add comments to sql table definitions

bolton_comments.ts

function removeUpTo(
  s: string | undefined,
  prefix: RegExp
){
  if (s === undefined){
    return undefined
  }
  s = s.trim()
  const i = s.search(prefix)
  if (i == -1){
    return undefined
  }
  const found = s.match(prefix)
  if (!found){
    throw Error('Impossible')
  } 
  return s.substr(i + found[0].length).trim()
}


function extractDescription(line: string){
  return [/--/, /@description\s*:?/].reduce(removeUpTo, line)
}

function firstWord(text: string){
  text = text.trim()
  return text.substr(0, text.indexOf(" "))
}

function extractIdentifier(line: string, currentTable: string | undefined){
  var identifier = removeUpTo(line, /create table/)
  if (identifier){
    return `table ${firstWord(identifier)}`
  }
  if (currentTable === undefined){
    throw Error('Impossible')
  }
  return `column ${currentTable}.${firstWord(line)}`
}

function extractCommentMap(lines: string){
  var map: { [identifier: string]: string } = {}
  var desc: string | undefined = undefined
  var currentTable: string | undefined = undefined
  for (var line of lines.split('\n')){
    if (desc){
      const ident = extractIdentifier(line, currentTable);
      if (ident.startsWith('table')){
        currentTable = ident.substr('table '.length)
      }
      map[ident] = desc;
      desc = undefined
    } else {
      desc = extractDescription(line);
    }
  }
  return map
}

function formatCommentMap(comments: { [identifier: string]: string }){
  return Object.keys(comments).map((ident) => `comment on ${ident} is '${comments[ident]}';`).join('\n')
}

function boltOnComments(sql: string){
  return sql + '\n' + formatCommentMap(extractCommentMap(sql))
}

console.log(boltOnComments(`
-- @description: A feed of \`Post\`s relevant to a particular \`User\`.
create table app_public.user_feed_posts (
  -- @description: An identifier for this entry in the feed.
  id               serial primary key,
  user_id          int not null references app_public.users on delete cascade,
  post_id          int not null references app_public.posts on delete cascade,
  -- @description: The time this feed item was added.
  created_at       timestamptz not null default now()
);
`));