#!/bin/bash
# =====================================================================
# Puts installation media where build.sh can find it, having checked it.
#
#   sudo ./fetch.sh ubuntu                  # download the pinned release
#   sudo ./fetch.sh ubuntu ~/Downloads/x.iso  # use one already downloaded
#   sudo ./fetch.sh windows ~/Downloads/x.iso
#
# EITHER WAY IT IS CHECKSUMMED
#
# A local file is not trusted more than a downloaded one - it is the same
# 6 GB of installer that becomes the machine every session runs from. For
# Ubuntu the hash is compared against Canonical's published SHA256SUMS
# for that series, fetched at the time, rather than a constant pasted in
# here that goes stale at the next point release and gets deleted.
#
# Windows media has no published list to check against, so its hash is
# only RECORDED. That is a real difference and it is not papered over:
# the manifest says where the file came from and what it hashed to, and
# that is all anyone can honestly claim about it.
#
# WHY UBUNTU IS NOT FETCHED WITH quickget
#
# quickget was adopted for image acquisition because the Windows side -
# locating an ISO, pairing it with the right virtio-win build - is
# genuinely fiddly and well solved there. Ubuntu is not that. Acquisition
# is one download and one checksum, and doing it directly keeps a
# 2,400-line bash dependency off the path that builds the image this
# suite runs on every session.
# =====================================================================
set -euo pipefail
cd "$(dirname "$(readlink -f "$0")")"

ISO_DIR=/var/lib/owuivm/iso

[ "$(id -u)" -eq 0 ] || { echo "run as root" >&2; exit 1; }
install -d -o owuivmadm -g owuivmadm -m 0755 "$ISO_DIR"

# The series to check against, and the release to download when no local
# file is given. Bump both together.
UBUNTU_SERIES="26.04"
UBUNTU_ISO="ubuntu-26.04.1-desktop-amd64.iso"
UBUNTU_BASE="https://releases.ubuntu.com/${UBUNTU_SERIES}"

verify_against_canonical() {   # verify_against_canonical <path> <basename>
  local path="$1" name="$2" want got
  echo "==> checking $name against Canonical's SHA256SUMS"
  want=$(curl -fsSL "$UBUNTU_BASE/SHA256SUMS" | awk -v f="*$name" '$2==f{print $1}')
  [ -n "$want" ] || {
    echo "$name is not in the published list for $UBUNTU_SERIES." >&2
    echo "Either it is from another series, or the name has been changed." >&2
    exit 1
  }
  got=$(sha256sum "$path" | awk '{print $1}')
  [ "$want" = "$got" ] || {
    echo "CHECKSUM MISMATCH - refusing to use this file." >&2
    echo "  want $want" >&2
    echo "  got  $got" >&2
    exit 1
  }
  echo "    ok  $got"
  printf '%s  %s  verified against %s/SHA256SUMS\n' "$name" "$got" "$UBUNTU_BASE" \
    > "$ISO_DIR/ubuntu.manifest"
}

fetch_ubuntu() {
  local supplied="${1:-}"
  if [ -n "$supplied" ]; then
    [ -f "$supplied" ] || { echo "no such file: $supplied" >&2; exit 1; }
    local name; name=$(basename "$supplied")
    verify_against_canonical "$supplied" "$name"
    # Copied rather than symlinked: the source is in somebody's Downloads
    # folder, and a base image build that fails halfway through because
    # the ISO was tidied away is a bad afternoon.
    echo "==> copying into $ISO_DIR"
    install -o owuivmadm -g owuivmadm -m 0644 "$supplied" "$ISO_DIR/$name"
  else
    local dest="$ISO_DIR/$UBUNTU_ISO"
    if [ -f "$dest" ]; then
      echo "already present: $dest"
    else
      echo "==> downloading $UBUNTU_ISO"
      curl -fL --retry 3 --continue-at - -o "$dest.part" "$UBUNTU_BASE/$UBUNTU_ISO"
      mv -f "$dest.part" "$dest"
      chown owuivmadm:owuivmadm "$dest"
    fi
    verify_against_canonical "$dest" "$UBUNTU_ISO"
  fi
  echo
  cat "$ISO_DIR/ubuntu.manifest"
}

# The virtio driver disk. Windows setup cannot see a virtio-blk disk
# without it and will tell you there are no drives to install to, which
# reads like a broken VM rather than a missing driver. Fetched from the
# same place every Windows-on-KVM guide uses; it is not signed by anyone
# whose signature we can check, so the hash is recorded rather than
# verified - exactly like the Windows media itself.
VIRTIO_URL="https://fedorapeople.org/groups/virt/virtio-win/direct-downloads/stable-virtio/virtio-win.iso"

fetch_virtio() {
  local dest="$ISO_DIR/virtio-win.iso"
  if [ -f "$dest" ]; then
    echo "already present: $dest"
  else
    echo "==> downloading virtio-win.iso"
    curl -fL --retry 3 --continue-at - -o "$dest.part" "$VIRTIO_URL"
    mv -f "$dest.part" "$dest"
    chown owuivmadm:owuivmadm "$dest"; chmod 0644 "$dest"
  fi
  printf 'virtio-win.iso  %s  recorded only - from %s\n' \
    "$(sha256sum "$dest" | awk '{print $1}')" "$VIRTIO_URL" > "$ISO_DIR/virtio.manifest"
  cat "$ISO_DIR/virtio.manifest"
}

fetch_windows() {
  local supplied="${1:-}"
  [ -n "$supplied" ] || { echo "Windows media must be supplied: $0 windows /path/to.iso" >&2; exit 2; }
  [ -f "$supplied" ] || { echo "no such file: $supplied" >&2; exit 1; }
  local name got
  name=$(basename "$supplied")
  # The maintenance boot picks Windows media by name, so a file that does
  # not look like Windows media would either be ignored or - worse - the
  # Ubuntu ISO would be picked instead. Checked here, once, where it can
  # still be fixed by renaming rather than debugged from a boot failure.
  case "$name" in
    [Ww]in*.iso|*[Ww]indows*.iso) ;;
    *) echo "refusing '$name': Windows media must have a name starting with Win or containing Windows," >&2
       echo "because that is how the maintenance boot tells it apart from the Ubuntu ISO." >&2
       exit 1 ;;
  esac
  got=$(sha256sum "$supplied" | awk '{print $1}')
  install -o owuivmadm -g owuivmadm -m 0644 "$supplied" "$ISO_DIR/$name"
  # RECORDED, not verified. See the header.
  printf '%s  %s  recorded only - no published checksum to compare against\n' "$name" "$got" \
    > "$ISO_DIR/windows.manifest"
  cat "$ISO_DIR/windows.manifest"
  echo
  fetch_virtio
}

case "${1:-}" in
  ubuntu)  fetch_ubuntu "${2:-}" ;;
  windows) fetch_windows "${2:-}" ;;
  virtio)  fetch_virtio ;;
  *) echo "usage: $0 {ubuntu|windows|virtio} [/path/to/local.iso]" >&2; exit 2 ;;
esac