Add cachy-auto-update: unattended background updates for CachyOS

A root systemd service applies pacman, AUR, Flatpak and AppImage updates on
its own, gated on battery state, gaming activity and whether anybody else is
using the package system. The CLI is deliberately two switches plus status.

No user password is stored anywhere: pacman runs as root directly, and the AUR
step - which makepkg forbids running as root - drops to a locked system account
that sudoers permits to call pacman without a password.

src/lib/config.sh

@@ -0,0 +1,111 @@
+# shellcheck shell=bash
+#
+# Reading and writing /etc/cachy-auto-update/cachy-auto-update.conf.
+#
+# The file is deliberately *parsed* rather than sourced: it is edited by a
+# root-run daemon, and sourcing it would turn a stray line into arbitrary code
+# execution. The format is one "Key=Value" per line, '#' starts a comment.
+
+# cau_config_get <Key> [default]
+cau_config_get() {
+	local key="$1" default="${2:-}" val
+
+	[[ -r $CAU_CONFIG ]] || { printf '%s\n' "$default"; return; }
+
+	val="$(sed -nE "s/^[[:space:]]*${key}[[:space:]]*=[[:space:]]*(.*)$/\\1/p" \
+		"$CAU_CONFIG" 2>/dev/null | tail -n1)"
+
+	# strip a trailing comment and surrounding whitespace/quotes
+	val="${val%%#*}"
+	val="${val#"${val%%[![:space:]]*}"}"
+	val="${val%"${val##*[![:space:]]}"}"
+	val="${val%\"}"
+	val="${val#\"}"
+
+	if [[ -n $val ]]; then
+		printf '%s\n' "$val"
+	else
+		printf '%s\n' "$default"
+	fi
+}
+
+# cau_config_bool <Key> <default: yes|no>
+# Succeeds when the key is truthy.
+cau_config_bool() {
+	local val
+	val="$(cau_config_get "$1" "$2")"
+	case "${val,,}" in
+		yes|y|true|1|on|enabled) return 0 ;;
+		*) return 1 ;;
+	esac
+}
+
+# cau_config_int <Key> <default>
+cau_config_int() {
+	local val
+	val="$(cau_config_get "$1" "$2")"
+	[[ $val =~ ^-?[0-9]+$ ]] && printf '%s\n' "$val" || printf '%s\n' "$2"
+}
+
+# cau_config_set <Key> <Value>
+# Replaces the key in place if present (including a commented-out template
+# line), otherwise appends it. Requires write access to the config file.
+cau_config_set() {
+	local key="$1" value="$2" tmp
+
+	if [[ ! -e $CAU_CONFIG ]]; then
+		mkdir -p "$(dirname "$CAU_CONFIG")" || return 1
+		printf '# %s configuration\n' "$CAU_NAME" > "$CAU_CONFIG" || return 1
+	fi
+	[[ -w $CAU_CONFIG ]] || return 1
+
+	tmp="$(mktemp "${CAU_CONFIG}.XXXXXX")" || return 1
+	# keep the original permissions rather than mktemp's 0600
+	chmod --reference="$CAU_CONFIG" "$tmp" 2>/dev/null || chmod 0644 "$tmp"
+
+	if grep -qE "^[[:space:]]*#?[[:space:]]*${key}[[:space:]]*=" "$CAU_CONFIG"; then
+		awk -v key="$key" -v value="$value" '
+			!done && $0 ~ "^[[:space:]]*#?[[:space:]]*" key "[[:space:]]*=" {
+				print key "=" value; done = 1; next
+			}
+			# drop any further occurrences so the file cannot grow duplicates
+			$0 ~ "^[[:space:]]*" key "[[:space:]]*=" { next }
+			{ print }
+		' "$CAU_CONFIG" > "$tmp" || { rm -f "$tmp"; return 1; }
+	else
+		cat "$CAU_CONFIG" > "$tmp" || { rm -f "$tmp"; return 1; }
+		printf '%s=%s\n' "$key" "$value" >> "$tmp"
+	fi
+
+	mv -f "$tmp" "$CAU_CONFIG"
+}
+
+# ---------------------------------------------------------------------------
+# Resolved settings
+# ---------------------------------------------------------------------------
+# Loaded once per process into plain variables so the rest of the code does not
+# re-parse the file for every lookup.
+
+cau_config_load() {
+	CFG_ENABLED=no;               cau_config_bool Enabled              no  && CFG_ENABLED=yes
+	CFG_NOTIFICATIONS=no;         cau_config_bool Notifications        yes && CFG_NOTIFICATIONS=yes
+	CFG_REQUIRE_AC=no;            cau_config_bool RequireAC            no  && CFG_REQUIRE_AC=yes
+	CFG_SKIP_GAMING=no;           cau_config_bool SkipWhenGaming       yes && CFG_SKIP_GAMING=yes
+	CFG_AUR=no;                   cau_config_bool UpdateAUR            yes && CFG_AUR=yes
+	CFG_FLATPAK=no;               cau_config_bool UpdateFlatpak        yes && CFG_FLATPAK=yes
+	CFG_APPIMAGE=no;              cau_config_bool UpdateAppImages      yes && CFG_APPIMAGE=yes
+	CFG_DEVEL=no;                 cau_config_bool UpdateDevel          no  && CFG_DEVEL=yes
+	CFG_RESOLVE_CONFLICTS=no;     cau_config_bool AutoResolveConflicts yes && CFG_RESOLVE_CONFLICTS=yes
+	CFG_CLEAN_CACHE=no;           cau_config_bool CleanCache           no  && CFG_CLEAN_CACHE=yes
+	CFG_REMOVE_ORPHANS=no;        cau_config_bool RemoveOrphans        no  && CFG_REMOVE_ORPHANS=yes
+	CFG_NOTIFY_SUCCESS=no;        cau_config_bool NotifyOnSuccess      yes && CFG_NOTIFY_SUCCESS=yes
+	CFG_NOTIFY_ERROR=no;          cau_config_bool NotifyOnError        yes && CFG_NOTIFY_ERROR=yes
+	CFG_NOTIFY_REBOOT=no;         cau_config_bool NotifyReboot         yes && CFG_NOTIFY_REBOOT=yes
+
+	CFG_INTERVAL="$(cau_config_get UpdateInterval 1d)"
+	CFG_INTERVAL_SECONDS="$(cau_duration_to_seconds "$CFG_INTERVAL" 86400)"
+	CFG_MIN_BATTERY="$(cau_config_int MinBatteryPercent 40)"
+	CFG_KEEP_OLD="$(cau_config_int KeepOldPackages 3)"
+	CFG_AUR_HELPER="$(cau_config_get AURHelper auto)"
+	CFG_IGNORE_PKG="$(cau_config_get IgnorePkg '')"
+}