import * as React from "react";
import flatpickr from "flatpickr";
import "flatpickr/dist/flatpickr.min.css";

/** Subset of flatpickr instance API we use (avoids tight coupling to type export paths). */
interface FlatpickrHandle {
  destroy(): void;
  readonly selectedDates: Date[];
  setDate(date: Date | string, triggerChange?: boolean, formatStr?: string): void;
  clear(triggerChange?: boolean): void;
  set<K extends string>(key: K, value: unknown): void;
  input: HTMLInputElement;
}

function pad2(n: number) {
  return String(n).padStart(2, "0");
}

/** Same string shape previously used for `datetime-local` inputs (local wall time). */
export function toDatetimeLocalValue(isoOrDate: string | Date | undefined): string {
  if (!isoOrDate) return "";
  const d = typeof isoOrDate === "string" ? new Date(isoOrDate) : isoOrDate;
  if (Number.isNaN(d.getTime())) return "";
  return `${d.getFullYear()}-${pad2(d.getMonth() + 1)}-${pad2(d.getDate())}T${pad2(d.getHours())}:${pad2(d.getMinutes())}`;
}

function parseDatetimeLocal(s: string): Date | undefined {
  if (!s.trim()) return undefined;
  const d = new Date(s);
  return Number.isNaN(d.getTime()) ? undefined : d;
}

function parseDateOnly(s: string): Date | undefined {
  const raw = s.trim();
  if (!raw) return undefined;
  if (/^\d{4}-\d{2}-\d{2}$/.test(raw)) {
    const [y, m, d] = raw.split("-").map(Number);
    const date = new Date(y, m - 1, d);
    return Number.isNaN(date.getTime()) ? undefined : date;
  }
  const d = new Date(raw);
  return Number.isNaN(d.getTime()) ? undefined : d;
}

/** Local calendar date as `YYYY-MM-DD`. */
export function toDateOnlyValue(isoOrDate: string | Date | undefined): string {
  if (!isoOrDate) return "";
  const d = typeof isoOrDate === "string" ? parseDateOnly(isoOrDate) : isoOrDate;
  if (!d || Number.isNaN(d.getTime())) return "";
  return `${d.getFullYear()}-${pad2(d.getMonth() + 1)}-${pad2(d.getDate())}`;
}

export interface FlatpickrDateInputProps {
  value: string;
  onChange: (value: string) => void;
  style?: React.CSSProperties;
  disabled?: boolean;
  placeholder?: string;
  hasError?: boolean;
}

/** Date-only picker (Flatpickr) that reads/writes `YYYY-MM-DD`. */
export function FlatpickrDateInput({
  value,
  onChange,
  style,
  disabled,
  placeholder = "Select date…",
  hasError,
}: FlatpickrDateInputProps) {
  const inputRef = React.useRef<HTMLInputElement>(null);
  const fpRef = React.useRef<FlatpickrHandle | null>(null);

  React.useEffect(() => {
    const el = inputRef.current;
    if (!el) return;

    const fp = flatpickr(el, {
      enableTime: false,
      dateFormat: "Y-m-d",
      allowInput: true,
      defaultDate: parseDateOnly(value),
      onChange: dates => {
        const d = dates[0];
        onChange(d ? toDateOnlyValue(d) : "");
      },
    }) as FlatpickrHandle;
    fpRef.current = fp;

    return () => {
      fp.destroy();
      fpRef.current = null;
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps -- init once
  }, []);

  React.useEffect(() => {
    const fp = fpRef.current;
    if (!fp) return;

    const selected = fp.selectedDates[0];
    const cur = selected ? toDateOnlyValue(selected) : "";
    if (value === cur) return;

    const d = parseDateOnly(value);
    if (d) fp.setDate(d, false);
    else fp.clear(false);
  }, [value]);

  React.useEffect(() => {
    const fp = fpRef.current;
    if (!fp) return;
    const input = fp.input as HTMLInputElement;
    input.disabled = !!disabled;
    fp.set("clickOpens", !disabled);
  }, [disabled]);

  return (
    <input
      ref={inputRef}
      type="text"
      placeholder={placeholder}
      readOnly={false}
      autoComplete="off"
      style={{
        ...style,
        ...(hasError ? { borderColor: "var(--destructive)" } : {}),
      }}
    />
  );
}

export interface FlatpickrDatetimeInputProps {
  value: string;
  onChange: (value: string) => void;
  style?: React.CSSProperties;
  disabled?: boolean;
  placeholder?: string;
  hasError?: boolean;
}

/**
 * Date + time picker (Flatpickr) that reads/writes the same `YYYY-MM-DDTHH:mm` local values
 * as native `datetime-local` inputs.
 */
export function FlatpickrDatetimeInput({
  value,
  onChange,
  style,
  disabled,
  placeholder = "Select date & time…",
  hasError,
}: FlatpickrDatetimeInputProps) {
  const inputRef = React.useRef<HTMLInputElement>(null);
  const fpRef = React.useRef<FlatpickrHandle | null>(null);

  React.useEffect(() => {
    const el = inputRef.current;
    if (!el) return;

    const fp = flatpickr(el, {
      enableTime: true,
      time_24hr: true,
      dateFormat: "Y-m-d H:i",
      allowInput: true,
      defaultDate: parseDatetimeLocal(value),
      onChange: dates => {
        const d = dates[0];
        onChange(d ? toDatetimeLocalValue(d) : "");
      },
    }) as FlatpickrHandle;
    fpRef.current = fp;

    return () => {
      fp.destroy();
      fpRef.current = null;
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps -- init once
  }, []);

  React.useEffect(() => {
    const fp = fpRef.current;
    if (!fp) return;

    const selected = fp.selectedDates[0];
    const cur = selected ? toDatetimeLocalValue(selected) : "";
    if (value === cur) return;

    const d = parseDatetimeLocal(value);
    if (d) fp.setDate(d, false);
    else fp.clear(false);
  }, [value]);

  React.useEffect(() => {
    const fp = fpRef.current;
    if (!fp) return;
    const input = fp.input as HTMLInputElement;
    input.disabled = !!disabled;
    fp.set("clickOpens", !disabled);
  }, [disabled]);

  return (
    <input
      ref={inputRef}
      type="text"
      placeholder={placeholder}
      readOnly={false}
      autoComplete="off"
      style={{
        ...style,
        ...(hasError ? { borderColor: "var(--destructive)" } : {}),
      }}
    />
  );
}