#!/bin/bash

decode() {
  sed '
    :a
      s/=?\(ISO-8859-15\?\|windows-1252\|UTF-8\)?Q?\([^=_]*\)?=/\2/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)_/\1 /
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=E4/\1ä/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=E9/\1é/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=F6/\1ö/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=F8/\1ř/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=FC/\1ü/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=FD/\1ý/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=DF/\1ß/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=22/\1"/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=2C/\1,/
      s/\(=?\(ISO-8859-15\?\|windows-1252\)?Q?[^=]*\)=2E/\1,/
      s/\(=?UTF-8?Q?[^=]*\)_/\1 /
      s/\(=?UTF-8?Q?[^=]*\)=c3=a4/\1ä/
      s/\(=?UTF-8?Q?[^=]*\)=c3=b6/\1ö/
      s/\(=?UTF-8?Q?[^=]*\)=c3=bc/\1ü/
      s/\(=?UTF-8?Q?[^=]*\)=c3=9f/\1ß/
      s/\(=?UTF-8?Q?[^=]*\)=c3=98/\1ø/
      s/\(=?UTF-8?Q?[^=]*\)=22/\1"/
      s/\(=?UTF-8?Q?[^=]*\)=2c/\1,/
      ta
  '
}

sed '
  :a
    N
    s/\n\s\+/ /
    ta
  P
  D
' \
| sed -n '
  s@^\(bcc\|Bcc\|BCC\|cc\|Cc\|CC\|To\|Reply-To\): @@
  T
  :b
    s@^\(\([^"]*"[^"]*"\)*[^"]*\),\s\+@\1\n@g
    tb
  p
' \
| sed '
  s#^\(.*\S\)\s*<\(\S\+@\S\+\)>$#\2 \1#
  t
  /^\S\+@\S\+$/!d
' \
| sort -uf \
| while read -r email comment; do
  printf '%s %s %s\n' \
    "${#comment}" \
    "$(echo "$comment" | base64 -w0)" \
    "${email}"
done \
| sort -k3,3 -k1nr,1 \
| uniq -f2 \
| while read -r _ comment email; do
  printf '\t%s\t%s\n' \
    "$(
      printf '%s\n' "${comment}" \
      | base64 -d \
      | sed 's@^\(["'"'"']\)\(.*\)\1@\2@' \
      | decode
    )" \
    "${email}"
done