import datetime
import json
import logging
import os
import random

from opencensus.common.schedule import PeriodicTask

logger = logging.getLogger(__name__)


def _fmt(timestamp):
    return timestamp.strftime('%Y-%m-%dT%H%M%S.%f')


def _now():
    return datetime.datetime.utcnow()


def _seconds(seconds):
    return datetime.timedelta(seconds=seconds)


class LocalFileBlob(object):
    def __init__(self, fullpath):
        self.fullpath = fullpath

    def delete(self):
        try:
            os.remove(self.fullpath)
        except Exception:
            pass  # keep silent

    def get(self):
        try:
            with open(self.fullpath, 'r') as file:
                return tuple(
                    json.loads(line.strip())
                    for line in file.readlines()
                )
        except Exception:
            pass  # keep silent

    def put(self, data, lease_period=0):
        try:
            fullpath = self.fullpath + '.tmp'
            with open(fullpath, 'w') as file:
                for item in data:
                    file.write(json.dumps(item))
                    # The official Python doc: Do not use os.linesep as a line
                    # terminator when writing files opened in text mode (the
                    # default); use a single '\n' instead, on all platforms.
                    file.write('\n')
            if lease_period:
                timestamp = _now() + _seconds(lease_period)
                self.fullpath += '@{}.lock'.format(_fmt(timestamp))
            os.rename(fullpath, self.fullpath)
            return self
        except Exception:
            pass  # keep silent

    def lease(self, period):
        timestamp = _now() + _seconds(period)
        fullpath = self.fullpath
        if fullpath.endswith('.lock'):
            fullpath = fullpath[: fullpath.rindex('@')]
        fullpath += '@{}.lock'.format(_fmt(timestamp))
        try:
            os.rename(self.fullpath, fullpath)
        except Exception:
            return None
        self.fullpath = fullpath
        return self


class LocalFileStorage(object):
    def __init__(
            self,
            path,
            max_size=50*1024*1024,  # 50MiB
            maintenance_period=60,  # 1 minute
            retention_period=7*24*60*60,  # 7 days
            write_timeout=60,  # 1 minute
    ):
        self.path = os.path.abspath(path)
        self.max_size = max_size
        self.maintenance_period = maintenance_period
        self.retention_period = retention_period
        self.write_timeout = write_timeout
        # Run maintenance routine once upon instantiating
        self._maintenance_routine()
        self._maintenance_task = PeriodicTask(
            interval=self.maintenance_period,
            function=self._maintenance_routine,
        )
        self._maintenance_task.daemon = True
        self._maintenance_task.start()

    def close(self):
        self._maintenance_task.cancel()
        self._maintenance_task.join()

    def __enter__(self):
        return self

    def __exit__(self, type, value, traceback):
        self.close()

    def _maintenance_routine(self):
        try:
            if not os.path.isdir(self.path):
                os.makedirs(self.path)
        except Exception:
            # Race case will throw OSError which we can ignore
            pass
        try:
            for blob in self.gets():
                pass
        except Exception:
            pass  # keep silent

    def gets(self):
        now = _now()
        lease_deadline = _fmt(now)
        retention_deadline = _fmt(now - _seconds(self.retention_period))
        timeout_deadline = _fmt(now - _seconds(self.write_timeout))
        for name in sorted(os.listdir(self.path)):
            path = os.path.join(self.path, name)
            if not os.path.isfile(path):
                continue  # skip if not a file
            if path.endswith('.tmp'):
                if name < timeout_deadline:
                    try:
                        os.remove(path)  # TODO: log data loss
                    except Exception:
                        pass  # keep silent
            if path.endswith('.lock'):
                if path[path.rindex('@') + 1: -5] > lease_deadline:
                    continue  # under lease
                new_path = path[: path.rindex('@')]
                try:
                    os.rename(path, new_path)
                except Exception:
                    continue  # keep silent
                path = new_path
            if path.endswith('.blob'):
                if name < retention_deadline:
                    try:
                        os.remove(path)  # TODO: log data loss
                    except Exception:
                        pass  # keep silent
                else:
                    yield LocalFileBlob(path)

    def get(self):
        cursor = self.gets()
        try:
            return next(cursor)
        except StopIteration:
            pass
        return None

    def put(self, data, lease_period=0):
        if not self._check_storage_size():
            return None
        blob = LocalFileBlob(os.path.join(
            self.path,
            '{}-{}.blob'.format(
                _fmt(_now()),
                '{:08x}'.format(random.getrandbits(32)),  # thread-safe random
            ),
        ))
        return blob.put(data, lease_period=lease_period)

    def _check_storage_size(self):
        size = 0
        for dirpath, dirnames, filenames in os.walk(self.path):
            for f in filenames:
                fp = os.path.join(dirpath, f)
                # skip if it is symbolic link
                if not os.path.islink(fp):
                    try:
                        size += os.path.getsize(fp)
                    except OSError:
                        logger.error(
                            "Path %s does not exist or is inaccessible.", fp
                        )
                        continue
                    if size >= self.max_size:
                        logger.warning(
                            "Persistent storage max capacity has been "
                            "reached. Currently at %fKB. Telemetry will be "
                            "lost. Please consider increasing the value of "
                            "'storage_max_size' in exporter config.",
                            format(size/1024)
                        )
                        return False
        return True
