From 8361d9c8ff5f33b87f50bd2d5c74d3250eb422fc Mon Sep 17 00:00:00 2001
From: Christian Kellner <Christian.Kellner1@ibm.com>
Date: Fri, 12 Nov 2021 09:14:55 +0100
Subject: [PATCH] splitting telegram messages into chunks to avoid errors when
 message exceeds limit of 4096 chars

---
 lib/notification/adapter/telegram.js | 45 ++++++++++++++++++++--------
 1 file changed, 32 insertions(+), 13 deletions(-)

diff --git a/lib/notification/adapter/telegram.js b/lib/notification/adapter/telegram.js
index 6cfc7bc..745a71e 100644
--- a/lib/notification/adapter/telegram.js
+++ b/lib/notification/adapter/telegram.js
@@ -1,6 +1,19 @@
 const { markdown2Html } = require('../../services/markdown');
 const axios = require('axios');
 
+/**
+ * splitting an array into chunks because Telegram only allows for messages up to
+ * 4096 chars, thus we have to split messages into chunks
+ * @param inputArray
+ * @param perChunk
+ */
+const arrayChunks = (inputArray, perChunk) =>
+  inputArray.reduce((all, one, i) => {
+    const ch = Math.floor(i / perChunk);
+    all[ch] = [].concat(all[ch] || [], one);
+    return all;
+  }, []);
+
 /**
  * sends new listings to telegram
  * @param serviceName e.g immowelt
@@ -12,22 +25,28 @@ const axios = require('axios');
 exports.send = ({ serviceName, newListings, notificationConfig, jobKey }) => {
   const { token, chatId } = notificationConfig.find((adapter) => adapter.id === 'telegram').fields;
 
-  let message = `Job: ${jobKey} | Service <b>${serviceName}</b> found <b>${newListings.length}</b> new listings:\n\n`;
+  //we have to split messages into chunk, because otherwise messages are going to become too big and will fail
+  const chunks = arrayChunks(newListings, 3);
 
-  message += newListings.map(
-    (o) =>
-      `<b>${shorten(o.title.replace(/\*/g, ''), 45)}</b>\n` +
-      [o.address, o.price, o.size].join(' | ') +
-      '\n' +
-      `<a href="${o.link}">${o.link}</a>\n\n`
-  );
+  const promises = chunks.map((chunk) => {
+    let message = `Job: ${jobKey} | Service <b>${serviceName}</b> found <b>${newListings.length}</b> new listings:\n\n`;
+    message += chunk.map(
+      (o) =>
+        `<b>${shorten(o.title.replace(/\*/g, ''), 45)}</b>\n` +
+        [o.address, o.price, o.size].join(' | ') +
+        '\n' +
+        `<a href="${o.link}">${o.link}</a>\n\n`
+    );
 
-  return axios.post(`https://api.telegram.org/bot${token}/sendMessage`, {
-    chat_id: chatId,
-    text: message,
-    parse_mode: 'HTML',
-    disable_web_page_preview: true,
+    return axios.post(`https://api.telegram.org/bot${token}/sendMessage`, {
+      chat_id: chatId,
+      text: message,
+      parse_mode: 'HTML',
+      disable_web_page_preview: true,
+    });
   });
+
+  return Promise.all(promises);
 };
 
 function shorten(str, len = 30) {