import { useState, useMemo } from "react";
import { useParams } from "react-router-dom";
import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query";
import { getChannel, getChannelVideos, followChannel, unfollowChannel, indexChannel, downloadChannel } from "../api";
import VideoCard from "../components/VideoCard";
import SortPicker from "../components/SortPicker";

function formatSubs(n) {
  if (!n) return null;
  if (n >= 1_000_000) return `${(n / 1_000_000).toFixed(n >= 10_000_000 ? 0 : 1)}M`;
  if (n >= 1_000) return `${Math.round(n / 1_000)}K`;
  return String(n);
}

const VIDEO_SORTS = [
  { value: "newest",    label: "Newest" },
  { value: "oldest",    label: "Oldest" },
  { value: "title",     label: "Title A–Z" },
  { value: "unwatched", label: "Unwatched first" },
];

function sortVideos(items, sort) {
  const arr = [...items];
  if (sort === "oldest")    return arr.sort((a, b) => new Date(a.published_at ?? 0) - new Date(b.published_at ?? 0));
  if (sort === "title")     return arr.sort((a, b) => (a.title ?? "").localeCompare(b.title ?? ""));
  if (sort === "unwatched") return arr.sort((a, b) => Number(a.is_watched) - Number(b.is_watched));
  return arr.sort((a, b) => new Date(b.published_at ?? 0) - new Date(a.published_at ?? 0));
}

export default function ChannelPage() {
  const { id } = useParams();
  const qc = useQueryClient();

  const { data: channel, isLoading: loadingChannel } = useQuery({
    queryKey: ["channel", id],
    queryFn: () => getChannel(id).then((r) => r.data),
  });

  const { data: videos, isLoading: loadingVideos } = useQuery({
    queryKey: ["channel-videos", id],
    queryFn: () => getChannelVideos(id).then((r) => r.data),
  });

  const followMut = useMutation({
    mutationFn: () =>
      channel?.status === "followed" ? unfollowChannel(id) : followChannel(id),
    onSuccess: () => {
      qc.invalidateQueries({ queryKey: ["channel", id] });
      qc.invalidateQueries({ queryKey: ["channels"] });
    },
  });

  const indexMut = useMutation({
    mutationFn: () => indexChannel(id),
    onSuccess: () => setTimeout(() => qc.invalidateQueries({ queryKey: ["channel-videos", id] }), 4000),
  });

  const [dlResult, setDlResult] = useState(null);
  const [videoSort, setVideoSort] = useState("newest");
  const dlMut = useMutation({
    mutationFn: () => downloadChannel(id),
    onSuccess: (res) => {
      setDlResult(res.data.queued);
      qc.invalidateQueries({ queryKey: ["downloads"] });
    },
  });

  if (loadingChannel) {
    return (
      <div className="flex items-center justify-center py-16">
        <div className="w-8 h-8 border-2 border-accent border-t-transparent rounded-full animate-spin" />
      </div>
    );
  }

  if (!channel) return <p className="text-zinc-500">Channel not found.</p>;

  const isFollowed = channel.status === "followed";

  return (
    <div className="flex flex-col gap-8">
      {/* Channel header — banner with overlay, or plain if no banner */}
      <div className={`-mx-4 -mt-6 relative ${channel.banner_url ? "" : "bg-zinc-900"} rounded-b-2xl overflow-hidden`}>
        {channel.banner_url && (
          <img src={channel.banner_url} alt="" className="w-full h-36 sm:h-52 object-cover" />
        )}
        {/* Gradient overlay */}
        <div className={`${channel.banner_url ? "absolute inset-0 bg-gradient-to-t from-black/80 via-black/30 to-transparent" : ""}`} />

        {/* Info row sits at the bottom of the banner */}
        <div className={`${channel.banner_url ? "absolute bottom-0 inset-x-0" : ""} px-4 pb-4 pt-3 flex items-end gap-4`}>
          {/* Avatar */}
          {channel.thumbnail_url ? (
            <img
              src={channel.thumbnail_url}
              alt={channel.name}
              className="w-16 h-16 sm:w-20 sm:h-20 rounded-full object-cover shrink-0 ring-2 ring-black/40"
            />
          ) : (
            <div className="w-16 h-16 sm:w-20 sm:h-20 rounded-full bg-zinc-800 flex items-center justify-center text-2xl sm:text-3xl font-display font-bold text-zinc-400 shrink-0">
              {channel.name?.[0]?.toUpperCase()}
            </div>
          )}

          {/* Name + meta */}
          <div className="flex-1 min-w-0">
            <h1 className="font-display font-bold text-xl sm:text-2xl text-white drop-shadow">{channel.name}</h1>
            <p className="text-xs sm:text-sm text-zinc-300 mt-0.5 drop-shadow">
              {[
                formatSubs(channel.subscriber_count) && `${formatSubs(channel.subscriber_count)} subscribers`,
                `${channel.video_count} videos indexed`,
              ].filter(Boolean).join(" · ")}
            </p>
          </div>

          {/* Action buttons */}
          <div className="flex items-center gap-2 shrink-0 flex-wrap justify-end">
          {dlResult != null && (
            <span className="text-sm text-accent font-mono">
              {dlResult === 0 ? "Already up to date" : `${dlResult} queued`}
            </span>
          )}
          <button
            onClick={() => dlMut.mutate()}
            disabled={dlMut.isPending}
            className="text-sm font-medium px-4 py-2 rounded-lg bg-accent text-black hover:bg-yellow-300 transition-colors disabled:opacity-60 flex items-center gap-2"
          >
            {dlMut.isPending ? "Queuing…" : "Download all"}
          </button>
          <button
            onClick={() => indexMut.mutate()}
            disabled={indexMut.isPending || indexMut.isSuccess}
            className="text-sm font-medium px-4 py-2 rounded-lg bg-zinc-800/80 text-zinc-300 hover:bg-zinc-700 transition-colors disabled:opacity-60"
          >
            {indexMut.isPending ? "Indexing…" : indexMut.isSuccess ? "Done ✓" : "Re-index"}
          </button>
          <button
            onClick={() => followMut.mutate()}
            disabled={followMut.isPending}
            className={`text-sm font-medium px-4 py-2 rounded-lg transition-colors ${
              isFollowed
                ? "bg-zinc-700/80 text-zinc-300 hover:bg-zinc-600"
                : "bg-zinc-800/80 text-zinc-300 hover:bg-zinc-700"
            }`}
          >
            {isFollowed ? "Following" : "Follow"}
          </button>
        </div>
        </div>
      </div>

      {/* Description below banner */}
      {channel.description && (
        <p className="text-sm text-zinc-400 line-clamp-3 -mt-4">{channel.description}</p>
      )}

      {/* Video grid */}
      {loadingVideos ? (
        <div className="flex items-center justify-center py-8">
          <div className="w-6 h-6 border-2 border-accent border-t-transparent rounded-full animate-spin" />
        </div>
      ) : videos?.length ? (
        <>
          <div className="flex justify-end">
            <SortPicker value={videoSort} onChange={setVideoSort} options={VIDEO_SORTS} />
          </div>
          <div className="grid grid-cols-2 sm:grid-cols-3 lg:grid-cols-4 gap-4">
          {sortVideos(videos, videoSort).map((v) => (
            <VideoCard key={v.youtube_video_id} video={{ ...v, channel_name: channel.name }} />
          ))}
          </div>
        </>
      ) : (
        <p className="text-zinc-500 text-sm">No videos indexed yet. Hit Re-index to fetch them.</p>
      )}
    </div>
  );
}