#!/bin/bash
# /usr/local/bin/dos-shell
# Prepare the SvarDOS environment and launch dosemu.

set -euo pipefail

ALLOWED_LIST="${DOS_ALLOWED_LIST:-/etc/dos_allowed}"
ALLOWED_REPO="${DOS_ALLOWED_REPO:-/opt/allowed_repo}"
EXTRA_DRIVE_ROOT="${DOS_EXTRA_DRIVE_ROOT:-/opt/dos_drives}"
RESERVED_DRIVES_RAW="${DOS_RESERVED_DRIVES:-CDE}"
ENV_DIR="/etc/dos_env"
AUTOEXEC_TEMPLATE="${ENV_DIR}/AUTOEXEC.BAT"
CONFIG_TEMPLATE="${ENV_DIR}/CONFIG.SYS"
SVARDOS_ROOT="${SVARDOS_ROOT:-/opt/svardos}"
SVARDOS_BASE="${SVARDOS_BASE:-${SVARDOS_ROOT}/base}"
ALLOW_MODE="${DOS_ALLOW_MODE:-all}"
DEFAULT_DOS_USER="dosuser"
INSTALL_SENTINEL_NAME=".svardos_installed"
PRE_BOOT_HOOK="${DOS_PRE_BOOT_HOOK:-${ENV_DIR}/pre-boot.sh}"
LINUX_SHELL="${DOS_LINUX_SHELL:-/bin/bash}"

if [ "$(id -u)" -eq 0 ]; then
  DOS_USER="${DEFAULT_DOS_USER}"
  DOS_HOME="$(getent passwd "${DOS_USER}" | cut -d: -f6)"
else
  DOS_USER="$(id -un)"
  DOS_HOME="${HOME}"
fi

if [ -z "${DOS_HOME}" ]; then
  echo "Unable to determine home directory for ${DOS_USER}" >&2
  exit 1
fi

shell_passthrough=0
shell_payload=""

if [ "${1:-}" = "--help" ]; then
  cat <<'EOF'
Usage: dos-shell [--linux-shell [command]]

Default invocation boots the DOS environment via dosemu.
Use --linux-shell to open the underlying Linux shell instead.
EOF
  exit 0
fi

if [ "${1:-}" = "--linux-shell" ]; then
  shift
  shell_passthrough=1
  if [ $# -gt 0 ]; then
    shell_payload="$*"
  fi
fi

if [ "${shell_passthrough}" -eq 0 ] && [ -n "${SSH_ORIGINAL_COMMAND:-}" ]; then
  case "${SSH_ORIGINAL_COMMAND}" in
    linux-shell)
      shell_passthrough=1
      shell_payload=""
      ;;
    linux-shell[[:space:]]*)
      shell_passthrough=1
      shell_payload="${SSH_ORIGINAL_COMMAND#linux-shell}"
      shell_payload="${shell_payload#"${shell_payload%%[![:space:]]*}"}"
      ;;
  esac
fi

if [ "${shell_passthrough}" -eq 1 ]; then
  if [ "$(id -u)" -eq 0 ]; then
    if [ -n "${shell_payload}" ]; then
      exec runuser -u "${DOS_USER}" -- "${LINUX_SHELL}" -lc "${shell_payload}"
    else
      exec runuser -u "${DOS_USER}" -- "${LINUX_SHELL}" -l
    fi
  else
    if [ -n "${shell_payload}" ]; then
      exec "${LINUX_SHELL}" -lc "${shell_payload}"
    else
      exec "${LINUX_SHELL}" -l
    fi
  fi
fi

DOSEMU_DIR="${DOS_HOME}/.dosemu"
C_DRIVE="${DOSEMU_DIR}/drive_c"
INSTALL_SENTINEL_PATH="${DOSEMU_DIR}/${INSTALL_SENTINEL_NAME}"
DOSEMU_ARGS=()

detect_dosemu_args() {
  local mode="${DOS_TERMINAL_MODE:-auto}"
  if [ "${mode}" = "auto" ]; then
    if [ -n "${DISPLAY:-}" ]; then
      mode="x"
    else
      mode="terminal"
    fi
  fi

  case "${mode,,}" in
    x|sdl|window|gui)
      DOSEMU_ARGS=(-X -K "${C_DRIVE}")
      ;;
    terminal|tty|text)
      DOSEMU_ARGS=(-t -K "${C_DRIVE}")
      ;;
    dumb)
      DOSEMU_ARGS=(-dumb -K "${C_DRIVE}")
      ;;
    *)
      echo "Unknown DOS_TERMINAL_MODE '${mode}', defaulting to terminal mode." >&2
      DOSEMU_ARGS=(-t -K "${C_DRIVE}")
      ;;
  esac
}
allowed_entries=()
extra_drive_logs=()
declare -A reserved_letters=()

mkdir -p "${DOSEMU_DIR}" "${C_DRIVE}"
if [ "$(id -u)" -eq 0 ] && [ ! -d "${ENV_DIR}" ]; then
  mkdir -p "${ENV_DIR}"
fi

reset_drive_c() {
  if [ ! -d "${SVARDOS_BASE}" ] || [ -z "$(ls -A "${SVARDOS_BASE}")" ]; then
    echo "SvarDOS base directory ${SVARDOS_BASE} is empty. Aborting." >&2
    exit 1
  fi

  rm -rf "${C_DRIVE:?}/"*

  cp -a "${SVARDOS_BASE}/." "${C_DRIVE}/"

  if [ "$(id -u)" -eq 0 ]; then
    chown -R "${DOS_USER}:${DOS_USER}" "${DOSEMU_DIR}"
  fi

  if [ -f "${DOS_HOME}/.dosemurc" ]; then
    rm -f "${DOS_HOME}/.dosemurc"
  fi

  echo "SvarDOS base staged to ${C_DRIVE}"
}

normalise_reserved_drives() {
  local raw="$1"
  local cleaned="${raw//[^[:alpha:]]/}"
  local i letter
  for ((i=0; i<${#cleaned}; i++)); do
    letter="${cleaned:i:1}"
    letter="${letter,,}"
    reserved_letters["${letter}"]=1
  done
}

normalise_reserved_drives "${RESERVED_DRIVES_RAW}"

sync_allowed_content() {
  allowed_entries=()
  local mode="${ALLOW_MODE}"
  if [ "${mode}" = "all" ]; then
    if [ -d "${ALLOWED_REPO}" ] && [ "$(ls -A "${ALLOWED_REPO}" 2>/dev/null)" ]; then
      cp -a "${ALLOWED_REPO}/." "${C_DRIVE}/"
      allowed_entries+=("ALL")
    fi
    return
  fi

  if [ "${mode}" != "list" ] && [ "${mode}" != "allowlist" ]; then
    echo "Unknown DOS_ALLOW_MODE '${mode}', defaulting to allowlist mode." >&2
    mode="list"
    ALLOW_MODE="${mode}"
  fi

  if [ -f "${ALLOWED_LIST}" ]; then
    while IFS= read -r line || [ -n "$line" ]; do
      line="$(printf '%s' "$line" | sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//')"
      case "$line" in
        ''|\#*) continue ;;
      esac
      allowed_entries+=("$line")
    done < "${ALLOWED_LIST}"
  fi

  for entry in "${allowed_entries[@]}"; do
    src="${ALLOWED_REPO}/${entry}"
    if [ -e "$src" ]; then
      dst_dir="$(dirname "${entry}")"
      mkdir -p "${C_DRIVE}/${dst_dir}"
      cp -a "$src" "${C_DRIVE}/${dst_dir}/"
    else
      echo "Warning: allowed file not found: $src" >&2
    fi
  done
}

sync_extra_drives() {
  extra_drive_logs=()
  local root="${EXTRA_DRIVE_ROOT}"
  local -A seen_letters=()

  if [ -d "${root}" ]; then
    shopt -s nullglob
    local entry base letter letter_lower letter_upper dest
    for entry in "${root}"/*; do
      if [ ! -d "$entry" ]; then
        continue
      fi
      base="$(basename "$entry")"
      case "$base" in
        [A-Za-z]|[A-Za-z]:)
          letter="${base:0:1}"
          ;;
        *)
          continue
          ;;
      esac
      letter_lower="${letter,,}"
      letter_upper="${letter^^}"
      if [ -n "${reserved_letters[${letter_lower}]+x}" ]; then
        echo "dos-shell: skipping extra drive '${base}' (${letter_upper}: is reserved)" >&2
        continue
      fi
      dest="${DOSEMU_DIR}/drive_${letter_lower}"
      if [ -e "${dest}" ] && [ ! -L "${dest}" ]; then
        echo "dos-shell: cannot map ${letter_upper}: - ${dest} already exists and is not a symlink" >&2
        continue
      fi
      if ! ln -sfn "$entry" "$dest"; then
        echo "dos-shell: failed to link ${letter_upper}: to ${entry}" >&2
        continue
      fi
      seen_letters["${letter_lower}"]=1
      extra_drive_logs+=("${letter_upper}: ${entry}")
    done
    shopt -u nullglob
  fi

  shopt -s nullglob
  local link base letter target
  for link in "${DOSEMU_DIR}"/drive_[[:lower:]]; do
    [ -L "$link" ] || continue
    base="$(basename "$link")"
    letter="${base#drive_}"
    if [ -z "$letter" ] || [ "$letter" = "c" ]; then
      continue
    fi
    if [ -n "${seen_letters[$letter]+x}" ]; then
      continue
    fi
    target="$(readlink "$link")"
    case "$target" in
      "${EXTRA_DRIVE_ROOT}"/*)
        rm -f "$link"
        ;;
    esac
  done
  shopt -u nullglob
}

apply_templates() {
  if [ -f "${AUTOEXEC_TEMPLATE}" ]; then
    cp "${AUTOEXEC_TEMPLATE}" "${C_DRIVE}/AUTOEXEC.BAT"
  fi
  if [ -f "${CONFIG_TEMPLATE}" ]; then
    cp "${CONFIG_TEMPLATE}" "${C_DRIVE}/CONFIG.SYS"
  fi
}

detect_dosemu_args

run_pre_boot_hook() {
  if [ ! -e "${PRE_BOOT_HOOK}" ]; then
    return
  fi

  if [ ! -x "${PRE_BOOT_HOOK}" ]; then
    echo "dos-shell: pre-boot hook found but not executable: ${PRE_BOOT_HOOK}" >&2
    return
  fi

  echo "dos-shell: running pre-boot hook: ${PRE_BOOT_HOOK}" >&2
  if [ "$(id -u)" -eq 0 ]; then
    runuser -u "${DOS_USER}" -- env \
      C_DRIVE="${C_DRIVE}" \
      DOSEMU_DIR="${DOSEMU_DIR}" \
      DOS_HOME="${DOS_HOME}" \
      ALLOWED_REPO="${ALLOWED_REPO}" \
      SVARDOS_ROOT="${SVARDOS_ROOT}" \
      SVARDOS_BASE="${SVARDOS_BASE}" \
      "${PRE_BOOT_HOOK}"
  else
    C_DRIVE="${C_DRIVE}" \
    DOSEMU_DIR="${DOSEMU_DIR}" \
    DOS_HOME="${DOS_HOME}" \
    ALLOWED_REPO="${ALLOWED_REPO}" \
    SVARDOS_ROOT="${SVARDOS_ROOT}" \
    SVARDOS_BASE="${SVARDOS_BASE}" \
      "${PRE_BOOT_HOOK}"
  fi
}

FORCE_CPU_EMULATION=0
detect_kvm_support() {
  if [ ! -c /dev/kvm ]; then
    return 1
  fi

  if [ "$(id -u)" -eq 0 ]; then
    if command -v runuser >/dev/null 2>&1; then
      runuser -u "${DOS_USER}" -- test -r /dev/kvm 2>/dev/null || return 1
      return 0
    fi
    return 0
  fi

  [ -r /dev/kvm ]
}

if ! detect_kvm_support; then
  echo "dos-shell: disabling KVM acceleration (no usable /dev/kvm)" >&2
  FORCE_CPU_EMULATION=1
fi

should_disable_audio=0
audio_mode="${DOS_AUDIO_MODE:-auto}"
case "${audio_mode,,}" in
  mute|off|disabled)
    should_disable_audio=1
    ;;
  force|on|enabled)
    should_disable_audio=0
    ;;
  auto)
    if [ -n "${SSH_CONNECTION:-}" ]; then
      if [ -z "${PULSE_SERVER:-}" ] && [ -z "${PIPEWIRE_REMOTE:-}" ]; then
        should_disable_audio=1
      fi
    fi
    ;;
  *)
    echo "Unknown DOS_AUDIO_MODE '${audio_mode}', defaulting to auto." >&2
    if [ -n "${SSH_CONNECTION:-}" ] && [ -z "${PULSE_SERVER:-}" ] && [ -z "${PIPEWIRE_REMOTE:-}" ]; then
      should_disable_audio=1
    fi
    ;;
esac

if [ "${should_disable_audio}" -eq 1 ]; then
  echo "dos-shell: muting DOS audio for this session" >&2
  export AO_DRIVER="${AO_DRIVER:-null}"
fi

detect_landlock_support() {
  local header
  for header in /usr/include/linux/landlock.h \
                /usr/include/uapi/linux/landlock.h \
                /usr/lib*/gcc/*/*/include/uapi/linux/landlock.h; do
    if [ -f "$header" ] && grep -q 'LANDLOCK_ACCESS_FS_REFER' "$header" 2>/dev/null; then
      return 0
    fi
  done
  return 1
}

landlock_mode="${DOS_LANDLOCK_MODE:-auto}"
case "${landlock_mode,,}" in
  auto)
    if detect_landlock_support; then
      :
    else
      echo "dos-shell: disabling Landlock sandbox (ABI mismatch detected)" >&2
      DOSEMU_ARGS+=(-p)
    fi
    ;;
  off|disable|disabled)
    echo "dos-shell: Landlock sandbox disabled by DOS_LANDLOCK_MODE" >&2
    DOSEMU_ARGS+=(-p)
    ;;
  force|on|enabled)
    ;;
  *)
    echo "Unknown DOS_LANDLOCK_MODE '${landlock_mode}', defaulting to auto." >&2
    if detect_landlock_support; then
      :
    else
      echo "dos-shell: disabling Landlock sandbox (ABI mismatch detected)" >&2
      DOSEMU_ARGS+=(-p)
    fi
    ;;
esac

write_autoconfig() {
  local need_config=0
  local conf_path="${DOSEMU_DIR}/dosemurc"
  local legacy_conf="${DOS_HOME}/.dosemurc"
  local managed_marker="# Managed by dos-shell for compatibility"

  if [ "${FORCE_CPU_EMULATION}" -eq 1 ] || [ "${should_disable_audio}" -eq 1 ]; then
    need_config=1
  fi

  if [ "${need_config}" -eq 1 ]; then
    if [ -f "${legacy_conf}" ] && grep -qF "${managed_marker}" "${legacy_conf}" 2>/dev/null; then
      rm -f "${legacy_conf}"
    fi
    local tmp_conf="${conf_path}.tmp"
    {
      echo "${managed_marker}"
      echo "define parser_version_3"
      if [ "${FORCE_CPU_EMULATION}" -eq 1 ]; then
        echo '$_cpu_vm = "emulated"'
        echo '$_cpu_vm_dpmi = "emulated"'
      fi
      if [ "${should_disable_audio}" -eq 1 ]; then
        echo '$_sound = (off)'
        echo '$_pcm_hpf = (off)'
      fi
    } > "${tmp_conf}"
    mv "${tmp_conf}" "${conf_path}"
    if [ "$(id -u)" -eq 0 ]; then
      chown "${DOS_USER}:${DOS_USER}" "${conf_path}"
    fi
    echo "dos-shell: wrote ${conf_path} overrides" >&2
  else
    for candidate in "${conf_path}" "${legacy_conf}"; do
      if [ -f "${candidate}" ] && grep -qF "${managed_marker}" "${candidate}" 2>/dev/null; then
        rm -f "${candidate}"
        echo "dos-shell: removed autogenerated ${candidate}" >&2
      fi
    done
  fi
}

if [ "${DOS_FORCE_INSTALL:-0}" = "1" ] || [ ! -f "${INSTALL_SENTINEL_PATH}" ]; then
  reset_drive_c
  touch "${INSTALL_SENTINEL_PATH}"
  if [ "$(id -u)" -eq 0 ]; then
    chown "${DOS_USER}:${DOS_USER}" "${INSTALL_SENTINEL_PATH}"
  fi
else
  echo "Reusing existing SvarDOS installation on ${C_DRIVE}" >&2
fi

sync_allowed_content
sync_extra_drives
apply_templates
run_pre_boot_hook
write_autoconfig

if [ "$(id -u)" -eq 0 ]; then
  chown -R "${DOS_USER}:${DOS_USER}" "${DOSEMU_DIR}"
fi

if [ "${ALLOW_MODE}" = "all" ] && [ "${#allowed_entries[@]}" -gt 0 ]; then
  echo "All files in ${ALLOWED_REPO} are available on drive C:."
elif [ "${#allowed_entries[@]}" -gt 0 ]; then
  echo "Allowlisted files copied to C: from ${ALLOWED_REPO}:"
  for entry in "${allowed_entries[@]}"; do
    echo "  ${entry}"
  done
fi

if [ "${#extra_drive_logs[@]}" -gt 0 ]; then
  echo "Additional DOS drives mapped:"
  for mapping in "${extra_drive_logs[@]}"; do
    echo "  ${mapping}"
  done
fi

if [ "$(id -u)" -eq 0 ]; then
  exec runuser -u "${DOS_USER}" -- dosemu "${DOSEMU_ARGS[@]}"
else
  exec dosemu "${DOSEMU_ARGS[@]}"
fi