/**
 * Per-chunk decode quality checks for the long-form pipeline's temperature
 * fallback (D-WS3a) — faster-whisper's `generate_with_fallback` criteria.
 */

export interface FallbackOptions {
  /** Decode temperatures in order; the first is the normal (greedy) pass. */
  temperatures: number[];
  /** Reject a decode whose text compresses better than this (a loop). */
  compressionRatioThreshold: number;
  /** Reject a decode whose average token log-probability is below this. */
  logProbThreshold: number;
}

/** faster-whisper / OpenAI Whisper defaults (spec Goal 3). */
export const DEFAULT_FALLBACK: FallbackOptions = {
  temperatures: [0, 0.2, 0.4, 0.6, 0.8, 1.0],
  compressionRatioThreshold: 2.4,
  logProbThreshold: -1.0,
};

/**
 * UTF-8 length over zlib-deflated length — `get_compression_ratio` in
 * faster-whisper (`zlib.compress`). `CompressionStream("deflate")` is the
 * same zlib format and exists in workers and Bun alike.
 */
export async function compressionRatio(text: string): Promise<number> {
  const bytes = new TextEncoder().encode(text);
  if (bytes.length === 0) return 0;
  const stream = new Blob([bytes]).stream().pipeThrough(new CompressionStream("deflate"));
  const compressed = await new Response(stream).arrayBuffer();
  return bytes.length / compressed.byteLength;
}

/** Whether a decode should be retried at the next temperature. */
export function needsFallback(
  result: { compressionRatio: number; avgLogProb: number | null },
  thresholds: Pick<FallbackOptions, "compressionRatioThreshold" | "logProbThreshold"> = DEFAULT_FALLBACK,
): boolean {
  if (result.compressionRatio > thresholds.compressionRatioThreshold) return true;
  return result.avgLogProb !== null && result.avgLogProb < thresholds.logProbThreshold;
}