import type { PFrameInternal } from "@milaboratories/pl-model-middle-layer";
import type { IncomingMessage } from "node:http";

export function parseRange(request: IncomingMessage): PFrameInternal.HttpRange | null | undefined {
  const range = request.headers["range"];
  if (range === undefined) return undefined;

  const match = range.match(/^bytes=(\d*)-(\d*)$/);
  if (!match) return null;

  const [, startStr, endStr] = match;
  const start = startStr ? parseInt(startStr, 10) : null;
  const end = endStr ? parseInt(endStr, 10) : null;
  if (
    (start !== null && (isNaN(start) || start < 0)) ||
    (end !== null && (isNaN(end) || end < 0)) ||
    (start !== null && end !== null && start > end)
  )
    return null;

  // Both start and end are specified - bounded range
  if (start !== null && end !== null) {
    return { type: "bounded", start, end };
  }

  // Only start is specified - offset range (e.g., bytes=500-)
  if (start !== null && end === null) {
    return { type: "offset", offset: start };
  }

  // Only end is specified - suffix range (e.g., bytes=-500)
  if (start === null && end !== null) {
    return { type: "suffix", suffix: end };
  }

  // Neither start nor end specified (bytes=-) - invalid
  return null;
}