# Copyright 2020 Mycroft AI Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
"""Mycroft file utils.

This module contains functions handling mycroft resource files and things like
accessing and curating mycroft's cache.
"""

import os
import psutil
from stat import S_ISREG, ST_MTIME, ST_MODE, ST_SIZE
import tempfile

import mycroft.configuration
from .log import LOG


def resolve_resource_file(res_name):
    """Convert a resource into an absolute filename.

    Resource names are in the form: 'filename.ext'
    or 'path/filename.ext'

    The system wil look for ~/.mycroft/res_name first, and
    if not found will look at /opt/mycroft/res_name,
    then finally it will look for res_name in the 'mycroft/res'
    folder of the source code package.

    Example:
    With mycroft running as the user 'bob', if you called
        resolve_resource_file('snd/beep.wav')
    it would return either '/home/bob/.mycroft/snd/beep.wav' or
    '/opt/mycroft/snd/beep.wav' or '.../mycroft/res/snd/beep.wav',
    where the '...' is replaced by the path where the package has
    been installed.

    Arguments:
        res_name (str): a resource path/name
    Returns:
        (str) path to resource or None if no resource found
    """
    config = mycroft.configuration.Configuration.get()

    # First look for fully qualified file (e.g. a user setting)
    if os.path.isfile(res_name):
        return res_name

    # Now look for ~/.mycroft/res_name (in user folder)
    filename = os.path.expanduser("~/.mycroft/" + res_name)
    if os.path.isfile(filename):
        return filename

    # Next look for /opt/mycroft/res/res_name
    data_dir = os.path.join(os.path.expanduser(config['data_dir']), 'res')
    filename = os.path.expanduser(os.path.join(data_dir, res_name))
    if os.path.isfile(filename):
        return filename

    # Finally look for it in the source package
    filename = os.path.join(os.path.dirname(__file__), '..', 'res', res_name)
    filename = os.path.abspath(os.path.normpath(filename))
    if os.path.isfile(filename):
        return filename

    return None  # Resource cannot be resolved


def read_stripped_lines(filename):
    """Read a file and return a list of stripped lines.

    Arguments:
        filename (str): path to file to read.

    Returns:
        (list) list of lines stripped from leading and ending white chars.
    """
    with open(filename, 'r') as f:
        for line in f:
            line = line.strip()
            if line:
                yield line


def read_dict(filename, div='='):
    """Read file into dict.

    A file containing:
        foo = bar
        baz = bog

    results in a dict
    {
        'foo': 'bar',
        'baz': 'bog'
    }

    Arguments:
        filename (str):   path to file
        div (str): deviders between dict keys and values

    Returns:
        (dict) generated dictionary
    """
    d = {}
    with open(filename, 'r') as f:
        for line in f:
            key, val = line.split(div)
            d[key.strip()] = val.strip()
    return d


def mb_to_bytes(size):
    """Takes a size in MB and returns the number of bytes.

    Arguments:
        size(int/float): size in Mega Bytes

    Returns:
        (int/float) size in bytes
    """
    return size * 1024 * 1024


def _get_cache_entries(directory):
    """Get information tuple for all regular files in directory.

    Arguments:
        directory (str): path to directory to check

    Returns:
        (tuple) (modification time, size, filepath)
    """
    entries = (os.path.join(directory, fn) for fn in os.listdir(directory))
    entries = ((os.stat(path), path) for path in entries)

    # leave only regular files, insert modification date
    return ((stat[ST_MTIME], stat[ST_SIZE], path)
            for stat, path in entries if S_ISREG(stat[ST_MODE]))


def _delete_oldest(entries, bytes_needed):
    """Delete files with oldest modification date until space is freed.

    Arguments:
        entries (tuple): file + file stats tuple
        bytes_needed (int): disk space that needs to be freed
    """
    space_freed = 0
    for moddate, fsize, path in sorted(entries):
        try:
            os.remove(path)
            space_freed += fsize
        except Exception:
            pass

        if space_freed > bytes_needed:
            break  # deleted enough!


def curate_cache(directory, min_free_percent=5.0, min_free_disk=50):
    """Clear out the directory if needed.

    The curation will only occur if both the precentage and actual disk space
    is below the limit. This assumes all the files in the directory can be
    deleted as freely.

    Arguments:
        directory (str): directory path that holds cached files
        min_free_percent (float): percentage (0.0-100.0) of drive to keep free,
                                  default is 5% if not specified.
        min_free_disk (float): minimum allowed disk space in MB, default
                               value is 50 MB if not specified.
    """
    # Simpleminded implementation -- keep a certain percentage of the
    # disk available.
    # TODO: Would be easy to add more options, like whitelisted files, etc.
    space = psutil.disk_usage(directory)

    min_free_disk = mb_to_bytes(min_free_disk)
    percent_free = 100.0 - space.percent
    if percent_free < min_free_percent and space.free < min_free_disk:
        LOG.info('Low diskspace detected, cleaning cache')
        # calculate how many bytes we need to delete
        bytes_needed = (min_free_percent - percent_free) / 100.0 * space.total
        bytes_needed = int(bytes_needed + 1.0)

        # get all entries in the directory w/ stats
        entries = _get_cache_entries(directory)
        # delete as many as needed starting with the oldest
        _delete_oldest(entries, bytes_needed)


def get_cache_directory(domain=None):
    """Get a directory for caching data.

    This directory can be used to hold temporary caches of data to
    speed up performance.  This directory will likely be part of a
    small RAM disk and may be cleared at any time.  So code that
    uses these cached files must be able to fallback and regenerate
    the file.

    Arguments:
        domain (str): The cache domain.  Basically just a subdirectory.

    Returns:
        (str) a path to the directory where you can cache data
    """
    config = mycroft.configuration.Configuration.get()
    directory = config.get("cache_path")
    if not directory:
        # If not defined, use /tmp/mycroft/cache
        directory = os.path.join(tempfile.gettempdir(), "mycroft", "cache")
    return ensure_directory_exists(directory, domain)


def ensure_directory_exists(directory, domain=None, permissions=0o777):
    """Create a directory and give access rights to all

    Arguments:
        directory (str): Root directory
        domain (str): Domain. Basically a subdirectory to prevent things like
                      overlapping signal filenames.
        rights (int): Directory permissions (default is 0o777)

    Returns:
        (str) a path to the directory
    """
    if domain:
        directory = os.path.join(directory, domain)

    # Expand and normalize the path
    directory = os.path.normpath(directory)
    directory = os.path.expanduser(directory)

    if not os.path.isdir(directory):
        try:
            save = os.umask(0)
            os.makedirs(directory, permissions)
        except OSError:
            LOG.warning("Failed to create: " + directory)
        finally:
            os.umask(save)

    return directory


def create_file(filename):
    """Create the file filename and create any directories needed

    Arguments:
        filename: Path to the file to be created
    """
    ensure_directory_exists(os.path.dirname(filename), permissions=0o775)
    with open(filename, 'w') as f:
        f.write('')
