import React, { useCallback, useEffect, useRef, useState } from "react";

import {
  Alert,
  Box,
  Button,
  CircularProgress,
  Divider,
  IconButton,
  Popover,
  Stack,
  Tooltip,
  Typography,
} from "@mui/material";
import CloseIcon from "@mui/icons-material/Close";
import DeleteOutlineIcon from "@mui/icons-material/DeleteOutline";
import DoneIcon from "@mui/icons-material/Done";

import { api, getApiErrorMessage } from "../api";
import { useI18n } from "../i18n/I18nProvider";
import { notificationDateLabel, UserNotification } from "../notifications";

type Props = {
  anchorEl: HTMLElement | null;
  onClose: () => void;
  onNavigate: (path: string) => void;
  onChanged: () => void;
};

export default function NotificationsPopover({ anchorEl, onClose, onNavigate, onChanged }: Props) {
  const { language, t } = useI18n();
  const open = Boolean(anchorEl);
  const [notifications, setNotifications] = useState<UserNotification[]>([]);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<{ cause: unknown; action: boolean } | null>(null);
  const [busyId, setBusyId] = useState<string | null>(null);
  const activeLoad = useRef<AbortController | null>(null);
  const openGeneration = useRef(0);
  const pendingAction = useRef(false);
  const contentRef = useRef<HTMLDivElement>(null);
  const headingRef = useRef<HTMLHeadingElement>(null);
  const actionFocus = useRef<HTMLElement | null>(null);

  const load = useCallback(async () => {
    if (activeLoad.current || pendingAction.current) return;
    const controller = new AbortController();
    activeLoad.current = controller;
    setLoading(true);
    try {
      const response = await api.get<UserNotification[]>("/notifications?limit=10", { signal: controller.signal });
      if (controller.signal.aborted) return;
      setNotifications(response.data ?? []);
      setError(null);
    } catch (requestError) {
      if (!controller.signal.aborted) setError({ cause: requestError, action: false });
    } finally {
      if (activeLoad.current === controller) { activeLoad.current = null; setLoading(false); }
    }
  }, []);

  useEffect(() => {
    openGeneration.current += 1;
    if (open) void load();
    else {
      activeLoad.current?.abort();
      setNotifications([]);
      setError(null);
      setBusyId(null);
    }
    return () => {
      openGeneration.current += 1;
      activeLoad.current?.abort();
      activeLoad.current = null;
      pendingAction.current = false;
      actionFocus.current = null;
    };
  }, [load, open]);

  useEffect(() => {
    if (!open || loading || busyId || !actionFocus.current) return;
    const target = actionFocus.current;
    actionFocus.current = null;
    if (document.activeElement !== contentRef.current) return;
    if (target.isConnected && !target.matches(":disabled")) target.focus();
    else headingRef.current?.focus();
  }, [busyId, loading, notifications, open]);

  const rememberFocus = () => {
    const active = document.activeElement;
    if (active instanceof HTMLElement && active !== contentRef.current && contentRef.current?.contains(active)) {
      actionFocus.current = active;
      contentRef.current.focus();
    }
  };

  const markRead = async (notification: UserNotification) => {
    if (notification.readAtUtc) return true;
    if (pendingAction.current) return false;
    pendingAction.current = true;
    const generation = openGeneration.current;
    rememberFocus();
    setBusyId(notification.id);
    try {
      await api.post(`/notifications/${notification.id}/read`);
      if (generation !== openGeneration.current) return false;
      setNotifications((items) => items.map((item) => item.id === notification.id
        ? { ...item, readAtUtc: new Date().toISOString() }
        : item));
      setError(null);
      onChanged();
      return true;
    } catch (requestError) {
      if (generation === openGeneration.current) setError({ cause: requestError, action: true });
      return false;
    } finally {
      if (generation === openGeneration.current) { pendingAction.current = false; setBusyId(null); }
    }
  };

  const dismiss = async (notification: UserNotification) => {
    if (pendingAction.current) return;
    pendingAction.current = true;
    const generation = openGeneration.current;
    rememberFocus();
    setBusyId(notification.id);
    try {
      await api.delete(`/notifications/${notification.id}`);
      if (generation !== openGeneration.current) return;
      setNotifications((items) => items.filter((item) => item.id !== notification.id));
      setError(null);
      onChanged();
    } catch (requestError) {
      if (generation === openGeneration.current) setError({ cause: requestError, action: true });
    } finally {
      if (generation === openGeneration.current) { pendingAction.current = false; setBusyId(null); }
    }
  };

  const openNotification = async (notification: UserNotification) => {
    if (!notification.linkPath || pendingAction.current) return;
    const generation = openGeneration.current;
    if (!notification.readAtUtc && !await markRead(notification)) return;
    if (generation !== openGeneration.current) return;
    pendingAction.current = true;
    onClose();
    onNavigate(notification.linkPath);
  };

  return (
    <Popover
      open={open}
      anchorEl={anchorEl}
      onClose={onClose}
      anchorOrigin={{ vertical: "bottom", horizontal: "right" }}
      transformOrigin={{ vertical: "top", horizontal: "right" }}
      slotProps={{
        paper: {
          role: "dialog",
          "aria-label": t("notificationsPanel"),
          sx: {
            mt: 1,
            width: "min(420px, calc(100vw - 24px))",
            maxHeight: "min(70vh, 600px)",
            borderRadius: 1,
            display: "flex",
            flexDirection: "column",
            overflow: "hidden",
          },
        },
      }}
    >
      <Stack direction="row" alignItems="center" justifyContent="space-between" sx={{ px: 2, py: 1.5, flexShrink: 0 }}>
        <Box>
          <Typography component="h2" variant="sectionTitle" ref={headingRef} tabIndex={-1}>{t("notifications")}</Typography>
          <Typography variant="caption" color="text.secondary">{t("notificationsRecent")}</Typography>
        </Box>
        <Tooltip title={t("close")}>
          <IconButton size="small" aria-label={t("close")} onClick={onClose}><CloseIcon fontSize="small" /></IconButton>
        </Tooltip>
      </Stack>
      <Divider />

      <Box ref={contentRef} role="region" aria-label={t("notificationsRecent")} tabIndex={-1} aria-busy={loading} sx={{ overflowY: "auto", minHeight: 0, p: 1 }}>
        {loading ? <Box role="status" sx={{ py: 4, display: "grid", placeItems: "center" }}><CircularProgress size={28} aria-label={t("loading")} /></Box> : null}
        {error ? <Alert severity="error" action={<Button color="inherit" size="small" disabled={loading || busyId !== null} onClick={() => { rememberFocus(); void load(); }}>{t("retry")}</Button>} sx={{ m: 0.5, overflowWrap: "anywhere" }}>{getApiErrorMessage(error.cause, t(error.action ? "notificationsActionFailed" : "notificationsLoadFailed"))}</Alert> : null}
        {!loading && !error && notifications.length === 0 ? (
          <Box sx={{ py: 4, px: 2, textAlign: "center" }}>
            <Typography sx={{ fontWeight: 800 }}>{t("notificationsEmptyTitle")}</Typography>
            <Typography variant="body2" color="text.secondary">{t("notificationsEmptyBody")}</Typography>
          </Box>
        ) : null}
        {!loading ? notifications.map((notification) => (
          <Box
            key={notification.id}
            sx={{
              p: 1.5,
              mb: 0.75,
              borderRadius: 1,
              border: "1px solid",
              borderColor: "divider",
              bgcolor: notification.readAtUtc ? "transparent" : "action.selected",
            }}
          >
            <Typography sx={{ fontWeight: notification.readAtUtc ? 600 : 700, overflowWrap: "anywhere" }}>{notification.title}</Typography>
            {!notification.readAtUtc ? <Typography variant="caption" color="text.secondary">{t("notificationsUnread")}</Typography> : null}
            <Typography variant="body2" color="text.secondary" sx={{ mt: 0.25, overflowWrap: "anywhere" }}>{notification.message}</Typography>
            <Typography variant="caption" color="text.secondary">{notificationDateLabel(notification.createdAtUtc, language === "nb" ? "nb-NO" : "en-GB")}</Typography>
            <Stack direction="row" useFlexGap spacing={0.5} alignItems="center" sx={{ mt: 0.75, flexWrap: "wrap", "& .MuiButton-root": { whiteSpace: "normal", overflowWrap: "anywhere", minHeight: 40 } }}>
              {notification.linkPath ? <Button size="small" disabled={busyId !== null} onClick={() => void openNotification(notification)}>{t("notificationsOpen")}</Button> : null}
              {!notification.readAtUtc ? (
                <Button size="small" startIcon={<DoneIcon />} disabled={busyId !== null} onClick={() => void markRead(notification)}>{t("notificationsMarkRead")}</Button>
              ) : null}
              <Button size="small" color="inherit" startIcon={<DeleteOutlineIcon />} disabled={busyId !== null} onClick={() => void dismiss(notification)}>{t("notificationsDismiss")}</Button>
            </Stack>
          </Box>
        )) : null}
      </Box>

      <Divider />
      <Box sx={{ p: 1, flexShrink: 0 }}>
        <Button fullWidth onClick={() => { onClose(); onNavigate("/operations"); }}>{t("notificationsViewAll")}</Button>
      </Box>
    </Popover>
  );
}