from collections import namedtuple

_AB = namedtuple("_AB", ["a", "b"])

class ABController:
    def __init__(self, enabled=True, callback=None):
        self.setPositionCallback = callback
        self._limits = dict() # dictionary of all songs
        self._songLimits = None # list of limits for selected song
        self._currentLimits = None # a/b positions of selected limit
        self._enabled = enabled

    def _ensureSongExists(self, path):
        if path not in self._limits:
            self._limits[path] = list()

    def setCurrentSong(self, path):
        self._ensureSongExists(path)
        self._songLimits = self._limits[path]
        self._currentLimits = None

    def addLimits(self, aLimit, bLimit, song=None):
        if song is not None:
            self._ensureSongExists(song)
            songLimits = self._limits[song]
        else:
            songLimits = self._songLimits

        if songLimits is None:
            return

        ab = _AB(aLimit, bLimit)
        songLimits.append(ab)

    def setCurrentLimits(self, index):
        if not self._songLimits:
            return

        if index >= 0 and index < len(self._songLimits):
            self._currentLimits = self._songLimits[index]

    def positionChanged(self, position):
        if not self._currentLimits:
            return
        if position > self._currentLimits.b and self.setPositionCallback and self._enabled:
            self.setPositionCallback(self._currentLimits.a)

    def setEnable(self, enable):
        self._enabled = enable

    def getLimits(self, song):
        return self._limits.get(song)