"""Explicit automatic and manual five-zone configuration for running load."""

from datetime import date, datetime
from itertools import pairwise
from zoneinfo import ZoneInfo

# Published as Stride's formula, not an exact reproduction of Strava's zones.
ZONE_FRACTIONS = (0.65, 0.80, 0.87, 0.95)


def zones(user, today=None):
    today = today or datetime.now(ZoneInfo(user.timezone)).date()
    config = user.hr_zones or {"mode": "auto"}
    mode = config.get("mode", "auto")
    maximum = None
    if mode == "custom":
        boundaries = config["boundaries"]
        source = "Manual zone boundaries"
    else:
        maximum = config.get("max_hr") if mode == "max" else None
        if maximum is not None:
            source = "Manual maximum HR"
        elif config.get("birthday"):
            birthday = date.fromisoformat(config["birthday"])
            age = (
                today.year
                - birthday.year
                - ((today.month, today.day) < (birthday.month, birthday.day))
            )
            maximum = 220 - age
            source = "Automatic · 220 minus age · updates on your birthday"
        else:
            maximum = 190
            source = "Automatic · default maximum 190 bpm (birthday not set)"
        boundaries = [round(maximum * fraction) for fraction in ZONE_FRACTIONS]
    labels = [f"0–{boundaries[0] - 1}"]
    labels += [f"{a}–{b - 1}" for a, b in pairwise(boundaries)]
    labels += [f"{boundaries[-1]}+"]
    return {
        "boundaries": boundaries,
        "source": source,
        "max_hr": maximum,
        "mode": mode,
        "labels": labels,
        "config": config,
    }