import csv
import os.path
from itertools import islice

from yt.config import ytcfg
from yt.funcs import mylog
from yt.utilities.object_registries import output_type_registry
from yt.utilities.parallel_tools.parallel_analysis_interface import (
    parallel_simple_proxy,
)

_field_names = ("hash", "bn", "fp", "tt", "ctid", "class_name", "last_seen")


class NoParameterShelf(Exception):
    pass


class UnknownDatasetType(Exception):
    def __init__(self, name):
        self.name = name

    def __str__(self):
        return f"{self.name}"

    def __repr__(self):
        return f"{self.name}"


class ParameterFileStore:
    """
    This class is designed to be a semi-persistent storage for parameter
    files.  By identifying each dataset with a unique hash, objects
    can be stored independently of datasets -- when an object is
    loaded, the dataset is as well, based on the hash.  For
    storage concerns, only a few hundred will be retained in cache.

    """

    _shared_state = {}  # type: ignore
    _distributed = True
    _processing = False
    _owner = 0
    _register = True

    def __new__(cls, *p, **k):
        self = object.__new__(cls, *p, **k)
        self.__dict__ = cls._shared_state
        return self

    def __init__(self, in_memory=False):
        """
        Create the dataset database if yt is configured to store them.
        Otherwise, use read-only settings.

        """
        if not self._register:
            return
        if ytcfg.get("yt", "store_parameter_files"):
            self._read_only = False
            self.init_db()
            self._records = self.read_db()
        else:
            self._read_only = True
            self._records = {}
        self._register = False

    @parallel_simple_proxy
    def init_db(self):
        """
        This function ensures that the storage database exists and can be used.
        """
        dbn = self._get_db_name()
        dbdir = os.path.dirname(dbn)
        try:
            if not os.path.isdir(dbdir):
                os.mkdir(dbdir)
        except OSError:
            raise NoParameterShelf()
        open(dbn, "ab")  # make sure it exists, allow to close
        # Now we read in all our records and return them
        # these will be broadcast

    def _get_db_name(self):
        base_file_name = ytcfg.get("yt", "parameter_file_store")
        if not os.access(os.path.expanduser("~/"), os.W_OK):
            return os.path.abspath(base_file_name)
        return os.path.expanduser(f"~/.yt/{base_file_name}")

    def get_ds_hash(self, hash):
        """This returns a dataset based on a hash."""
        return self._convert_ds(self._records[hash])

    def get_ds_ctid(self, ctid):
        """This returns a dataset based on a CurrentTimeIdentifier."""
        for h in self._records:
            if self._records[h]["ctid"] == ctid:
                return self._convert_ds(self._records[h])

    def _adapt_ds(self, ds):
        """This turns a dataset into a CSV entry."""
        return dict(
            bn=ds.basename,
            fp=ds.directory,
            tt=ds.current_time,
            ctid=ds.unique_identifier,
            class_name=ds.__class__.__name__,
            last_seen=ds._instantiated,
        )

    def _convert_ds(self, ds_dict):
        """This turns a CSV entry into a dataset."""
        bn = ds_dict["bn"]
        fp = ds_dict["fp"]
        fn = os.path.join(fp, bn)
        class_name = ds_dict["class_name"]
        if class_name not in output_type_registry:
            raise UnknownDatasetType(class_name)
        mylog.info("Checking %s", fn)
        if os.path.exists(fn):
            ds = output_type_registry[class_name](os.path.join(fp, bn))
        else:
            raise OSError
        # This next one is to ensure that we manually update the last_seen
        # record *now*, for during write_out.
        self._records[ds._hash()]["last_seen"] = ds._instantiated
        return ds

    def check_ds(self, ds):
        """
        This will ensure that the dataset (*ds*) handed to it is
        recorded in the storage unit.  In doing so, it will update path
        and "last_seen" information.
        """
        hash = ds._hash()
        if hash not in self._records:
            self.insert_ds(ds)
            return
        ds_dict = self._records[hash]
        self._records[hash]["last_seen"] = ds._instantiated
        if ds_dict["bn"] != ds.basename or ds_dict["fp"] != ds.directory:
            self.wipe_hash(hash)
            self.insert_ds(ds)

    def insert_ds(self, ds):
        """This will insert a new *ds* and flush the database to disk."""
        self._records[ds._hash()] = self._adapt_ds(ds)
        self.flush_db()

    def wipe_hash(self, hash):
        """
        This removes a *hash* corresponding to a dataset from the
        storage.
        """
        if hash not in self._records:
            return
        del self._records[hash]
        self.flush_db()

    def flush_db(self):
        """This flushes the storage to disk."""
        if self._read_only:
            return
        self._write_out()
        self.read_db()

    def get_recent(self, n=10):
        recs = sorted(self._records.values(), key=lambda a: -a["last_seen"])[:n]
        return recs

    @parallel_simple_proxy
    def _write_out(self):
        if self._read_only:
            return
        fn = self._get_db_name()
        f = open(f"{fn}.tmp", "w")
        w = csv.DictWriter(f, _field_names)
        maxn = ytcfg.get("yt", "maximum_stored_datasets")  # number written
        for h, v in islice(
            sorted(self._records.items(), key=lambda a: -a[1]["last_seen"]), 0, maxn
        ):
            v["hash"] = h
            w.writerow(v)
        f.close()
        os.rename(f"{fn}.tmp", fn)

    @parallel_simple_proxy
    def read_db(self):
        """This will read the storage device from disk."""
        f = open(self._get_db_name())
        vals = csv.DictReader(f, _field_names)
        db = {}
        for v in vals:
            db[v.pop("hash")] = v
            if v["last_seen"] is None:
                v["last_seen"] = 0.0
            else:
                v["last_seen"] = float(v["last_seen"])
        f.close()
        return db
