#!/bin/bash
#
# swapon — create, enable and persist an 8GB swap file.
#
# Runs on each managed server (Alpine/OpenRC). Deploy with ./update_sbin, then:
#
#     rex doas /4server/sbin/swapon
#
# The script aborts if any swap is already active or if /swapfile already
# exists, so it is safe to run against the whole fleet.
#
# Optional first argument: swap size in MiB (default 8192 = 8GB).

set -euo pipefail

SWAPFILE="/swapfile"
SWAP_SIZE_MB="${1:-8192}"
FSTAB="/etc/fstab"

log() {
    echo "[$(hostname)] $*"
}

die() {
    echo "[$(hostname)] ERROR: $*" >&2
    exit 1
}

case "$SWAP_SIZE_MB" in
    ''|*[!0-9]*) die "swap size must be a positive integer in MiB" ;;
esac
[ "$SWAP_SIZE_MB" -gt 0 ] || die "swap size must be greater than zero"

# Remove a partially created swap file if anything fails before it is enabled.
CREATED=0
cleanup() {
    [ "$CREATED" -eq 1 ] || return 0
    [ -e "$SWAPFILE" ] || return 0
    if grep -q "^${SWAPFILE}[[:space:]]" /proc/swaps; then
        return 0
    fi
    log "removing incomplete ${SWAPFILE}"
    rm -f "$SWAPFILE"
}
trap cleanup EXIT

# --- must run as root ---------------------------------------------------
[ "$(id -u)" -eq 0 ] || die "must be run as root (use: rex doas /4server/sbin/swapon)"

# --- abort if swap is already active ------------------------------------
# /proc/swaps always has a header line; anything more means swap is in use.
if [ "$(wc -l < /proc/swaps)" -gt 1 ]; then
    echo "[$(hostname)] ERROR: swap is already active:" >&2
    cat /proc/swaps >&2
    exit 1
fi

# --- abort if the swap file already exists ------------------------------
if [ -e "$SWAPFILE" ]; then
    die "$SWAPFILE already exists; remove it manually before recreating swap"
fi

# --- persistence requires OpenRC's swap service --------------------------
[ -x /etc/init.d/swap ] || \
    die "/etc/init.d/swap not found; cannot persist swap across reboots"

# --- make sure there is enough room on / ---------------------------------
AVAIL_KB=$(df -Pk / | awk 'NR==2 {print $4}')
# Leave a 100MiB margin for filesystem metadata.
REQUIRED_KB=$((SWAP_SIZE_MB * 1024 + 102400))
[ "$AVAIL_KB" -ge "$REQUIRED_KB" ] || \
    die "not enough free space on / (need ${SWAP_SIZE_MB}MiB, have $((AVAIL_KB / 1024))MiB)"

# --- create the swap file -----------------------------------------------
log "creating ${SWAP_SIZE_MB}MiB swap file at ${SWAPFILE}"
CREATED=1
dd if=/dev/zero of="$SWAPFILE" bs=1M count="$SWAP_SIZE_MB"
chmod 600 "$SWAPFILE"
/sbin/mkswap "$SWAPFILE"

# --- persist across reboots ---------------------------------------------
# OpenRC's swap service runs `swapon -a`, which reads /etc/fstab.
if ! grep -qE "^[[:space:]]*${SWAPFILE}[[:space:]]" "$FSTAB"; then
    # Terminate the last line first in case fstab has no trailing newline.
    [ -z "$(tail -c 1 "$FSTAB")" ] || echo >> "$FSTAB"
    echo "${SWAPFILE} none swap sw 0 0" >> "$FSTAB"
    log "added ${SWAPFILE} to ${FSTAB}"
fi

rc-update add swap boot >/dev/null 2>&1 || \
    die "could not add the swap service to the boot runlevel"

# --- enable it now -------------------------------------------------------
# Absolute path avoids recursing into this script if /4server/sbin is on PATH.
/sbin/swapon "$SWAPFILE"

log "swap enabled:"
cat /proc/swaps