import datasets
import zstandard as zstd
import io


class LichessConfig(datasets.BuilderConfig):
    def __init__(self, features, **kwargs):
        super(LichessConfig, self).__init__(**kwargs)
        self.features = features


class Lichess(datasets.GeneratorBasedBuilder):
    BUILDER_CONFIG_CLASS = LichessConfig
    BUILDER_CONFIGS = [LichessConfig(features=["WhiteElo",
                                               "BlackElo",
                                               "fens",
                                               "moves",
                                               "scores"])]

    def _info(self):
        features_dict = {feature: datasets.Value("uint16") for feature in self.config.features}

        features_dict["fens"] = datasets.Value("null")
        features_dict["moves"] = datasets.Value("null")
        features_dict["scores"] = datasets.Value("null")

        info = datasets.DatasetInfo(datasets.Features(features_dict))
        return info

    def _get_filepaths(self):
        months = ["01", "02", "03", "04", "05", "06",
                  "07", "08", "09", "10", "11", "12"]
        shards = ["0", "1", "2", "3"]
        filepaths = ["fen/2023/" + m for m in months]
        
        paths = []
        for shard in shards:
            paths.extend([filepath + "/" + shard + "_fen.zst" for filepath in filepaths])
        return paths

    def _split_generators(self, dl_manager: datasets.DownloadManager):
        filepaths = self._get_filepaths()
        downloaded_files = dl_manager.download(filepaths)
        generator = datasets.SplitGenerator(name=datasets.Split.TRAIN,
                                            gen_kwargs={'filepaths': downloaded_files})
        return [generator]
    
    def _generate_examples(self, filepaths):
        """ Each worker receives a random set of the .zst files (the raw dataset).
            Each worker will cycle through its set of files. They read a single game
            from file 1, then a single game from file 2, etc. ...
            The purpose is to create batches that contain games from a diverse mix
            of time periods. -> Reduces distribution shift.
        """
        files =          [open(filepath, "rb")     for filepath in filepaths]
        dctxs =          [zstd.ZstdDecompressor()  for file in files]
        stream_readers = [dctx.stream_reader(file) for dctx, file in zip(dctxs, files)]
        pgns =           [io.TextIOWrapper(sr)     for sr in stream_readers]

        n = 0
        n_files = len(files)
        # approximate number of positions per .zst file
        n_positions = 2 * 10**6
        while n <= n_files * n_positions:
            # cycle through the different shards
            pgn = pgns[n % n_files]

            elos = pgn.readline()
            game = pgn.readline()

            if game:
                white_elo, black_elo = elos.split(" ")
                fens, moves, scores = game.split(";")
                _id = n
                n += 1
                yield _id, {"WhiteElo": int(white_elo),
                            "BlackElo": int(black_elo),
                            "fens": fens.split(","),
                            "moves": moves.split(","),
                            "scores": scores.rstrip("\n").split(",")}
            else:
                break