"use client";

import { useCallback, useEffect, useMemo, useRef, useState } from "react";
import {
  AudioLinesIcon,
  GaugeIcon,
  PauseIcon,
  PlayIcon,
  RotateCcwIcon,
  SlidersHorizontalIcon,
} from "lucide-react";

import { Button } from "@/components/ui/button";
import { Card, CardContent, CardDescription, CardHeader, CardTitle } from "@/components/ui/card";
import { Input } from "@/components/ui/input";
import { Label } from "@/components/ui/label";
import { Switch } from "@/components/ui/switch";
import { cn } from "@/lib/utils";
import { parseEmotionTags } from "@/lib/voiceover/emotionTags";
import {
  DEFAULT_WORDS_PER_MINUTE,
  MAX_WORDS_PER_MINUTE,
  MIN_WORDS_PER_MINUTE,
  buildPacingTimeline,
} from "@/lib/voiceover/pacing";

const MIN_SCROLL_SPEED = 5;
const MAX_SCROLL_SPEED = 100;
const DEFAULT_SCROLL_SPEED = 20;

const TAG_COLORS = [
  { text: "text-sky-200/75", underline: "decoration-sky-300/50", label: "text-sky-300/80" },
  { text: "text-amber-200/75", underline: "decoration-amber-300/50", label: "text-amber-300/80" },
  {
    text: "text-emerald-200/75",
    underline: "decoration-emerald-300/50",
    label: "text-emerald-300/80",
  },
  { text: "text-rose-200/75", underline: "decoration-rose-300/50", label: "text-rose-300/80" },
  {
    text: "text-violet-200/75",
    underline: "decoration-violet-300/50",
    label: "text-violet-300/80",
  },
  { text: "text-teal-200/75", underline: "decoration-teal-300/50", label: "text-teal-300/80" },
  {
    text: "text-fuchsia-200/75",
    underline: "decoration-fuchsia-300/50",
    label: "text-fuchsia-300/80",
  },
  {
    text: "text-orange-200/75",
    underline: "decoration-orange-300/50",
    label: "text-orange-300/80",
  },
] as const;

function tagColor(tags: readonly string[]) {
  const key = tags.join(", ");
  let hash = 0;
  for (let index = 0; index < key.length; index += 1) {
    hash = (hash * 31 + key.charCodeAt(index)) >>> 0;
  }
  return TAG_COLORS[hash % TAG_COLORS.length];
}

export function TeleprompterReader({ script }: { readonly script: string }) {
  const readerRef = useRef<HTMLDivElement | null>(null);
  const elapsedRef = useRef(0);
  const [isScrolling, setIsScrolling] = useState(false);
  const [scrollSpeed, setScrollSpeed] = useState(DEFAULT_SCROLL_SPEED);
  const [pacingEnabled, setPacingEnabled] = useState(false);
  const [wordsPerMinute, setWordsPerMinute] = useState(DEFAULT_WORDS_PER_MINUTE);
  const [elapsedMs, setElapsedMs] = useState(0);
  const segments = useMemo(() => parseEmotionTags(script), [script]);
  const timeline = useMemo(
    () => buildPacingTimeline(segments, wordsPerMinute),
    [segments, wordsPerMinute],
  );

  const toggleScrolling = useCallback(() => {
    setIsScrolling((scrolling) => !scrolling);
  }, []);

  const scrollMultiplier = useCallback(
    (elapsed: number) => {
      let multiplier = 1;
      for (const directive of timeline.scrollDirectives) {
        if (elapsed < directive.atMs) break;
        multiplier = directive.multiplier;
      }
      return multiplier;
    },
    [timeline.scrollDirectives],
  );

  useEffect(() => {
    if (!isScrolling) return;

    let animationFrame = 0;
    let previousTime = performance.now();

    const scroll = (now: number) => {
      const reader = readerRef.current;
      if (!reader) {
        setIsScrolling(false);
        return;
      }

      const delta = now - previousTime;
      previousTime = now;

      if (pacingEnabled) {
        elapsedRef.current += delta;
        setElapsedMs(elapsedRef.current);
      }

      const effectiveSpeed =
        scrollSpeed * (pacingEnabled ? scrollMultiplier(elapsedRef.current) : 1);

      const maxScrollTop = reader.scrollHeight - reader.clientHeight;
      const scrollFinished = maxScrollTop <= 0 || reader.scrollTop >= maxScrollTop;
      const pacingFinished = !pacingEnabled || elapsedRef.current >= timeline.totalMs;

      if (scrollFinished && pacingFinished) {
        setIsScrolling(false);
        return;
      }

      if (!scrollFinished) {
        reader.scrollTop = Math.min(
          maxScrollTop,
          reader.scrollTop + (effectiveSpeed * delta) / 1000,
        );
      }
      animationFrame = requestAnimationFrame(scroll);
    };

    animationFrame = requestAnimationFrame(scroll);
    return () => cancelAnimationFrame(animationFrame);
  }, [isScrolling, scrollSpeed, pacingEnabled, timeline.totalMs, scrollMultiplier]);

  useEffect(() => {
    const handleKeyDown = (event: KeyboardEvent) => {
      if (event.code !== "Space" || event.repeat) return;

      const target = event.target;
      if (
        target instanceof HTMLElement &&
        (target.isContentEditable ||
          ["BUTTON", "INPUT", "SELECT", "TEXTAREA"].includes(target.tagName))
      ) {
        return;
      }

      event.preventDefault();
      toggleScrolling();
    };

    window.addEventListener("keydown", handleKeyDown);
    return () => window.removeEventListener("keydown", handleKeyDown);
  }, [toggleScrolling]);

  function resetReader() {
    const reader = readerRef.current;
    if (reader) reader.scrollTop = 0;
    elapsedRef.current = 0;
    setElapsedMs(0);
    setIsScrolling(false);
  }

  function handlePacingToggle(enabled: boolean) {
    elapsedRef.current = 0;
    setElapsedMs(0);
    setPacingEnabled(enabled);
  }

  function handleWordsPerMinuteChange(value: string) {
    const next = Number(value);
    if (!Number.isFinite(next)) return;
    setWordsPerMinute(Math.min(MAX_WORDS_PER_MINUTE, Math.max(MIN_WORDS_PER_MINUTE, next)));
  }

  function renderSpokenText(
    segment: (typeof segments)[number],
    pacing: (typeof timeline.segmentPacing)[number],
    wordClass?: string,
  ) {
    if (!pacingEnabled || !pacing || pacing.words.length === 0) {
      return segment.text;
    }

    return (
      <>
        {pacing.leadingWhitespace}
        {pacing.words.map((word, wordIndex) => (
          <span
            key={`word-${wordIndex}`}
            className={cn(
              "transition-opacity duration-500",
              wordClass,
              elapsedMs >= word.endMs && "opacity-35",
            )}
          >
            {word.text}
            {word.whitespaceAfter}
          </span>
        ))}
      </>
    );
  }

  function handleSpeedChange(value: string) {
    const nextSpeed = Number(value);
    if (!Number.isFinite(nextSpeed)) return;
    setScrollSpeed(Math.min(MAX_SCROLL_SPEED, Math.max(MIN_SCROLL_SPEED, nextSpeed)));
  }

  return (
    <Card>
      <CardHeader className="gap-3 border-b border-border">
        <div className="flex flex-wrap items-start justify-between gap-3">
          <div className="flex flex-col gap-1">
            <CardTitle>Teleprompter</CardTitle>
            <CardDescription>Press spacebar to start or pause the reader.</CardDescription>
          </div>
          <div className="flex items-end gap-2">
            <div className="flex flex-col gap-1.5">
              <div className="flex items-center gap-2">
                <Switch
                  id="voiceover-pacing"
                  checked={pacingEnabled}
                  onCheckedChange={handlePacingToggle}
                  aria-label="Toggle pacing highlighter"
                />
                <Label
                  htmlFor="voiceover-pacing"
                  className="cursor-pointer text-xs text-muted-foreground"
                >
                  Follow along
                </Label>
              </div>
              {pacingEnabled && (
                <div className="flex items-center gap-1.5">
                  <Input
                    id="voiceover-wpm"
                    type="number"
                    min={MIN_WORDS_PER_MINUTE}
                    max={MAX_WORDS_PER_MINUTE}
                    step={10}
                    value={wordsPerMinute}
                    onChange={(event) => handleWordsPerMinuteChange(event.target.value)}
                    className="h-7 w-20 text-xs"
                    aria-label="Speaking pace in words per minute"
                  />
                  <span className="text-xs text-muted-foreground">wpm</span>
                </div>
              )}
            </div>
            <div className="flex flex-col gap-1.5">
              <Label htmlFor="voiceover-scroll-speed" className="text-xs text-muted-foreground">
                Speed (px/s)
              </Label>
              <Input
                id="voiceover-scroll-speed"
                type="number"
                min={MIN_SCROLL_SPEED}
                max={MAX_SCROLL_SPEED}
                step={5}
                value={scrollSpeed}
                onChange={(event) => handleSpeedChange(event.target.value)}
                className="w-24"
              />
            </div>
            <Button type="button" onClick={toggleScrolling} aria-pressed={isScrolling}>
              {isScrolling ? (
                <PauseIcon data-icon="inline-start" />
              ) : (
                <PlayIcon data-icon="inline-start" />
              )}
              {isScrolling ? "Pause" : "Start"}
            </Button>
            <Button type="button" variant="outline" size="icon" onClick={resetReader}>
              <RotateCcwIcon />
              <span className="sr-only">Reset teleprompter</span>
            </Button>
          </div>
        </div>
      </CardHeader>

      <CardContent className="flex flex-col gap-3 p-4 sm:p-6">
        <div
          ref={readerRef}
          tabIndex={0}
          aria-label="Voiceover script reader"
          className="max-h-[34rem] min-h-[24rem] overflow-y-auto scroll-auto rounded-md border border-border bg-background/70 px-4 py-8 outline-none focus-visible:ring-2 focus-visible:ring-ring sm:px-8 sm:py-12"
        >
          <p className="whitespace-pre-wrap text-xl leading-relaxed tracking-wide text-foreground sm:text-2xl">
            {segments.map((segment, index) => {
              if (segment.directive) {
                return (
                  <span
                    key={`directive-${index}`}
                    className="my-3 flex items-center gap-1.5 text-[10px] uppercase tracking-widest text-muted-foreground/70"
                  >
                    <SlidersHorizontalIcon className="size-3 shrink-0" aria-hidden />
                    {segment.directive}
                  </span>
                );
              }

              if (segment.sfx) {
                return (
                  <span
                    key={`sfx-${index}`}
                    className="my-6 flex items-center gap-1.5 text-xs italic text-muted-foreground"
                  >
                    <AudioLinesIcon className="size-3.5 shrink-0" aria-hidden />
                    {segment.sfx}
                  </span>
                );
              }

              if (segment.tags.length === 0) {
                return (
                  <span key={`text-${index}`}>
                    {renderSpokenText(segment, timeline.segmentPacing[index])}
                  </span>
                );
              }

              const color = tagColor(segment.tags);
              const segmentPacing = timeline.segmentPacing[index];
              const pacingActive = pacingEnabled && segmentPacing !== undefined;

              return (
                <span key={`tagged-${index}`} className="relative inline">
                  <span
                    className={cn(
                      "absolute -top-3.5 left-0 whitespace-nowrap text-[10px] italic leading-none",
                      color.label,
                    )}
                    aria-label={`Stage direction: ${segment.tags.join(", ")}`}
                  >
                    {segment.tags.join(", ")}
                  </span>
                  <span
                    className={cn(
                      "underline-offset-4",
                      color.text,
                      !pacingActive && "underline",
                      color.underline,
                    )}
                  >
                    {renderSpokenText(
                      segment,
                      segmentPacing,
                      pacingActive ? cn("underline", color.underline) : undefined,
                    )}
                  </span>
                </span>
              );
            })}
          </p>
        </div>
        <div className="flex items-center gap-2 text-xs text-muted-foreground">
          <GaugeIcon className="size-3.5" />
          <span>Constant scroll speed · {scrollSpeed} px/s</span>
        </div>
      </CardContent>
    </Card>
  );
}