Refactor the custom scripts

A lot of them are reaching to be bigger so I've refactored them
similarly to C codebases with the `main()` entrypoint.

Apparently, this is how bigger shell scripts are written like Neofetch,
pfetch, and some Kubernetes helper scripts.

bin/bangs

@@ -38,8 +38,7 @@ HELP
 
 # Simply prints the given string into percent-encoded equivalent.
 #
-# > urlencode "Hello world"
+# `urlencode "Hello world"` will give "Hello%20world"
-#   Hello%20world
 #
 # Stolen from https://gist.github.com/cdown/1163649 and https://gist.github.com/cdown/1163649#gistcomment-1256298.
 # Just ported it in Oil script.

bin/convert-newpipe-db

@@ -23,11 +23,16 @@ var channel_id_eggex = / 'https://www.youtube.com/channel/' (word) /
 
 var NEWPIPE_DB = "newpipe.db"
 var TEMP_FOLDER_NAME = "newpipe"
-var NEWPIPE_DB_QUERY = "SELECT name, url, service_id, group_concat(tag, ',') AS tags FROM (SELECT subscriptions.name, subscriptions.url, subscriptions.service_id, '/' || feed_group.name AS tag
+
+# The SQL query to get the required metadata.
+var NEWPIPE_DB_QUERY = "
+    SELECT name, url, service_id, group_concat(tag, ',') AS tags FROM (
+        SELECT subscriptions.name, subscriptions.url, subscriptions.service_id, '/' || feed_group.name AS tag
         FROM subscriptions
         LEFT JOIN feed_group_subscription_join AS subs_join
         LEFT JOIN feed_group
-ON subs_join.subscription_id = subscriptions.uid AND feed_group.uid = subs_join.group_id) GROUP BY name ORDER BY name COLLATE NOCASE;"
+        ON subs_join.subscription_id = subscriptions.uid AND feed_group.uid = subs_join.group_id
+    ) GROUP BY name ORDER BY name COLLATE NOCASE;"
 
 # Print the beginning of the template.
 cat <<OPML
@@ -56,13 +61,24 @@ proc print-outline(title, xml_url, html_url, tags = "") {
 # Print the channels in the OPML body.
 # This only occurs if the given file does have a Newpipe database.
 if unzip -l $FILENAME | rg --quiet $NEWPIPE_DB {
+    # Make the temporary directory (preferably on the current directory to make cleanup easier).
     mkdir $TEMP_FOLDER_NAME && unzip -q -u $FILENAME -d $TEMP_FOLDER_NAME
-    file --mime "${TEMP_FOLDER_NAME}/${NEWPIPE_DB}" | rg --quiet "application/x-sqlite3" || exit 1
+
+    # Setting up some automatic cleanup upon exit.
     trap "rm --recursive $TEMP_FOLDER_NAME" EXIT
+
+    # Quickly check if a SQLite database is in the Newpipe database folder.
+    file --mime "${TEMP_FOLDER_NAME}/${NEWPIPE_DB}" | rg --quiet "application/x-sqlite3" || exit 1
+
+    # Extract the data from the database and process them individually.
+    # Note that we formatted the data in CSV to be in one line per object since as of version 0.8.11, Oil has some problems when taking fully nested data from external commands (not yet completely verified).
+    # We have to rewrite this part once Oil fixes the issue with nested objects.
     sqlite3 "${TEMP_FOLDER_NAME}/${NEWPIPE_DB}" "${NEWPIPE_DB_QUERY}" --csv --header \
     | dasel select --parser csv --multiple --selector '.[*]' --compact --write json \
     | while read channel {
+        # We have separate each channel as a JSON object per line.
         echo $channel | json read :channel
+
         setvar name = channel['name']
         setvar url = channel['url']
         setvar service_id = channel['service_id']

bin/split-album

@@ -1,5 +1,5 @@
 #! /usr/bin/env nix-shell
-#! nix-shell -i oil -p coreutils moreutils ffmpeg gnused ripgrep
+#! nix-shell -i oil -p coreutils moreutils ffmpeg gnused ripgrep file
 
 shopt --set strict:all
 
@@ -85,8 +85,31 @@ There will be a folder created with the safe name of the album (in kebab-case) c
 The original file will be kept, do what you want with it.
 "
 
+
+proc warnf(msg, @args) {
+    >&2 printf "${msg}\\n" @args
+}
+
+proc errorf(msg, @args) {
+    >&2 printf "${msg}\\n" @args
+    exit 1
+}
+
+proc prompt(msg, :out, prefix = ">> ") {
+    >&2 printf '%s\n%s' $msg $prefix
+    read --line
+    setref out = $_line
+}
+
+proc kebab-case(word) {
+    write -- $word | sed --regexp-extended --expression 's/./\L&/g' --expression 's/\s+/-/g' --expression 's/[^a-z0-9-]//g' --expression 's/^-+|-+$//g' --expression 's/-+/-/g'
+}
+
+proc main {
+  # This could be configured by setting the 'EXTENSION' environment variable.
   const EXTENSION = ${EXTENSION:-"opus"}
 
+  # Set up the variables.
   var audio_file = ''
   var timestamp_file = ''
 
@@ -98,6 +121,7 @@ var prints_json = false
   var strict_mode = false
   var skip = false
 
+  # Parse the arguments.
   while test $len(ARGV) -gt 0 {
     case $[ARGV[0]] {
       -h|--help)
@@ -148,32 +172,18 @@ while test $len(ARGV) -gt 0 {
       }
   }
 
-proc warnf(msg, @args) {
+  # Check the files if it is valid.
-    >&2 printf "${msg}\\n" @args
-}
-
-proc errorf(msg, @args) {
-    >&2 printf "${msg}\\n" @args
-    exit 1
-}
-
-proc prompt(msg, :out, prefix = ">> ") {
-    >&2 printf '%s\n%s' $msg $prefix
-    read --line
-    setref out = $_line
-}
-
-proc kebab-case(word) {
-    write -- $word | sed --regexp-extended --expression 's/./\L&/g' --expression 's/\s+/-/g' --expression 's/[^a-z0-9-]//g' --expression 's/^-+|-+$//g' --expression 's/-+/-/g'
-}
-
   test -f $audio_file || errorf '%s is not a regular file' $audio_file
   test -f $timestamp_file || errorf '%s is not a regular file' $timestamp_file
 
+  # Prompt for the missing values if not passed from the command line.
   test $album || prompt "What is the title of the album?" :album
   test $author || prompt "Who is the author of the album?" :author
   test $pub_date || prompt "When is the album published?" :pub_date
 
+  # Populate the output data.
+  # This is going to be used throughout the processing.
+  # Additionally, the object will be printed when `--json` flag is passed.
   const output_data = {}
   setvar output_data['file'] = $audio_file
   setvar output_data['chapters'] = []
@@ -182,24 +192,34 @@ setvar output_data['author'] = $author
   setvar output_data['date'] = $pub_date
   setvar output_data['extension'] = $EXTENSION
 
+  # The following variable stores an eggex, a simplified notation for regular expressions.
+  # Pretty nice to use especially that literals are quoted and classes are not.
   const timestamp_regex = / %start digit{2,} ':' digit{2} ':' digit{2} <'.' digit+>? %end /
+
+  # We'll keep track whether the pipeline has encountered an error.
+  # If it has, the script will exit throughout various points of the process.
   var has_error = false
 
   # Deserialize the given input into the chapters data.
+  # This script accept several formats from a JSON file to a plain-text file derived from Luke Smith's 'booksplit' script.
   case $(file --mime-type --brief $timestamp_file) {
     "application/json")
       json read :chapters < $timestamp_file
       setvar output_data['chapters'] = chapters
       ;;
 
-    # Also cleans up the timestamp file with comments (i.e., lines starting with '#') and empty lines allowing for more commenting options.
+    # The text file is formatted quite similarly to the required format from the booksplit script.
-    # I just want to improve the timestamp format a little bit.
+    # I improved some things in the format such as allowing comments (i.e., lines starting with '#') and empty lines allowing for cleaner input.
     "text/plain")
       sed --regexp-extended --expression '/^\s*$/d' --expression '/^#/d' $timestamp_file | while read --line {
+        # We'll build the chapter data to be added later to the output data.
         var chapter = {}
         setvar chapter['title'] = $(write -- $_line | cut -d' ' -f2-)
         setvar chapter['timestamp'] = $(write -- $_line | cut -d' ' -f1)
 
+        # Mark the input to be erreneous if the timestamp format is not valid.
+        # This will cause the script to exit in the next part of the process.
+        # We won't be exiting immediately to give all possible errors.
         write -- ${chapter['timestamp']} | rg --quiet $timestamp_regex || {
           warnf "'%s' %s is not a valid timestamp" ${chapter['timestamp']} ${chapter['title']}
           setvar has_error = true
@@ -211,8 +231,11 @@ case $(file --mime-type --brief $timestamp_file) {
     ;;
   }
 
+  # Exit if the script is set as strict and has erreneous input.
+  # If the user cares about the input, they have to set it to strict mode.
   if (strict_mode and has_error) { exit 1 }
 
+  # Set parts of the output data and prepare for the splitting process.
   const title_slug = $(kebab-case $album)
   setvar output_data['directory'] = $(realpath --canonicalize-missing $title_slug)
   mkdir -p $title_slug
@@ -222,6 +245,8 @@ mkdir -p $title_slug
   const chapter_len = len(output_data['chapters'])
   var job_queue = %()
 
+  # Iterate through the chapters and populate the job queue.
+  # We'll also fill up the rest of the chapter-related data into the output data.
   for index in @(seq $[chapter_len]) {
     var index = Int(index)
     var chapter = output_data['chapters'][index - 1]
@@ -230,7 +255,8 @@ for index in @(seq $[chapter_len]) {
     var filename = $(printf "%.2d-%s.%s" $index $(kebab-case ${chapter['title']}) $EXTENSION)
     setvar output_data['chapters'][index - 1]['file'] = filename
 
-    # Check for incorrect timestamp order.
+    # Check for incorrect timestamp order and set the pipeline as erreneous if it is.
+    # We can't let the splitting process proceed since it will surely make problematic output.
     if (start > end and end is not null) {
       warnf '%s (start) is ahead compared to %s (end)' $start $end
       setvar has_error = true
@@ -239,8 +265,14 @@ for index in @(seq $[chapter_len]) {
     append :job_queue ">&2 printf '[%d/%d] %s\\n' $[index] $[chapter_len] \"$[output_data['chapters'][index - 1]['title']]\"; ffmpeg -loglevel quiet -nostdin -i '${audio_file}' -ss ${start} $['-to ' + end if index != chapter_len else ''] ${title_slug}/${filename}"
   }
 
+  # Exit the process if an error detected.
   if (has_error) { exit 1 }
 
+  # Start the splitting process if the `--skip` is absent.
   if (not skip) { parallel -- @job_queue }
-if (prints_json) { json write :output_data }
 
+  # Print the output data as JSON if the `--json` flag is passed.
+  if (prints_json) { json write :output_data }
+}
+
+main @ARGV