Melodia/archiver/archive.py

from django.db import models

from song import Song

"""
This is the archive model for the archiving backend of Melodia.
It's purpose is to control the high-level functionality of managing
multiple archives of music. It is different from a playlist both conceptually
and practically - an archive describes a group of files, while a playlist
describes a group of songs.
In this way, you back up archives of music - you don't back up the songs in a
playlist. Additionally, you may want to re-organize your music to use a
cleaner directory structure - a playlist doesn't care about this.
"""

class Archive (models.Model):
	import datetime

	"""
	The archive model itself, and all functions used to interact with it.
	The archive is built up from a grouping of songs, and the functions
	that are used to interact with many songs at a single time. The archive
	for example allows you to re-organize a specific set of music files into
	a cleaner directory structure.
	The archive is given a folder to use as its root directory - it finds all
	music files under there, and takes control of them from there.
	"""

	name        = models.CharField(max_length = 64)

	#Note that we're not using FilePathField since this is actually a folder
	root_folder = models.CharField(max_length = 255)

	#And a reference to the songs in this archive
	songs       = models.ManyToManyField(Song)

	#Backup settings
	backup_location  = models.CharField(max_length = 255, default = "/dev/null")
	backup_frequency = models.IntegerField(default = 604800) #1 week in seconds
	last_backup      = models.DateTimeField(default = datetime.datetime.now()) #Note that this by default will be the time the archive was instantiated

	def _scan_filesystem(self):
		"Scan the archive's root filesystem and add any new songs without adding metadata, delete songs that exist no more"
		#This method is implemented since the other scan methods all need to use the same code
		#DRY FTW
		import re, os, itertools
		from django.core.exceptions import ObjectDoesNotExist
		from Melodia.melodia_settings import SUPPORTED_AUDIO_EXTENSIONS
		from Melodia.melodia_settings import HASH_FUNCTION as hash

		_regex = '|'.join(( '.*' + ext + '$' for ext in SUPPORTED_AUDIO_EXTENSIONS))
		regex  = re.compile(_regex, re.IGNORECASE)

		#It's hackish, but far fewer transactions to delete everything first, and add it all back.
		#If we get interrupted, just re-run it.
		self.songs.all().delete()

		#Add new songs
		for dirname, dirnames, filenames in os.walk(self.root_folder):
			#For each filename that is supported
			for filename in itertools.ifilter(lambda filename: re.match(regex, filename), filenames):
				rel_url = os.path.join(dirname, filename)
				full_url = os.path.abspath(rel_url)
				new_song = Song(url = full_url)
				new_song.save()
				self.songs.add(new_song)

	def _update_song_metadata(self, use_echonest = False, progress_callback = lambda x, y: None):
		"""Scan every song in this archive (database only) and make sure all songs are correct
		The progress_callback function is called with the current song being operated on first, and the total songs second."""
		#This method operates only on the songs that are in the database - if you need to make
		#sure that new songs are added, use the _scan_filesystem() method in addition
		total_songs  = self.songs.count()

		for index, song in enumerate(self.songs.all()):
			song.populate_metadata(use_echonest = use_echonest)
			song.save()
			progress_callback(index + 1, total_songs)

	def _needs_backup(self):
		"Check if the current archive is due for a backup"
		import datetime

		prev_backup_time = self.last_backup
		current_time     = datetime.datetime.now()

		delta = current_time - prev_backup_time
		if delta > datetime.timedelta(seconds = self.backup_frequency):
			return True
		else:
			return False

	def quick_scan(self):
		"Scan this archive's root folder and make sure that	all songs are in the database."
		#This is a quick scan - only validate whether or not songs should exist in the database

		self._scan_filesystem()

	def scan(self):
		"Scan this archive's root folder and make sure any local metadata are correct."
		#This is a longer scan - validate whether songs should exist, and use local data to update
		#the database

		self._scan_filesystem()
		self._update_song_metadata()

	def deep_scan(self):
		"Scan this archive's root folder and make sure that	all songs are in the database, and use EchoNest to update metadata as necessary"
		#This is a very long scan - validate whether songs should exist, and use Echonest to make sure
		#that metadata is as accurate as possible.
		self._scan_filesystem()
		self._update_song_metadata(use_echonest = True)

	
	def run_backup(self, force_backup = False):
		"Backup the current archive"
		if force_backup or self._needs_backup():
			import subprocess
			subprocess.call(['rsync', '-av', self.root_folder, self.backup_location])

	def reorganize(self, format_string, progress_function = lambda w, x, y, z: None, dry_run = False):
		"""Reorganize a music archive using a specified format string.
		Recognized escape characters:
		%a - Artist Name                       %A - Album Name
		%d - Disc Number                       %e - Number of discs
		%f - Current Filename (with extension) %g - Current Filename (no extension)
		%n - Track Number                      %o - Number of tracks on disc
		%y - Album year

		Note that all organization takes place relative to the archive's root folder.
		The progress_function is called with the current song number as its first argument, total songs as its second,
		current song URL as the third argument, and new URL as the fourth.
		"""
		import os, shutil, errno

		total_songs = self.songs.count()

		for index, song in enumerate(self.songs.all()):
			_current_filename              = os.path.basename(song.url)
			_current_filename_no_extension = os.path.splitext(_current_filename)[0]

			_release_year = song.release_date.year

			new_location = format_string.replace("%a", song.artist)\
										.replace("%A", song.album)\
										.replace("%d", str(song.disc_number))\
										.replace("%e", str(song.disc_total))\
										.replace("%f", _current_filename)\
										.replace("%g", _current_filename_no_extension)\
										.replace("%n", str(song.track_number))\
										.replace("%o", str(song.track_total))\
										.replace("%y", str(_release_year))

			new_url = os.path.join(self.root_folder, new_location)

			progress_function(index + 1, total_songs, song.url, new_url)

			if not dry_run:
				new_folder = os.path.dirname(new_url)
				try:
					#`mkdir -p` functionality
					if not os.path.isdir(new_folder):
						os.makedirs(new_folder)

					#Safely copy the file - don't 'move' it, but do a full 'copy' 'rm'
					#This way if the process is ever interrupted, we have an unaltered copy
					#of the file.
					shutil.copyfile(song.url, new_url)
					shutil.copystat(song.url, new_url)

					#Notify the database about the new URL
					old_url  = song.url
					song.url = new_url
					song.save()

					#Actually remove the file since all references to the original location have been removed
					os.remove(old_url)

				except OSError as exc:
					if exc.errno == errno.EEXIST and os.path.isdir(new_folder):
						#This is safe to skip - makedirs() is complaining about a folder already existing
						pass
					else: raise

				except IOError as exc:
					#shutil error - likely that folders weren't specified correctly
					raise