import { useEffect, useState } from "react";
import { formatQuantity, meterDef } from "~/lib/meters";
import type { MeterDef } from "~/lib/meters";

type Day = { day: string; meter: string; quantity: number };

function daysOf(period: string): string[] {
  const [year, month] = period.split("-").map(Number);
  const count = new Date(Date.UTC(year, month, 0)).getUTCDate();
  return Array.from({ length: count }, (_, index) => `${period}-${String(index + 1).padStart(2, "0")}`);
}

const LABEL_DAYS = new Set([1, 8, 15, 22]);

/**
 * Daily usage of one meter across the whole billing period: one slot per calendar day, so a single day of usage
 * is a single bar instead of a full-width block. Includes a legend, a y-axis maximum and day labels.
 */
export function UsageChart({ days, meter, period }: { days: Day[]; meter: string; period: string }) {
  const def = meterDef(meter);
  const unit: MeterDef["unit"] = def?.unit ?? "count";
  const byDay = new Map(days.filter((day) => day.meter === meter).map((day) => [day.day, day.quantity]));
  const slots = daysOf(period).map((day) => ({ day, quantity: byDay.get(day) ?? 0 }));
  const total = slots.reduce((sum, slot) => sum + slot.quantity, 0);
  const peak = slots.reduce((best, slot) => (slot.quantity > best.quantity ? slot : best), slots[0]);
  const max = Math.max(peak?.quantity ?? 0, 0);
  const [today, setToday] = useState("9999-12-31");
  useEffect(() => setToday(new Date().toISOString().slice(0, 10)), []);
  return (
    <div className="space-y-3 px-4 py-4">
      <div className="flex flex-wrap items-center gap-x-4 gap-y-1 text-xs text-kumo-subtle">
        <span className="flex items-center gap-1.5">
          <span aria-hidden className="size-2.5 rounded-sm bg-accent-500" />
          <span className="text-kumo-default">{def?.label ?? meter}</span>
          <span>per day</span>
        </span>
        <span>
          Total <span className="font-mono text-kumo-default">{formatQuantity(unit, total)}</span>
        </span>
        {max > 0 && peak && (
          <span>
            Peak <span className="font-mono text-kumo-default">{formatQuantity(unit, max)}</span> on {peak.day.slice(5)}
          </span>
        )}
      </div>
      {total === 0 ? (
        <p className="py-6 text-sm text-kumo-subtle">No usage recorded for this meter in {period}.</p>
      ) : (
        <div className="grid grid-cols-[auto_1fr] gap-x-2">
          <div className="flex h-36 flex-col justify-between text-right font-mono text-[10px] text-kumo-subtle">
            <span>{formatQuantity(unit, max)}</span>
            <span>0</span>
          </div>
          <figure
            aria-label={`${def?.label ?? meter} per day in ${period}: total ${formatQuantity(unit, total)}`}
            className="m-0 flex h-36 items-end gap-[3px] border-b border-l border-kumo-hairline pl-1"
          >
            {slots.map((slot) => (
              <div key={slot.day} className="flex h-full min-w-0 flex-1 items-end justify-center">
                <div
                  title={`${slot.day}: ${formatQuantity(unit, slot.quantity)}`}
                  className={
                    slot.quantity > 0
                      ? "w-full max-w-4 rounded-t-sm bg-accent-500 hover:bg-accent-400"
                      : slot.day > today
                        ? "h-px w-full max-w-4 bg-transparent"
                        : "h-px w-full max-w-4 bg-kumo-interact"
                  }
                  style={slot.quantity > 0 ? { height: `${Math.max(2, (slot.quantity / max) * 100)}%` } : undefined}
                />
              </div>
            ))}
          </figure>
          <div />
          <div className="flex gap-[3px] pl-1 pt-1 font-mono text-[10px] text-kumo-subtle">
            {slots.map((slot, index) => (
              <span key={slot.day} className="min-w-0 flex-1 text-center">
                {LABEL_DAYS.has(index + 1) || index === slots.length - 1 ? index + 1 : ""}
              </span>
            ))}
          </div>
        </div>
      )}
    </div>
  );
}