/** Date filtering for the oil/diesel "Booked out" table. Days are South African calendar days. */
export type LogPreset = "today" | "week" | "month" | "all" | "range";

const dayFmt = new Intl.DateTimeFormat("en-CA", { timeZone: "Africa/Johannesburg" });

/** "2026-10-22" for an instant, in SA time. PocketBase stamps look like "2026-10-22 08:15:00.000Z". */
export function saDay(stamp: string): string {
  if (!stamp || Number.isNaN(new Date(stamp.replace(" ", "T")).getTime())) return "";
  return dayFmt.format(new Date(stamp.replace(" ", "T")));
}

function addDays(day: string, n: number): string {
  const d = new Date(`${day}T00:00:00Z`);
  d.setUTCDate(d.getUTCDate() + n);
  return d.toISOString().slice(0, 10);
}

/** Inclusive [from, to] day bounds for a preset; null bound = open. Weeks start Monday. */
export function presetBounds(preset: LogPreset, today: string, from = "", to = ""): [string | null, string | null] {
  switch (preset) {
    case "today": return [today, today];
    case "week": {
      const dow = (new Date(`${today}T00:00:00Z`).getUTCDay() + 6) % 7; // Mon=0
      return [addDays(today, -dow), today];
    }
    case "month": return [`${today.slice(0, 7)}-01`, today];
    case "range": return [from || null, to || null];
    default: return [null, null];
  }
}

export function inBounds(day: string, [from, to]: [string | null, string | null]): boolean {
  if (!day) return !from && !to; // undated rows only show when no period is applied
  return (!from || day >= from) && (!to || day <= to);
}

/**
 * When a movement happened. `created` is NOT reliable on oil_stock_movements (the collection
 * was made through the API, so the field never auto-fills), so book-outs store a full ISO
 * instant in `occurred_on`. Older rows hold a bare date. Returns "" when neither is usable.
 */
export function movementAt(m: { [k: string]: any }): string {
  for (const v of [m.occurred_on, m.created] as (string | undefined)[]) {
    if (v && !Number.isNaN(new Date(v.replace(" ", "T")).getTime())) return v;
  }
  return "";
}