secret-santa

#!/bin/sh

__usage () {
cat << EOH
$0 -i file [-n file] [-o file]

$0 generates a Secret Santa list, making sure that no one in the same
team gifts each other (e.g. spouses), and that no one gifts themselves. The
output is one single loop of santa-santee: A gifts B, B gifts C,... Z gifts A.

There are no checks for sanity of input files, and no protection against
infinite loops. Proceed with caution.

-i file:
  input file; default: none

Input: full participant description, one per line
# email            team    Full Name with spaces
  santa@cla.us     XMas    Santa Claus
  moviuro@popho.be noob    Moviuro

-o file:
  output file; default: out.${0##*/}
  this file will be overwritten if it exists

Output: pair information, one per line
# email_santa      Full Santee Name
  santa@cla.us     Moviuro
  moviuro@popho.be Santa Claus

-n file:
  negate file; default: <none>
  this file holds data that we do not wish to see in the output; this can be
  used with previous results of $0 so that noone has
  to gift the same person N years in a row.
  Abusing this functionnality can cause an infinite loop if there are no valid
  list of santa-santee left.

Negate: pair information, one per line, same as Output
# email_santa      Full Santee Name
  santa@cla.us     Foo Bar
  santa@cla.us     Moviuro
  moviuro@popho.be Santa Claus
  foo@example.org  Jane Doe
EOH
}

while getopts ":hi:n:o:" _opt; do
  case "$_opt" in
    h) __usage ; exit ;;
    i) _in="$OPTARG" ;;
    o) _out="$OPTARG" ;;
    n) _nfile="$OPTARG" ;;
    *) __usage >&2 ; exit 1 ;;
  esac
done

[ -z "$_out" ] && _out="out.${0##*/}"
: "${_in?requires an input file}"
_tmp="$(mktemp)"
__cleanup() {
  [ -e "$_tmp" ] && rm "$_tmp"
}
trap __cleanup INT TERM

printf '%s\n' "This might take a while." >&2
: > "$_out"

# Validate the tmp file: if the current line has the same team as the
# previous one, it's not OK.
__check() {
  [ "$(wc -l < "$1")" -lt 2 ] && return 1
  _prev_team=""
  _ret=0
  while read -r _email _team _fullname; do
    case "$_team" in
      "$_prev_team") _ret=1; break;;
      *) _prev_team="$_team";;
    esac
  done < "$1"
  return "$_ret"
}

# Output is only valid if it has as many lines as the input
while ! [ "$(wc -l < "$_out")" -eq "$(wc -l < "$_in")" ]; do
  # Shuffle the input file until it passes the __check
  # The first and last line are the same to avoid dealing with start/end
  # conditions in __check
  : > "$_tmp"
  while ! __check "$_tmp"; do
    sort -R "$_in" > "$_tmp"
    head -n1 "$_tmp" >> "$_tmp"
  done

  # Create a usable out file from the (valid) tmp file
  _prev_name=""
  while read -r _email _ _fullname; do
    if [ -n "$_prev_name" ]; then
      echo "$_email $_prev_name"
    fi
    _prev_name="$_fullname"
  done < "$_tmp" | grep -vxf "$_nfile" > "$_out"
  # grep -vx rejects pairings we don't want to see in the output
done

__cleanup