meuro/meuro.py

#!/usr/bin/python3
import requests, json, os.path
from datetime import datetime
from dateutil import relativedelta
from dateutil import parser as dparser
from dateutil.parser._parser import ParserError as DateParserError
from collections import defaultdict

# Our inflation-table as a global-var
_years = None

# Gives you the exchange rate between euros and meuros for the given date.
# (Should always be a float < 1)
# date should be either a datetime-object or None (= current date)
def exchangeRate(date=None):
    global _years
    if _years==None:
        reload()
    if date==None:
        date = datetime.now()
    month, year = date.month, date.year
    if year < 2001:
        raise Exception('µeuro-values for €uro prices before the start of this millenium are undefined.')
    akk = 1
    for fullYear in range(2001, year):
        yearlyInf = 1
        for m in _years[fullYear]:
            monthlyInf = _years[fullYear][m]
            yearlyInf *= monthlyInf
        akk *= yearlyInf

    for fullMonth in range(1, month):
        monthlyInf = _years[year][fullMonth]
        akk *= monthlyInf

    beginningOfMonth = date.replace(hour=0, minute=0, second=0, microsecond=0, day=1)
    endOfMonth = beginningOfMonth + relativedelta.relativedelta(months=1)
    fracOfMonth = (date - beginningOfMonth).total_seconds() / (endOfMonth - beginningOfMonth).total_seconds()
    inflationThisMonth = 1 + fracOfMonth * (_years[year][month]-1)

    akk *= inflationThisMonth

    return 1/akk

# Converts the given amount of euros to meuros for the given date. (wholeCents means it rounds to two decimal places)
# date should be either a datetime-object or None (= current date)
def euroToMeuro(eur,date=None,wholeCents=True):
    return round(eur * exchangeRate(date),[64,2][wholeCents])

# Converts the given amount of meuros to euros for the given date. (wholeCents means it rounds to two decimal places)
# date should be either a datetime-object or None (= current date)
def meuroToEuro(meur,date=None,wholeCents=True):
    return round(meur / exchangeRate(date),[64,2][wholeCents])

# Print the current amount of meuros for the given amunt of euros every <interval>-seconds.
# Comes in handy when you want to watch your life savings slowly fade away thanks to inflation.
def liveValue(eur,interval=10):
    import time
    while True:
        print(str(eur*exchangeRate())+'µ')
        time.sleep(interval)

def _extractDate(s):
    try:
        return dparser.parse(s, fuzzy=True, dayfirst=True)
    except DateParserError:
        return datetime.now()

def reload(maxCacheSeconds=3600):
    global _years
    if os.path.isfile('cache.json'):
        with open('cache.json', 'r') as f:
            cacheUpdate, cacheYears = json.loads(f.read())
        if (datetime.now() - dparser.isoparse(cacheUpdate)).total_seconds() < maxCacheSeconds:
            # JSON does not allow integers as keys; so we convert them back here
            cacheYears = {int(y):{int(m):float(n) for m,n in ms.items()} for y,ms in cacheYears.items()}
            # For every month we dont have data for, we assume the ECB nailed their 2%-target
            _years = defaultdict(lambda: {m:1 + 0.02/12 for m in range(1,13)}, cacheYears)
            return
    _years = _loadYearsTableWeb()

def _loadYearsTableWeb():
    print('[i] Fetching new data from ECB-Servers...')
    #url = 'https://sdw.ecb.europa.eu/quickviewexport.do?SERIES_KEY=122.ICP.M.U2.N.000000.4.ANR&type=csv'
    #resp = requests.get(url)
    url = 'https://data.ecb.europa.eu/download-api/csv/wide'
    resp = requests.post(url, {'serieskeys': ['ICP.M.U2.N.000000.4.ANR']})
    lines = resp.text.split('\n')[6:]
    years = defaultdict(lambda: {m:1 + 0.02/12 for m in range(1,13)})
    for line in lines:
        vals = line.split(',')
        year = int(vals[0][:4])
        month = datetime.strptime(vals[0][4:],'%b').month
        inflation = float(vals[1])
        years[year][month] = 1 + (inflation/100)/12

    with open('cache.json', 'w') as f:
        f.write(json.dumps([datetime.now().isoformat(),years]))
    return years


def cliInterface():
    import sys, re
    arg = " ".join(sys.argv[1:]).replace(',','')
    reFromEur = re.compile(r'(\d+(.\d\d)?)\W?(€|e|E)')
    reFromMeur = re.compile(r'(\d+(.\d\d)?)\W?(μ|m|M)')
    if (m := reFromEur.search(arg))!=None:
        eurS = m.groups()[0]
        date = _extractDate(arg[:m.span()[0]] + '-' + arg[m.span()[1]:])
        eur = float(eurS)
        meur = euroToMeuro(eur, date)
        print('Exchange rate for '+date.strftime("%d.%m.%Y at %H:%M")+':')
        print(f'{eur:,.2f}€ = {meur:,.2f}µ')
    elif (m:= reFromMeur.search(arg))!=None:
        meurS = m.groups()[0]
        date = _extractDate(arg[:m.span()[0]] + '-' + arg[m.span()[1]:])
        meur = float(meurS)
        eur = meuroToEuro(meur, date)
        print('Exchange rate for '+date.strftime("%d.%m.%Y at %H:%M")+':')
        print(f'{meur:,.2f}µ = {eur:,.2f}€')
    else:
        print('[!] Unable to parse input')

if __name__=='__main__':
    cliInterface()