#!/usr/bin/env bash

set -e

# FIXME: clean up repetition
! read -rd '' FILTER_AWK <<'EOF'
function flr(n, s) { return int(n / s) * s }

BEGIN {
	if (match(retain, /([*0-9]+)h/, md)) hr = md[1]
	if (match(retain, /([*0-9]+)d/, md)) dr = md[1]
	if (match(retain, /([*0-9]+)w/, md)) wr = md[1]
	if (match(retain, /([*0-9]+)m/, md)) mr = md[1]
}

{
	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 || hr == "*" || hc++ < hr { hkeep[h] = $1 }
d in dkeep || dr == "*" || dc++ < dr { dkeep[d] = $1 }
w in wkeep || wr == "*" || wc++ < wr { wkeep[w] = $1 }
m in mkeep || mr == "*" || mc++ < mr { 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}"
	retain="${3:-"*h*d*w*m"}"

	[[ "$((dcount++))" -ne 0 ]] && echo
	echo "[${dcount}] [${retain}] ${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 -v "retain=${retain}" "${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]}"
		retain=
		continue
	fi

	if [[ "${f1}" == '$'* ]]; then
		if [[ "${f1}" == '$retain' ]]; then
			retain="${f2}"
		fi

		continue
	fi

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