fix: Update the message-id check to use messageId parsing from mail gem (#8743)

- Update the message ID parsing logic to use the mail gem
- Update the code to improve readability

app/jobs/inboxes/fetch_imap_emails_job.rb

@@ -27,7 +27,6 @@ class Inboxes::FetchImapEmailsJob < MutexApplicationJob
   end
 
   def process_email_for_channel(channel)
-    # fetching email for microsoft provider
     if channel.microsoft?
       fetch_mail_for_ms_provider(channel)
     else
@@ -38,42 +37,66 @@ class Inboxes::FetchImapEmailsJob < MutexApplicationJob
   end
 
   def fetch_mail_for_channel(channel)
-    imap_inbox = authenticated_imap_inbox(channel, channel.imap_password, 'PLAIN')
+    imap_client = build_imap_client(channel, channel.imap_password, 'PLAIN')
 
-    fetch_message_ids(imap_inbox, channel).each do |message_id_uid_pair|
-      uid, message_id = message_id_uid_pair
-      next if email_already_present?(channel, message_id)
-
-      inbound_mail = Mail.read_from_string(imap_inbox.fetch(uid, 'RFC822')[0].attr['RFC822'])
-      mail_info_logger(channel, inbound_mail, uid)
-
-      process_mail(inbound_mail, channel)
+    message_ids_with_seq = fetch_message_ids_with_sequence(imap_client, channel)
+    message_ids_with_seq.each do |message_id_with_seq|
+      process_message_id(channel, imap_client, message_id_with_seq)
     end
   end
 
-  def fetch_message_ids(imap_inbox, channel)
-    uids = fetch_uids(imap_inbox)
-    Rails.logger.info "FETCH_EMAILS_FROM: #{channel.email} - Found #{uids.length} emails \n\n\n\n"
+  def process_message_id(channel, imap_client, message_id_with_seq)
+    seq_no, message_id = message_id_with_seq
 
-    message_ids = []
-    uids.each_slice(10).each do |batch|
-      uid_fetched = imap_inbox.fetch(batch, 'BODY.PEEK[HEADER.FIELDS (MESSAGE-ID)]')
-      # print uid_fetched
-      uid_fetched.each do |data|
-        message_id = data.attr['BODY[HEADER.FIELDS (MESSAGE-ID)]'].to_s.scan(/<(.+?)>/).flatten.first
-        message_ids.push([data.seqno, message_id])
+    return if email_already_present?(channel, message_id)
+
+    # Fetch the original mail content using the sequence no
+    mail_str = imap_client.fetch(seq_no, 'RFC822')[0].attr['RFC822']
+
+    if mail_str.blank?
+      Rails.logger.info "[IMAP::FETCH_EMAIL_SERVICE] Fetch failed for #{channel.email} with message-id <#{message_id}>."
+      return
+    end
+
+    inbound_mail = build_mail_from_string(mail_str)
+    mail_info_logger(channel, inbound_mail, seq_no)
+    process_mail(inbound_mail, channel)
+  end
+
+  # Sends a FETCH command to retrieve data associated with a message in the mailbox.
+  # You can send batches of message sequence number in `.fetch` method.
+  def fetch_message_ids_with_sequence(imap_client, channel)
+    seq_nums = fetch_available_mail_sequence_numbers(imap_client)
+
+    Rails.logger.info "[IMAP::FETCH_EMAIL_SERVICE] Fetching mails from #{channel.email}, found #{seq_nums.length}."
+
+    message_ids_with_seq = []
+    seq_nums.each_slice(10).each do |batch|
+      # Fetch only message-id only without mail body or contents.
+      batch_message_ids = imap_client.fetch(batch, 'BODY.PEEK[HEADER.FIELDS (MESSAGE-ID)]')
+
+      # .fetch returns an array of Net::IMAP::FetchData or nil
+      # (instead of an empty array) if there is no matching message.
+      # Check
+      if batch_message_ids.blank?
+        Rails.logger.info "[IMAP::FETCH_EMAIL_SERVICE] Fetching the batch failed for #{channel.email}."
+        next
+      end
+
+      batch_message_ids.each do |data|
+        message_id = build_mail_from_string(data.attr['BODY[HEADER.FIELDS (MESSAGE-ID)]']).message_id
+        message_ids_with_seq.push([data.seqno, message_id])
       end
     end
 
-    message_ids
+    message_ids_with_seq
   end
 
-  def email_already_present?(channel, message_id)
-    channel.inbox.messages.find_by(source_id: message_id).present?
-  end
-
-  def fetch_uids(imap_inbox)
-    imap_inbox.search(['BEFORE', tomorrow, 'SINCE', yesterday])
+  # Sends a SEARCH command to search the mailbox for messages that were
+  # created between yesterday and today and returns message sequence numbers.
+  # Return <message set>
+  def fetch_available_mail_sequence_numbers(imap_client)
+    imap_client.search(['BEFORE', tomorrow, 'SINCE', yesterday])
   end
 
   def fetch_mail_for_ms_provider(channel)
@@ -83,16 +106,15 @@ class Inboxes::FetchImapEmailsJob < MutexApplicationJob
 
     return unless access_token
 
-    imap_inbox = authenticated_imap_inbox(channel, access_token, 'XOAUTH2')
-
-    process_mails(imap_inbox, channel)
+    imap_client = build_imap_client(channel, access_token, 'XOAUTH2')
+    process_mails(imap_client, channel)
   end
 
-  def process_mails(imap_inbox, channel)
-    fetch_uids(imap_inbox).each do |message_id|
-      inbound_mail = Mail.read_from_string imap_inbox.fetch(message_id, 'RFC822')[0].attr['RFC822']
+  def process_mails(imap_client, channel)
+    fetch_available_mail_sequence_numbers(imap_client).each do |seq_no|
+      inbound_mail = Mail.read_from_string imap_client.fetch(seq_no, 'RFC822')[0].attr['RFC822']
 
-      mail_info_logger(channel, inbound_mail, message_id)
+      mail_info_logger(channel, inbound_mail, seq_no)
 
       next if channel.inbox.messages.find_by(source_id: inbound_mail.message_id).present?
 
@@ -107,19 +129,19 @@ class Inboxes::FetchImapEmailsJob < MutexApplicationJob
       #{channel.provider} Email id: #{inbound_mail.from} - message_source_id: #{inbound_mail.message_id} - sequence id: #{uid}")
   end
 
-  def authenticated_imap_inbox(channel, access_token, auth_method)
+  def build_imap_client(channel, access_token, auth_method)
     imap = Net::IMAP.new(channel.imap_address, channel.imap_port, true)
     imap.authenticate(auth_method, channel.imap_login, access_token)
     imap.select('INBOX')
     imap
   end
 
-  def yesterday
-    (Time.zone.today - 1).strftime('%d-%b-%Y')
+  def email_already_present?(channel, message_id)
+    channel.inbox.messages.find_by(source_id: message_id).present?
   end
 
-  def tomorrow
-    (Time.zone.today + 1).strftime('%d-%b-%Y')
+  def build_mail_from_string(raw_email_content)
+    Mail.read_from_string(raw_email_content)
   end
 
   def process_mail(inbound_mail, channel)
@@ -134,4 +156,12 @@ class Inboxes::FetchImapEmailsJob < MutexApplicationJob
   def valid_access_token(channel)
     Microsoft::RefreshOauthTokenService.new(channel: channel).access_token
   end
+
+  def yesterday
+    (Time.zone.today - 1).strftime('%d-%b-%Y')
+  end
+
+  def tomorrow
+    (Time.zone.today + 1).strftime('%d-%b-%Y')
+  end
 end