#!/usr/bin/env bash

set -e

! read -rd '' FILTER_AWK <<'EOF'
function flr(n, s) { return int(n / s) * s }

{
	t = mktime(gensub(/(.*\/|^)(.+)-(..)-(..)-(..)(..)(..)/,
		"\\2 \\3 \\4 \\5 \\6 \\7", 1), 1)

	h = flr(t, 60*60)
	d = flr(t, 24*60*60)
	m = mktime(strftime("%Y %m", t, 1) " 01 00 00 00", 1)
	w = m + flr(t - m, 7*24*60*60)
}

h in hkeep || hc++ < 24 { hkeep[h] = $1 }
d in dkeep || dc++ < 7 { dkeep[d] = $1 }
w in wkeep || wc++ < 4 { wkeep[w] = $1 }
{ mkeep[m] = $1 }

END {
	for (i in hkeep) keep[hkeep[i]]++
	for (i in dkeep) keep[dkeep[i]]++
	for (i in wkeep) keep[wkeep[i]]++
	for (i in mkeep) keep[mkeep[i]]++

	asorti(keep)
	for (i in keep) print keep[i]
}
EOF

run() {
	echo "* ${@}"
	"${@}"
}

backup() {
	dest_dir="${1}"
	src_path="${2}"

	[[ "$((dcount++))" -ne 0 ]] && echo
	echo "[${dcount}] ${src_path} => ${dest_dir}"
	mapfile -t snaps < <(shopt -s nullglob;
		printf '%s\n' "${dest_dir}/"* | sort -r | head -c -1)

	dest_path="${dest_dir}/$(date -u '+%Y-%m-%d-%H%M%S')"
	run rsync -ac --mkpath ${snaps[0]:+"--link-dest=${snaps[0]}"} \
		"${src_path}" "${dest_path}"
	snaps=("${dest_path}" "${snaps[@]}")

	mapfile -t keep < <(
		awk "${FILTER_AWK}" < <(printf '%s\n' "${snaps[@]}"))
	if [[ -z "${keep}" ]]; then
		echo "WARNING: dirs to keep shouldn't be empty; skipping" >&2
		return
	fi

	for ((i = ${#snaps[@]} - 1, ki = 0; i >= 0; --i)); do
		if [[ "${snaps[i]}" == "${keep[ki]}" ]]; then
			((++ki))
		else
			run rm -r "${snaps[i]}"
		fi
	done

	printf 'kept %s\n' "${keep[@]}"
}

while IFS='=' read -r f1 f2; do
	[[ -z "${f1}" ]] && continue

	if [[ "${f1}" =~ ^\[(.*)]$ ]]; then
		base_path="${BASH_REMATCH[1]}"
		continue
	fi

	backup "${base_path}/${f1}" "${f2}"
done < "${1}"