feat: If a required argument is not supplied, ask for it and then resolve the command listener.

Thanks to @amovah for his contributions

lib/functions/argument-parser.js

@@ -6,6 +6,7 @@ const ESCAPABLE = '.^$*+?()[{\\|}]'.split('');
 
 const REQUIRED = 0;
 const OPTIONAL = 1;
+const REST = 2;
 
 /**
  * Parses a message for arguments, based on format
@@ -39,8 +40,7 @@ export default function argumentParser(format, string) {
   string = string.replace(/[^\s]+/, '').trim();
   format = format.replace(/[^\s]+/, '').trim();
 
-  if (!format)
-    return {args: {}, params: {}};
+  if (!format) return {args: {}, params: {}};
 
   let indexes = [],
       params = {};
@@ -60,6 +60,7 @@ export default function argumentParser(format, string) {
     });
   format = format.replace(FORMAT_REST, (full, arg, offset) => {
     indexes.push({offset, arg});
+    params[arg] = REST;
     return getFormat(null, 'rest');
   });
 

lib/index.js

@@ -13,6 +13,9 @@ const DEFAULTS = {
   }
 };
 
+const REQUIRED = 0;
+const OPTIONAL = 1;
+
 /**
  * Bot class used to connect to a new bot
  * Bots have an api property which gives access to all Telegram API methods,
@@ -165,40 +168,43 @@ export default class Bot extends EventEmitter {
         return;
       }
 
-      if (ev.parse) {
-        let {params, args} = ev.parse(res.message.text);
-        if (!Object.keys(params).length) {
+      if (!ev.parse) {
+        ev.listener(res.message);
+        return;
+      }
+
+      let {params, args} = ev.parse(res.message.text);
+
+      const requiredParams = Object.keys(params).filter(param => {
+        return params[param] === REQUIRED;
+      });
+
+      if (!requiredParams.length) {
+        ev.listener(res.message);
+        return;
+      }
+
+      const bot = this;
+      function* getAnswer() {
+        for (let param of requiredParams) {
+          const msg = new Message().to(res.message.chat.id)
+                                   .text(`Enter value for ${param}`);
+          yield bot.send(msg).then(answer => {
+            args[param] = answer.text;
+          });
+        }
+      }
+
+      const iterator = getAnswer();
+      (function loop() {
+        const next = iterator.next();
+        if (next.done) {
           ev.listener(res.message);
           return;
         }
-        var bot = this;
-        function ask(param) {
-          if (!args[param]) {
-            bot.send(new Message().text(`Enter value for ${param}`).to(res.message.chat.id))
-            .then(answer => {
-              args[param] = answer.text;
-              iter.next();
-            });
-          }
-        }
-        function* gen(par) {
-          let index = 0;
-          while (index < par.length) {
-            while (args[par[index]] && index < par.length) index++;
-            yield ask(par[index]);
-            index++;
-            if (index == par.length) {
-              res.message.args = args;
-              ev.listener(res.message);
-              return;
-            }
-          }
-        }
-        var iter = gen(Object.keys(params));
-        iter.next();
-      } else {
-        ev.listener(res.message);
-      }
+
+        next.value.then(loop);
+      }());
     });
   }
 }