Clean up web-search plugin logic to allow easier changes

plugins/web-search/web-search.plugin.zsh

 # web_search from terminal
 
 function web_search() {
-  # get the open command
-  local open_cmd
-  if [[ "$OSTYPE" = darwin* ]]; then
-    open_cmd='open'
-  else
-    open_cmd='xdg-open'
-  fi
+  emulate -L zsh
+
+  # define search engine URLS
+  typeset -A urls
+  urls=(
+    google      "https://www.google.com/search?q="
+    bing        "https://www.bing.com/search?q="
+    yahoo       "https://www.yahoo.com/search?q="
+    duckduckgo  "https://www.duckduckgo.com/?q="
+  )
+
+  # define the open command
+  case "$OSTYPE" in
+    darwin*)  open_cmd="open" ;;
+    linux*)   open_cmd="xdg-open" ;;
+    *)        echo "Platform $OSTYPE not supported"
+              return 1
+              ;;
+  esac
 
   # check whether the search engine is supported
-  if [[ ! $1 =~ '(google|bing|yahoo|duckduckgo)' ]];
-  then
+  if [[ -z "$urls[$1]" ]]; then
     echo "Search engine $1 not supported."
     return 1
   fi
 
-  local url="http://www.$1.com"
-
-  # no keyword provided, simply open the search engine homepage
-  if [[ $# -le 1 ]]; then
-    $open_cmd "$url"
-    return
-  fi
-  if [[ $1 == 'duckduckgo' ]]; then
-  #slightly different search syntax for DDG
-    url="${url}/?q="
+  # search or go to main page depending on number of arguments passed
+  if [[ $# -gt 1 ]]; then
+    # build search url:
+    # join arguments passed with '+', then append to search engine URL
+    url="${urls[$1]}${(j:+:)@[2,-1]}"
   else
-    url="${url}/search?q="
+    # build main page url:
+    # split by '/', then rejoin protocol (1) and domain (2) parts with '//'
+    url="${(j://:)${(s:/:)urls[$1]}[1,2]}"
   fi
-  shift   # shift out $1
-
-  while [[ $# -gt 0 ]]; do
-    url="${url}$1+"
-    shift
-  done
 
-  url="${url%?}" # remove the last '+'
   nohup $open_cmd "$url" >/dev/null 2&>1
 }