Merge the database dump scripts into db-dump

garmin-dump, weather-dump and library-dump differed only in project, database and rotation; one
db-dump PROJECT DATABASE week|day replaces them. The units keep their names and only change ExecStart.

.local/bin/db-dump

@@ -0,0 +1,38 @@
+#!/bin/bash
+# Usage: db-dump PROJECT DATABASE week|day
+# Dump a MariaDB database to ~/.local/share/PROJECT/dumps with login ~/.config/PROJECT/dump.cnf.
+# week: per-ISO-week files, keeping the two newest; day: per-weekday files (seven self-rotating copies).
+set -euo pipefail
+
+if (($# != 3)) || [[ $3 != week && $3 != day ]]; then
+    echo "usage: ${0##*/} PROJECT DATABASE week|day" >&2
+    exit 2
+fi
+project=$1 db=$2 mode=$3
+
+cnf=${XDG_CONFIG_HOME:-$HOME/.config}/$project/dump.cnf
+dir=${XDG_DATA_HOME:-$HOME/.local/share}/$project/dumps
+if [[ $mode == week ]]; then
+    out=$dir/$db-$(date +%G-W%V).sql.gz
+else
+    out=$dir/$db-$(LC_ALL=C date +%a).sql.gz
+fi
+keep=2
+
+umask 077
+mkdir -p "$dir"
+
+# Write to a temporary file so a failed dump never replaces a good one
+tmp=$(mktemp "$dir/.dump.XXXXXX")
+trap 'rm -f "$tmp"' EXIT
+
+mariadb-dump --defaults-extra-file="$cnf" --single-transaction --databases "$db" | gzip > "$tmp"
+mv "$tmp" "$out"
+
+# Weekly names sort by week, so all but the last $keep are the old ones
+if [[ $mode == week ]]; then
+    dumps=("$dir/$db"-[0-9][0-9][0-9][0-9]-W[0-9][0-9].sql.gz)
+    if ((${#dumps[@]} > keep)); then
+        rm -f -- "${dumps[@]:0:${#dumps[@]}-keep}"
+    fi
+fi