import { useQuery, useQueryClient } from "@tanstack/react-query";
import * as Crypto from "expo-crypto";
import { useLocalSearchParams, useRouter } from "expo-router";
import React, { useCallback, useEffect, useMemo, useRef, useState } from "react";
import { AppState, FlatList, Text, View } from "react-native";
import { useApp } from "../../src/app-context";
import { ChatInputBar } from "../../src/components/ChatInputBar";
import { ChatScreenHeader } from "../../src/components/ChatScreenHeader";
import { GuestAuthGate } from "../../src/components/GuestAuthGate";
import { MessageBubble } from "../../src/components/MessageBubble";
import { ScreenShell } from "../../src/components/ScreenShell";
import { isMessageBlockedError } from "../../src/api";
import {
  clearPendingFileIntent,
  clearPendingTextIntent,
  loadPendingFileIntent,
  loadPendingTextIntent,
} from "../../src/pending-intent";
import { DEFAULT_MESSAGE_MAX_LENGTH, normalizeMessageText } from "../../src/message-text";
import { pickFiles, type NativeFile } from "../../src/native-files";
import { RealtimeClient, reconcileMessages } from "../../src/realtime";
import { dialogApi, profileApi, publicApi, uploadAttachment } from "../../src/services";
import type { Message } from "../../src/types";
import { Button, ErrorNotice, Loading, styles } from "../../src/ui";
import { colors, spacing } from "../../src/theme";

const statusLabel: Record<string, string> = {
  open: "Открыт",
  waiting_for_company: "Ожидает ответа",
  waiting_for_client: "Ожидает вашего ответа",
  closed: "Закрыт",
};

export default function ChatScreen() {
  const { dialogId } = useLocalSearchParams<{ dialogId: string }>();
  const app = useApp();
  const client = useQueryClient();
  const router = useRouter();
  const listRef = useRef<FlatList<Message>>(null);
  const [text, setText] = useState("");
  const [error, setError] = useState<unknown>();
  const [sending, setSending] = useState(false);
  const [retryPending, setRetryPending] = useState<(() => void) | undefined>();
  const pendingStarted = useRef<string | undefined>(undefined);
  const config = useQuery({ queryKey: ["public-config"], queryFn: publicApi.config });
  const dialog = useQuery({ queryKey: ["dialog", dialogId], queryFn: () => dialogApi.get(dialogId), enabled: Boolean(dialogId) && app.authStatus === "authenticated" });
  const messages = useQuery({ queryKey: ["messages", dialogId], queryFn: () => dialogApi.messages(dialogId), enabled: Boolean(dialogId) && app.authStatus === "authenticated" });

  const realtime = useMemo(() => new RealtimeClient(
    dialogId ? [dialogId] : [],
    (event) => {
      if (event.type === "message.new") merge([event.message]);
      if (event.type === "message.status") {
        client.setQueryData(["messages", dialogId], (old: typeof messages.data) => old && ({
          ...old,
          items: old.items.map((item) => item.message_id === event.message_id ? { ...item, safety_status: event.safety_status, delivery_status: event.delivery_status } : item),
        }));
      }
      if (event.type === "dialog.status") void dialog.refetch();
    },
    (_, incoming) => merge(incoming),
    app.setRealtimeState,
  ), [dialogId]);

  function merge(incoming: Message[]) {
    client.setQueryData(["messages", dialogId], (old: typeof messages.data) => ({
      items: reconcileMessages(old?.items ?? [], incoming),
      next_cursor: old?.next_cursor ?? null,
    }));
  }

  useEffect(() => {
    if (app.authStatus !== "authenticated") return;
    const syncRealtime = (state: string) => {
      if (state === "active") realtime.start();
      else realtime.stop();
    };
    syncRealtime(AppState.currentState);
    const subscription = AppState.addEventListener("change", syncRealtime);
    return () => {
      subscription.remove();
      realtime.stop();
    };
  }, [realtime, app.authStatus]);

  useEffect(() => {
    const items = messages.data?.items ?? [];
    if (items.length) listRef.current?.scrollToEnd({ animated: true });
  }, [messages.data?.items.length]);

  const handleSendError = async (reason: unknown) => {
    if (isMessageBlockedError(reason)) {
      setError(undefined);
      await messages.refetch();
      return true;
    }
    setError(reason);
    return false;
  };

  const sendText = async (value = text, messageKey = Crypto.randomUUID()) => {
    const normalized = normalizeMessageText(value);
    if (!normalized || !dialogId) return;
    const maxLength = config.data?.messages?.max_text_length ?? DEFAULT_MESSAGE_MAX_LENGTH;
    if (normalized.length > maxLength) {
      setError(new Error(`Сообщение слишком длинное. Максимум — ${maxLength} символов.`));
      return false;
    }
    setSending(true); setError(undefined);
    try {
      const message = await dialogApi.sendText(dialogId, normalized, messageKey);
      merge([message]); setText("");
      return true;
    } catch (reason) {
      return await handleSendError(reason);
    }
    finally { setSending(false); }
  };

  const chooseFile = async () => {
    try {
      const [file] = await pickFiles({ mimeTypes: ["image/*", "application/pdf"] });
      if (file) await sendFile(file);
    } catch (reason) {
      setError(reason);
    }
  };

  const sendFile = async (file: NativeFile, messageKey = Crypto.randomUUID()) => {
    const limits = config.data?.attachments;
    const max = (limits?.max_size_mb ?? 5) * 1024 * 1024;
    const allowed = limits?.allowed_mime_types ?? ["image/jpeg", "image/png", "image/webp", "application/pdf"];
    if (file.size > max || !allowed.includes(file.mimeType)) {
      setError(new Error("Недопустимый тип файла или превышен допустимый размер."));
      return;
    }
    setSending(true); setError(undefined);
    try {
      const uploaded = await uploadAttachment(dialogId, file);
      const message = await dialogApi.sendFile(dialogId, uploaded.attachmentId, uploaded.checksum, messageKey);
      merge([message]);
      return true;
    } catch (reason) {
      return await handleSendError(reason);
    }
    finally { setSending(false); }
  };

  useEffect(() => {
    if (!dialogId || app.authStatus !== "authenticated") return;
    const textIntent = loadPendingTextIntent();
    const fileIntent = loadPendingFileIntent(dialogId);
    const intentKey = textIntent?.dialogId === dialogId
      ? textIntent.messageKey
      : fileIntent?.messageKey;
    if (!intentKey || pendingStarted.current === intentKey) return;
    pendingStarted.current = intentKey;

    const submit = async () => {
      const completed = textIntent?.dialogId === dialogId
        ? await sendText(textIntent.text, textIntent.messageKey)
        : fileIntent
          ? await sendFile(fileIntent.file, fileIntent.messageKey)
          : true;
      if (completed) {
        await Promise.all([
          clearPendingTextIntent(),
          clearPendingFileIntent(),
        ]);
        setRetryPending(undefined);
        return;
      }
      setRetryPending(() => () => {
        setRetryPending(undefined);
        void submit().catch(setError);
      });
    };
    void submit().catch(setError);
  }, [dialogId, app.authStatus]);

  const getAttachmentUrl = useCallback(async (attachmentId: string) => {
    const result = await profileApi.attachmentUrl(dialogId, attachmentId);
    return result.download_url;
  }, [dialogId]);

  const closed = dialog.data?.status === "closed";
  const items = messages.data?.items ?? [];
  const subtitle = dialog.data?.status ? (statusLabel[dialog.data.status] ?? "Онлайн") : "Онлайн";

  if (app.authStatus !== "authenticated") {
    return (
      <ScreenShell>
        <ChatScreenHeader title="Чат" subtitle="Требуется вход" />
        <GuestAuthGate
          icon="message-circle"
          title="Чат доступен после входа"
          description="Авторизуйтесь, чтобы переписываться с оператором и получать ответы."
        />
      </ScreenShell>
    );
  }

  return (
    <ScreenShell>
      <ChatScreenHeader subtitle={subtitle} />
      <View style={{ flex: 1, backgroundColor: colors.background }}>
        {(dialog.isLoading || messages.isLoading) && (
          <View style={{ padding: spacing.lg }}><Loading /></View>
        )}
        {(dialog.error || messages.error) && (
          <View style={{ padding: spacing.lg }}>
            <ErrorNotice error={dialog.error ?? messages.error} retry={() => { void dialog.refetch(); void messages.refetch(); }} />
          </View>
        )}
        <FlatList
          accessibilityLiveRegion="polite"
          ref={listRef}
          data={items}
          keyExtractor={(item) => item.message_id}
          keyboardDismissMode="on-drag"
          keyboardShouldPersistTaps="handled"
          contentContainerStyle={{ paddingHorizontal: spacing.lg, paddingVertical: spacing.lg, flexGrow: 1 }}
          ListEmptyComponent={!messages.isLoading ? <Text style={[styles.muted, { textAlign: "center", marginTop: 40 }]}>Сообщений пока нет.</Text> : null}
          renderItem={({ item }) => (
            <MessageBubble
              getAttachmentUrl={getAttachmentUrl}
              message={item}
              onAttachmentError={setError}
            />
          )}
        />
        {closed ? (
          <View style={{ padding: spacing.lg, borderTopWidth: 1, borderTopColor: colors.border }}>
            <Text style={[styles.muted, { marginBottom: spacing.sm }]}>Предыдущая беседа завершена.</Text>
            <Button title="Продолжить общение" onPress={() => router.replace("/dialogs")} />
          </View>
        ) : (
          <>
            <ChatInputBar
              disabled={sending}
              hint=""
              onAttach={() => void chooseFile()}
              onChangeText={setText}
              onSubmit={() => void sendText()}
              placeholder="Напишите сообщение..."
              sending={sending}
              value={text}
              maxLength={config.data?.messages?.max_text_length ?? DEFAULT_MESSAGE_MAX_LENGTH}
            />
            {error && (
              <View style={{ paddingHorizontal: spacing.lg, paddingBottom: spacing.sm }}>
                <ErrorNotice
                  error={error}
                  {...(retryPending ? { retry: retryPending } : {})}
                />
              </View>
            )}
          </>
        )}
      </View>
    </ScreenShell>
  );
}