var ssId = "<YourGoogleSheetID>";
var ss = SpreadsheetApp.openById(ssId);
var sheetProduct = ss.getSheetByName("product");
var sheetLog = ss.getSheetByName("log"); //get sheet for log

function doPost(e) {
  var data = JSON.parse(e.postData.contents); //convert request srting in JSON format into JavaScript object

  //Log text message
  var timeStamp = data.originalDetectIntentRequest.payload.data.timestamp;
  var d = new Date(timeStamp); //creates a JS date object form milliseconds
  var formattedDate = d.getDate() + "/" + (d.getMonth() + 1) + "/" + d.getFullYear();

  var userId = data.originalDetectIntentRequest.payload.data.source.userId;
  var userText = data.originalDetectIntentRequest.payload.data.message.text;
  var intentName = data.queryResult.intent.displayName;

  //set valus to sheet
  var lastRow = sheetLog.getLastRow();
  sheetLog.getRange(lastRow + 1, 1).setValue(formattedDate);
  sheetLog.getRange(lastRow + 1, 2).setValue(userId);
  sheetLog.getRange(lastRow + 1, 3).setValue(userText);
  sheetLog.getRange(lastRow + 1, 4).setValue(intentName);

  //get product quantity
  var userMsg = data.originalDetectIntentRequest.payload.data.message.text;
  var values = sheetProduct.getRange(2, 1, sheetProduct.getLastRow(), sheetProduct.getLastColumn()).getValues();
  for (var i = 0; i < values.length; i++) {
    if (values[i][0] == userMsg) {
      i = i + 2;
      var Data = sheetProduct.getRange(i, 2).getValue();

      var result = {
        fulfillmentMessages: [
          {
            platform: "line",
            type: 4,
            payload: {
              line: {
                type: "text",
                text: Data
              }
            }
          }
        ]
      };

      //response to dialogflow
      var replyJSON = ContentService.createTextOutput(JSON.stringify(result)).setMimeType(ContentService.MimeType.JSON);
      return replyJSON;
    }
  }
}