add carousel maker

Author: mathdroid

README.md

@@ -140,9 +140,11 @@ By default, webhook will listen on port `5463`. You should change it if it inter
 
   - `.addSticker({packageId, stickerId})` // both params are of number type. see https://devdocs.line.me/files/sticker_list.pdf
 
-  - `.addButtons({thumbnailImageUrl, altText, title, text, actions})` // Buttons template message. `actions` must follow Action template. length of `actions` <=4
+  - `.addButtons({thumbnailImageUrl, altText, title, text, actions})` // Buttons template message. `actions` is an array of [`action` objects](https://devdocs.line.me/en/#template-action). length of `actions` <=4
 
-  - `.addConfirm({altText, text, actions})` // confirmation type. actions max length = 2
+  - `.addConfirm({altText, text, actions})` // confirmation type. `actions` max length = 2
+
+  - `.addCarousel({altText, columns})` // where `columns` is an array of [`column` object](https://devdocs.line.me/en/#column-object). Column object is in the shape of `{thumbnailImageUrl, title, text, actions}`. `actions` is an array of [`action` objects](https://devdocs.line.me/en/#template-action).
 
   - `.addVideo, etc` (WIP)
 

src/messages.js

@@ -181,6 +181,34 @@ class Messages {
     return this
   }
 
+  addCarousel ({altText, columns}) {
+    if (!altText) {
+      console.error('altText must not be empty.')
+      return this
+    }
+    if (this._payload.length >= 5) {
+      console.error('Maximum payload length is 5.')
+      return this
+    }
+
+    this._payload.push({
+      type: 'template',
+      altText,
+      template: {
+        type: 'carousel',
+        columns: columns.slice(0, 4).map(({thumbnailImageUrl, title, text, actions}) => {
+          return ({
+            thumbnailImageUrl,
+            title,
+            text,
+            actions
+          })
+        })
+      }
+    })
+    return this
+  }
+
   commit () {
     return this._payload
   }