import { Granularity } from "../types/dashboard";

export function iso8601Week(value: Date) {
  // Create a copy of the current date, we don't want to mutate the original
  const date = new Date(value.getTime());

  // Find Thursday of this week starting on Monday
  date.setDate(date.getDate() + 4 - (date.getDay() || 7));
  const thursday = date.getTime();

  // Find January 1st
  date.setMonth(0); // January
  date.setDate(1); // 1st
  const jan1st = date.getTime();

  // Round the amount of days to compensate for daylight saving time
  const days = Math.round((thursday - jan1st) / 86400000); // 1 day = 86400000 ms
  return Math.floor(days / 7) + 1;
}

export function getDateValueFormatter(granularity: Granularity) {
  // TODO: Add date range args to allow less verbose labels, e.g. only show year when
  //       range span multiple years
  return (value: Date): string => {
    switch (granularity) {
      case "day":
        return value.toLocaleDateString("default", { month: "short", day: "numeric" });
      case "week":
        return `v${iso8601Week(value)}\n${value.getFullYear().toString()}`;
      case "month":
        return value.toLocaleString("default", { month: "short" });
      case "quarter":
        return `Q${Math.floor(value.getMonth() / 3) + 1}\n${value.getFullYear().toString()}`;
      case "year":
        return value.getFullYear().toString();
    }
  };
}