#autoload

# Usage:
#   _combination [-s S] TAG STYLE \
#     Ki1[:Ni1]=Pi1 Ki2[:Ni2]=Pi2 ... Kim[:Nim]=Pim Kj[:Nj] EXPL...
#
#  STYLE should be of the form K1-K2-...-Kn.
#
# Example: telnet
#
#  Assume an user sets the style `users-hosts-ports' as for the my-accounts
#  tag:
#
#    zstyle ':completion:*:*:telnet:*:my-accounts' users-hosts-ports \
#      @host0: user1@host1: user2@host2:
#      @mail-server:{smtp,pop3}
#      @news-server:nntp
#      @proxy-server:8000
# 
#
#  `_telnet' completes hosts as:
#
#    _combination my-accounts users-hosts-ports \
#      ${opt_args[-l]:+users=${opt_args[-l]:q}} \
#      hosts "$expl[@]"
#
#  This completes `host1', `host2', `mail-server', `news-server' and
#  `proxy-server' according to the user given with `-l' if it is exists.
#  And if it is failed, `_hosts' is called.
# 
#  `_telnet' completes ports as:
#
#    _combination my-accounts users-hosts-ports \
#      ${opt_args[-l]:+users=${opt_args[-l]:q}} \
#      hosts="${line[2]:q}" \
#      ports "$expl[@]"
#
#  This completes `smtp', `pop3', `nntp' and `8000' according to the
#  host argument --- $line[2] and the user option argument if it is
#  exists. And if it is failed, `_ports' is called.
#
#  `_telnet' completes users for an argument of option `-l' as:
#
#    _combination my-accounts users-hosts-ports \
#      ${line[2]:+hosts="${line[2]:q}"} \
#      ${line[3]:+ports="${line[3]:q}"} \
#      users "$expl[@]"
#
#  This completes `user1' and `user2' according to the host argument and
#  the port argument if they are exist. And if it is failed, `_users' is
#  called.

local sep tag style keys pats key num tmp

if [[ "$1" = -s ]]; then
  sep="$2"
  shift 2
elif [[ "$1" = -s* ]]; then
  sep="${1[3,-1]}"
  shift
else
  sep=:
fi

tag="$1"
style="$2"
shift 2

keys=( ${(s/-/)style} )
pats=( "${(@)keys/*/*}" )

while [[ "$1" = *=* ]]; do
  tmp="${1%%\=*}"
  key="${tmp%:*}"
  num="${${tmp##*:}:-1}"
  pats[$keys[(in:num:)$key]]="${1#*\=}"
  shift
done

key="${1%:*}"
num="${${1##*:}:-1}"
shift

if zstyle -a ":completion:${curcontext}:$tag" "$style" tmp; then
  eval "tmp=( \"\${(@M)tmp:#\${(j($sep))~pats}}\" )"
  if (( keys[(in:num:)$key] != 1 )); then
    eval "tmp=( \${tmp#\${(j(${sep}))~\${(@)\${(@)keys[2,(rn:num:)\$key]}/*/*}}${~sep}} )"
  fi
  tmp=( ${tmp%%${~sep}*} )

  compadd "$@" - $tmp || { (( $+functions[_$key] )) && "_$key" "$@" }
else
  (( $+functions[_$key] )) && "_$key" "$@"
fi