# This function is the common guts of the gen-applied-string /
# gen-unapplied-string / set-patch-format dance of several backends.
#
# Parameters:
# $1 - name of an array parameter to be the argument to gen-applied-string
# $2 - name of a parameter to store the applied-string in
# $3 - name of an array parameter to be the argument to gen-unapplied-string
# $4 - name of a parameter to store the unapplied-string in
# $5 - context argument for use in zstyle getters
# $6 - name of a parameter to store a patch-format format string in
#
# Output:
# - $hook_com is overwritten and the keys 'applied', 'applied-n',
#   'unapplied', 'unapplied-n', 'all-n' are set.
{
    local REPLY
    if VCS_INFO_hook 'gen-applied-string' "${(@P)1}"; then
        if (( ${(P)#1} )); then
            REPLY=${(P)1[1]}
        else
            REPLY=""
        fi
    else
        REPLY=${hook_com[applied-string]}
    fi
    : ${(P)2::=$REPLY}
    hook_com=()

    if VCS_INFO_hook 'gen-unapplied-string' "${(@P)3}"; then
        REPLY=${(P)#3}
    else
        REPLY=${hook_com[unapplied-string]}
    fi
    : ${(P)4::=$REPLY}
    hook_com=()

    if (( ${(P)#1} )); then
        zstyle -s "${5}" patch-format REPLY || REPLY="%p (%n applied)"
    else
        zstyle -s "${5}" nopatch-format REPLY || REPLY="no patch applied"
    fi
    : ${(P)6::=$REPLY}

    hook_com=(
      applied-n ${(P)#1}
      applied "${(P)2}"
      unapplied-n ${(P)#3}
      unapplied "${(P)4}"
    )
    hook_com[all-n]=$(( ${hook_com[applied-n]} + ${hook_com[unapplied-n]} ))
}