beets/beetsplug/aura.py

# This file is part of beets.
# Copyright 2020, Callum Brown.
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.

"""An AURA server using Flask."""


import os.path
import re
from mimetypes import guess_type
from os.path import getsize, isfile

from flask import (
    Blueprint,
    Flask,
    current_app,
    make_response,
    request,
    send_file,
)

from beets import config
from beets.dbcore.query import (
    AndQuery,
    FixedFieldSort,
    MatchQuery,
    MultipleSort,
    NotQuery,
    RegexpQuery,
    SlowFieldSort,
)
from beets.library import Album, Item
from beets.plugins import BeetsPlugin
from beets.ui import Subcommand, _open_library
from beets.util import py3_path

# Constants

# AURA server information
# TODO: Add version information
SERVER_INFO = {
    "aura-version": "0",
    "server": "beets-aura",
    "server-version": "0.1",
    "auth-required": False,
    "features": ["albums", "artists", "images"],
}

# Maps AURA Track attribute to beets Item attribute
TRACK_ATTR_MAP = {
    # Required
    "title": "title",
    "artist": "artist",
    # Optional
    "album": "album",
    "track": "track",  # Track number on album
    "tracktotal": "tracktotal",
    "disc": "disc",
    "disctotal": "disctotal",
    "year": "year",
    "month": "month",
    "day": "day",
    "bpm": "bpm",
    "genre": "genre",
    "recording-mbid": "mb_trackid",  # beets trackid is MB recording
    "track-mbid": "mb_releasetrackid",
    "composer": "composer",
    "albumartist": "albumartist",
    "comments": "comments",
    # Optional for Audio Metadata
    # TODO: Support the mimetype attribute, format != mime type
    # "mimetype": track.format,
    "duration": "length",
    "framerate": "samplerate",
    # I don't think beets has a framecount field
    # "framecount": ???,
    "channels": "channels",
    "bitrate": "bitrate",
    "bitdepth": "bitdepth",
    "size": "filesize",
}

# Maps AURA Album attribute to beets Album attribute
ALBUM_ATTR_MAP = {
    # Required
    "title": "album",
    "artist": "albumartist",
    # Optional
    "tracktotal": "albumtotal",
    "disctotal": "disctotal",
    "year": "year",
    "month": "month",
    "day": "day",
    "genre": "genre",
    "release-mbid": "mb_albumid",
    "release-group-mbid": "mb_releasegroupid",
}

# Maps AURA Artist attribute to beets Item field
# Artists are not first-class in beets, so information is extracted from
# beets Items.
ARTIST_ATTR_MAP = {
    # Required
    "name": "artist",
    # Optional
    "artist-mbid": "mb_artistid",
}


class AURADocument:
    """Base class for building AURA documents."""

    @staticmethod
    def error(status, title, detail):
        """Make a response for an error following the JSON:API spec.

        Args:
            status: An HTTP status code string, e.g. "404 Not Found".
            title: A short, human-readable summary of the problem.
            detail: A human-readable explanation specific to this
                occurrence of the problem.
        """
        document = {
            "errors": [{"status": status, "title": title, "detail": detail}]
        }
        return make_response(document, status)

    def translate_filters(self):
        """Translate filters from request arguments to a beets Query."""
        # The format of each filter key in the request parameter is:
        # filter[<attribute>]. This regex extracts <attribute>.
        pattern = re.compile(r"filter\[(?P<attribute>[a-zA-Z0-9_-]+)\]")
        queries = []
        for key, value in request.args.items():
            match = pattern.match(key)
            if match:
                # Extract attribute name from key
                aura_attr = match.group("attribute")
                # Get the beets version of the attribute name
                beets_attr = self.attribute_map.get(aura_attr, aura_attr)
                converter = self.get_attribute_converter(beets_attr)
                value = converter(value)
                # Add exact match query to list
                # Use a slow query so it works with all fields
                queries.append(MatchQuery(beets_attr, value, fast=False))
        # NOTE: AURA doesn't officially support multiple queries
        return AndQuery(queries)

    def translate_sorts(self, sort_arg):
        """Translate an AURA sort parameter into a beets Sort.

        Args:
            sort_arg: The value of the 'sort' query parameter; a comma
                separated list of fields to sort by, in order.
                E.g. "-year,title".
        """
        # Change HTTP query parameter to a list
        aura_sorts = sort_arg.strip(",").split(",")
        sorts = []
        for aura_attr in aura_sorts:
            if aura_attr[0] == "-":
                ascending = False
                # Remove leading "-"
                aura_attr = aura_attr[1:]
            else:
                # JSON:API default
                ascending = True
            # Get the beets version of the attribute name
            beets_attr = self.attribute_map.get(aura_attr, aura_attr)
            # Use slow sort so it works with all fields (inc. computed)
            sorts.append(SlowFieldSort(beets_attr, ascending=ascending))
        return MultipleSort(sorts)

    def paginate(self, collection):
        """Get a page of the collection and the URL to the next page.

        Args:
            collection: The raw data from which resource objects can be
                built. Could be an sqlite3.Cursor object (tracks and
                albums) or a list of strings (artists).
        """
        # Pages start from zero
        page = request.args.get("page", 0, int)
        # Use page limit defined in config by default.
        default_limit = config["aura"]["page_limit"].get(int)
        limit = request.args.get("limit", default_limit, int)
        # start = offset of first item to return
        start = page * limit
        # end = offset of last item + 1
        end = start + limit
        if end > len(collection):
            end = len(collection)
            next_url = None
        else:
            # Not the last page so work out links.next url
            if not request.args:
                # No existing arguments, so current page is 0
                next_url = request.url + "?page=1"
            elif not request.args.get("page", None):
                # No existing page argument, so add one to the end
                next_url = request.url + "&page=1"
            else:
                # Increment page token by 1
                next_url = request.url.replace(
                    f"page={page}", "page={}".format(page + 1)
                )
        # Get only the items in the page range
        data = [self.resource_object(collection[i]) for i in range(start, end)]
        return data, next_url

    def get_included(self, data, include_str):
        """Build a list of resource objects for inclusion.

        Args:
            data: An array of dicts in the form of resource objects.
            include_str: A comma separated list of resource types to
                include. E.g. "tracks,images".
        """
        # Change HTTP query parameter to a list
        to_include = include_str.strip(",").split(",")
        # Build a list of unique type and id combinations
        # For each resource object in the primary data, iterate over it's
        # relationships. If a relationship matches one of the types
        # requested for inclusion (e.g. "albums") then add each type-id pair
        # under the "data" key to unique_identifiers, checking first that
        # it has not already been added. This ensures that no resources are
        # included more than once.
        unique_identifiers = []
        for res_obj in data:
            for rel_name, rel_obj in res_obj["relationships"].items():
                if rel_name in to_include:
                    # NOTE: Assumes relationship is to-many
                    for identifier in rel_obj["data"]:
                        if identifier not in unique_identifiers:
                            unique_identifiers.append(identifier)
        # TODO: I think this could be improved
        included = []
        for identifier in unique_identifiers:
            res_type = identifier["type"]
            if res_type == "track":
                track_id = int(identifier["id"])
                track = current_app.config["lib"].get_item(track_id)
                included.append(TrackDocument.resource_object(track))
            elif res_type == "album":
                album_id = int(identifier["id"])
                album = current_app.config["lib"].get_album(album_id)
                included.append(AlbumDocument.resource_object(album))
            elif res_type == "artist":
                artist_id = identifier["id"]
                included.append(ArtistDocument.resource_object(artist_id))
            elif res_type == "image":
                image_id = identifier["id"]
                included.append(ImageDocument.resource_object(image_id))
            else:
                raise ValueError(f"Invalid resource type: {res_type}")
        return included

    def all_resources(self):
        """Build document for /tracks, /albums or /artists."""
        query = self.translate_filters()
        sort_arg = request.args.get("sort", None)
        if sort_arg:
            sort = self.translate_sorts(sort_arg)
            # For each sort field add a query which ensures all results
            # have a non-empty, non-zero value for that field.
            for s in sort.sorts:
                query.subqueries.append(
                    NotQuery(
                        # Match empty fields (^$) or zero fields, (^0$)
                        RegexpQuery(s.field, "(^$|^0$)", fast=False)
                    )
                )
        else:
            sort = None
        # Get information from the library
        collection = self.get_collection(query=query, sort=sort)
        # Convert info to AURA form and paginate it
        data, next_url = self.paginate(collection)
        document = {"data": data}
        # If there are more pages then provide a way to access them
        if next_url:
            document["links"] = {"next": next_url}
        # Include related resources for each element in "data"
        include_str = request.args.get("include", None)
        if include_str:
            document["included"] = self.get_included(data, include_str)
        return document

    def single_resource_document(self, resource_object):
        """Build document for a specific requested resource.

        Args:
            resource_object: A dictionary in the form of a JSON:API
                resource object.
        """
        document = {"data": resource_object}
        include_str = request.args.get("include", None)
        if include_str:
            # [document["data"]] is because arg needs to be list
            document["included"] = self.get_included(
                [document["data"]], include_str
            )
        return document


class TrackDocument(AURADocument):
    """Class for building documents for /tracks endpoints."""

    attribute_map = TRACK_ATTR_MAP

    def get_collection(self, query=None, sort=None):
        """Get Item objects from the library.

        Args:
            query: A beets Query object or a beets query string.
            sort: A beets Sort object.
        """
        return current_app.config["lib"].items(query, sort)

    def get_attribute_converter(self, beets_attr):
        """Work out what data type an attribute should be for beets.

        Args:
            beets_attr: The name of the beets attribute, e.g. "title".
        """
        # filesize is a special field (read from disk not db?)
        if beets_attr == "filesize":
            converter = int
        else:
            try:
                # Look for field in list of Item fields
                # and get python type of database type.
                # See beets.library.Item and beets.dbcore.types
                converter = Item._fields[beets_attr].model_type
            except KeyError:
                # Fall back to string (NOTE: probably not good)
                converter = str
        return converter

    @staticmethod
    def resource_object(track):
        """Construct a JSON:API resource object from a beets Item.

        Args:
            track: A beets Item object.
        """
        attributes = {}
        # Use aura => beets attribute map, e.g. size => filesize
        for aura_attr, beets_attr in TRACK_ATTR_MAP.items():
            a = getattr(track, beets_attr)
            # Only set attribute if it's not None, 0, "", etc.
            # NOTE: This could result in required attributes not being set
            if a:
                attributes[aura_attr] = a

        # JSON:API one-to-many relationship to parent album
        relationships = {
            "artists": {"data": [{"type": "artist", "id": track.artist}]}
        }
        # Only add album relationship if not singleton
        if not track.singleton:
            relationships["albums"] = {
                "data": [{"type": "album", "id": str(track.album_id)}]
            }

        return {
            "type": "track",
            "id": str(track.id),
            "attributes": attributes,
            "relationships": relationships,
        }

    def single_resource(self, track_id):
        """Get track from the library and build a document.

        Args:
            track_id: The beets id of the track (integer).
        """
        track = current_app.config["lib"].get_item(track_id)
        if not track:
            return self.error(
                "404 Not Found",
                "No track with the requested id.",
                "There is no track with an id of {} in the library.".format(
                    track_id
                ),
            )
        return self.single_resource_document(self.resource_object(track))


class AlbumDocument(AURADocument):
    """Class for building documents for /albums endpoints."""

    attribute_map = ALBUM_ATTR_MAP

    def get_collection(self, query=None, sort=None):
        """Get Album objects from the library.

        Args:
            query: A beets Query object or a beets query string.
            sort: A beets Sort object.
        """
        return current_app.config["lib"].albums(query, sort)

    def get_attribute_converter(self, beets_attr):
        """Work out what data type an attribute should be for beets.

        Args:
            beets_attr: The name of the beets attribute, e.g. "title".
        """
        try:
            # Look for field in list of Album fields
            # and get python type of database type.
            # See beets.library.Album and beets.dbcore.types
            converter = Album._fields[beets_attr].model_type
        except KeyError:
            # Fall back to string (NOTE: probably not good)
            converter = str
        return converter

    @staticmethod
    def resource_object(album):
        """Construct a JSON:API resource object from a beets Album.

        Args:
            album: A beets Album object.
        """
        attributes = {}
        # Use aura => beets attribute name map
        for aura_attr, beets_attr in ALBUM_ATTR_MAP.items():
            a = getattr(album, beets_attr)
            # Only set attribute if it's not None, 0, "", etc.
            # NOTE: This could mean required attributes are not set
            if a:
                attributes[aura_attr] = a

        # Get beets Item objects for all tracks in the album sorted by
        # track number. Sorting is not required but it's nice.
        query = MatchQuery("album_id", album.id)
        sort = FixedFieldSort("track", ascending=True)
        tracks = current_app.config["lib"].items(query, sort)
        # JSON:API one-to-many relationship to tracks on the album
        relationships = {
            "tracks": {
                "data": [{"type": "track", "id": str(t.id)} for t in tracks]
            }
        }
        # Add images relationship if album has associated images
        if album.artpath:
            path = py3_path(album.artpath)
            filename = path.split("/")[-1]
            image_id = f"album-{album.id}-{filename}"
            relationships["images"] = {
                "data": [{"type": "image", "id": image_id}]
            }
        # Add artist relationship if artist name is same on tracks
        # Tracks are used to define artists so don't albumartist
        # Check for all tracks in case some have featured artists
        if album.albumartist in [t.artist for t in tracks]:
            relationships["artists"] = {
                "data": [{"type": "artist", "id": album.albumartist}]
            }

        return {
            "type": "album",
            "id": str(album.id),
            "attributes": attributes,
            "relationships": relationships,
        }

    def single_resource(self, album_id):
        """Get album from the library and build a document.

        Args:
            album_id: The beets id of the album (integer).
        """
        album = current_app.config["lib"].get_album(album_id)
        if not album:
            return self.error(
                "404 Not Found",
                "No album with the requested id.",
                "There is no album with an id of {} in the library.".format(
                    album_id
                ),
            )
        return self.single_resource_document(self.resource_object(album))


class ArtistDocument(AURADocument):
    """Class for building documents for /artists endpoints."""

    attribute_map = ARTIST_ATTR_MAP

    def get_collection(self, query=None, sort=None):
        """Get a list of artist names from the library.

        Args:
            query: A beets Query object or a beets query string.
            sort: A beets Sort object.
        """
        # Gets only tracks with matching artist information
        tracks = current_app.config["lib"].items(query, sort)
        collection = []
        for track in tracks:
            # Do not add duplicates
            if track.artist not in collection:
                collection.append(track.artist)
        return collection

    def get_attribute_converter(self, beets_attr):
        """Work out what data type an attribute should be for beets.

        Args:
            beets_attr: The name of the beets attribute, e.g. "artist".
        """
        try:
            # Look for field in list of Item fields
            # and get python type of database type.
            # See beets.library.Item and beets.dbcore.types
            converter = Item._fields[beets_attr].model_type
        except KeyError:
            # Fall back to string (NOTE: probably not good)
            converter = str
        return converter

    @staticmethod
    def resource_object(artist_id):
        """Construct a JSON:API resource object for the given artist.

        Args:
            artist_id: A string which is the artist's name.
        """
        # Get tracks where artist field exactly matches artist_id
        query = MatchQuery("artist", artist_id)
        tracks = current_app.config["lib"].items(query)
        if not tracks:
            return None

        # Get artist information from the first track
        # NOTE: It could be that the first track doesn't have a
        # MusicBrainz id but later tracks do, which isn't ideal.
        attributes = {}
        # Use aura => beets attribute map, e.g. artist => name
        for aura_attr, beets_attr in ARTIST_ATTR_MAP.items():
            a = getattr(tracks[0], beets_attr)
            # Only set attribute if it's not None, 0, "", etc.
            # NOTE: This could mean required attributes are not set
            if a:
                attributes[aura_attr] = a

        relationships = {
            "tracks": {
                "data": [{"type": "track", "id": str(t.id)} for t in tracks]
            }
        }
        album_query = MatchQuery("albumartist", artist_id)
        albums = current_app.config["lib"].albums(query=album_query)
        if len(albums) != 0:
            relationships["albums"] = {
                "data": [{"type": "album", "id": str(a.id)} for a in albums]
            }

        return {
            "type": "artist",
            "id": artist_id,
            "attributes": attributes,
            "relationships": relationships,
        }

    def single_resource(self, artist_id):
        """Get info for the requested artist and build a document.

        Args:
            artist_id: A string which is the artist's name.
        """
        artist_resource = self.resource_object(artist_id)
        if not artist_resource:
            return self.error(
                "404 Not Found",
                "No artist with the requested id.",
                "There is no artist with an id of {} in the library.".format(
                    artist_id
                ),
            )
        return self.single_resource_document(artist_resource)


def safe_filename(fn):
    """Check whether a string is a simple (non-path) filename.

    For example, `foo.txt` is safe because it is a "plain" filename. But
    `foo/bar.txt` and `../foo.txt` and `.` are all non-safe because they
    can traverse to other directories other than the current one.
    """
    # Rule out any directories.
    if os.path.basename(fn) != fn:
        return False

    # In single names, rule out Unix directory traversal names.
    if fn in (".", ".."):
        return False

    return True


class ImageDocument(AURADocument):
    """Class for building documents for /images/(id) endpoints."""

    @staticmethod
    def get_image_path(image_id):
        """Works out the full path to the image with the given id.

        Returns None if there is no such image.

        Args:
            image_id: A string in the form
                "<parent_type>-<parent_id>-<img_filename>".
        """
        # Split image_id into its constituent parts
        id_split = image_id.split("-")
        if len(id_split) < 3:
            # image_id is not in the required format
            return None
        parent_type = id_split[0]
        parent_id = id_split[1]
        img_filename = "-".join(id_split[2:])
        if not safe_filename(img_filename):
            return None

        # Get the path to the directory parent's images are in
        if parent_type == "album":
            album = current_app.config["lib"].get_album(int(parent_id))
            if not album or not album.artpath:
                return None
            # Cut the filename off of artpath
            # This is in preparation for supporting images in the same
            # directory that are not tracked by beets.
            artpath = py3_path(album.artpath)
            dir_path = "/".join(artpath.split("/")[:-1])
        else:
            # Images for other resource types are not supported
            return None

        img_path = os.path.join(dir_path, img_filename)
        # Check the image actually exists
        if isfile(img_path):
            return img_path
        else:
            return None

    @staticmethod
    def resource_object(image_id):
        """Construct a JSON:API resource object for the given image.

        Args:
            image_id: A string in the form
                "<parent_type>-<parent_id>-<img_filename>".
        """
        # Could be called as a static method, so can't use
        # self.get_image_path()
        image_path = ImageDocument.get_image_path(image_id)
        if not image_path:
            return None

        attributes = {
            "role": "cover",
            "mimetype": guess_type(image_path)[0],
            "size": getsize(image_path),
        }
        try:
            from PIL import Image
        except ImportError:
            pass
        else:
            im = Image.open(image_path)
            attributes["width"] = im.width
            attributes["height"] = im.height

        relationships = {}
        # Split id into [parent_type, parent_id, filename]
        id_split = image_id.split("-")
        relationships[id_split[0] + "s"] = {
            "data": [{"type": id_split[0], "id": id_split[1]}]
        }

        return {
            "id": image_id,
            "type": "image",
            # Remove attributes that are None, 0, "", etc.
            "attributes": {k: v for k, v in attributes.items() if v},
            "relationships": relationships,
        }

    def single_resource(self, image_id):
        """Get info for the requested image and build a document.

        Args:
            image_id: A string in the form
                "<parent_type>-<parent_id>-<img_filename>".
        """
        image_resource = self.resource_object(image_id)
        if not image_resource:
            return self.error(
                "404 Not Found",
                "No image with the requested id.",
                "There is no image with an id of {} in the library.".format(
                    image_id
                ),
            )
        return self.single_resource_document(image_resource)


# Initialise flask blueprint
aura_bp = Blueprint("aura_bp", __name__)


@aura_bp.route("/server")
def server_info():
    """Respond with info about the server."""
    return {"data": {"type": "server", "id": "0", "attributes": SERVER_INFO}}


# Track endpoints


@aura_bp.route("/tracks")
def all_tracks():
    """Respond with a list of all tracks and related information."""
    doc = TrackDocument()
    return doc.all_resources()


@aura_bp.route("/tracks/<int:track_id>")
def single_track(track_id):
    """Respond with info about the specified track.

    Args:
        track_id: The id of the track provided in the URL (integer).
    """
    doc = TrackDocument()
    return doc.single_resource(track_id)


@aura_bp.route("/tracks/<int:track_id>/audio")
def audio_file(track_id):
    """Supply an audio file for the specified track.

    Args:
        track_id: The id of the track provided in the URL (integer).
    """
    track = current_app.config["lib"].get_item(track_id)
    if not track:
        return AURADocument.error(
            "404 Not Found",
            "No track with the requested id.",
            "There is no track with an id of {} in the library.".format(
                track_id
            ),
        )

    path = py3_path(track.path)
    if not isfile(path):
        return AURADocument.error(
            "404 Not Found",
            "No audio file for the requested track.",
            (
                "There is no audio file for track {} at the expected location"
            ).format(track_id),
        )

    file_mimetype = guess_type(path)[0]
    if not file_mimetype:
        return AURADocument.error(
            "500 Internal Server Error",
            "Requested audio file has an unknown mimetype.",
            (
                "The audio file for track {} has an unknown mimetype. "
                "Its file extension is {}."
            ).format(track_id, path.split(".")[-1]),
        )

    # Check that the Accept header contains the file's mimetype
    # Takes into account */* and audio/*
    # Adding support for the bitrate parameter would require some effort so I
    # left it out. This means the client could be sent an error even if the
    # audio doesn't need transcoding.
    if not request.accept_mimetypes.best_match([file_mimetype]):
        return AURADocument.error(
            "406 Not Acceptable",
            "Unsupported MIME type or bitrate parameter in Accept header.",
            (
                "The audio file for track {} is only available as {} and "
                "bitrate parameters are not supported."
            ).format(track_id, file_mimetype),
        )

    return send_file(
        path,
        mimetype=file_mimetype,
        # Handles filename in Content-Disposition header
        as_attachment=True,
        # Tries to upgrade the stream to support range requests
        conditional=True,
    )


# Album endpoints


@aura_bp.route("/albums")
def all_albums():
    """Respond with a list of all albums and related information."""
    doc = AlbumDocument()
    return doc.all_resources()


@aura_bp.route("/albums/<int:album_id>")
def single_album(album_id):
    """Respond with info about the specified album.

    Args:
        album_id: The id of the album provided in the URL (integer).
    """
    doc = AlbumDocument()
    return doc.single_resource(album_id)


# Artist endpoints
# Artist ids are their names


@aura_bp.route("/artists")
def all_artists():
    """Respond with a list of all artists and related information."""
    doc = ArtistDocument()
    return doc.all_resources()


# Using the path converter allows slashes in artist_id
@aura_bp.route("/artists/<path:artist_id>")
def single_artist(artist_id):
    """Respond with info about the specified artist.

    Args:
        artist_id: The id of the artist provided in the URL. A string
            which is the artist's name.
    """
    doc = ArtistDocument()
    return doc.single_resource(artist_id)


# Image endpoints
# Image ids are in the form <parent_type>-<parent_id>-<img_filename>
# For example: album-13-cover.jpg


@aura_bp.route("/images/<string:image_id>")
def single_image(image_id):
    """Respond with info about the specified image.

    Args:
        image_id: The id of the image provided in the URL. A string in
            the form "<parent_type>-<parent_id>-<img_filename>".
    """
    doc = ImageDocument()
    return doc.single_resource(image_id)


@aura_bp.route("/images/<string:image_id>/file")
def image_file(image_id):
    """Supply an image file for the specified image.

    Args:
        image_id: The id of the image provided in the URL. A string in
            the form "<parent_type>-<parent_id>-<img_filename>".
    """
    img_path = ImageDocument.get_image_path(image_id)
    if not img_path:
        return AURADocument.error(
            "404 Not Found",
            "No image with the requested id.",
            "There is no image with an id of {} in the library".format(
                image_id
            ),
        )
    return send_file(img_path)


# WSGI app


def create_app():
    """An application factory for use by a WSGI server."""
    config["aura"].add(
        {
            "host": "127.0.0.1",
            "port": 8337,
            "cors": [],
            "cors_supports_credentials": False,
            "page_limit": 500,
        }
    )

    app = Flask(__name__)
    # Register AURA blueprint view functions under a URL prefix
    app.register_blueprint(aura_bp, url_prefix="/aura")
    # AURA specifies mimetype MUST be this
    app.config["JSONIFY_MIMETYPE"] = "application/vnd.api+json"
    # Disable auto-sorting of JSON keys
    app.config["JSON_SORT_KEYS"] = False
    # Provide a way to access the beets library
    # The normal method of using the Library and config provided in the
    # command function is not used because create_app() could be called
    # by an external WSGI server.
    # NOTE: this uses a 'private' function from beets.ui.__init__
    app.config["lib"] = _open_library(config)

    # Enable CORS if required
    cors = config["aura"]["cors"].as_str_seq(list)
    if cors:
        from flask_cors import CORS

        # "Accept" is the only header clients use
        app.config["CORS_ALLOW_HEADERS"] = "Accept"
        app.config["CORS_RESOURCES"] = {r"/aura/*": {"origins": cors}}
        app.config["CORS_SUPPORTS_CREDENTIALS"] = config["aura"][
            "cors_supports_credentials"
        ].get(bool)
        CORS(app)

    return app


# Beets Plugin Hook


class AURAPlugin(BeetsPlugin):
    """The BeetsPlugin subclass for the AURA server plugin."""

    def __init__(self):
        """Add configuration options for the AURA plugin."""
        super().__init__()

    def commands(self):
        """Add subcommand used to run the AURA server."""

        def run_aura(lib, opts, args):
            """Run the application using Flask's built in-server.

            Args:
                lib: A beets Library object (not used).
                opts: Command line options. An optparse.Values object.
                args: The list of arguments to process (not used).
            """
            app = create_app()
            # Start the built-in server (not intended for production)
            app.run(
                host=self.config["host"].get(str),
                port=self.config["port"].get(int),
                debug=opts.debug,
                threaded=True,
            )

        run_aura_cmd = Subcommand("aura", help="run an AURA server")
        run_aura_cmd.parser.add_option(
            "-d",
            "--debug",
            action="store_true",
            default=False,
            help="use Flask debug mode",
        )
        run_aura_cmd.func = run_aura
        return [run_aura_cmd]