import { ChevronLeftIcon, ChevronRightIcon } from "@heroicons/react/solid";
import dayjs from "dayjs";
import isToday from "dayjs/plugin/isToday";
import { useMemo, useState } from "react";

import classNames from "@calcom/lib/classNames";
import { daysInMonth, yyyymmdd } from "@calcom/lib/date-fns";
import { weekdayNames } from "@calcom/lib/weekday";

dayjs.extend(isToday);

export type DatePickerProps = {
  /** which day of the week to render the calendar. Usually Sunday (=0) or Monday (=1) - default: Sunday */
  weekStart?: 0 | 1 | 2 | 3 | 4 | 5 | 6;
  /** Fires whenever a selected date is changed. */
  onChange: (date: Date) => void;
  /** Fires when the month is changed. */
  onMonthChange?: (date: Date) => void;
  /** which date is currently selected (not tracked from here) */
  selected?: Date;
  /** defaults to current date. */
  minDate?: Date;
  /** Furthest date selectable in the future, default = UNLIMITED */
  maxDate?: Date;
  /** locale, any IETF language tag, e.g. "hu-HU" - defaults to Browser settings */
  locale: string;
  /** Defaults to [], which dates are not bookable. Array of valid dates like: ["2022-04-23", "2022-04-24"] */
  excludedDates?: string[];
  /** defaults to all, which dates are bookable (inverse of excludedDates) */
  includedDates?: string[];
  /** allows adding classes to the container */
  className?: string;
  /** Shows a small loading spinner next to the month name */
  isLoading?: boolean;
};

const Day = ({
  date,
  active,
  ...props
}: JSX.IntrinsicElements["button"] & { active: boolean; date: Date }) => {
  return (
    <button
      style={props.disabled ? {} : {}}
      className={classNames(
        "absolute top-0 left-0 right-0 bottom-0 mx-auto w-full rounded-sm border border-transparent text-center",
        props.disabled
          ? "text-bookinglighter cursor-default font-light"
          : "hover:border-brand font-medium dark:hover:border-white",
        active
          ? "bg-brand text-brandcontrast dark:bg-darkmodebrand dark:text-darkmodebrandcontrast"
          : !props.disabled
          ? " bg-gray-100 dark:bg-gray-600 dark:text-white"
          : ""
      )}
      data-testid="day"
      data-disabled={props.disabled}
      {...props}>
      {date.getDate()}
      {dayjs(date).isToday() && <span className=" absolute left-0 bottom-1 mx-auto w-full text-4xl">.</span>}
    </button>
  );
};

const Days = ({
  minDate,
  excludedDates = [],
  includedDates = [],
  browsingDate,
  weekStart,
  selected,
  ...props
}: Omit<DatePickerProps, "locale" | "className" | "weekStart"> & {
  browsingDate: Date;
  weekStart: number;
}) => {
  // Create placeholder elements for empty days in first week
  const weekdayOfFirst = new Date(new Date(browsingDate).setDate(1)).getDay();
  // memoize to prevent a flicker on redraw on the current day
  const minDateValueOf = useMemo(() => {
    return minDate?.valueOf() || new Date().valueOf();
  }, [minDate]);

  const days: (Date | null)[] = Array((weekdayOfFirst - weekStart + 7) % 7).fill(null);
  for (let day = 1, dayCount = daysInMonth(browsingDate); day <= dayCount; day++) {
    const date = new Date(new Date(browsingDate).setDate(day));
    days.push(date);
  }

  return (
    <>
      {days.map((day, idx) => (
        <div
          key={day === null ? `e-${idx}` : `day-${day}`}
          style={{
            paddingTop: "100%",
          }}
          className="relative w-full">
          {day === null ? (
            <div key={`e-${idx}`} />
          ) : (
            <Day
              date={day}
              onClick={() => props.onChange(day)}
              disabled={
                !includedDates.includes(yyyymmdd(day)) ||
                excludedDates.includes(yyyymmdd(day)) ||
                day.valueOf() < minDateValueOf
              }
              active={selected ? yyyymmdd(selected) === yyyymmdd(day) : false}
            />
          )}
        </div>
      ))}
    </>
  );
};

const Spinner = () => (
  <svg
    className="mt-[-9px] mr-1 inline h-5 w-5 animate-spin text-black dark:text-white"
    xmlns="http://www.w3.org/2000/svg"
    fill="none"
    viewBox="0 0 24 24">
    <circle className="opacity-25" cx={12} cy={12} r={10} stroke="currentColor" strokeWidth={4} />
    <path
      className="opacity-75"
      fill="currentColor"
      d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"
    />
  </svg>
);

const DatePicker = ({
  weekStart = 0,
  className,
  locale,
  selected,
  onMonthChange,
  isLoading = false,
  ...passThroughProps
}: DatePickerProps) => {
  const [month, setMonth] = useState(selected ? selected.getMonth() : new Date().getMonth());

  const changeMonth = (newMonth: number) => {
    setMonth(newMonth);
    if (onMonthChange) {
      const d = new Date();
      d.setMonth(newMonth, 1);
      onMonthChange(d);
    }
  };

  return (
    <div className={className}>
      <div className="mb-4 flex justify-between text-xl font-light">
        <span className="w-1/2 dark:text-white">
          <strong className="text-bookingdarker dark:text-white">
            {new Date(new Date().setMonth(month)).toLocaleString(locale, { month: "long" })}
          </strong>{" "}
          <span className="text-bookinglight">{new Date(new Date().setMonth(month)).getFullYear()}</span>
        </span>
        <div>
          {isLoading && <Spinner />}
          <button
            onClick={() => changeMonth(month - 1)}
            className={classNames(
              "group p-1 hover:text-black ltr:mr-2 rtl:ml-2 dark:hover:text-white",
              month <= new Date().getMonth() &&
                "text-bookinglighter disabled:text-bookinglighter dark:text-gray-600"
            )}
            disabled={month <= new Date().getMonth()}
            data-testid="decrementMonth">
            <ChevronLeftIcon className="h-5 w-5" />
          </button>
          <button className="group p-1" onClick={() => changeMonth(month + 1)} data-testid="incrementMonth">
            <ChevronRightIcon className="h-5 w-5 group-hover:text-black dark:group-hover:text-white" />
          </button>
        </div>
      </div>
      <div className="border-bookinglightest grid grid-cols-7 gap-4 border-t border-b text-center dark:border-gray-800 sm:border-0">
        {weekdayNames(locale, weekStart, "short").map((weekDay) => (
          <div key={weekDay} className="text-bookinglight my-4 text-xs uppercase tracking-widest">
            {weekDay}
          </div>
        ))}
      </div>
      <div className="grid grid-cols-7 gap-2 text-center">
        <Days
          browsingDate={new Date(new Date().setMonth(month))}
          weekStart={weekStart}
          selected={selected}
          {...passThroughProps}
        />
      </div>
    </div>
  );
};

export default DatePicker;