Extract kickstart.package.installed functions for each package manager

kickstart/recipes/kickstart/package.sh

@@ -5,26 +5,24 @@ kickstart.package.manager() {
   kickstart.info "kickstart supports apt-get, yum or brew" && exit 1
 }
 
+kickstart.package.installed.apt-get() {
+  dpkg -s "$@" >/dev/null 2>&1
+}
+
+kickstart.package.installed.brew() {
+  ! $(brew info "$@" | kickstart.stream.contains "Not installed")
+}
+
+kickstart.package.installed.yum() {
+  local yum_packages="`yum list installed`"
+  for package in "$@"; do
+    kickstart.stream.contains $package <<<$yum_packages || return 1
+  done
+  return 0
+}
+
 kickstart.package.installed() {
-  local pkg_manager=`kickstart.package.manager`
+  kickstart.package.installed.`kickstart.package.manager` "$@"
-
-  if [ $pkg_manager = 'apt-get' ]; then
-    dpkg -s "$@" >/dev/null 2>&1
-    return $?
-  fi
-
-  if [ $pkg_manager = 'brew' ]; then
-    ! $(brew info "$@" | kickstart.stream.contains "Not installed")
-    return $?
-  fi
-
-  if [ $pkg_manager = 'yum' ]; then
-    local yum_packages="`yum list installed`"
-    for package in "$@"; do
-      kickstart.stream.contains $package <<<$yum_packages || return 1
-    done
-    return 0
-  fi
 }
 
 kickstart.package.install() {