/**
 * Solved-by-difficulty ring — LeetCode's profile gauge. A 270° arc split into
 * one segment per difficulty, each sized by that difficulty's share of the
 * catalog; the faint track is the whole set, the solid arc the solved part.
 * The centre reads the total, or one difficulty while its segment (or its
 * stat box) is hovered. "Attempting" is the open-miss count: problems whose
 * latest attempt failed.
 */
import { useState } from "react";
import { Pie, PieChart } from "recharts";
import { Card, CardContent } from "../ui/card";
import { type ChartConfig, ChartContainer } from "../ui/chart";
import { DIFFICULTIES, type Difficulty, useStats } from "../../lib/stats";
import { cn } from "../../lib/utils";
import { StatsPending } from "./shared";

const chartConfig = {
  easy: { label: "Easy", color: "var(--chart-1)" },
  medium: { label: "Med.", color: "var(--chart-2)" },
  hard: { label: "Hard", color: "var(--chart-3)" },
} satisfies ChartConfig;

// Static class names, so Tailwind's scanner sees every one (the chart's
// --color-* variables exist only inside ChartContainer).
const DIFFICULTY_TEXT: Record<Difficulty, string> = {
  easy: "text-chart-1",
  medium: "text-chart-2",
  hard: "text-chart-3",
};

// The gauge opens at the bottom: from 225° (lower left) clockwise to -45°
// (lower right), in Recharts' counter-clockwise-from-3-o'clock degrees.
const START = 225;
const SWEEP = 270;
const GAP = 8;

export default function SolvedRing() {
  const load = useStats();
  const [focus, setFocus] = useState<Difficulty | null>(null);

  if (load.phase !== "ready") {
    return (
      <Card>
        <CardContent>
          <StatsPending load={load} className="h-52 w-full" />
        </CardContent>
      </Card>
    );
  }

  const rows = DIFFICULTIES.map(
    (difficulty) => load.stats.difficulty.find((d) => d.difficulty === difficulty) ?? { difficulty, total: 0, done: 0 },
  );
  const total = rows.reduce((n, r) => n + r.total, 0);
  const done = rows.reduce((n, r) => n + r.done, 0);
  const span = SWEEP - GAP * (rows.length - 1);

  const segments: ((typeof rows)[number] & { from: number; to: number; solvedTo: number })[] = [];
  let cursor = START;
  for (const r of rows) {
    const size = total > 0 ? (span * r.total) / total : 0;
    const solved = r.total > 0 ? size * (r.done / r.total) : 0;
    segments.push({ ...r, from: cursor, to: cursor - size, solvedTo: cursor - solved });
    cursor -= size + GAP;
  }

  const focused = focus ? rows.find((r) => r.difficulty === focus) : undefined;
  const arc = { innerRadius: "80%", outerRadius: "88%", cornerRadius: 99, stroke: "none", dataKey: "value" } as const;

  return (
    <Card>
      <CardContent className="flex flex-col items-center gap-6 sm:flex-row">
        <div className="relative w-full max-w-56 shrink-0">
          <ChartContainer config={chartConfig} className="aspect-square w-full">
            <PieChart>
              {segments.map((s) => (
                <Pie
                  key={`${s.difficulty}-track`}
                  {...arc}
                  data={[{ value: 1 }]}
                  startAngle={s.from}
                  endAngle={s.to}
                  fill={`var(--color-${s.difficulty})`}
                  fillOpacity={focus && focus !== s.difficulty ? 0.12 : 0.25}
                  isAnimationActive={false}
                  onMouseEnter={() => setFocus(s.difficulty)}
                  onMouseLeave={() => setFocus(null)}
                />
              ))}
              {segments
                .filter((s) => s.done > 0)
                .map((s) => (
                  <Pie
                    key={`${s.difficulty}-solved`}
                    {...arc}
                    data={[{ value: 1 }]}
                    startAngle={s.from}
                    endAngle={s.solvedTo}
                    fill={`var(--color-${s.difficulty})`}
                    fillOpacity={focus && focus !== s.difficulty ? 0.35 : 1}
                    onMouseEnter={() => setFocus(s.difficulty)}
                    onMouseLeave={() => setFocus(null)}
                  />
                ))}
            </PieChart>
          </ChartContainer>
          <div className="pointer-events-none absolute inset-0 flex flex-col items-center justify-center gap-1">
            <div className="flex items-baseline">
              <span className="font-semibold text-4xl tabular-nums">{focused ? focused.done : done}</span>
              <span className="text-muted-foreground tabular-nums">/{focused ? focused.total : total}</span>
            </div>
            <span className={cn("text-sm", focused ? DIFFICULTY_TEXT[focused.difficulty] : "text-muted-foreground")}>
              {focused ? chartConfig[focused.difficulty].label : "Solved"}
            </span>
          </div>
          <div className="pointer-events-none absolute inset-x-0 bottom-3 text-center text-muted-foreground text-xs">
            <span className="font-semibold text-foreground tabular-nums">{load.stats.attempting}</span> Attempting
          </div>
        </div>
        <div className="flex w-full flex-col gap-2 sm:w-auto sm:flex-1">
          {rows.map((r) => (
            <div
              key={r.difficulty}
              className={cn(
                "flex flex-col items-center gap-0.5 rounded-lg bg-muted px-4 py-2 transition-opacity",
                focus && focus !== r.difficulty && "opacity-50",
              )}
              onPointerEnter={() => setFocus(r.difficulty)}
              onPointerLeave={() => setFocus(null)}
            >
              <span className={cn("font-medium text-sm", DIFFICULTY_TEXT[r.difficulty])}>
                {chartConfig[r.difficulty].label}
              </span>
              <span className="text-sm tabular-nums">
                {r.done}/{r.total}
              </span>
            </div>
          ))}
        </div>
      </CardContent>
    </Card>
  );
}