from datetime import timedelta
from typing import Optional

from django.contrib import messages
from django.contrib.admin.views.decorators import staff_member_required
from django.shortcuts import redirect, render
from django.urls import reverse
from django.utils import timezone
from django.utils.dateparse import parse_date

from tracker.api import build_day, pulse_trend
from tracker.models import DoseLog, PulseReading, ScheduledDose

CHART_WIDTH = 320
CHART_HEIGHT = 140
CHART_PADDING = 24


def build_chart(readings: list[PulseReading]) -> Optional[dict]:
    """Lay the readings out as SVG coordinates, so the page needs no JavaScript."""
    if len(readings) < 2:
        return None

    bpms = [r.bpm for r in readings]
    low, high = min(bpms), max(bpms)
    # A flat line would divide by zero, and a narrow range exaggerates noise.
    span = max(high - low, 10)
    mid = (high + low) / 2
    low, high = mid - span / 2, mid + span / 2

    first_day = readings[0].date
    total_days = max((readings[-1].date - first_day).days, 1)

    inner_width = CHART_WIDTH - 2 * CHART_PADDING
    inner_height = CHART_HEIGHT - 2 * CHART_PADDING

    points = []
    for reading in readings:
        x = CHART_PADDING + (reading.date - first_day).days / total_days * inner_width
        y = CHART_PADDING + (high - reading.bpm) / (high - low) * inner_height
        points.append({"x": round(x, 1), "y": round(y, 1), "reading": reading})

    return {
        "points": points,
        "polyline": " ".join(f"{p['x']},{p['y']}" for p in points),
        "low": round(low),
        "high": round(high),
        "average": round(sum(bpms) / len(bpms), 1),
        "trend": pulse_trend(readings),
        "width": CHART_WIDTH,
        "height": CHART_HEIGHT,
        "first_date": first_day,
        "last_date": readings[-1].date,
    }


@staff_member_required
def today(request):
    """The main screen: tick off the day's doses and record the pulse."""
    day = parse_date(request.GET.get("date", "")) or timezone.localdate()

    if request.method == "POST":
        day = parse_date(request.POST.get("date", "")) or timezone.localdate()
        doses = ScheduledDose.objects.filter(is_active=True, medication__is_active=True)

        for dose in doses:
            taken = f"dose-{dose.id}" in request.POST
            log, _ = DoseLog.objects.get_or_create(
                scheduled_dose=dose, date=day, defaults={"taken": taken}
            )
            log.taken = taken
            log.save()

        bpm = (request.POST.get("bpm") or "").strip()
        if bpm:
            try:
                PulseReading.objects.update_or_create(
                    date=day, defaults={"bpm": int(bpm)}
                )
            except ValueError:
                messages.error(request, f"'{bpm}' is not a valid pulse.")
        else:
            # Clearing the field removes the reading for that day.
            PulseReading.objects.filter(date=day).delete()

        messages.success(request, f"Saved for {day:%A %d %B}.")
        return redirect(f"{reverse('tracker:today')}?date={day.isoformat()}")

    readings = list(
        PulseReading.objects.filter(
            date__gte=timezone.localdate() - timedelta(days=90)
        ).order_by("date")
    )

    return render(
        request,
        "tracker/today.html",
        {
            "title": "Today",
            "day": build_day(day),
            "is_today": day == timezone.localdate(),
            "previous_date": day - timedelta(days=1),
            "next_date": day + timedelta(days=1),
            "chart": build_chart(readings),
            "reading_count": len(readings),
        },
    )