version 1

check.gs

let HOMEWORK_NOTE_ID = 'your note id';
let HACKMD_API_KEY = 'your key';
let EMAIL = {
  'recipient': '',
  'subject': 'Thanks for handing in your home work!',
  'body': ''
}

function onOpen(e) {
  let currentForm = FormApp.getActiveForm();
  let usernameValidation = FormApp.createTextValidation() // To prevent injection
    .setHelpText('Please provide a valid usename')
    .requireTextMatchesPattern('[a-zA-Z0-9\-_]+')
    .build();
  let noteValidation = FormApp.createTextValidation()
    .setHelpText('Please provide a valid hackmd published note link')
    .requireTextMatchesPattern('https:\/\/hackmd\.io\/@[a-zA-Z0-9\-_]+\/\[a-zA-Z0-9\-_]+')
    .build();
  let githubValidation = FormApp.createTextValidation()
    .setHelpText('Please provide a valid github repository link')
    .requireTextMatchesPattern('https:\/\/github\.com\/[a-zA-Z0-9\-_]+\/\[a-zA-Z0-9\-_]+')
    .build();

  const items = currentForm.getItems();
  items[0].asTextItem().setValidation(usernameValidation);
  items[1].asTextItem().setValidation(noteValidation);
  items[2].asTextItem().setValidation(githubValidation);
  items[3].asTextItem().setValidation(noteValidation);
  console.log(`Text validation set on questions`);

  // Optional. Deletes all triggers in the current project.
  //let triggers = ScriptApp.getProjectTriggers(); // why sometimes get an error on no permission?
  //for (var i = 0; i < triggers.length; i++) {
  //  ScriptApp.deleteTrigger(triggers[i]);
  //}

  ScriptApp.newTrigger('onSubmit')
    .forForm(currentForm)
    .onFormSubmit()
    .create();
}

function onSubmit(e){
  let reponses =  e.response.getItemResponses();
  let username = reponses[0].getResponse(); // should be sanitized
  let note_1 = reponses[1].getResponse();
  let repo = reponses[2].getResponse();
  let note_2 = reponses[3].getResponse();
  EMAIL.recipient = reponses[4].getResponse();

  if(emailResult(checkNotePermission(note_1)) && emailResult(checkNotePermission(note_2))){
    // second one won't be check if failed on the first one
    let content_to_insert = `    * [開發紀錄](${note_1}) / [GitHub](${repo})\n    * [開發紀錄 (Quiz)](${note_2})`;
    emailResult(updateNote(HOMEWORK_NOTE_ID, username, content_to_insert)); // May fail
  }

  GmailApp.sendEmail(EMAIL.recipient, EMAIL.subject, EMAIL.body);
  console.log('Email sent!');
}

function checkNotePermission(url){
  console.log(`Check note: ${url}`);
  let response;

  let GET_options = {
    'method': 'get',
    'muteHttpExceptions': true,
    'headers': {
      'Authorization': `Bearer ${HACKMD_API_KEY}`
    }
  };
  //do{
  //  response = UrlFetchApp.fetch(`${url}/edit`, {'muteHttpExceptions': true});
  //}
  //while(response.getResponseCode() !== 302);
  response = UrlFetchApp.fetch(`${url}/edit`, {'muteHttpExceptions': true}); // May 403 (even with public note)
  if(response.getResponseCode() !== 302){
    return response.getResponseCode();
  }
  let noteID = response.getHeaders()['hackmd-note-id']; 
  console.log(`Note ID: ${noteID}`);

  response = UrlFetchApp.fetch(`https://api.hackmd.io/v1/notes/${noteID}`, GET_options); // May fail
  let body = JSON.parse(response);
  if(body['readPermission'] !== 'guest'){ // should be reported at the first check though
    return 10;
  }
  if(body['writePermission'] !== 'signed_in'){
    return 11;
  }
  if(body['publishedAt'] === null){
    return 12;
  }

  console.log('All check passed!'); // I don't know why this won't show
  return 200;
}

/// @noteID: String
function updateNote(noteID, username, linksStr){
  let reponse;
  let data = {
    'content': '',
    'readPermission': '',
    'writePermission': '',
    'permalink': ''
  }
  let GET_options = {
    'method': 'get',
    'muteHttpExceptions': true,
    'headers': {
      'Authorization': `Bearer ${HACKMD_API_KEY}`
    }
  };
  reponse = UrlFetchApp.fetch(`https://api.hackmd.io/v1/notes/${noteID}`, GET_options); // May fail
  if(reponse.getResponseCode() !== 200){
    return 13;
  }
  let body = JSON.parse(reponse);
  // Shallow copy
  data.readPermission = body.readPermission;
  data.writePermission = body.writePermission;
  data.permalink = body.permalink;

  // Check if ID existed. Update or Add accordingly.
  let pattern = new RegExp(username);
  let result = body.content.match(pattern);
  if(result === null){
    // Add an entry to buttom
    data.content = body.content + `- [ ] ${username}\n${linksStr}\n`;
    console.log(`Note updated with new entry as: ${data.content}`);
  }
  else if(result.length === 1){
    // Update the existed links
    const toReplace = new RegExp(`- \\[ \\] ${username}\n.*\n.*\n`); // wildcard does not include \n
    data.content = body.content.replace(toReplace, `- [ ] ${username}\n${linksStr}\n- [ ]`);
    console.log(`Note updated as: ${data.content}`);
  }
  else{
    console.log('WTF');
    // cases that other that 0 or 1 is unexpected and should be unreachable
    return 14;
  }
  
  let PATCH_options = {
    'method': 'patch',
    'muteHttpExceptions': true,
    'contentType': 'application/json',
    'payload' : JSON.stringify(data),
    'headers': {
      'Authorization': `Bearer ${HACKMD_API_KEY}`
    }
  };
  reponse = UrlFetchApp.fetch(`https://api.hackmd.io/v1/notes/${noteID}`, PATCH_options); // May fail
  if(reponse.getResponseCode() !== 202){
    return 15;
  }

  console.log('Updated successfully.');
  return 200;
}

function emailResult(result){
  let msg;
  switch(result){
    case 200:
      console.log('ok. continue');
      return true;
    case 403:
      console.log('We do not have permisison to view the note or something wrong with HackMD.');
      EMAIL.body += 'We do not have permisison to view the note or something wrong with HackMD.';
      break;
    case 404:
      console.log('We can not find your note.');
      EMAIL.body += 'We can not find your note.';
      break;
    case 10:
      console.log('Read permission should be set to everyone.');
      EMAIL.body += 'Read permission should be set to everyone.';
      break;
    case 11:
      console.log('Write permission should be set to signed-in user.');
      EMAIL.body += 'Write permission should be set to signed-in user.';
      break;
    case 12:
      console.log('Note should be published.');
      EMAIL.body += 'Note should be published.';
      break;
    case 13:
      console.log('Not responded with 200 while getting the note.');
      EMAIL.body += 'Not responded with 200 while getting the note.';
      break;
    case 14:
      console.log('More than one entry in the note with same username');
      EMAIL.body += 'More than one entry in the note with same username';
      break;
    case 15:
      console.log('Not responded with 202 while updating the note.');
      EMAIL.body += 'Not responded with 202 while updating the note.';
      break;
    default:
      console.log(`Unexpected error code ${result}. Please report this problem.`);
      EMAIL.body += `Unexpected error code ${result}. Please report this problem.`;
  }

  return false;
}

// Sometimes it won't work, with no error message attached.....
function test(){
  let currentForm = FormApp.getActiveForm();
  const formResponse = currentForm.createResponse();
  const items = currentForm.getItems();
  formResponse.withItemResponse(items[0].asTextItem().createResponse('superman'));
  formResponse.withItemResponse(items[1].asTextItem().createResponse('https://hackmd.io/@idoleat/AudioAdventureMap'));
  formResponse.withItemResponse(items[2].asTextItem().createResponse('https://github.com/idoleat/Christmas-card'));
  formResponse.withItemResponse(items[3].asTextItem().createResponse('https://hackmd.io/@idoleat/AudioAdventureMap'));
  formResponse.withItemResponse(items[4].asTextItem().createResponse('idoleat@ccns.ncku.edu.tw'));
  formResponse.submit();
}