package orchestrator

import (
	"fmt"
	"os/exec"
	"strings"
)

// setupBridge creates the host bridge + enables NAT if it doesn't exist.
func (o *Orchestrator) setupBridge() error {
	if o.cfg.Bridge == "none" {
		return nil
	}

	// check if bridge already exists
	if err := run("ip", "link", "show", o.cfg.Bridge); err == nil {
		return nil // already up
	}

	if err := run("ip", "link", "add", o.cfg.Bridge, "type", "bridge"); err != nil {
		return fmt.Errorf("create bridge: %w", err)
	}
	if err := run("ip", "addr", "add", o.cfg.BridgeCIDR, "dev", o.cfg.Bridge); err != nil {
		return fmt.Errorf("add bridge addr: %w", err)
	}
	if err := run("ip", "link", "set", o.cfg.Bridge, "up"); err != nil {
		return fmt.Errorf("bring bridge up: %w", err)
	}

	// find default route interface for NAT
	out, err := exec.Command("ip", "-4", "route", "show", "default").Output()
	if err == nil {
		fields := strings.Fields(string(out))
		for i, f := range fields {
			if f == "dev" && i+1 < len(fields) {
				iface := fields[i+1]
				_ = run("sysctl", "-qw", "net.ipv4.ip_forward=1")
				// idempotent: ignore error if rule exists
				_ = run("iptables", "-t", "nat", "-A", "POSTROUTING",
					"-o", iface, "-j", "MASQUERADE")
				break
			}
		}
	}
	o.log.Infof("bridge %s up on %s", o.cfg.Bridge, o.cfg.BridgeCIDR)
	return nil
}

// createTap creates a tap device and attaches it to the bridge.
func (o *Orchestrator) createTap(name string) error {
	if err := run("ip", "tuntap", "add", "dev", name, "mode", "tap"); err != nil {
		return fmt.Errorf("create tap %s: %w", name, err)
	}
	if err := run("ip", "link", "set", name, "up"); err != nil {
		return fmt.Errorf("bring tap %s up: %w", name, err)
	}
	if o.cfg.Bridge != "none" {
		if err := run("ip", "link", "set", name, "master", o.cfg.Bridge); err != nil {
			return fmt.Errorf("attach tap %s to bridge: %w", name, err)
		}
	}
	return nil
}

func destroyTap(name string) {
	_ = run("ip", "link", "del", name)
}

// run executes a command, returning an error if it fails.
func run(name string, args ...string) error {
	return exec.Command(name, args...).Run()
}