forex_print.py

#!/usr/bin/env python3
"""Print currency exchange rates on the S01 thermal printer.

Shows live rates (ECB data via frankfurter.app) from a base currency to the
majors, plus a 30-day trend chart for one pair.

Examples:
    python forex_print.py                  # USD base
    python forex_print.py --base EUR
    python forex_print.py --base GBP --chart JPY
    python forex_print.py --no-print
"""
from __future__ import annotations

import argparse
from datetime import date, timedelta
from pathlib import Path

from PIL import Image, ImageDraw

from print_common import ROOT, Card, font, get_json

API = "https://api.frankfurter.app"
MAJORS = ["EUR", "GBP", "JPY", "CHF", "CAD", "AUD", "CNY", "USD"]


def fmt(r: float) -> str:
    return f"{r:.2f}" if r >= 10 else f"{r:.4f}"


def draw_chart(series: list[float], w: int, h: int = 130) -> Image.Image:
    img = Image.new("L", (w, h), 255)
    d = ImageDraw.Draw(img)
    lo, hi = min(series), max(series)
    span = (hi - lo) or 1
    n = len(series)
    pad = 4
    pts = [(pad + i / (n - 1) * (w - 2 * pad), pad + (1 - (v - lo) / span) * (h - 2 * pad))
           for i, v in enumerate(series)]
    d.line(pts, fill=0, width=2, joint="curve")
    y0 = pad + (1 - (series[0] - lo) / span) * (h - 2 * pad)
    for x in range(0, w, 6):
        d.point((x, y0), fill=0)
    lx, ly = pts[-1]
    d.ellipse((lx - 3, ly - 3, lx + 3, ly + 3), fill=0)
    tiny = font(False, 11)
    d.text((pad, pad), fmt(hi), fill=0, font=tiny)
    d.text((pad, h - 16), fmt(lo), fill=0, font=tiny)
    return img


def main() -> int:
    parser = argparse.ArgumentParser(description="Print currency exchange rates on the S01 thermal printer.")
    parser.add_argument("--base", default="USD", help="Base currency (default: USD).")
    parser.add_argument("--chart", default=None, help="Currency to chart vs base (default: EUR, or USD).")
    parser.add_argument("--out", type=Path, default=ROOT / "forex.png")
    parser.add_argument("--darkness", type=int, choices=range(1, 6), default=3)
    parser.add_argument("--bottom-feed", type=int, default=24)
    parser.add_argument("--no-print", action="store_true")
    args = parser.parse_args()

    base = args.base.upper()
    targets = [c for c in MAJORS if c != base]
    print(f"Fetching rates for {base} ...")
    latest = get_json(f"{API}/latest?from={base}&to={','.join(targets)}")
    rates = latest["rates"]

    chart_to = (args.chart or ("EUR" if base != "EUR" else "USD")).upper()
    end = date.fromisoformat(latest["date"])
    start = end - timedelta(days=30)
    ts = get_json(f"{API}/{start}..{end}?from={base}&to={chart_to}")
    series = [v[chart_to] for _, v in sorted(ts["rates"].items())]

    card = Card()
    card.title("EXCHANGE RATES")
    card.heading(f"1 {base} buys", size=15)
    card.gap(2).divider()
    for cur in targets:
        if cur in rates:
            card.kv(cur, fmt(rates[cur]))
    if series:
        card.gap(4).line(f"{base}/{chart_to}  -  30 days", size=12, bold=True, center=True)
        card.gap(2).image(draw_chart(series, card.inner_w), border=True)
    card.footer("frankfurter.app (ECB)", latest["date"])
    return card.finish(args.out, args.bottom_feed, args.darkness, do_print=not args.no_print)


if __name__ == "__main__":
    raise SystemExit(main())