mail: Add contacts lookup script

Added `mail-searchcontacts` script, which uses notmuch to search for all
contacts of the mail database.

Can be invoked without any arguments to list *all* contacts of the
dataase in descending order of message count.
Otherwise, it will filter known contacts, first by prioritizing the
'from:' field, and otherwise by searching through the whole database for
the keywords passed in.

It will also re-format the results so that the list consists of
tab-delineated 'mail name' rows. If there is no name, the row will only
contain the bare e-mail address. This format is best accepted by aerc,
for which the script is written.

aerc uses the contacts script for its address completion in editing
e-mail headers.

Renamed `checkmail` to `mail-check` to fit the naming scheme of
`mail-[action]` for mail scripts, to better be able to group them in the
shell.

mail/.local/bin/mail-check

@@ -0,0 +1,69 @@
+#!/usr/bin/env sh
+# runs mbsync, with pre-hooks and post-hooks
+# by default, first runs imapfilter
+# and after indexes with notmuch
+#
+# To run without invoking any hooks or retry attempts,
+# run `checkmail raw`
+# this will simply invoke a single isync run on all
+# boxes with the correct config file set.
+#
+# for more advanced, per-account/channel hooks, see
+# https://sourceforge.net/p/isync/feature-requests/8/
+
+MBSYNC_MAX_TRIES=3
+MBSYNC_PRE="imapfilter -c /home/marty/.config/imapfilter/config.lua"
+MBSYNC_POST="notmuch new && afew --tag --new"
+
+# fail the routine and optionally send a message why
+fail() {
+  [ -n "$1" ] && echo "$1"
+  exit 1
+}
+
+checkmail() {
+  mbsync -c "$XDG_CONFIG_HOME/isync/mbsyncrc" -a
+}
+
+checkonline() {
+  # Ping 1.1.1.1 to confirm that we are on the internet
+  ping -c 1 "1.1.1.1" >/dev/null 2>/dev/null || fail "checkmail can not access the internet."
+}
+
+# Routine start
+
+# check
+
+# skip any retries and pre/post hooks, just run mbsync
+if [ "$1" = "raw" ]; then
+  checkmail
+  exit
+fi
+
+main() {
+  $MBSYNC_PRE
+
+  tries=0
+  while true; do
+    if checkmail; then
+      break
+    fi
+
+    tries=$((tries + 1))
+    if [ $tries -gt $MBSYNC_MAX_TRIES ]; then
+      fail "maximum retries reached without success."
+    fi
+  done
+  unset tries
+
+  $MBSYNC_POST
+}
+
+notmuch_foldertags() {
+  notmuch tag +dump -inbox -deleted -- folder:Dump and not folder:Inbox
+  notmuch tag +archived -inbox -deleted -- folder:Archive and not folder:Inbox
+  notmuch tag +deleted -inbox -archived -- folder:Trash and not folder:Inbox
+}
+
+main
+notmuch_foldertags