#!/usr/bin/env python3

import os.path
import sys
import json
import struct
import subprocess

FILES_LOCATION = os.path.expanduser('~/web2mp3')
CACHE_LOCATION = os.path.join(FILES_LOCATION, '.cache')
ACTIONS = {
    'download-youtube-ids': lambda m: download_youtube_ids(m['ids']),
}


def get_message():
    """Read a message from stdin and decode it."""
    rawLength = sys.stdin.buffer.read(4)
    if len(rawLength) == 0:
        sys.exit(0)
    messageLength = struct.unpack('@I', rawLength)[0]
    message = sys.stdin.buffer.read(messageLength).decode('utf-8')
    return json.loads(message)


def encode_message(message):
    """Encode a message for transmission, given its content."""
    encoded_content = json.dumps(message).encode('utf-8')
    encoded_length = struct.pack('@I', len(encoded_content))
    return {'length': encoded_length, 'content': encoded_content}


def send_message(message):
    """Send an encoded message to stdout"""
    encoded = encode_message(message)
    sys.stdout.buffer.write(encoded['length'])
    sys.stdout.buffer.write(encoded['content'])
    sys.stdout.buffer.flush()


def load_cache():
    """Loads the cache from the disk"""
    if os.path.isfile(CACHE_LOCATION):
        with open(CACHE_LOCATION, 'r') as f:
            return json.load(f)
    else:
        return []


def save_cache(cache):
    """Save downloaded ids in the cache"""
    with open(CACHE_LOCATION, 'w+') as f:
        json.dump(cache, f)


def download_youtube_song(id_):
    url = '"https://www.youtube.com/watch?v=%s"' % id_
    command = 'youtube-dl {0} -x --audio-format mp3 -o "{1}/%(title)s.%(ext)s"'.format(url, FILES_LOCATION)
    process = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE)
    exit_status = process.wait()
    if exit_status != 0:
        raise Exception()


def download_youtube_ids(ids):
    cache = load_cache()
    filtered_ids = [id_ for id_ in ids if id_ not in cache]
    if len(filtered_ids) == 0:
        send_message({"type": "status", "status": "Nothing to download!"})
    else:
        send_message({"type": "status", "status": "Downloading %s songs" % len(filtered_ids)})

    for i, id_ in enumerate(filtered_ids):
        try:
            send_message({"type": "progression", 'progression': i})
            download_youtube_song(id_)
            cache.append(id_)
            save_cache(cache)
        except:
            send_message({"type": "status", "status": "There were an error during the download of your music, check the console for more information."})
    send_message({"type": "status", "status": "Your songs have been downloaded and are available in {0}. Enjoy!".format(FILES_LOCATION)})


while True:
    message = get_message()
    message_type = message.get('type')
    if message_type in ACTIONS:
        ACTIONS[message_type](message)