import { timeMonday, timeSunday, timeDay, timeMonth } from 'd3-time';
import { timeFormat } from 'd3-time-format';
import type { DayEntry } from '../types';

export const DAY_LABELS_MONDAY = ['Mon', '', 'Wed', '', 'Fri', '', ''];
export const DAY_LABELS_SUNDAY = ['Sun', '', 'Tue', '', 'Thu', '', 'Sat'];

export function getDayLabels(weekStart: string): string[] {
  return weekStart === 'sunday' ? DAY_LABELS_SUNDAY : DAY_LABELS_MONDAY;
}

export const MONTH_FORMAT = timeFormat('%b');
export const DATE_FORMAT = timeFormat('%Y-%m-%d');
export const DISPLAY_FORMAT = timeFormat('%a, %b %-d, %Y');

export interface DayCell {
  date: Date;
  dateStr: string;
  entry: DayEntry | null;
  week: number;
  day: number;
  isWeekend: boolean;
}

export function buildDateMap(days: DayEntry[]): Map<string, DayEntry> {
  const map = new Map<string, DayEntry>();
  for (const d of days) {
    map.set(d.date, d);
  }
  return map;
}

export function getWeekInterval(weekStart: string) {
  return weekStart === 'sunday' ? timeSunday : timeMonday;
}

export function generateCells(
  begin: Date,
  end: Date,
  dateMap: Map<string, DayEntry>,
  weekStart: string = 'monday',
): DayCell[] {
  const weekInterval = getWeekInterval(weekStart);
  const firstWeekDay = weekInterval.floor(begin);
  const cells: DayCell[] = [];
  let current = new Date(begin);

  while (current <= end) {
    const dateStr = DATE_FORMAT(current);
    const weeksSinceStart = weekInterval.count(firstWeekDay, current);
    const jsDay = current.getDay(); // 0=Sunday, 6=Saturday
    const dayOfWeek = weekStart === 'sunday'
      ? jsDay // Sunday=0 already first
      : (jsDay + 6) % 7; // Monday=0, Sunday=6
    const isWeekend = jsDay === 0 || jsDay === 6;

    cells.push({
      date: new Date(current),
      dateStr,
      entry: dateMap.get(dateStr) || null,
      week: weeksSinceStart,
      day: dayOfWeek,
      isWeekend,
    });

    current = timeDay.offset(current, 1);
  }

  return cells;
}