ordigi/elodie/localstorage.py

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"""
Methods for interacting with information Elodie caches about stored media.
"""
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from builtins import map
from builtins import object
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import hashlib
import json
from math import radians, cos, sqrt
import os
import sys
from elodie import constants
class Db(object):
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"""A class for interacting with the JSON files created by Elodie."""
def __init__(self):
# verify that the application directory (~/.elodie) exists,
# else create it
if not os.path.exists(constants.application_directory):
os.makedirs(constants.application_directory)
# If the hash db doesn't exist we create it.
# Otherwise we only open for reading
if not os.path.isfile(constants.hash_db):
with open(constants.hash_db, 'a'):
os.utime(constants.hash_db, None)
self.hash_db = {}
# We know from above that this file exists so we open it
# for reading only.
with open(constants.hash_db, 'r') as f:
try:
self.hash_db = json.load(f)
except ValueError:
pass
# If the location db doesn't exist we create it.
# Otherwise we only open for reading
if not os.path.isfile(constants.location_db):
with open(constants.location_db, 'a'):
os.utime(constants.location_db, None)
self.location_db = []
# We know from above that this file exists so we open it
# for reading only.
with open(constants.location_db, 'r') as f:
try:
self.location_db = json.load(f)
except ValueError:
pass
def add_hash(self, key, value, write=False):
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"""Add a hash to the hash db.
:param str key:
:param str value:
:param bool write: If true, write the hash db to disk.
"""
self.hash_db[key] = value
if(write is True):
self.update_hash_db()
def check_hash(self, key):
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"""Check whether a hash is present for the given key.
:param str key:
:returns: bool
"""
return key in self.hash_db
def get_hash(self, key):
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"""Get the hash value for a given key.
:param str key:
:returns: str or None
"""
if(self.check_hash(key) is True):
return self.hash_db[key]
return None
def update_hash_db(self):
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"""Write the hash db to disk."""
with open(constants.hash_db, 'w') as f:
json.dump(self.hash_db, f)
def checksum(self, file_path, blocksize=65536):
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"""Create a hash value for the given file.
See http://stackoverflow.com/a/3431835/1318758.
:param str file_path: Path to the file to create a hash for.
:param int blocksize: Read blocks of this size from the file when
creating the hash.
:returns: str or None
"""
hasher = hashlib.sha256()
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with open(file_path, 'rb') as f:
buf = f.read(blocksize)
while len(buf) > 0:
hasher.update(buf)
buf = f.read(blocksize)
return hasher.hexdigest()
return None
# Location database
# Currently quite simple just a list of long/lat pairs with a name
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# If it gets many entries a lookup might take too long and a better
# structure might be needed. Some speed up ideas:
# - Sort it and inter-half method can be used
# - Use integer part of long or lat as key to get a lower search list
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# - Cache a small number of lookups, photos are likely to be taken in
# clusters around a spot during import.
def add_location(self, latitude, longitude, place, write=False):
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"""Add a location to the database.
:param float latitude: Latitude of the location.
:param float longitude: Longitude of the location.
:param str place: Name for the location.
:param bool write: If true, write the location db to disk.
"""
data = {}
data['lat'] = latitude
data['long'] = longitude
data['name'] = place
self.location_db.append(data)
if(write is True):
self.update_location_db()
def get_location_name(self, latitude, longitude, threshold_m):
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"""Find a name for a location in the database.
:param float latitude: Latitude of the location.
:param float longitude: Longitude of the location.
:param int threshold_m: Location in the database must be this close to
the given latitude and longitude.
:returns: str, or None if a matching location couldn't be found.
"""
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last_d = sys.maxsize
name = None
for data in self.location_db:
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# As threshold is quite small use simple math
# From http://stackoverflow.com/questions/15736995/how-can-i-quickly-estimate-the-distance-between-two-latitude-longitude-points # noqa
# convert decimal degrees to radians
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lon1, lat1, lon2, lat2 = list(map(
radians,
[longitude, latitude, data['long'], data['lat']]
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))
r = 6371000 # radius of the earth in m
x = (lon2 - lon1) * cos(0.5 * (lat2 + lat1))
y = lat2 - lat1
d = r * sqrt(x * x + y * y)
# Use if closer then threshold_km reuse lookup
if(d <= threshold_m and d < last_d):
name = data['name']
last_d = d
return name
def get_location_coordinates(self, name):
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"""Get the latitude and longitude for a location.
:param str name: Name of the location.
:returns: tuple(float), or None if the location wasn't in the database.
"""
for data in self.location_db:
if data['name'] == name:
return (data['lat'], data['long'])
return None
def update_location_db(self):
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"""Write the location db to disk."""
with open(constants.location_db, 'w') as f:
json.dump(self.location_db, f)