import { InvalidNominalLocalError } from "./errors.js";
import type { NominalLocal, WallClock } from "./timezone.js";

/** Format a wall clock as a nominal local date-time string, `YYYY-MM-DDTHH:mm`. */
export function formatNominal(wall: WallClock): NominalLocal {
  const y = String(wall.year).padStart(4, "0");
  const mo = String(wall.month).padStart(2, "0");
  const d = String(wall.day).padStart(2, "0");
  const h = String(wall.hour).padStart(2, "0");
  const mi = String(wall.minute).padStart(2, "0");
  return `${y}-${mo}-${d}T${h}:${mi}`;
}

const NOMINAL_RE = /^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})(?::(\d{2}))?$/;

/**
 * Parse a nominal local date-time string back into a wall clock. Rejects
 * malformed strings and impossible calendar values with
 * `InvalidNominalLocalError`. Note the string may denote a wall time that does
 * not exist in a zone (gap) or exists twice (fold); existence is a
 * materialization concern, not a parse concern.
 */
export function parseNominal(nominal: NominalLocal): WallClock {
  const match = NOMINAL_RE.exec(nominal);
  if (!match) {
    throw new InvalidNominalLocalError(`malformed nominal local date-time: "${nominal}"`);
  }
  const wall: WallClock = {
    year: Number(match[1]),
    month: Number(match[2]),
    day: Number(match[3]),
    hour: Number(match[4]),
    minute: Number(match[5]),
    second: match[6] === undefined ? 0 : Number(match[6]),
  };
  if (wall.month < 1 || wall.month > 12) {
    throw new InvalidNominalLocalError(`month out of range in "${nominal}"`);
  }
  if (wall.day < 1 || wall.day > 31) {
    throw new InvalidNominalLocalError(`day out of range in "${nominal}"`);
  }
  if (wall.hour > 23 || wall.minute > 59 || wall.second > 59) {
    throw new InvalidNominalLocalError(`time of day out of range in "${nominal}"`);
  }
  return wall;
}

/** Total ordering over wall clocks; safe because fields are validated. */
export function compareWall(a: WallClock, b: WallClock): number {
  if (a.year !== b.year) return a.year < b.year ? -1 : 1;
  if (a.month !== b.month) return a.month < b.month ? -1 : 1;
  if (a.day !== b.day) return a.day < b.day ? -1 : 1;
  if (a.hour !== b.hour) return a.hour < b.hour ? -1 : 1;
  if (a.minute !== b.minute) return a.minute < b.minute ? -1 : 1;
  return a.second < b.second ? -1 : a.second > b.second ? 1 : 0;
}

export function wallEquals(a: WallClock, b: WallClock): boolean {
  return compareWall(a, b) === 0;
}

/** Milliseconds between two wall readings when interpreted as UTC. */
export function wallAsEpochMs(wall: WallClock): number {
  return Date.UTC(wall.year, wall.month - 1, wall.day, wall.hour, wall.minute, wall.second);
}