Implement OCR using tesseract

@@ -17,6 +17,12 @@ const languagedetect_api_url = 'https://openapi.naver.com/v1/papago/detectLangs'
 const db = require('./db');
 db.init();
 
+// Tesseract module for image recognition
+const tesseract = require('node-tesseract-ocr');
+
+// fs module for saving/removing image file upon/after recognition
+const fs = require('fs');
+
 // /echo [whatever]
 bot.onText(/\/echo (.+)/, (msg, match) => {
   // 'msg' is the received Message from Telegram
@@ -184,6 +190,55 @@ bot.onText(/^\/(t|translate)($| ((.|\n)+))/, (msg, match) => {
   }
 });
 
+// When an image file is received, temporarily save it in current directory
+// and use tesseract to recognize its text. The texts are then translated
+// and sent to the user.
+bot.on('photo', (msg) => {
+  const user = msg.from;
+  const chatId = msg.chat.id;
+  const photo = msg.photo[2];
+  const photoId = photo.file_id;
+
+  // Download the image, which will later be deleted to avoid git detection
+  bot.downloadFile(photoId, '.').then(function (filePath) {
+    console.log('Image downloaded: ', filePath);
+
+    // Begin tesseract OCR
+    tesseract.recognize(filePath).then(function (text) {
+      console.log('OCR result: ', text);
+
+      // Translate the result
+      translate(user, text).then(function (result) {
+        // Send recognized text to user
+        bot.sendMessage(chatId, result);
+        // Delete the image
+        fs.unlink(filePath, function (error) {
+          if (error) {
+            console.log('Error deleting image: ', error);
+          } else {
+            console.log('Successfully deleted file ', filePath);
+          }
+        });
+      });
+    }).catch(function (error) {
+      // OCR failed
+      console.log('OCR error: ', error);
+
+      // Delete the image
+      fs.unlink(filePath, function (error) {
+        if (error) {
+          console.log('Error deleting image: ', error);
+        } else {
+          console.log('Successfully deleted file ', filePath);
+        }
+      });
+    });
+  }).catch(function (error) {
+    // Image download failed
+    console.log('Image download error: ', error);
+  });
+});
+
 // /l(anguage)
 // Let user select the language he wants his message to translate to.
 // When triggered, bot will send an inline keyboard message with a list

@@ -417,6 +417,11 @@
         }
       }
     },
+    "node-tesseract-ocr": {
+      "version": "0.1.0",
+      "resolved": "https://registry.npmjs.org/node-tesseract-ocr/-/node-tesseract-ocr-0.1.0.tgz",
+      "integrity": "sha512-gUp+fy8Wiy2ZZQiSe33ApfyaBPOOlTz8nrHjZqWGAX4l06lW01uO6ABA5KWBhO3B1DmWl1Y9T1aLasfXYpm2Dg=="
+    },
     "oauth-sign": {
       "version": "0.9.0",
       "resolved": "https://registry.npmjs.org/oauth-sign/-/oauth-sign-0.9.0.tgz",

@@ -12,6 +12,7 @@
   "dependencies": {
     "mongodb": "^3.2.6",
     "node-telegram-bot-api": "^0.30.0",
+    "node-tesseract-ocr": "^0.1.0",
     "request": "^2.88.0"
   }
 }