import { HttpException, HttpStatus } from "@nestjs/common";

/** Carries the plaintext size for the controller’s unsatisfied Content-Range header. */
export class FileRangeNotSatisfiableException extends HttpException {
  constructor(readonly total: number) {
    super("requested range is not satisfiable", HttpStatus.REQUESTED_RANGE_NOT_SATISFIABLE);
  }
}

/** Inclusive HTTP byte bounds, clipped to the plaintext EOF. */
export function playbackRange(total: number, start: number, end: number): { start: number; end: number } {
  if (!Number.isSafeInteger(start) || !Number.isSafeInteger(end) || start < 0 || start >= total || end < start) {
    throw new FileRangeNotSatisfiableException(total);
  }
  return { start, end: Math.min(end, total - 1) };
}

/** Query bounds take precedence; also accept the single Range browsers send. */
export function requestedPlaybackRange(total: number, start: unknown, end: unknown, range?: string): { start: number; end: number } {
  const fail = (): never => { throw new FileRangeNotSatisfiableException(total); };
  const integer = (value: unknown): number => {
    if (typeof value !== "string" || !/^\d+$/.test(value) || !Number.isSafeInteger(Number(value))) return fail();
    return Number(value);
  };
  if (start !== undefined || end !== undefined) {
    return playbackRange(total, start === undefined ? 0 : integer(start), end === undefined ? total - 1 : integer(end));
  }
  if (range === undefined) return playbackRange(total, 0, total - 1);
  const match = /^bytes=(\d*)-(\d*)$/.exec(range);
  if (match === null || (match[1] === "" && match[2] === "")) return fail();
  if (match[1] === "") {
    const suffix = integer(match[2]);
    if (suffix === 0) return fail();
    return playbackRange(total, Math.max(0, total - suffix), total - 1);
  }
  return playbackRange(total, integer(match[1]), match[2] === "" ? total - 1 : integer(match[2]));
}