#!/bin/bash

set +e

verwendung() {
  >&2 echo 'digest-mailer collects emails into digests before sending them.'
  >&2 echo ''
  >&2 echo 'Usage: digest-mailer [OPTIONS]'
  >&2 echo '  -f:'
  >&2 echo '    flush all pending emails'
  >&2 echo '  -f $receiver:'
  >&2 echo '    flush pending emails to $receiver (hash)'
  >&2 echo \
'#HELPTEXT#    #'
  exit 1
}

extract_receiver_hash() {
  sed -n '
    /^$/q
    s/^To:\s*//
    T
    p
  ' | \
    sha224sum | \
    awk '{print $1}'
}

if [ "x$1" = 'x--help' ]; then
  verwendung
fi

if [ "x$1" = 'x--version' ]; then
  echo '#VERSION#'
  exit
fi

if [ "x$1" = 'x-f' ]; then
  flush=true
  shift
  if [ $# -eq 0 ]; then
    receiver=''
  else
    receiver="$1"
    shift
  fi
else
  flush=false
fi

if [ $# -ne 0 ]; then
  verwendung
fi

min_delay=3600
max_delay=3600
agressivity=0
mail_cmd='sendmail -t'

if [ -r '#ETCDIR#/digest-mailer.conf' ]
then
  . '#ETCDIR#/digest-mailer.conf'
fi

sender=$(
  whoami | \
    sha224sum | \
    awk '{print $1}'
)
if ${flush} && \
  [ -z "${receiver}" ]; then
  exec 9> '#LIBDIR#/digest-mailer/digest-mailer.flush.from.'"${sender}"'.lock'
  if ! flock -n 9; then
    # silently fail if lock is not available ("flush" is not _that_ important)
    exit
  fi
  find '#LIBDIR#/digest-mailer' -regextype grep -maxdepth 1 -mindepth 1 \
    -regex ".*/${sender}\.[0-9a-f]\+\.[0-9]\+\.[0-9a-f]\+\$" | \
    while read -r file; do
      extract_receiver_hash < "${file}"
    done | \
    sort -u | \
    xargs -rn1 "$0" -f
  exit
fi

time=$(
  date +%s
)
if ! ${flush}; then
  message=$(
    cat
  )
  receiver=$(
    printf '%s\n' "${message}" | \
      extract_receiver_hash
  )
  hash=$(
    printf '%s' "${message}" | \
      sha224sum | \
      awk '{print $1}'
  )
  exec 9> '#LIBDIR#/digest-mailer/digest-mailer.from.'"${sender}"'.to.'"${receiver}"'.lock'
  flock 9
  # we block if that lock is not available - the sender expects his mails delivered!
  printf '%s' "${message}" > "#LIBDIR#/digest-mailer/${sender}.${receiver}.${time}.${hash}"
else
  exec 9> '#LIBDIR#/digest-mailer/digest-mailer.from.'"${sender}"'.to.'"${receiver}"'.lock'
  if ! flock -n 9; then
    # silently fail if lock is not available ("flush" is not _that_ important)
    exit
  fi
fi

if [ -s "#LIBDIR#/digest-mailer/${sender}.${receiver}.last-sent" ]; then
  last_sent=$(
    cat "#LIBDIR#/digest-mailer/${sender}.${receiver}.last-sent"
  )
else
  last_sent='0'
fi

first_unsent=$(
  find '#LIBDIR#/digest-mailer' -regextype grep -maxdepth 1 -mindepth 1 \
    -regex ".*/${sender}\.${receiver}\.[0-9]\+\.[0-9a-f]\+\$" \
    -printf '%f\n' | \
    cut -d. -f3 | \
    sort -nr | \
    tail -n1
)
if ${flush} && \
  [ -z "${first_unsent}" ]; then
  # no pending emails at all
  exit
fi
to_send=$(
  find '#LIBDIR#/digest-mailer' -regextype grep -maxdepth 1 -mindepth 1 \
    -regex ".*/${sender}\.${receiver}\.[0-9]\+\.[0-9a-f]\+\$" | \
    sort
)
to_send_count=$(
  printf '%s\n' "${to_send}" | \
    wc -l
)
if [ $((last_sent + min_delay)) -gt ${time} ]; then
  # last email was sent too close
  exit
fi
if [ ${to_send_count} -gt 1 ] && \
  printf '%s - (%s+%s)*%s - (%s+%s)*(1-%s)\n' \
    "${time}" \
    "${min_delay}" "${last_sent}" "${agressivity}" \
    "${max_delay}" "${first_unsent}" "${agressivity}" | \
    bc | \
    grep -q '^-' && \
  [ $((first_unsent + max_delay)) -ge ${time} ]; then
  exit
fi

printf '%s' "${time}" > "#LIBDIR#/digest-mailer/${sender}.${receiver}.last-sent"

if [ ${to_send_count} -eq 1 ]; then
  ${mail_cmd} < "${to_send}"
  rm "${to_send}"
  exit
fi

{
  sed -n '
    /^$/q
    s/^Subject:.*$/Subject: mail-digest ('"${to_send_count}"')/
    p
  ' "$(
    printf '%s\n' "${to_send}" | \
      head -n1
    )"
  printf '\n'
  counter=1
  printf '%s\n' "${to_send}" | \
    while read -r file; do
      sed -n '
        s/^Subject:\s*//
        T
        p
      ' "${file}"
    done | \
    sort | \
    uniq -c | \
    sort -k1nr,1 -k2,2 | \
    sed '
      s/^\s*\([0-9]\+\)\s\+/\1: /
    '
  printf '%s\n' "${to_send}" | \
    while read -r file; do
      date=$(
        printf '%s\n' "${file##*/}" | \
          cut -d. -f3
      )
      date=$(
        date -d"@${date}"
      )
      printf 'vvvvv %s. (%s) vvvvv\n' \
        "${counter}" \
        "${date}"
      cat "${file}"
      printf '\n^^^^^ %s. (%s) ^^^^^\n' \
        "${counter}" \
        "${date}"
      counter=$((counter+1))
      rm "${file}"
    done
} | ${mail_cmd}