import { useMemo, useState } from "react";
import { Button, Group, Modal, Stack, Text, TextInput, Textarea } from "@mantine/core";
import toast from "react-hot-toast";

import { trainSchedulingService } from "@/services/trainScheduling.service";

/** `min` for a `datetime-local` input: now, in the browser's local zone. */
function nowLocalDateTime(): string {
  const now = new Date();
  const pad = (n: number) => String(n).padStart(2, "0");
  return (
    `${now.getFullYear()}-${pad(now.getMonth() + 1)}-${pad(now.getDate())}` +
    `T${pad(now.getHours())}:${pad(now.getMinutes())}`
  );
}

export function RescheduleTrainDialog({
  scheduleId,
  currentBookingIds,
  opened,
  onClose,
  onComplete,
}: {
  scheduleId: string;
  currentBookingIds: string[];
  opened: boolean;
  onClose: () => void;
  onComplete?: () => void;
}) {
  const [newDepartureDate, setNewDepartureDate] = useState("");
  const [reason, setReason] = useState("");
  const [loading, setLoading] = useState(false);
  // Earliest selectable departure, refreshed each time the dialog opens.
  const minDepartureDate = useMemo(
    () => (opened ? nowLocalDateTime() : ""),
    [opened],
  );

  const handleSubmit = async () => {
    if (!newDepartureDate) {
      toast.error("Select a new departure date");
      return;
    }
    if (new Date(newDepartureDate).getTime() < Date.now()) {
      toast.error("New departure must be in the future");
      return;
    }
    setLoading(true);
    try {
      await trainSchedulingService.maintenanceReschedule(scheduleId, {
        incomingBookingIds: currentBookingIds,
        newDepartureDate: new Date(newDepartureDate).toISOString(),
        reason,
      });
      toast.success("Train rescheduled for maintenance");
      onComplete?.();
      onClose();
    } catch {
      toast.error("Reschedule failed");
    } finally {
      setLoading(false);
    }
  };

  return (
    <Modal opened={opened} onClose={onClose} title="Reschedule train (maintenance)" radius="lg">
      <Stack gap="md">
        <Text size="sm" c="dimmed">
          Updates departure and rebalances bookings on this train. Displaced bookings return to
          the operations queue when capacity is insufficient.
        </Text>
        <TextInput
          label="New departure"
          type="datetime-local"
          min={minDepartureDate}
          value={newDepartureDate}
          onChange={(e) => setNewDepartureDate(e.target.value)}
        />
        <Textarea
          label="Reason"
          placeholder="e.g. Locomotive maintenance"
          value={reason}
          onChange={(e) => setReason(e.target.value)}
        />
        <Group justify="flex-end">
          <Button variant="default" onClick={onClose}>
            Cancel
          </Button>
          <Button loading={loading} onClick={handleSubmit}>
            Reschedule
          </Button>
        </Group>
      </Stack>
    </Modal>
  );
}