import os
import random
import string
from datetime import datetime, timedelta
from functools import lru_cache
from mutagen.mp3 import MP3


def random_choices(population, k):
    """Emulate random.choices for Python < 3.6"""
    return [random.choice(population) for _ in range(k)]


def mp3_sources(data_dir, pattern):
    def start_time_for_source_fn(fn):
        return datetime.strptime(os.path.basename(fn), pattern)

    @lru_cache(maxsize=None)
    def length_for_source_fn(fn):
        return timedelta(seconds=MP3(fn).info.length)

    def get_sources():
        # Get a sorted list of all source files with start time and length
        sources = []
        for fn in os.listdir(data_dir):
            fn = os.path.join(data_dir, fn)
            try:
                start_time = start_time_for_source_fn(fn)
                length = length_for_source_fn(fn)
                sources.append({'fn': fn, 'start_time': start_time, 'length': length})
            except ValueError:
                pass
        return sources

    return get_sources


class Config:
    SECRET_KEY = os.environ.get('SECRET_KEY') or \
            ''.join(random_choices(string.ascii_letters, k=20))
    OUT_DIR    = os.environ.get('OUT_DIR') or '/var/tmp/prolefeeder-test-out'
    MAX_LENGTH = os.environ.get('MAX_LENGTH') or 180

    DEBUG      = False

    if not os.path.exists(OUT_DIR):
        raise RuntimeError("OUT_DIR does not exist")

    # Here's the interesting part: configuring the source.
    #
    # We need to return a function that returns a list of dicts of source files with metadata, e.g.
    # [ {"fn": "/path/to/foo-20:01.mp3", "start_time": datetime(...), "length": timedelta(hours=1)} ]

    data_dir   = os.environ.get('DATA_DIR') or '/var/tmp/prolefeeder-test-data'
    pattern    = 'qfhi-%Y%m%d-%H%M.mp3'

    if not os.path.exists(data_dir):
        raise RuntimeError("DATA_DIR does not exist")

    SOURCES = mp3_sources(data_dir, pattern)