# coding: utf-8

"""
Cache for remote files on local disk.
"""

__all__ = ["RemoteCache"]


import os
import shutil
import time
import tempfile
import weakref
import atexit
from contextlib import contextmanager

from law.config import Config
from law.util import (
    makedirs, human_bytes, parse_bytes, parse_duration, create_hash, user_owns_file, io_lock,
)
from law.logger import get_logger


logger = get_logger(__name__)


class RemoteCache(object):

    TMP = "__TMP__"

    lock_postfix = ".lock"

    _instances = []

    def __new__(cls, *args, **kwargs):
        inst = object.__new__(cls)

        # cache instances
        cls._instances.append(inst)

        return inst

    @classmethod
    def cleanup_all(cls):
        # clear all caches
        for inst in cls._instances:
            try:
                inst._cleanup()
            except:
                pass

    @classmethod
    def parse_config(cls, section, config=None, overwrite=False):
        from law.sandbox.base import _sandbox_switched

        # reads a law config section and returns parsed file system configs
        cfg = Config.instance()

        if config is None:
            config = {}

        # helper to add a config value if it exists, extracted with a config parser method
        def add(option, func):
            cache_option = "cache_" + option
            if cfg.is_missing_or_none(section, cache_option):
                return
            elif option not in config or overwrite:
                config[option] = func(section, cache_option)

        def get_size(section, cache_option):
            value = cfg.get_expanded(section, cache_option)
            return parse_bytes(value, input_unit="MB", unit="MB")

        def get_time(section, cache_option):
            value = cfg.get_expanded(section, cache_option)
            return parse_duration(value, input_unit="s", unit="s")

        add("root", cfg.get_expanded)
        add("cleanup", cfg.get_expanded_bool)
        add("max_size", get_size)
        add("mtime_patience", cfg.get_expanded_float)
        add("file_perm", cfg.get_expanded_int)
        add("dir_perm", cfg.get_expanded_int)
        add("wait_delay", get_time)
        add("max_waits", cfg.get_expanded_int)
        add("global_lock", cfg.get_expanded_bool)

        # inside sandboxes, never cleanup since the outer process will do that if needed
        if _sandbox_switched:
            config["cleanup"] = False

        return config

    def __init__(self, fs, root=TMP, cleanup=False, max_size=0, mtime_patience=1.0,
            file_perm=0o0660, dir_perm=0o0770, wait_delay=5.0, max_waits=120, global_lock=False):
        object.__init__(self)
        # max_size is in MB, wait_delay is in seconds

        # create a unique name based on fs attributes
        name = "{}_{}".format(fs.__class__.__name__, create_hash(fs.base[0]))

        # create the root dir, handle tmp
        root = os.path.expandvars(os.path.expanduser(root)) or self.TMP
        if not os.path.exists(root) and root == self.TMP:
            cfg = Config.instance()
            tmp_dir = cfg.get_expanded("target", "tmp_dir")
            base = tempfile.mkdtemp(dir=tmp_dir)
            cleanup = True
        else:
            base = os.path.join(root, name)
            makedirs(base, dir_perm)

        # save attributes and configs
        self.root = root
        self.fs_ref = weakref.ref(fs)
        self.base = base
        self.name = name
        self.cleanup = cleanup
        self.max_size = max_size
        self.mtime_patience = mtime_patience
        self.dir_perm = dir_perm
        self.file_perm = file_perm
        self.wait_delay = wait_delay
        self.max_waits = max_waits
        self.global_lock = global_lock

        # path to the global lock file which should guard global actions such as cache allocations
        self._global_lock_path = self._lock_path(os.path.join(base, "global"))

        # currently locked cache paths, only used to clean up broken files during cleanup
        self._locked_cpaths = set()

        logger.debug("created {} at '{}'".format(self.__class__.__name__, self.base))

    def __del__(self):
        try:
            self._cleanup()
        except (OSError, TypeError):
            pass

    def __repr__(self):
        return "<{} '{}' at {}>".format(self.__class__.__name__, self.base, hex(id(self)))

    def __contains__(self, rpath):
        return os.path.exists(self.cache_path(rpath))

    @property
    def fs(self):
        return self.fs_ref()

    def _cleanup(self):
        # full cleanup or remove open locks
        if getattr(self, "cleanup", False):
            if os.path.exists(self.base):
                shutil.rmtree(self.base)
        else:
            for cpath in set(self._locked_cpaths):
                self._unlock(cpath)
                self._remove(cpath)
            self._locked_cpaths.clear()
            self._unlock_global()
        logger.debug("cleanup RemoteCache at '{}'".format(self.base))

    def cache_path(self, rpath):
        basename = "{}_{}".format(create_hash(rpath), os.path.basename(rpath))
        return os.path.join(self.base, basename)

    def _lock_path(self, cpath):
        return cpath + self.lock_postfix

    def is_locked_global(self):
        return os.path.exists(self._global_lock_path)

    def _is_locked(self, cpath):
        return os.path.exists(self._lock_path(cpath))

    def is_locked(self, rpath):
        return self._is_locked(self.cache_path(rpath))

    def _unlock_global(self):
        try:
            os.remove(self._global_lock_path)
        except OSError:
            pass

    def _unlock(self, cpath):
        try:
            os.remove(self._lock_path(cpath))
        except OSError:
            pass

    def _await_global(self, delay=None, max_waits=None, silent=False):
        delay = delay if delay is not None else self.wait_delay
        max_waits = max_waits if max_waits is not None else self.max_waits
        _max_waits = max_waits

        while self.is_locked_global():
            if max_waits <= 0:
                if not silent:
                    raise Exception("max_waits of {} exceeded while waiting for global lock".format(
                        _max_waits))
                return False

            time.sleep(delay)
            max_waits -= 1

        return True

    def _await(self, cpath, delay=None, max_waits=None, silent=False, global_lock=None):
        delay = delay if delay is not None else self.wait_delay
        max_waits = max_waits if max_waits is not None else self.max_waits
        _max_waits = max_waits
        global_lock = self.global_lock if global_lock is None else global_lock

        # strategy: wait as long the file is locked and if the file size did not change, reduce
        # max_waits per iteration and raise when 0 is reached
        last_size = -1
        while self._is_locked(cpath) or (global_lock and self.is_locked_global()):
            if max_waits <= 0:
                if not silent:
                    raise Exception("max_waits of {} exceeded while waiting for file '{}'".format(
                        _max_waits, cpath))
                return False

            time.sleep(delay)

            # only reduce max_waits when the file size did not change
            # otherwise, set it to its original value again
            if os.path.exists(cpath):
                size = os.stat(cpath).st_size
                if size != last_size:
                    last_size = size
                    max_waits = _max_waits + 1

            max_waits -= 1

        return True

    @contextmanager
    def _lock_global(self, **kwargs):
        self._await_global(**kwargs)

        try:
            with io_lock:
                with open(self._global_lock_path, "w") as f:
                    f.write("")
                os.utime(self._global_lock_path, None)

            yield
        finally:
            self._unlock_global()

    @contextmanager
    def _lock(self, cpath, **kwargs):
        lock_path = self._lock_path(cpath)

        self._await(cpath, **kwargs)

        try:
            with io_lock:
                with open(lock_path, "w") as f:
                    f.write("")
                self._locked_cpaths.add(cpath)
                try:
                    os.utime(lock_path, None)
                except OSError:
                    pass

            yield
        except:
            # when something went really wrong, conservatively delete the cached file
            self._remove(cpath, lock=False)
            raise
        finally:
            # unlock again
            self._unlock(cpath)
            if cpath in self._locked_cpaths:
                self._locked_cpaths.remove(cpath)

    def lock(self, rpath):
        return self._lock(self.cache_path(rpath))

    def allocate(self, size):
        logger.debug("allocating {0[0]:.2f} {0[1]} in cache '{1}'".format(human_bytes(size), self))

        # determine stats and current cache size
        file_stats = []
        for elem in os.listdir(self.base):
            if elem.endswith(self.lock_postfix):
                continue
            cpath = os.path.join(self.base, elem)
            file_stats.append((cpath, os.stat(cpath)))
        current_size = sum(stat.st_size for _, stat in file_stats)

        # get the available space of the disk that contains the cache in bytes, leave 10%
        fs_stat = os.statvfs(self.base)
        free_size = fs_stat.f_frsize * fs_stat.f_bavail * 0.9

        # determine the maximum size of the cache
        # make sure it is always smaller than what is available
        if self.max_size <= 0:
            max_size = current_size + free_size
        else:
            max_size = min(self.max_size * 1024**2, current_size + free_size)

        # determine the size of files that need to be deleted
        delete_size = current_size + size - max_size
        if delete_size <= 0:
            logger.debug("cache space sufficient, {0[0]:.2f} {0[1]} remaining".format(
                human_bytes(-delete_size)))
            return True

        logger.info("need to delete {0[0]:.2f} {0[1]} from cache".format(
            human_bytes(delete_size)))

        # delete files, ordered by their access time, skip locked ones
        for cpath, cstat in sorted(file_stats, key=lambda tpl: tpl[1].st_atime):
            if self._is_locked(cpath):
                continue
            self._remove(cpath)
            delete_size -= cstat.st_size
            if delete_size <= 0:
                return True

        logger.warning("could not allocate remaining {0[0]:.2f} {0[1]} in cache".format(
            human_bytes(delete_size)))

        return False

    def _touch(self, cpath, times=None):
        if os.path.exists(cpath):
            if user_owns_file(cpath):
                os.chmod(cpath, self.file_perm)
            os.utime(cpath, times)

    def touch(self, rpath, times=None):
        self._touch(self.cache_path(rpath), times=times)

    def _mtime(self, cpath):
        return os.stat(cpath).st_mtime

    def mtime(self, rpath):
        return self._mtime(self.cache_path(rpath))

    def check_mtime(self, rpath, rmtime):
        if self.mtime_patience < 0:
            return True

        return abs(self.mtime(rpath) - rmtime) <= self.mtime_patience

    def _remove(self, cpath, lock=True):
        def remove():
            try:
                os.remove(cpath)
            except OSError:
                pass

        if lock:
            with self._lock(cpath):
                remove()
        else:
            remove()

    def remove(self, rpath, lock=True):
        return self._remove(self.cache_path(rpath), lock=lock)


atexit.register(RemoteCache.cleanup_all)
