// Package nocloud builds cloud-init NoCloud seed ISOs in process, shared by
// the providers that attach a seed as a CD-ROM (kvm2, proxmox). It never
// parses or logs the payload.
package nocloud

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"mime/multipart"
	"net/textproto"
	"strings"

	"github.com/kdomanski/iso9660"
)

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

// ErrEmptyName is returned by BuildSeedISO for an empty instance name.
var ErrEmptyName = errors.New("seed ISO: instance name is empty")

// GuestAgentScript is the vendor-data payload that gets qemu-guest-agent
// running so the provider can read the VM's address from the hypervisor. It is
// a shell script and not a cloud-config on purpose: cloud-init merges a
// vendor-data cloud-config under the user-data with mergers that keep the
// user-data's value for every top-level key and never append lists, so a
// Proxy with its own packages: would silently lose the agent. Scripts
// bypass the merge.
const GuestAgentScript = `#!/bin/sh
# Added by egress-proxies-operator: installs and starts qemu-guest-agent so
# the operator can learn this VM's IP address from the hypervisor.
# To leave this out, set installGuestAgent: false in the provider's config.
set -e
if command -v qemu-ga >/dev/null 2>&1 || [ -x /usr/sbin/qemu-ga ]; then
  echo "egress-proxies-operator: qemu-guest-agent already installed"
elif command -v apt-get >/dev/null 2>&1; then
  export DEBIAN_FRONTEND=noninteractive
  apt-get update
  apt-get install -y qemu-guest-agent
elif command -v dnf >/dev/null 2>&1; then
  dnf install -y qemu-guest-agent
elif command -v yum >/dev/null 2>&1; then
  yum install -y qemu-guest-agent
elif command -v zypper >/dev/null 2>&1; then
  zypper --non-interactive install qemu-guest-agent
elif command -v apk >/dev/null 2>&1; then
  apk add qemu-guest-agent
else
  echo "egress-proxies-operator: no supported package manager found; install qemu-guest-agent by hand" >&2
  exit 1
fi
if command -v systemctl >/dev/null 2>&1; then
  systemctl enable --now qemu-guest-agent
else
  rc-update add qemu-guest-agent default
  rc-service qemu-guest-agent start
fi
`

// BuildSeedISO writes a NoCloud seed to w: user-data byte for byte,
// meta-data naming the instance, and vendor-data (an empty file when there
// is none, so cloud-init does not look elsewhere). iso9660.NewWriter stages
// the files in os.MkdirTemp("", ""), that is under os.TempDir(): $TMPDIR
// when set, else /tmp, the manager's 64Mi emptyDir. The staging dir is
// removed before returning. Nothing about the payload is logged here.
func BuildSeedISO(name, userData, vendorData string, w io.Writer) (err error) {
	if name == "" {
		return ErrEmptyName
	}
	iw, err := iso9660.NewWriter()
	if err != nil {
		return fmt.Errorf("creating seed ISO staging dir: %w", err)
	}
	defer func() {
		if cerr := iw.Cleanup(); cerr != nil {
			err = errors.Join(err, fmt.Errorf("removing seed ISO staging dir: %w", cerr))
		}
	}()
	metaData := "instance-id: " + name + "\nlocal-hostname: " + name + "\n"
	files := []struct{ name, content string }{
		{"user-data", userData},
		{"meta-data", metaData},
		{"vendor-data", vendorData},
	}
	for _, f := range files {
		if err := iw.AddFile(strings.NewReader(f.content), f.name); err != nil {
			return fmt.Errorf("adding %s to seed ISO: %w", f.name, err)
		}
	}
	if err := iw.WriteTo(w, SeedLabel); err != nil {
		return fmt.Errorf("writing seed ISO: %w", err)
	}
	return nil
}

// BuildVendorData composes the seed's vendor-data from the configured
// document and the guest agent script. With both, they travel as separate
// parts of a MIME multipart, so cloud-init handles each by its own type; the
// MIME-Version header comes first because cloud-init detects multipart by
// finding "mime-version:" within the first 4096 bytes.
func BuildVendorData(configured string, installAgent bool) (string, error) {
	switch {
	case !installAgent:
		return configured, nil
	case strings.TrimSpace(configured) == "":
		return GuestAgentScript, nil
	}
	var buf bytes.Buffer
	mw := multipart.NewWriter(&buf)
	fmt.Fprintf(&buf, "MIME-Version: 1.0\r\nContent-Type: multipart/mixed; boundary=%q\r\n\r\n", mw.Boundary())
	parts := []struct{ contentType, body string }{
		{"text/plain", configured},
		{"text/x-shellscript", GuestAgentScript},
	}
	for _, p := range parts {
		pw, err := mw.CreatePart(textproto.MIMEHeader{"Content-Type": {p.contentType}})
		if err != nil {
			return "", fmt.Errorf("creating vendor-data part %s: %w", p.contentType, err)
		}
		if _, err := io.WriteString(pw, p.body); err != nil {
			return "", fmt.Errorf("writing vendor-data part %s: %w", p.contentType, err)
		}
	}
	if err := mw.Close(); err != nil {
		return "", fmt.Errorf("closing vendor-data multipart: %w", err)
	}
	return buf.String(), nil
}