import { useEffect, useMemo, useRef, useState } from "preact/hooks";
import { LogOut, MessageSquare, Plus, SendHorizontal, ShieldCheck } from "lucide-preact";
import { Button } from "@/components/ui/button";
import { Input } from "@/components/ui/input";
import { Textarea } from "@/components/ui/textarea";
import { Separator } from "@/components/ui/separator";
import {
  createChat,
  getChat,
  getConfiguredToken,
  listChats,
  runCompletion,
  setAuthToken,
  verifySession,
  type ChatDetail,
  type ChatSummary,
  type CompletionRequestMessage,
} from "@/lib/api";
import { cn } from "@/lib/utils";

type Provider = "openai" | "anthropic" | "xai";
type AuthMode = "open" | "token";

const PROVIDER_DEFAULT_MODELS: Record<Provider, string> = {
  openai: "gpt-4.1-mini",
  anthropic: "claude-3-5-sonnet-latest",
  xai: "grok-3-mini",
};
const TOKEN_STORAGE_KEY = "sybil_admin_token";

function getChatTitle(chat: Pick<ChatSummary, "title">, messages?: ChatDetail["messages"]) {
  if (chat.title?.trim()) return chat.title.trim();
  const firstUserMessage = messages?.find((m) => m.role === "user")?.content.trim();
  if (firstUserMessage) return firstUserMessage.slice(0, 48);
  return "New chat";
}

function formatDate(value: string) {
  return new Intl.DateTimeFormat(undefined, {
    month: "short",
    day: "numeric",
    hour: "numeric",
    minute: "2-digit",
  }).format(new Date(value));
}

function readStoredToken() {
  return localStorage.getItem(TOKEN_STORAGE_KEY)?.trim() || null;
}

function persistToken(token: string | null) {
  if (token) {
    localStorage.setItem(TOKEN_STORAGE_KEY, token);
    return;
  }
  localStorage.removeItem(TOKEN_STORAGE_KEY);
}

function normalizeAuthError(message: string) {
  if (message.includes("missing bearer token") || message.includes("invalid bearer token")) {
    return "Authentication failed. Enter the ADMIN_TOKEN configured in server/.env.";
  }
  return message;
}

export default function App() {
  const initialToken = readStoredToken() ?? getConfiguredToken() ?? "";

  const [authTokenInput, setAuthTokenInput] = useState(initialToken);
  const [isCheckingSession, setIsCheckingSession] = useState(true);
  const [isSigningIn, setIsSigningIn] = useState(false);
  const [isAuthenticated, setIsAuthenticated] = useState(false);
  const [authMode, setAuthMode] = useState<AuthMode | null>(null);
  const [authError, setAuthError] = useState<string | null>(null);

  const [chats, setChats] = useState<ChatSummary[]>([]);
  const [selectedChatId, setSelectedChatId] = useState<string | null>(null);
  const [selectedChat, setSelectedChat] = useState<ChatDetail | null>(null);
  const [isLoadingChats, setIsLoadingChats] = useState(false);
  const [isLoadingChat, setIsLoadingChat] = useState(false);
  const [isSending, setIsSending] = useState(false);
  const [composer, setComposer] = useState("");
  const [provider, setProvider] = useState<Provider>("openai");
  const [model, setModel] = useState(PROVIDER_DEFAULT_MODELS.openai);
  const [error, setError] = useState<string | null>(null);
  const transcriptEndRef = useRef<HTMLDivElement>(null);

  const completeSessionCheck = async (tokenCandidate: string | null) => {
    setAuthToken(tokenCandidate);
    const session = await verifySession();
    setIsAuthenticated(true);
    setAuthMode(session.mode);
    setAuthError(null);
    persistToken(tokenCandidate);
  };

  const handleAuthFailure = (message: string) => {
    setIsAuthenticated(false);
    setAuthMode(null);
    setAuthError(normalizeAuthError(message));
    setAuthToken(null);
    persistToken(null);
    setChats([]);
    setSelectedChatId(null);
    setSelectedChat(null);
  };

  const refreshChats = async (preferredChatId?: string) => {
    setIsLoadingChats(true);
    try {
      const nextChats = await listChats();
      setChats(nextChats);

      setSelectedChatId((current) => {
        if (preferredChatId && nextChats.some((chat) => chat.id === preferredChatId)) {
          return preferredChatId;
        }
        if (current && nextChats.some((chat) => chat.id === current)) {
          return current;
        }
        return nextChats[0]?.id ?? null;
      });
    } catch (err) {
      const message = err instanceof Error ? err.message : String(err);
      if (message.includes("bearer token")) {
        handleAuthFailure(message);
      } else {
        setError(message);
      }
    } finally {
      setIsLoadingChats(false);
    }
  };

  const refreshChat = async (chatId: string) => {
    setIsLoadingChat(true);
    try {
      const chat = await getChat(chatId);
      setSelectedChat(chat);
    } catch (err) {
      const message = err instanceof Error ? err.message : String(err);
      if (message.includes("bearer token")) {
        handleAuthFailure(message);
      } else {
        setError(message);
      }
    } finally {
      setIsLoadingChat(false);
    }
  };

  useEffect(() => {
    const token = readStoredToken() ?? getConfiguredToken();
    void (async () => {
      try {
        await completeSessionCheck(token);
      } catch (err) {
        const message = err instanceof Error ? err.message : String(err);
        handleAuthFailure(message);
      } finally {
        setIsCheckingSession(false);
      }
    })();
  }, []);

  useEffect(() => {
    if (!isAuthenticated) return;
    void refreshChats();
  }, [isAuthenticated]);

  useEffect(() => {
    if (!isAuthenticated) {
      setSelectedChat(null);
      return;
    }
    if (!selectedChatId) {
      setSelectedChat(null);
      return;
    }
    void refreshChat(selectedChatId);
  }, [isAuthenticated, selectedChatId]);

  useEffect(() => {
    transcriptEndRef.current?.scrollIntoView({ behavior: "smooth", block: "end" });
  }, [selectedChat?.messages.length, isSending]);

  const messages = selectedChat?.messages ?? [];

  const selectedChatTitle = useMemo(() => {
    if (!selectedChat) return "Sybil";
    return getChatTitle(selectedChat, selectedChat.messages);
  }, [selectedChat]);

  const handleCreateChat = async () => {
    setError(null);
    try {
      const chat = await createChat();
      setSelectedChatId(chat.id);
      setSelectedChat({
        id: chat.id,
        title: chat.title,
        createdAt: chat.createdAt,
        updatedAt: chat.updatedAt,
        messages: [],
      });
      await refreshChats(chat.id);
    } catch (err) {
      const message = err instanceof Error ? err.message : String(err);
      if (message.includes("bearer token")) {
        handleAuthFailure(message);
      } else {
        setError(message);
      }
    }
  };

  const handleSend = async () => {
    const content = composer.trim();
    if (!content || isSending) return;

    setComposer("");
    setError(null);
    setIsSending(true);

    let chatId = selectedChatId;

    try {
      if (!chatId) {
        const chat = await createChat();
        chatId = chat.id;
        setSelectedChatId(chatId);
      }

      if (!chatId) {
        throw new Error("Unable to initialize chat");
      }

      let baseChat = selectedChat;
      if (!baseChat || baseChat.id !== chatId) {
        baseChat = await getChat(chatId);
      }

      const optimisticUserMessage = {
        id: `temp-user-${Date.now()}`,
        createdAt: new Date().toISOString(),
        role: "user" as const,
        content,
        name: null,
      };

      const optimisticAssistantMessage = {
        id: `temp-assistant-${Date.now()}`,
        createdAt: new Date().toISOString(),
        role: "assistant" as const,
        content: "",
        name: null,
      };

      setSelectedChat((current) => {
        if (!current || current.id !== chatId) return current;
        return {
          ...current,
          messages: [...current.messages, optimisticUserMessage, optimisticAssistantMessage],
        };
      });

      const requestMessages: CompletionRequestMessage[] = [
        ...baseChat.messages.map((message) => ({
          role: message.role,
          content: message.content,
          ...(message.name ? { name: message.name } : {}),
        })),
        {
          role: "user",
          content,
        },
      ];

      await runCompletion({
        chatId,
        provider,
        model: model.trim(),
        messages: requestMessages,
      });

      await Promise.all([refreshChats(chatId), refreshChat(chatId)]);
    } catch (err) {
      const message = err instanceof Error ? err.message : String(err);
      if (message.includes("bearer token")) {
        handleAuthFailure(message);
      } else {
        setError(message);
      }
      if (chatId) {
        await refreshChat(chatId);
      }
    } finally {
      setIsSending(false);
    }
  };

  const handleSignIn = async (tokenCandidate: string | null) => {
    setIsSigningIn(true);
    setAuthError(null);
    try {
      await completeSessionCheck(tokenCandidate);
      await refreshChats();
    } catch (err) {
      const message = err instanceof Error ? err.message : String(err);
      setAuthError(normalizeAuthError(message));
      setIsAuthenticated(false);
      setAuthMode(null);
    } finally {
      setIsSigningIn(false);
    }
  };

  const handleLogout = () => {
    setAuthToken(null);
    persistToken(null);
    setIsAuthenticated(false);
    setAuthMode(null);
    setAuthError(null);
    setChats([]);
    setSelectedChatId(null);
    setSelectedChat(null);
    setComposer("");
    setError(null);
  };

  if (isCheckingSession) {
    return (
      <div className="flex h-full items-center justify-center bg-muted/70">
        <p className="text-sm text-muted-foreground">Checking session...</p>
      </div>
    );
  }

  if (!isAuthenticated) {
    return (
      <div className="flex h-full items-center justify-center bg-[radial-gradient(circle_at_top,#f8fafc_0%,#eef2f7_45%,#e2e8f0_100%)] p-4">
        <div className="w-full max-w-md rounded-2xl border bg-background p-6 shadow-xl">
          <div className="mb-5 flex items-start gap-3">
            <div className="rounded-lg bg-slate-900 p-2 text-slate-50">
              <ShieldCheck className="h-4 w-4" />
            </div>
            <div>
              <h1 className="text-lg font-semibold">Sign in to Sybil</h1>
              <p className="mt-1 text-sm text-muted-foreground">Use your backend admin token.</p>
            </div>
          </div>

          <form
            className="space-y-3"
            onSubmit={(event) => {
              event.preventDefault();
              void handleSignIn(authTokenInput.trim() || null);
            }}
          >
            <Input
              type="password"
              autoComplete="off"
              placeholder="ADMIN_TOKEN"
              value={authTokenInput}
              onInput={(event) => setAuthTokenInput(event.currentTarget.value)}
              disabled={isSigningIn}
            />
            <Button className="w-full" type="submit" disabled={isSigningIn}>
              {isSigningIn ? "Signing in..." : "Sign in"}
            </Button>
            <Button
              className="w-full"
              type="button"
              variant="secondary"
              disabled={isSigningIn}
              onClick={() => void handleSignIn(null)}
            >
              Continue without token
            </Button>
          </form>

          {authError ? <p className="mt-3 text-sm text-red-600">{authError}</p> : null}
          <p className="mt-3 text-xs text-muted-foreground">If `ADMIN_TOKEN` is set in `/server/.env`, token login is required.</p>
        </div>
      </div>
    );
  }

  return (
    <div className="h-full p-3 md:p-5">
      <div className="mx-auto flex h-full w-full max-w-[1560px] overflow-hidden rounded-2xl border bg-background shadow-xl">
        <aside className="flex w-80 shrink-0 flex-col border-r bg-slate-50">
          <div className="p-3">
            <Button className="w-full justify-start gap-2" onClick={handleCreateChat}>
              <Plus className="h-4 w-4" />
              New chat
            </Button>
          </div>
          <Separator />
          <div className="flex-1 overflow-y-auto p-2">
            {isLoadingChats && chats.length === 0 ? <p className="px-2 py-3 text-sm text-muted-foreground">Loading chats...</p> : null}
            {!isLoadingChats && chats.length === 0 ? (
              <div className="flex h-full flex-col items-center justify-center gap-2 p-5 text-center text-sm text-muted-foreground">
                <MessageSquare className="h-5 w-5" />
                Start your first conversation.
              </div>
            ) : null}
            {chats.map((chat) => {
              const active = chat.id === selectedChatId;
              return (
                <button
                  key={chat.id}
                  className={cn(
                    "mb-1 w-full rounded-lg px-3 py-2 text-left transition",
                    active ? "bg-slate-900 text-slate-50" : "hover:bg-slate-200"
                  )}
                  onClick={() => setSelectedChatId(chat.id)}
                  type="button"
                >
                  <p className="truncate text-sm font-medium">{getChatTitle(chat)}</p>
                  <p className={cn("mt-1 text-xs", active ? "text-slate-300" : "text-slate-500")}>{formatDate(chat.updatedAt)}</p>
                </button>
              );
            })}
          </div>
        </aside>

        <main className="flex min-w-0 flex-1 flex-col">
          <header className="flex flex-wrap items-center justify-between gap-3 border-b px-4 py-3">
            <div>
              <h1 className="text-sm font-semibold md:text-base">{selectedChatTitle}</h1>
              <p className="text-xs text-muted-foreground">
                Sybil Web{authMode ? ` (${authMode === "open" ? "open mode" : "token mode"})` : ""}
              </p>
            </div>
            <div className="flex w-full max-w-xl items-center gap-2 md:w-auto">
              <select
                className="h-9 rounded-md border border-input bg-background px-2 text-sm"
                value={provider}
                onChange={(event) => {
                  const nextProvider = event.currentTarget.value as Provider;
                  setProvider(nextProvider);
                  setModel(PROVIDER_DEFAULT_MODELS[nextProvider]);
                }}
                disabled={isSending}
              >
                <option value="openai">OpenAI</option>
                <option value="anthropic">Anthropic</option>
                <option value="xai">xAI</option>
              </select>
              <Input
                value={model}
                onInput={(event) => setModel(event.currentTarget.value)}
                placeholder="Model"
                disabled={isSending}
              />
              <Button variant="outline" size="sm" onClick={handleLogout}>
                <LogOut className="mr-1 h-4 w-4" />
                Logout
              </Button>
            </div>
          </header>

          <div className="flex-1 overflow-y-auto px-3 py-6 md:px-10">
            {isLoadingChat && messages.length === 0 ? <p className="text-sm text-muted-foreground">Loading messages...</p> : null}
            {!isLoadingChat && messages.length === 0 ? (
              <div className="mx-auto flex max-w-3xl flex-col items-center gap-3 rounded-xl border border-dashed p-8 text-center">
                <h2 className="text-lg font-semibold">How can I help today?</h2>
                <p className="text-sm text-muted-foreground">Ask a question to begin this conversation.</p>
              </div>
            ) : null}
            <div className="mx-auto max-w-3xl space-y-6">
              {messages.map((message) => {
                const isUser = message.role === "user";
                const isPendingAssistant = message.id.startsWith("temp-assistant-") && isSending;
                return (
                  <div key={message.id} className={cn("flex", isUser ? "justify-end" : "justify-start")}>
                    <div
                      className={cn(
                        "max-w-[85%] whitespace-pre-wrap rounded-2xl px-4 py-3 text-sm leading-6",
                        isUser ? "bg-slate-900 text-slate-50" : "bg-slate-100 text-slate-900"
                      )}
                    >
                      {isPendingAssistant ? "Thinking..." : message.content}
                    </div>
                  </div>
                );
              })}
            </div>
            <div ref={transcriptEndRef} />
          </div>

          <footer className="border-t p-3 md:p-4">
            <div className="mx-auto max-w-3xl rounded-xl border bg-background p-2 shadow-sm">
              <Textarea
                rows={3}
                value={composer}
                onInput={(event) => setComposer(event.currentTarget.value)}
                onKeyDown={(event) => {
                  if (event.key === "Enter" && !event.shiftKey) {
                    event.preventDefault();
                    void handleSend();
                  }
                }}
                placeholder="Message Sybil"
                className="resize-none border-0 shadow-none focus-visible:ring-0"
                disabled={isSending}
              />
              <div className="flex items-center justify-between px-2 pb-1">
                {error ? <p className="text-xs text-red-600">{error}</p> : <span className="text-xs text-muted-foreground">Enter to send</span>}
                <Button onClick={() => void handleSend()} size="icon" disabled={isSending || !composer.trim()}>
                  <SendHorizontal className="h-4 w-4" />
                </Button>
              </div>
            </div>
          </footer>
        </main>
      </div>
    </div>
  );
}