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import csv
import os
from datetime import datetime, timedelta
from .utils import human_datetime, human_timedelta
from .config import DUE_HOURS
class Database:
def __init__(self, path):
"""A database of all umbrellas and their current state.
Currently, the data are represented in a csv file.
Explanation of data types:
- id | a unique numerical identity of unsigned integer type.
- uint | whatever fits the regex /[0-9]+/. despite carrying a numerical value, it is
| internally represented as a string.
- string | any UTF-8 string.
- date | an ISO 8601 date of format "YYYY-MM-DDThh:mm:ss". default timezone is UTC+8.
The status of an umbrella consists of:
- serial | (id) unique identifier for the umbrella.
- alias | (string) future compatibility. a human readable (preferably cute) name
| for a particular umbrella
- status | (string) one of ("available", "lent", "withheld", "maintenance",
| "withheld", "unknown")
| available : is in service on the stand
| lent : is in temporary possession of a user
| maintenance : is on the stand but not in service
| withheld : is not on the stand but rather in the possession of an
| administrator
| unknown : none of the above
| NOTE: the values above are subject to changes.
- tenant_name | (string) the person in temporary possession of the umbrella.
- tenant_id | (uint) student or faculty ID.
- tenant_phone | (uint) phone number via which to contact tenant when the lease is due.
- tenant_email | (string) future compatibility. empty for the time being.
- lent_at | (date) if status is "lent", lent_at is the submission time of the user's
| jForm answer sheet. is blank otherwise.
"""
self.path = path
def _lock(self) -> int:
"""Create a lockfile for database.
If the database is called "db.csv", the lockfile, located in the same
directory, would be called "db.csv.lock".
Returns 1 if the lockfile is successfully created, 0 if the lockfile
already exists (strong hint of unrecovered crash or potential race
condition - caller of this method should abort whatever it is doing)
"""
try:
f = open(self.path + ".lock", "x")
f.close()
return 1
except FileExistsError:
return 0
def _unlock(self) -> None:
"""Remove lockfile created by _lock.
If there is no lockfile, simply ignore.
"""
try:
os.remove(self.path + ".lock")
except FileNotFoundError:
pass
def _read(self) -> list:
"""Deserialize database."""
# Create database if it does not yet exist
try:
f = open(self.path, "x")
f.close()
except FileExistsError:
pass
with open(self.path) as f:
reader = csv.reader(f)
umbrellas = [
{
"serial": int(row[0]),
"alias": row[1],
"status": row[2],
"tenant_name": row[3],
"tenant_id": row[4],
"tenant_phone": row[5],
"tenant_email": row[6],
"lent_at": datetime.fromisoformat(row[7]) if row[7] else None,
}
for row in reader
]
f.close()
return umbrellas
def _write(self, umbrellas: list) -> None:
"""Serialize database. When a failure occurs, abort and recover data."""
# make backup in memory
with open(self.path) as f:
backup = f.read()
f.close()
# wait until database is locked for this write
while not self._lock():
continue
f = open(self.path, "w")
try:
writer = csv.writer(f)
writer.writerows(
[
[
umb["serial"],
umb["alias"],
umb["status"],
umb["tenant_name"],
umb["tenant_id"],
umb["tenant_phone"],
umb["tenant_email"],
umb["lent_at"].isoformat(timespec="seconds")
if umb["lent_at"]
else "",
]
for umb in umbrellas
]
)
except:
# failure occurred on write
# abort write, and write back contents as they were before
# TODO: pass on exception and keep log
f.close()
f = open(self.path, "w")
f.write(backup)
f.close()
self._unlock()
def _update(self, update: dict) -> list:
"""Update status of one umbrella, and return the entire updated database."""
umbrellas = self._read()
for idx, umb in enumerate(umbrellas):
if umb["serial"] == update["serial"]:
umbrellas[idx] = update
self._write(umbrellas)
return umbrellas
def _find_by_serial(self, serial: int) -> dict:
"""Given a serial number, returns an umbrella with such serial.
If there is no such umbrella, returns None.
"""
umbrellas = self._read()
for umb in umbrellas:
if umb["serial"] == serial:
return umb
def read(self) -> list:
"""An interface to `_read()` with supplemental data included.
All exposed methods with a return value should use this method instead of `_read()`.
Supplemental data:
- lent_at_str: string representation for lent_at.
- lent_time_ago: time since umbrella was taken away by tenant. if umbrella is not
taken away, its value is None.
- lent_time_ago_str: string representation for lent_time_ago.
"""
umbrellas = self._read()
now = datetime.now()
for idx, umb in enumerate(umbrellas):
if umb["status"] == "lent":
umbrellas[idx]["lent_at_str"] = human_datetime(umb["lent_at"])
lent_time_ago = now - umb["lent_at"]
umbrellas[idx]["lent_time_ago"] = lent_time_ago
umbrellas[idx]["lent_time_ago_str"] = human_timedelta(lent_time_ago)
return umbrellas
def group_by_status(umbrellas) -> dict:
"""(static method) Returns umbrellas grouped into a dict by their status."""
keys = set([umb["status"] for umb in umbrellas])
statuses = {}
for key in keys:
statuses[key] = [umb for umb in umbrellas if umb["status"] == key]
return statuses
def find_overdue(umbrellas) -> list:
"""(static method) Returns umbrellas in possession of their tenant for too long."""
now = datetime.now()
return [
umb
for umb in umbrellas
if umb["lent_at"] is not None
and now - umb["lent_at"] > timedelta(hours=DUE_HOURS)
]
def take_away(
self, serial, tenant_name, tenant_id, tenant_phone="", tenant_email=""
) -> None:
"""When a user has borrowed an umbrella."""
umb = self._find_by_serial(serial)
if umb is None:
raise ValueError(f"No umbrella with serial {serial} found.")
elif umb["status"] != "available":
raise ValueError(f"Umbrella with serial {serial} is inavailable.")
umb["status"] = "lent"
umb["tenant_name"] = tenant_name
umb["tenant_id"] = tenant_id
umb["tenant_phone"] = tenant_phone
umb["tenant_email"] = tenant_email
umb["lent_at"] = datetime.now()
self._update(umb)
def give_back(self, serial) -> None:
"""When a user has returned an umbrella."""
umb = self._find_by_serial(serial)
if umb is None:
raise ValueError(f"No umbrella with serial {serial} found.")
elif umb["status"] != "lent":
raise ValueError(f"Umbrella with serial {serial} is not lent out.")
umb["status"] = "available"
for key in ["tenant_name", "tenant_id", "tenant_phone", "tenant_email"]:
umb[key] = ""
umb["lent_at"] = None
self._update(umb)
|
