import { useEffect, useState } from "react";
import { useTranslation } from "react-i18next";
import { useQuery } from "@tanstack/react-query";
import { ArrowLeft, ShieldCheck, SquarePen, ExternalLink } from "lucide-react";
import { api, type Conversation, type MessageUser } from "../lib/api";
import { useLiveQuery } from "../lib/useLiveQuery";
import { relativeTime } from "../lib/format";
import { partnerPub, POLL_MS, SYSTEM_ID, useKeyState } from "../lib/messaging";
import { useHistorySubview } from "../lib/history";
import { openChat } from "../lib/chatDock";
import * as e2ee from "../lib/e2ee";
import Avatar from "./Avatar";
import KeyGate from "./KeyGate";
import ChatThread from "./ChatThread";

type View = "list" | "new" | { partnerId: number; name?: string; avatar?: string | null; system?: boolean };

export default function Messages({ meId }: { meId: number }) {
  // Sub-views live in browser history, so Back returns to the conversation list before leaving
  // the module (open() pushes an entry; back() = history.back()).
  const { view, open, back } = useHistorySubview<View>("list");

  // Guard against a stale sub-view whose partnerId is the current user's own id (you can't
  // message yourself). This can be inherited across an account switch — fall back to the list.
  if (typeof view === "object" && view.partnerId !== meId) {
    return (
      <PageThread
        meId={meId}
        partnerId={view.partnerId}
        isSystem={!!view.system}
        seedName={view.name}
        seedAvatar={view.avatar}
        onBack={back}
      />
    );
  }
  if (view === "new") {
    return <Directory onPick={(u) => open({ partnerId: u.id, name: u.name, avatar: u.avatar_url })} onBack={back} />;
  }
  return (
    <ConversationList
      meId={meId}
      onOpen={(c) => open({ partnerId: c.partner.id, name: c.partner.name, avatar: c.partner.avatar_url, system: c.partner.id === SYSTEM_ID })}
      onNew={() => open("new")}
    />
  );
}

function ConversationList({
  meId,
  onOpen,
  onNew,
}: {
  meId: number;
  onOpen: (c: Conversation) => void;
  onNew: () => void;
}) {
  const { t } = useTranslation();
  const keyState = useKeyState();
  const ready = keyState === "ready";
  const q = useLiveQuery<{ items: Conversation[] }>(["conversations"], api.conversations, { intervalMs: POLL_MS });
  const items = q.data?.items ?? [];
  const [previews, setPreviews] = useState<Record<number, string>>({});

  // Decrypt conversation previews when fresh data arrives. Keyed on dataUpdatedAt (not `items`):
  // the `?? []` fallback is a new array each render, which would otherwise spin this effect
  // (and setPreviews) every render while the query is loading.
  useEffect(() => {
    if (!ready) return;
    let cancelled = false;
    (async () => {
      const out: Record<number, string> = {};
      for (const c of q.data?.items ?? []) {
        const m = c.last_message;
        if (m.kind === "user" && m.ciphertext && m.iv) {
          try {
            const pub = await partnerPub(c.partner.id);
            out[c.partner.id] = await e2ee.decryptFrom(c.partner.id, pub, m.ciphertext, m.iv);
          } catch {
            out[c.partner.id] = "⚠";
          }
        }
      }
      if (!cancelled) setPreviews(out);
    })();
    return () => {
      cancelled = true;
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [q.dataUpdatedAt, ready]);

  function previewText(c: Conversation): string {
    const m = c.last_message;
    if (m.kind === "system") return m.body ?? "";
    if (!ready) return "🔒 " + t("messages.encrypted");
    return previews[c.partner.id] ?? "…";
  }

  return (
    <div className="space-y-3">
      <div className="flex items-center justify-between">
        <div className="text-xs uppercase tracking-wide text-muted">{t("messages.conversations")}</div>
        {ready && (
          <button
            onClick={onNew}
            className="inline-flex items-center gap-1.5 text-xs px-2.5 py-1.5 rounded-lg bg-accent text-accent-fg hover:opacity-90 transition"
          >
            <SquarePen className="w-4 h-4" />
            {t("messages.new")}
          </button>
        )}
      </div>
      {(keyState === "setup" || keyState === "unlock") && <KeyGate meId={meId} />}
      {q.isLoading && !q.data ? (
        <div className="p-8 text-muted text-center">{t("common.loading")}</div>
      ) : items.length === 0 ? (
        <div className="glass rounded-2xl p-10 text-center text-muted">{t("messages.empty")}</div>
      ) : (
        <div className="flex flex-col gap-1.5">
          {items.map((c) => {
            const isSystem = c.partner.id === SYSTEM_ID;
            return (
              <div key={c.partner.id} className="group flex items-center gap-1 rounded-xl hover:bg-card transition">
                <button onClick={() => onOpen(c)} className="flex items-center gap-3 p-2.5 text-left min-w-0 flex-1">
                  <Avatar src={c.partner.avatar_url} fallback={c.partner.name} className="w-10 h-10 rounded-full shrink-0 text-sm" />
                  <div className="min-w-0 flex-1">
                    <div className="flex items-center gap-2">
                      <span className={`truncate ${c.unread > 0 ? "font-semibold" : "font-medium"}`}>{c.partner.name}</span>
                      <span className="ml-auto text-[11px] text-muted shrink-0">{relativeTime(c.last_message.created_at)}</span>
                    </div>
                    <div className="flex items-center gap-2">
                      <span className={`truncate text-sm ${c.unread > 0 ? "text-fg" : "text-muted"}`}>{previewText(c)}</span>
                      {c.unread > 0 && (
                        <span className="ml-auto shrink-0 min-w-5 h-5 px-1.5 grid place-items-center rounded-full bg-accent text-accent-fg text-[11px] font-semibold">
                          {c.unread}
                        </span>
                      )}
                    </div>
                  </div>
                </button>
                {!isSystem && ready && (
                  <button
                    onClick={() => openChat(c.partner)}
                    title={t("messages.popOut")}
                    aria-label={t("messages.popOut")}
                    className="shrink-0 mr-1.5 p-1.5 rounded-lg text-muted opacity-0 group-hover:opacity-100 hover:text-accent hover:bg-bg transition"
                  >
                    <ExternalLink className="w-4 h-4" />
                  </button>
                )}
              </div>
            );
          })}
        </div>
      )}
    </div>
  );
}

function Directory({ onPick, onBack }: { onPick: (u: MessageUser) => void; onBack: () => void }) {
  const { t } = useTranslation();
  const [filter, setFilter] = useState("");
  const q = useQuery({ queryKey: ["message-users"], queryFn: api.messageUsers });
  const users = (q.data ?? []).filter((u) => u.name.toLowerCase().includes(filter.trim().toLowerCase()));
  return (
    <div className="space-y-3">
      <div className="flex items-center gap-2">
        <button onClick={onBack} className="p-1.5 rounded-lg text-muted hover:text-fg hover:bg-card transition">
          <ArrowLeft className="w-4 h-4" />
        </button>
        <div className="text-xs uppercase tracking-wide text-muted">{t("messages.newTitle")}</div>
      </div>
      <input
        value={filter}
        onChange={(e) => setFilter(e.target.value)}
        placeholder={t("messages.searchPeople")}
        className="w-full bg-card border border-border rounded-xl px-3 py-2 text-sm outline-none focus:border-accent"
      />
      {q.isLoading ? (
        <div className="p-8 text-muted text-center">{t("common.loading")}</div>
      ) : users.length === 0 ? (
        <div className="glass rounded-2xl p-10 text-center text-muted">{t("messages.noPeople")}</div>
      ) : (
        <div className="flex flex-col gap-1">
          {users.map((u) => (
            <button
              key={u.id}
              onClick={() => onPick(u)}
              className="flex items-center gap-3 p-2.5 rounded-xl text-left hover:bg-card transition"
            >
              <Avatar src={u.avatar_url} fallback={u.name} className="w-9 h-9 rounded-full shrink-0 text-sm" />
              <span className="truncate font-medium">{u.name}</span>
            </button>
          ))}
        </div>
      )}
    </div>
  );
}

function PageThread({
  meId,
  partnerId,
  isSystem,
  seedName,
  seedAvatar,
  onBack,
}: {
  meId: number;
  partnerId: number;
  isSystem: boolean;
  seedName?: string;
  seedAvatar?: string | null;
  onBack: () => void;
}) {
  const { t } = useTranslation();
  const ready = useKeyState() === "ready";
  const name = seedName ?? "";
  return (
    <div className="flex flex-col h-[65vh] min-h-80">
      <div className="flex items-center gap-3 pb-3 border-b border-border">
        <button onClick={onBack} className="p-1.5 rounded-lg text-muted hover:text-fg hover:bg-card transition">
          <ArrowLeft className="w-4 h-4" />
        </button>
        <Avatar src={seedAvatar} fallback={name} className="w-9 h-9 rounded-full shrink-0 text-sm" />
        <span className="font-semibold truncate">{name}</span>
        {!isSystem && <ShieldCheck className="w-4 h-4 text-muted shrink-0" aria-label={t("messages.encryptedHint")} />}
        <div className="flex-1" />
        {!isSystem && ready && (
          <button
            onClick={() => openChat({ id: partnerId, name, avatar_url: seedAvatar ?? null })}
            title={t("messages.popOut")}
            aria-label={t("messages.popOut")}
            className="p-1.5 rounded-lg text-muted hover:text-accent hover:bg-card transition"
          >
            <ExternalLink className="w-4 h-4" />
          </button>
        )}
      </div>
      <ChatThread meId={meId} partnerId={partnerId} isSystem={isSystem} />
    </div>
  );
}
