added comments

main.ts

@@ -13,12 +13,15 @@ const REGEX_ALBUMTITLE = /^(.*?) MP3 - Download/i
 const REGEX_UNSAFEFORFILE = /[^a-z0-9\-_=+,.()\[\]{} ]/gi
 
 async function main() {
+  // deno main.ts <playlistURL> [<downloadPath>] [sync]
   const playlistURL = argv[2]
   const downloadPath = argv[3] || '.'
   const runSync = argv[4]?.toLowerCase() == 'sync'
 
+  // load all song details
   const playlist = await fetchPlaylist(playlistURL)
 
+  // if sync, download one at a time
   if (runSync) {
     for (const song of playlist) {
       await downloadSong(song, downloadPath || '.')
@@ -35,11 +38,12 @@ async function fetchPlaylist(url: string): Promise<PlaylistSongData[]> {
     throw `unaccepted url ${url}`
   }
 
+  // load the playlist page's dom
   const req = await fetch(url)
   const text = await req.text()
-
   const $ = cheerio.load(text)
 
+  // get the album name from the page title
   const title =
     $.extract({
       title: 'title',
@@ -50,6 +54,7 @@ async function fetchPlaylist(url: string): Promise<PlaylistSongData[]> {
   }
   const albumName = titleMatch[1]
 
+  // parse all rows in playlist
   const columns = getPlaylistTableHeaders($)
   const rows = getPlaylistRows($, columns, albumName)
 
@@ -73,13 +78,16 @@ interface PlaylistSongData {
 }
 
 function getPlaylistTableHeaders($: cheerio.CheerioAPI): PlaylistTableColumns {
+  // get table header row
   const header = $('#songlist tr#songlist_header')
   const headerCells = header.extract({
     cells: ['th'],
   })
 
+  // get the index for specific columns
   const indexes = headerCells.cells.reduce(
     (p, c, i) => {
+      // check the string content of the current cell
       switch (c.toLocaleLowerCase()) {
         case 'cd':
           p.cd = i
@@ -92,6 +100,7 @@ function getPlaylistTableHeaders($: cheerio.CheerioAPI): PlaylistTableColumns {
       }
       return p
     },
+    // default values
     {
       name: -1,
       track: -1,
@@ -114,6 +123,7 @@ function getPlaylistRows(
   const rows = $('#songlist tr:not(#songlist_header):not(#songlist_footer)')
   const rowsData: PlaylistSongData[] = []
 
+  // loop through each song in table
   rows.each((_, rowEl) => {
     const row = cheerio.load(rowEl)
     const rowData: PlaylistSongData = {
@@ -124,6 +134,7 @@ function getPlaylistRows(
       cd: -1,
     }
 
+    // prase values from row
     rowData.url =
       row.extract({
         url: {
@@ -162,6 +173,7 @@ function getPlaylistRows(
 }
 
 async function downloadSong(song: PlaylistSongData, location: string) {
+  // get full url
   let url = song.url
   if (!/^http/i.test(url)) {
     url = 'https://downloads.khinsider.com' + url
@@ -170,10 +182,12 @@ async function downloadSong(song: PlaylistSongData, location: string) {
     throw `unaccepted url ${url}`
   }
 
+  // load download page
   const resp = await fetch(url)
   const text = await resp.text()
-
   const $ = cheerio.load(text)
+
+  // extract the flac download link
   const flacUrl = $.extract({
     url: {
       selector: '#pageContent a[href*="flac"]',
@@ -185,11 +199,15 @@ async function downloadSong(song: PlaylistSongData, location: string) {
     throw `can't find download link for ${url}`
   }
 
+  // get the file and path to save the files
   const { pathname, fullpathname } = pathFor(location, song)
 
+  // ensure folder exists
   if (!existsSync(pathname)) {
     await mkdir(pathname)
   }
+
+  // skip file if it exists
   if (existsSync(fullpathname)) {
     console.log(`skipping file already exists ${fullpathname}`)
   }
@@ -197,9 +215,9 @@ async function downloadSong(song: PlaylistSongData, location: string) {
   console.log(`downloading ${fullpathname}`)
   console.log(`  from ${flacUrl}`)
 
+  // download the file
   const songresp = await fetch(flacUrl)
   const songblob = await songresp.arrayBuffer()
-
   return writeFile(fullpathname, toBuffer(songblob))
 }
 
@@ -209,6 +227,7 @@ interface SongPath {
 }
 
 function pathFor(location: string, song: PlaylistSongData): SongPath {
+  // clean strings for file paths
   const albumname = song.album.replace(REGEX_UNSAFEFORFILE, '')
   const songname = song.name.replace(REGEX_UNSAFEFORFILE, '')
 
@@ -216,6 +235,30 @@ function pathFor(location: string, song: PlaylistSongData): SongPath {
   const track = song.track >= 0 ? song.track + '.' : ''
   const separator = song.cd >= 0 || song.track >= 0 ? ' ' : ''
   const filename = `${cd}${track}${separator}${songname}.flac`
+  /*
+  for example
+  
+  song = {
+    songname: 'song',
+    track: 1,
+    cd: 1,
+  }
+  then filename = '1.1. song'
+
+  song = {
+    songname: 'song',
+    track: 1,
+    cd: -1,
+  }
+  then filename = '1. song'
+
+  song = {
+    songname: 'song',
+    track: -1,
+    cd: -1,
+  }
+  then filename = 'song'
+  */
 
   const pathname = path.resolve(location, albumname)
   const fullpathname = path.resolve(pathname, filename)
@@ -226,7 +269,8 @@ function pathFor(location: string, song: PlaylistSongData): SongPath {
   }
 }
 
-function toBuffer(arrayBuffer: ArrayBuffer) {
+// convert ArrayBuffer to Buffer<ArrayBuffer>
+function toBuffer(arrayBuffer: ArrayBuffer): Buffer<ArrayBuffer> {
   const buffer = Buffer.alloc(arrayBuffer.byteLength)
   const view = new Uint8Array(arrayBuffer)
   for (let i = 0; i < buffer.length; ++i) {