declare namespace kendo {
  namespace ui {
    interface Calendar {
      _todayClick(e: CalendarEvent): void;
    }
  }
}

namespace kendoExt {
  export type CalendarDepth = 'month' | 'year' | 'decade' | 'century';

  export interface MultiCalendarOptions extends kendo.ui.CalendarOptions {
    values?: Date[];
    maxSelectedItems?: number | null;
    cleanSelectedItemsOnTodayClick?: boolean;
  }

  export class MultiCalendar extends kendo.ui.Calendar {
    public static fn: MultiCalendar;

    private static _views: { [key: string]: number } = {
      month: 0,
      year: 1,
      decade: 2,
      century: 3
    };

    public options: MultiCalendarOptions;

    private _values: Date[];

    constructor(element: Element | JQuery | string, options?: MultiCalendarOptions) {
      super(element as Element, options);

      this._values = (options && options.values) || [];

      (this as any).navigate();
    }

    private static isSameDate(first: Date, second: Date) {
      return (
        first &&
        second &&
        first.getFullYear() === second.getFullYear() &&
        first.getMonth() === second.getMonth() &&
        first.getDate() === second.getDate()
      );
    }

    public values(newValues?: Date[]): Date[] {
      if (newValues !== undefined && this.canSelectItems(newValues.length)) {
        const valuesToClear = this._values.filter(value => {
          return newValues.every(newValue => !MultiCalendar.isSameDate(value, newValue));
        });

        let i = null;

        this._values = newValues.filter((item, index) => {
          for (i = index - 1; i >= 0; i -= 1) {
            if (MultiCalendar.isSameDate(item, newValues[i])) {
              return false;
            }
          }

          return true;
        });

        this.updateSelection(this._values, valuesToClear);
      }

      return this._values;
    }

    public value(newValue?: Date | string): Date {
      const valueIndex: number = (this._values || [])
        .reduce(
          (acc, val, index) => (MultiCalendar.isSameDate(val, newValue as Date) ? index : acc),
          -1
        );

      const shouldAddNewValue = valueIndex === -1;
      const canAddNewValue =
        shouldAddNewValue && this._values && this.canSelectItems(this._values.length + 1);

      if (!shouldAddNewValue || canAddNewValue) {
        super.value(newValue as Date);
      }

      if (newValue) {
        let valuesToClear: Date[] = [];

        if (canAddNewValue) {
          this._values.push(newValue as Date);
        } else if (!shouldAddNewValue) {
          valuesToClear = this._values.splice(valueIndex, 1);
        }

        this.updateSelection(this._values, valuesToClear);
      }

      return super.value();
    }

    public navigate(value: Date, view: string) {
      super.navigate(value, view);

      this.updateSelection(this._values);
    }

    public navigateDown(value: Date) {
      if (!value) {
        return;
      }

      const index: number = (this as any)._index;

      if (index === MultiCalendar._views[this.options.depth as string]) {
        this.value(value);
        this.trigger('change');

        return;
      }

      this.navigate(value, (index - 1) as any);
    }

    public _todayClick(e: kendo.ui.CalendarEvent) {
      this.selectToday();

      super._todayClick(e);
    }

    private canSelectItems(amount: number): boolean {
      const max = this.options.maxSelectedItems;

      return !max || amount <= max;
    }

    private cellByDate(value: string): JQuery {
      return (this as any)._table.find('td').filter(function () {
        return $(this.firstChild).attr((kendo as any).attr('value')) === value;
      });
    }

    private updateSelection(valuesToSelect: Date[], valuesToClear: Date[] = []) {
      if ((this as any)._index === MultiCalendar._views[this.options.depth as string]) {
        const selected = 'k-state-selected';

        const _value = (this as any)._value;

        if (_value) {
          this.cellByDate(this.view().toDateString(_value)).removeClass(selected);
        }

        valuesToSelect.forEach(value => {
          this.cellByDate(this.view().toDateString(value)).addClass(selected);
        });

        valuesToClear.forEach(value => {
          this.cellByDate(this.view().toDateString(value)).removeClass(selected);
        });
      }
    }

    private selectToday = () => {
      const today = new Date();
      const value = new Date(today.getFullYear(), today.getMonth(), today.getDate());
      const values = this.options.cleanSelectedItemsOnTodayClick
        ? [value]
        : [...this._values, value];

      this.values(values);
    }
  }

  MultiCalendar.fn = MultiCalendar.prototype;
  MultiCalendar.fn.options = {
    ...kendo.ui.Calendar.fn.options,
    ...{
      name: 'MultiCalendar',
      values: [],
      maxSelectedItems: null,
      cleanSelectedItemsOnTodayClick: true
    }
  };

  kendo.ui.plugin(MultiCalendar);
}

interface JQuery {
  kendoMultiCalendar(options?: kendoExt.MultiCalendarOptions): JQuery;
  data(key: 'kendoMultiCalendar'): kendoExt.MultiCalendar;
}