PHP – Gmail API Script for sending custom replied emails to my clients

What I want to do is on my personal admin website(php website) be able to read messages from my gmail account, and send a custom reply message to my clients using my personal php/mysql database. Only shows on my admin website the emails that have not been replied yet. The script should have two option buttons: 1. A “Send to Client” button, which will send the custom email directly to the client if the custom email answer 100% the question of the client. The email should be send with google api, therefore the email replies the inquiry email sent by the client. If I sign in my gmail account page, I should be able to see that the inquire email of the client was replied with my custom email (not a new email sent) and the sender should be see my corporate email address. 2. A “Send to Draft” button, which will send the custom email to my gmail draft if the answer needs to be edited in gmail before sending. The draft email should be match in the inquire email (email sent by client), so if I press send in the draft, the former email sent by the client will be replied. The script should be in PHP and use the Gmail API. To set up the email before sending it, ideally use phpmailer, mainly because I am familiar with it, and it is reliable. The email will have html tags. the script should support sending attachments. Please check the attached document. I include pictures to get a better idea of what I need.