/**
 * An "entry" is an element with a `[data-value]` attribute that is a valid ISO8601 string.
 *
 * It has an `.idl` property that represents the date range of this entry
 *
 * @module
 */

import { iso8601ToDate } from "@hesxenon/prelude/Codec.js";
import * as Either from "@hesxenon/prelude/Either.js";
import { pipe } from "@hesxenon/prelude/Function.js";
import * as Option from "@hesxenon/prelude/Option.js";

export type Entry = {
  element: HTMLElement;
  readonly content: string;
  readonly start: Date;
  readonly end: Date;
};
export namespace Entry {
  type Meta = Omit<Entry, "element">;
  type InitializedElement = HTMLElement & {
    [k in typeof entryIdlCacheKey]: Meta;
  };
  const entryIdlCacheKey = Symbol("entry idl cache key");

  const isInitialized = (
    element: HTMLElement,
  ): element is InitializedElement => {
    const values = (element as InitializedElement)[entryIdlCacheKey];
    return (
      values != null && values.content === element.getAttribute("data-value")
    );
  };

  export const fromElement = (
    datepicker: UwcDatepickerElement,
    element: HTMLElement,
  ): Entry | undefined => {
    return isInitialized(element)
      ? { element, ...element[entryIdlCacheKey] }
      : pipe(
          Option.fromNullable(element.getAttribute("data-value")),
          Option.flatMap((content) =>
            pipe(
              iso8601ToDate.decode(content),
              Either.match(
                () => Option.none,
                (start) => {
                  const meta: Meta = {
                    start,
                    end: datepicker.currentView.addOneUnit(start),
                    content,
                  };
                  (element as InitializedElement)[entryIdlCacheKey] = meta;
                  return Option.some<Entry>({ element, ...meta });
                },
              ),
            ),
          ),
          Option.toUndefined,
        );
  };

  export const fromEventTarget = (
    datepicker: UwcDatepickerElement,
    target: EventTarget | null,
  ): Entry | undefined => {
    if (!(target instanceof HTMLElement)) {
      return;
    }
    const element = target.closest<HTMLElement>("[data-value]");
    if (element == null || !datepicker.contains(element)) {
      return;
    }

    return fromElement(datepicker, element);
  };
}

export type Idl = Date | string | number;
export namespace Idl {
  export const asComparable = (idl: Idl) =>
    typeof idl === "string" ||
    idl === Number.NEGATIVE_INFINITY ||
    idl === Number.POSITIVE_INFINITY
      ? idl
      : idl instanceof Date
        ? idl.toISOString()
        : new Date(idl).toISOString();

  export const asDate = (idl: Idl) =>
    idl instanceof Date ? idl : new Date(idl);
}

export type Page = {
  entries: Entry[];
};