	}
	return false, nil
}