"use client";

import { useCallback, useEffect, useRef, useState } from "react";

import { ActivityRenderer } from "@/components/activities";
import { AiDisclaimer } from "@/components/AiDisclaimer";
import { XIcon } from "@/components/icons";
import { ReportQuestionButton } from "@/components/ReportQuestionButton";
import { ProgressBar } from "@/components/ui";
import type { Activity, Deck } from "@/lib/schemas";
import { useI18n } from "@/lib/i18n";
import { useWakeLock } from "@/lib/use-wake-lock";
import { cn } from "@/lib/utils";

export type SessionItem = { deck: Deck; activity: Activity };
export type SessionResult = { correct: boolean; userAnswer?: string };
export type SessionRenderResults = (state: {
  results: Record<string, SessionResult>;
  items: SessionItem[];
  correct: number;
  total: number;
  score: number;
}) => React.ReactNode;

/**
 * The scroll-snap activity feed shared by review, mistakes and exam sessions.
 * Same mechanics as the study feed (remount per run, scroll tracking, keyboard
 * navigation) but with a pluggable results slide and an optional timer.
 */
export function SessionFeed({
  title,
  items,
  timerSeconds,
  noHints = false,
  testId,
  onExit,
  onAnswered,
  renderResults,
}: {
  title: string;
  items: SessionItem[];
  timerSeconds?: number;
  noHints?: boolean;
  testId?: string;
  onExit: () => void;
  onAnswered?: (item: SessionItem, correct: boolean, meta?: { userAnswer?: string }) => void;
  renderResults: SessionRenderResults;
}) {
  const { t } = useI18n();
  useWakeLock(true);
  const [index, setIndex] = useState(0);
  const [results, setResults] = useState<Record<string, SessionResult>>({});
  /** Ids reported during this run: skipped, so they are not "missed". */
  const [skipped, setSkipped] = useState<string[]>([]);
  const [runId] = useState(0);
  const [remaining, setRemaining] = useState(timerSeconds ?? 0);
  const scrollRef = useRef<HTMLDivElement>(null);

  const total = items.length;
  const slideCount = total + 1;

  const goTo = useCallback(
    (target: number) => {
      const container = scrollRef.current;
      if (!container) return;
      const clamped = Math.max(0, Math.min(target, slideCount - 1));
      container.scrollTo({ top: clamped * container.clientHeight, behavior: "smooth" });
    },
    [slideCount],
  );

  const next = useCallback(() => goTo(index + 1), [goTo, index]);

  useEffect(() => {
    const container = scrollRef.current;
    if (!container) return;
    let frame = 0;
    const onScroll = () => {
      cancelAnimationFrame(frame);
      frame = requestAnimationFrame(() => {
        const height = container.clientHeight || 1;
        const current = Math.round(container.scrollTop / height);
        setIndex((previous) => (previous === current ? previous : current));
      });
    };
    container.addEventListener("scroll", onScroll, { passive: true });
    return () => {
      container.removeEventListener("scroll", onScroll);
      cancelAnimationFrame(frame);
    };
  }, [runId]);

  useEffect(() => {
    const onKey = (event: KeyboardEvent) => {
      const target = event.target as HTMLElement | null;
      if (target && (/^(INPUT|TEXTAREA|SELECT)$/.test(target.tagName) || target.isContentEditable)) return;
      if (event.metaKey || event.ctrlKey || event.altKey) return;
      if (event.key === "ArrowDown" || event.key === "PageDown" || event.key === "j") {
        event.preventDefault();
        next();
      } else if (event.key === "ArrowUp" || event.key === "PageUp" || event.key === "k") {
        event.preventDefault();
        goTo(index - 1);
      }
    };
    window.addEventListener("keydown", onKey);
    return () => window.removeEventListener("keydown", onKey);
  }, [goTo, index, next]);

  // Countdown (exam mode); reaching zero jumps to the results slide.
  useEffect(() => {
    if (!timerSeconds) return;
    const interval = window.setInterval(() => {
      setRemaining((value) => {
        if (value <= 1) {
          window.clearInterval(interval);
          return 0;
        }
        return value - 1;
      });
    }, 1000);
    return () => window.clearInterval(interval);
  }, [timerSeconds]);

  useEffect(() => {
    if (timerSeconds && remaining === 0) goTo(slideCount - 1);
  }, [remaining, timerSeconds, goTo, slideCount]);

  const handleAnswered = useCallback(
    (item: SessionItem, correct: boolean, meta?: { userAnswer?: string }) => {
      setResults((current) => {
        if (current[item.activity.id]) return current;
        return { ...current, [item.activity.id]: { correct, userAnswer: meta?.userAnswer } };
      });
      onAnswered?.(item, correct, meta);
    },
    [onAnswered],
  );

  const finished = index >= total;
  const correct = items.filter((item) => results[item.activity.id]?.correct).length;
  /** What the results slide counts: reported cards were never attempted. */
  const attemptedTotal = Math.max(0, total - skipped.length);
  const score = attemptedTotal > 0 ? Math.round((correct / attemptedTotal) * 100) : 0;

  return (
    <div className="frost-bg fixed inset-0 flex flex-col fade-in-mobile">
      <header className="pt-safe absolute inset-x-0 top-0 z-30 px-3">
        <div className="study-chrome mx-auto max-w-xl space-y-1.5 rounded-full px-3 py-2">
          <div className="flex items-center gap-3">
            <button
              type="button"
              onClick={onExit}
              aria-label={t("feed.back")}
              className="grid size-9 shrink-0 place-items-center rounded-xl bg-[var(--surface-sunken)] text-[var(--text)] transition hover:bg-[var(--hover)]"
            >
              <XIcon className="size-4" />
            </button>
            <div className="min-w-0 flex-1">
              <ProgressBar
                value={Math.min(index + 1, slideCount)}
                max={slideCount}
                label={t("feed.activityOf", { n: Math.min(index + 1, total), total })}
              />
            </div>
            {timerSeconds ? (
              <span
                className={cn(
                  "shrink-0 rounded-xl px-2 py-1 text-xs font-extrabold tabular-nums",
                  remaining <= 30 ? "tint-peach" : "bg-[var(--surface-sunken)] text-[var(--text-muted)]",
                )}
                aria-label={t("exam.timeLeft", { time: formatClock(remaining) })}
              >
                {formatClock(remaining)}
              </span>
            ) : null}
            {!finished && items[index] ? (
              <ReportQuestionButton
                deck={items[index].deck}
                activity={items[index].activity}
                onSkip={() => {
                  setSkipped((current) => [...current, items[index].activity.id]);
                  goTo(index + 1);
                }}
              />
            ) : null}
          </div>
          <div className="flex items-center justify-between gap-2 text-[11px] font-semibold text-[var(--text-muted)]">
            <span className="min-w-0 truncate">{title}</span>
            <span className="shrink-0 tabular-nums">
              {Math.min(index + 1, total)}/{total}
            </span>
          </div>
        </div>
      </header>

      <div
        key={runId}
        ref={scrollRef}
        data-testid={testId ?? "session-feed"}
        className="no-scrollbar h-full snap-y snap-mandatory overflow-y-scroll overscroll-y-contain [overflow-anchor:none]"
      >
        {items.map((item, itemIndex) => (
          <section
            key={`${item.deck.id}-${item.activity.id}-${runId}`}
            aria-label={t("feed.activityOf", { n: itemIndex + 1, total })}
            className="flex h-full snap-start snap-always items-stretch justify-center overflow-y-auto overscroll-y-contain"
          >
            <div className="mx-auto flex min-h-full w-full max-w-xl flex-col gap-4 px-4 pb-24 pt-24 [justify-content:safe_center]">
              <ActivityRenderer
                activity={item.activity}
                active={index === itemIndex}
                language={item.deck.language}
                noHints={noHints}
                onAnswered={(correct, meta) => handleAnswered(item, correct, meta)}
                onNext={next}
                isLast={itemIndex === total - 1}
                nextLabel={itemIndex === total - 1 ? t("review.seeResults") : undefined}
              />
              <AiDisclaimer />
            </div>
          </section>
        ))}

        <section
          aria-label={t("review.results")}
          className="flex h-full snap-start snap-always items-stretch justify-center overflow-y-auto overscroll-y-contain"
        >
          <div className="mx-auto flex min-h-full w-full max-w-xl flex-col gap-4 px-4 pb-24 pt-24 [justify-content:safe_center]">
            {finished
              ? (
                <>
                  {renderResults({ results, items, correct, total: attemptedTotal, score })}
                  <AiDisclaimer />
                </>
              )
              : (
                <div className="card space-y-2 p-5 text-center">
                  <p className="text-sm font-semibold text-[var(--text-muted)]">{t("review.results")}</p>
                  <p className="text-[13px] text-[var(--text-subtle)]">{t("review.finishFirst")}</p>
                </div>
              )}
          </div>
        </section>
      </div>
    </div>
  );
}

function formatClock(seconds: number): string {
  const safe = Math.max(0, seconds);
  const minutes = Math.floor(safe / 60);
  return `${minutes}:${String(safe % 60).padStart(2, "0")}`;
}