"use client";

import { useEffect, useRef, useState } from "react";
import { synthesizeVoice } from "../lib/api";

type PlaybackState = "idle" | "loading" | "playing" | "unavailable";

interface VoicePlaybackButtonProps {
  characterId: string;
  userId: string;
  text: string;
}

// P-6：語音播放介面——呼叫 /voice/:characterId/:userId/synthesize 取得合成結果後播放。
// TTS_PROVIDER=mock 回傳的 audioRef 是 `mock://` 佔位字串（非真實音檔），改用計時器模擬播放時長；
// 之後接上真實供應商、audioRef 變成可播放網址時走真正的 <audio> 播放，呼叫端不用改一行。
// 合成失敗（網路或後端錯誤）時直接隱藏這顆按鈕，退回純文字顯示，不影響訊息本身、不阻斷對話。
export function VoicePlaybackButton({ characterId, userId, text }: VoicePlaybackButtonProps) {
  const [state, setState] = useState<PlaybackState>("idle");
  const audioRef = useRef<HTMLAudioElement | null>(null);
  const timerRef = useRef<ReturnType<typeof setTimeout> | null>(null);

  useEffect(() => {
    return () => {
      audioRef.current?.pause();
      if (timerRef.current) {
        clearTimeout(timerRef.current);
      }
    };
  }, []);

  function stopPlayback() {
    audioRef.current?.pause();
    audioRef.current = null;
    if (timerRef.current) {
      clearTimeout(timerRef.current);
      timerRef.current = null;
    }
    setState("idle");
  }

  async function startPlayback() {
    setState("loading");
    try {
      const result = await synthesizeVoice(characterId, userId, text);
      if (result.audioRef.startsWith("mock://")) {
        setState("playing");
        timerRef.current = setTimeout(() => setState("idle"), Math.max(result.durationEstimateMs, 300));
        return;
      }
      const audio = new Audio(result.audioRef);
      audio.addEventListener("ended", () => setState("idle"));
      audio.addEventListener("error", () => setState("unavailable"));
      audioRef.current = audio;
      await audio.play();
      setState("playing");
    } catch {
      setState("unavailable");
    }
  }

  if (state === "unavailable") {
    return null;
  }

  return (
    <button
      type="button"
      onClick={() => (state === "playing" ? stopPlayback() : void startPlayback())}
      disabled={state === "loading"}
      aria-label={state === "playing" ? "停止播放語音" : "播放語音"}
      className="mt-1 inline-flex w-fit items-center gap-1 rounded-full px-2 py-0.5 text-[11px] disabled:opacity-50"
      style={{ color: "var(--accent)", background: "var(--chip-bg)" }}
    >
      {state === "loading" && "合成中…"}
      {state === "playing" && "■ 停止"}
      {state === "idle" && "▶ 播放語音"}
    </button>
  );
}