visual-meta / bibtex parser (incl. sections & multiplex/demultiplex of text/metadata)

visual-meta.js

var bibtex = {
  decode: (str) => {
    // bibtex:     ↓@   ↓<tag|tag{phrase,|{ruler}>  ↓property  ↓end
    let pat    = [ /@/, /^\S+[,{}]/,                /},/,      /}/ ]
    let tags   = [], text='', i=0, prop=''
    let lines  = str.replace(/\r?\n/g,'\n').split(/\n/)
    for( let i = 0; i < lines.length && !String(lines[i]).match( /^@/ ); i++ ) 
        text += lines[i]+'\n'

    str = lines.join('\n').substr( text.length )
    str.split( pat[0] ).map( (t) => {
        try{
           let v = {}
           if( !(t = t.trim())         ) return
           if( tag = t.match( pat[1] ) ) tag = tag[0]
           if( tag.match( /^{.*}$/ )   ) return tags.push({ruler:tag})
           if( tag.match( /}$/ )       ) return tags.push({k: tag.replace(/}$/,''), v: {}})
           t = t.substr( tag.length )
           t.split( pat[2] )
           .map( kv => {
             if( !(kv = kv.trim()) || kv == "}" ) return
             v[ kv.match(/\s?(\S+)\s?=/)[1] ] = kv.substr( kv.indexOf("{")+1 )
           })
           tags.push( { k:tag, v } )
        }catch(e){ console.error(e) }
    })
    return {text, tags}
  },

  encode: (text,tags) => {
    let str = text+"\n"
    for( let i in tags ){
      let item = tags[i]
      if( item.ruler ){
          str += `@${item.ruler}\n`
          continue;
      }
      str += `@${item.k}\n`
      for( let j in item.v ) str += `  ${j} = {${item.v[j]}}\n`
      str += `}\n`
    }
    return str
  }
}

str = `
hello world
Lorem ipsum dolor sit amet

@{some-section}
@flap{
  asdf = {23423}
}`

var {tags,text} = bibtex.decode(str)          // demultiplex text & bibtex
tags.find( (t) => t.k == 'flap{' ).v.asdf = 1 // edit tag
tags.push({ k:'bar{', v:{abc:123} })          // add tag
console.log( bibtex.encode(text,tags) )       // multiplex text & bibtex back together 
console.dir({tags,text})