//Calendar implementation for the HTWK Leipzig timetable. Evaluation and display of the individual dates in iCal format.
//Copyright (C) 2024 HTWKalender support@htwkalender.de

//This program is free software: you can redistribute it and/or modify
//it under the terms of the GNU Affero General Public License as published by
//the Free Software Foundation, either version 3 of the License, or
//(at your option) any later version.

//This program is distributed in the hope that it will be useful,
//but WITHOUT ANY WARRANTY; without even the implied warranty of
//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//GNU Affero General Public License for more details.

//You should have received a copy of the GNU Affero General Public License
//along with this program.  If not, see <https://www.gnu.org/licenses/>.

import ICAL from "ical.js";
import { CalendarComponent } from "ical";

/**
 * Interface for the color distinction event
 * @param title Event name
 * @param color Color code for the event
 */
export interface ColorDistinctionEvent {
  summary: string | undefined;
  color: string;
}

/**
 * Parses iCal data and returns an array of calendar components
 * @param icalData iCal data to parse
 * @returns Array of calendar components
 */
export function parseICalData(
  icalData: string | undefined,
): CalendarComponent[] {
  if (icalData === undefined || !icalData) {
    return [];
  } else {
    const jCalData = ICAL.parse(icalData);
    const comp = new ICAL.Component(jCalData);
    const vEvents = comp.getAllSubcomponents("vevent");
    const events: CalendarComponent[] = vEvents.map((vevent: CalendarComponent) => {
      return new ICAL.Event(vevent);
    });
    const colorDistinctionEvents: ColorDistinctionEvent[] = extractedColorizedEvents(events);

    return vEvents.map((vevent: CalendarComponent) => {
      const event = new ICAL.Event(vevent);

      return {
        title: event.summary,
        start: event.startDate.toJSDate(),
        end: event.endDate.toJSDate(),
        notes: event.description,
        allDay: event.startDate.isDate,
        color: colorDistinctionEvents.find(
          (e: ColorDistinctionEvent) => e.summary === event.summary,
        )?.color,
        id: event.uid,
        location: event.location,
      };
    });
  }
}

/**
 * Extracts the event names and assigns a color to each event
 * @param vEvents Array of calendar components
 * @returns Array of objects with event name and color
 */
function extractedColorizedEvents(
  vEvents: CalendarComponent[],
): ColorDistinctionEvent[] {
  return colorizeEvents(filterEventsDistinct(vEvents));
}

/**
 * Filters out duplicate events
 * @param vEvents Array of calendar components
 * @returns Array of calendar components without duplicates
 */
function filterEventsDistinct(
  vEvents: CalendarComponent[],
): CalendarComponent[] {
  return vEvents.filter(
    (vevent: CalendarComponent, index: number, self: CalendarComponent[]) => {
      return (
        self.findIndex((v) => {
          return v.summary === vevent.summary;
        }) === index
      );
    },
  );
}

/**
 * Assigns a color to each event
 * @param vEvents Array of calendar components
 * @returns Array of objects with event name and color
 */
function colorizeEvents(vEvents: CalendarComponent[]): ColorDistinctionEvent[] {
  return vEvents.map((vevent: CalendarComponent) => {
    const colors: string[] = [
      "var(--htwk-rot-200)",
      "var(--htwk-gruen-300)",
      "var(--htwk-magenta-400)",
      "var(--htwk-cyan-400)",
      "var(--htwk-silbergrau-600)",
      "var(--htwk-yellow-300)",
      "var(--htwk-blau-300)",
      "var(--htwk-dunkelblau-200)",
      "var(--htwk-rot-400)",
      "var(--htwk-gruen-400)",
      "var(--htwk-blau-200)",
    ];

    const randomColor =
      colors[
        vEvents.findIndex((e: CalendarComponent) => {
          return e.summary === vevent.summary;
        }) % colors.length
      ];

    return {
      summary: vevent.summary,
      color: randomColor,
    };
  });
}

// Exported for testing
export const exportedForTesting = {
  extractedColorizedEvents,
  filterEventsDistinct,
  colorizeEvents,
};