package kvm

import (
	"bytes"
	"fmt"
	"strings"

	"github.com/kdomanski/iso9660"
)

// seedLabel is the volume label cloud-init's NoCloud datasource looks for.
const seedLabel = "cidata"

// defaultVendorData is the cloud-init vendor-data shipped on every seed
// unless the config overrides it. cloud-init merges it under the Proxy's own
// user-data, so stock images grow a guest agent (which lets the provider
// read the VM's IP before ARP sees traffic) without the user's cloud-init
// having to know about it.
const defaultVendorData = `#cloud-config
packages:
  - qemu-guest-agent
runcmd:
  - [systemctl, enable, --now, qemu-guest-agent]
`

// buildSeedISO renders a NoCloud seed: user-data verbatim, vendor-data as
// given, and a meta-data whose instance-id is the deterministic VM name, so
// cloud-init never mistakes a reboot for a new instance. The ISO's volume
// descriptor carries the build time, so two builds differ in a few
// timestamp bytes; the files and label are identical.
func buildSeedISO(name, userData, vendorData string) ([]byte, error) {
	w, err := iso9660.NewWriter()
	if err != nil {
		return nil, fmt.Errorf("creating iso writer: %w", err)
	}
	defer w.Cleanup() //nolint:errcheck // temp-dir cleanup; nothing to do on failure

	files := []struct{ name, body string }{
		{"user-data", userData},
		{"meta-data", fmt.Sprintf("instance-id: %s\nlocal-hostname: %s\n", name, name)},
		{"vendor-data", vendorData},
	}
	for _, f := range files {
		if err := w.AddFile(strings.NewReader(f.body), f.name); err != nil {
			return nil, fmt.Errorf("adding %s to seed iso: %w", f.name, err)
		}
	}
	var buf bytes.Buffer
	if err := w.WriteTo(&buf, seedLabel); err != nil {
		return nil, fmt.Errorf("writing seed iso: %w", err)
	}
	return buf.Bytes(), nil
}