currency

#!/usr/bin/python3
"""
Get real-time currency exchange rates from wise.com
https://wise.com/us/currency-converter
"""

import os
import re
import sys
from typing import Tuple

import requests

valid_currencies = set(
    "aed,all,amd,ang,aoa,ars,aud,awg,azn,bam,bbd,bdt,bgn,bhd,bmd,bnd,bob,brl,bsd,btn,bwp,bzd,"
    "cad,chf,clp,cny,cop,crc,cve,czk,djf,dkk,dop,dzd,egp,etb,eur,fjd,fkp,gbp,gel,ggp,ghs,gip,"
    "gmd,gnf,gtq,gyd,hkd,hnl,hrk,htg,huf,idr,ils,imp,inr,isk,jep,jmd,jod,jpy,kes,kgs,khr,kmf,"
    "krw,kwd,kyd,kzt,lak,lbp,lkr,lrd,lsl,mad,mdl,mga,mkd,mnt,mop,mru,mur,mvr,mwk,mxn,myr,mzn,"
    "nad,ngn,nio,nok,npr,nzd,omr,pab,pen,pgk,php,pkr,pln,pyg,qar,ron,rsd,rwf,sar,sbd,scr,sek,"
    "sgd,shp,sll,srd,svc,szl,thb,tjs,tmt,tnd,top,try,ttd,twd,tzs,uah,ugx,usd,uyu,uzs,vnd,vuv,"
    "wst,xcd,xof,xpf,zar,zmw".split(",")
)


class NotFound(RuntimeError):
    pass


def parse_args(*args: str) -> Tuple[float, str, str]:
    amount: float | None = None
    from_: str | None = None
    to: str | None = None

    while len(args):
        if from_ is None:
            if amount is None:
                try:
                    amount = float(args[0])
                    args = args[1:]
                    continue
                except ValueError:
                    pass
            from_ = args[0]
            args = args[1:]
            continue

        # Allow an optional "to" between the currencies
        if args[0].lower() == "to":
            args = args[1:]
            continue

        if to is None:
            to = args[0]
            args = args[1:]
        else:
            raise ValueError(f"Unknown argument {args[0]}")

    amount = 1.0 if amount is None else amount
    if amount <= 0:
        raise ValueError(f"invalid amount: {amount}, must be greater than 0.")
    if from_ is None or from_ not in valid_currencies:
        raise ValueError(f"invalid currency: {from_}")
    if to is None or to not in valid_currencies:
        raise ValueError(f"invalid currency: {to}")

    return amount, from_, to


def get_rate(from_: str, to: str) -> float:
    url = f"https://wise.com/us/currency-converter/{from_}-to-{to}-rate"
    resp = requests.get(url, timeout=10)
    resp.raise_for_status()
    pattern = re.compile(r"text-success[^0-9.<]+([0-9.]+)")
    matches = pattern.findall(resp.text)
    if not matches:
        raise NotFound(f"No rate found for {from_} to {to}")

    return float(matches[-1])


def usage():
    name = os.path.basename(__file__)
    print(f"Usage: {name} [amount] <from> <to>\nExample: {name} 4.2 usd jpy\n", file=sys.stderr)


def fmt_number(num) -> str:
    s = f"{num:,.10f}"
    return s.rstrip("0").rstrip(".")


def main():
    try:
        (amount, from_, to) = parse_args(*sys.argv[1:])
    except ValueError as exc:
        print(f"Invalid usage: {exc}", file=sys.stderr)
        usage()
        return 1

    rate = get_rate(from_, to)
    print(f"{fmt_number(amount)} {from_.upper()} = {fmt_number(amount * rate)} {to.upper()}")
    return 0


if __name__ == "__main__":
    sys.exit(main())