{ config, pkgs, ... }:

let
  shell = "${pkgs.dash}/bin/dash";
  pidof = "${pkgs.procps}/bin/pidof";
  pgrep = "${pkgs.procps}/bin/pgrep";
  grep = "${pkgs.gnugrep}/bin/grep";
  sed = "${pkgs.gnused}/bin/sed";
  awk = "${pkgs.gawk}/bin/awk";
  perl = "${pkgs.perl}/bin/perl";
  find = "${pkgs.findutils}/bin/find";

  notifySend = "${pkgs.libnotify}/bin/notify-send";
  notmuch = "${pkgs.notmuch}/bin/notmuch";
  head = "${pkgs.coreutils}/bin/head";
  touch = "${pkgs.coreutils}/bin/touch";
  tr = "${pkgs.coreutils}/bin/tr";

  mbsyncrc = "${config.home.homeDirectory}/.mbsyncrc";
  mbsync = "${pkgs.isync}/bin/mbsync -c ${mbsyncrc}";

  maildir = "${config.home.homeDirectory}/Maildir";
  passwordStoreDir = "${config.home.homeDirectory}/.password-store";
  notmuchConfig = "${config.home.homeDirectory}/.config/notmuch/default/config";
  gnupghome = "${config.home.homeDirectory}/.gnupg";
  lastrun = "${config.home.homeDirectory}/.mailsynclastrun";
in pkgs.writeScriptBin "mailsync" ''
  #!${shell}

  # Run only if not already running in other instance
  ${pidof} mbsync >/dev/null && {
    echo "mbsync is already running."
    exit
  }

  export PASSWORD_STORE_DIR="${passwordStoreDir}"
  export NOTMUCH_CONFIG="${notmuchConfig}"
  export GNUPGHOME="${gnupghome}"
  export GPG_TTY=$TTY

  notify() {
    pgrepoutput="$(${pgrep} -a X\(org\|wayland\))"
    displays="$(echo "$pgrepoutput" | ${grep} -wo "[0-9]*:[0-9]\+" | sort -u)"
    [ -n "$pgrepoutput" ] && for x in ''${displays:-0:}; do
      export DISPLAY=$x
      ${notifySend} \
        --app-name="email" \
        "email" \
        "📬 $2 new mail(s) in \`$1\` account."
    done
  }

  messageinfo() {
    from="$1"
    subject="$2"
    pgrepoutput="$(${pgrep} -a X\(org\|wayland\))"
    displays="$(echo "$pgrepoutput" | ${grep} -wo "[0-9]*:[0-9]\+" | sort -u)"
    [ -n "$pgrepoutput" ] && for x in ''${displays:-0:}; do
      export DISPLAY=$x
      ${notifySend} \
        --app-name="email" \
        "📧$from:" \
        "$subject"
    done
  }

  # Check account for new mail. Notify if there is new content.
  syncandnotify() {
    accounts="$1"
    acc="$(echo "$account" | ${sed} "s/.*\///")"
    if [ -z "$opts" ]; then
      ${mbsync} "$acc"
    else
      ${mbsync} "$opts" "$acc"
    fi
    new=$(
      ${find} \
        "${maildir}/$acc/INBOX/new/" \
        "${maildir}/$acc/Inbox/new/" \
        "${maildir}/mail/$acc/inbox/new/" \
        -type f \
        -newer "${lastrun}" \
          2> /dev/null
    )
    newcount=$(echo "$new" | ${sed} '/^\s*$/d' | wc -l)
    if [ "$newcount" -gt 5 ]; then
      notify "$acc" "$newcount"
    elif [ "$newcount" -gt 0 ]; then
      for file in $new; do
        # Extract subject and sender from mail.
        from=$(
          ${awk} '/^From: / && ++n ==1,/^\<.*\>:/' "$file" | \
            ${perl} -CS -MEncode -ne 'print decode("MIME-Header", $_)' | \
            ${awk} '{ $1=""; if (NF>=3)$NF=""; print $0 }' | \
            ${sed} 's/^[[:blank:]]*[\"'\'''\<]*//;s/[\"'\'''\>]*[[:blank:]]*$//'
        )
        subject=$(
          ${awk} '/^Subject: / && ++n == 1,/^\<.*\>: / && ++i == 2' "$file" | \
            ${head} -n 1 | ${perl} -CS -MEncode -ne 'print decode("MIME-Header", $_)' | \
            ${sed} 's/^Subject: //' | \
            ${sed} 's/^{[[:blank:]]*[\"'\'''\<]*//;s/[\"'\'''\>]*[[:blank:]]*$//' | \
            ${tr} -d '\n'
        )
        messageinfo "$from" "$subject" &
      done
    fi
  }

  # Sync accounts passed as argument or all.
  if [ "$#" -eq "0" ]; then
    accounts="$(${awk} '/^Channel/ {print $2}' "${mbsyncrc}")"
  else
    for arg in "$@"; do
      [ "''${arg%''${arg#?}}" = '-' ] && \
        opts="''${opts:+''${opts} }''${arg}" && \
        shift 1
    done
    accounts=$*
  fi

  # Parallelize multiple accounts
  for account in $accounts; do
    syncandnotify "''${account}" &
  done

  wait

  ${notmuch} new 2>/dev/null

  #Create a touch file that indicates the time of the last run of mailsync
  ${touch} "${lastrun}"
''