// Volume arithmetic for BOTH players, kept out of the components so it can be unit-tested. Every
// rule here was established by a bug: a wheel spin that lost notches to the iframe's lagging
// getVolume, a partial stored object that became NaN and persisted as `null`, and a "corrupt →
// default" fallback that jumped an already-quiet session to full blast.
//
// The two players run on different native scales — the YouTube iframe API takes 0–100 integers, the
// HTML5 <video> element a 0..1 float with a separate `.muted` flag — so the pure core below is
// scale-agnostic (a `VolumeScale` parameterises the range, default, and integer rounding) and each
// player binds it to its own scale. The YouTube-bound wrappers keep the original 0–100 API.

/** A player's volume scale. `round` is true for the integer YouTube API, false for the 0..1 float. */
export interface VolumeScale {
  min: number;
  max: number;
  /** Level used when nothing trustworthy is available. */
  default: number;
  round: boolean;
}

/**
 * YouTube iframe API: 0–100 integers, no mute flag (level 0 IS muted).
 */
export const YT_SCALE: VolumeScale = { min: 0, max: 100, default: 100, round: true };
/** HTML5 <video>: a 0..1 float (mute is a separate flag the caller carries). */
export const PLEX_SCALE: VolumeScale = { min: 0, max: 1, default: 1, round: false };

function clampTo(n: number, s: VolumeScale): number {
  const c = Math.max(s.min, Math.min(s.max, n));
  return s.round ? Math.round(c) : c;
}

/**
 * Coerce anything that claims to be a volume into a usable level ON `scale`.
 *
 * Only a real, finite `number` is accepted: the stored blob is JSON, so a level is a number or it
 * is corrupt — `null`, `undefined`, `"80"` and `NaN` all mean "we don't know", and `Number(null)`
 * being `0` (silently muting the player) is exactly the coercion to avoid. `fallback` is the last
 * level known to work; it is itself validated, so a corrupt value can never travel through it.
 */
export function normalizeVolumeIn(raw: unknown, fallback: unknown, scale: VolumeScale): number {
  if (typeof raw === "number" && Number.isFinite(raw)) return clampTo(raw, scale);
  if (typeof fallback === "number" && Number.isFinite(fallback)) return clampTo(fallback, scale);
  return scale.default;
}

/** One volume step (wheel notch / arrow key) from `current`, on `scale`.
 *
 * `delta` and `fallback` ride in an options object on purpose: as two adjacent `number`
 * parameters they were transposable without a type error, and swapping them silently steps the
 * volume BY the current level. */
export function stepVolumeIn(
  current: unknown,
  opts: { delta: number; fallback: unknown },
  scale: VolumeScale,
): number {
  return clampTo(normalizeVolumeIn(current, opts.fallback, scale) + opts.delta, scale);
}

// --- YouTube-bound convenience wrappers (0–100 integers) — the original API, behaviour unchanged. ---

/** Level used when nothing trustworthy is available (YouTube scale). */
export const DEFAULT_VOLUME = YT_SCALE.default;

export function normalizeVolume(raw: unknown, fallback: unknown = DEFAULT_VOLUME): number {
  return normalizeVolumeIn(raw, fallback, YT_SCALE);
}

export function stepVolume(current: unknown, opts: { delta: number; fallback: unknown }): number {
  return stepVolumeIn(current, opts, YT_SCALE);
}