// Screen-share quality presets modelled on Discord's tiers. Values are the
// upper bounds — LiveKit + WebRTC's congestion control dynamically drop to
// lower spatial/temporal layers (SVC with VP9) when the uplink degrades, so
// these numbers behave as "up to" caps, not constant bitrates.

const STORAGE_KEY = 'chatapp.screenshare';

export type ScreenSharePreset =
  | 'auto'
  | '720p30'
  | '720p60'
  | '1080p30'
  | '1080p60'
  | '1440p60'
  | '4k60';

export interface ScreenShareSettings {
  preset: ScreenSharePreset;
}

const DEFAULTS: ScreenShareSettings = {
  preset: 'auto',
};

export interface PresetParams {
  dims: { width: number; height: number } | null; // null = browser picks native
  framerate: number;
  bitrateKbps: number;
  label: string;
}

const PRESET_PARAMS: Record<ScreenSharePreset, PresetParams> = {
  auto: { dims: null, framerate: 60, bitrateKbps: 8000, label: 'Auto (Original)' },
  '720p30': {
    dims: { width: 1280, height: 720 },
    framerate: 30,
    bitrateKbps: 2500,
    label: '720p · 30 fps',
  },
  '720p60': {
    dims: { width: 1280, height: 720 },
    framerate: 60,
    bitrateKbps: 3500,
    label: '720p · 60 fps',
  },
  '1080p30': {
    dims: { width: 1920, height: 1080 },
    framerate: 30,
    bitrateKbps: 4000,
    label: '1080p · 30 fps',
  },
  '1080p60': {
    dims: { width: 1920, height: 1080 },
    framerate: 60,
    bitrateKbps: 6000,
    label: '1080p · 60 fps',
  },
  '1440p60': {
    dims: { width: 2560, height: 1440 },
    framerate: 60,
    bitrateKbps: 8000,
    label: '1440p · 60 fps',
  },
  '4k60': {
    dims: { width: 3840, height: 2160 },
    framerate: 60,
    bitrateKbps: 10_000,
    label: '4K · 60 fps',
  },
};

export const PRESET_ORDER: ReadonlyArray<ScreenSharePreset> = [
  'auto',
  '720p30',
  '720p60',
  '1080p30',
  '1080p60',
  '1440p60',
  '4k60',
];

export function getPresetParams(p: ScreenSharePreset): PresetParams {
  return PRESET_PARAMS[p];
}

type Listener = (s: ScreenShareSettings) => void;
const listeners = new Set<Listener>();

let cached: ScreenShareSettings | null = null;

function isPreset(v: unknown): v is ScreenSharePreset {
  return typeof v === 'string' && v in PRESET_PARAMS;
}

function read(): ScreenShareSettings {
  if (cached) return cached;
  try {
    const raw = window.localStorage.getItem(STORAGE_KEY);
    if (!raw) {
      cached = DEFAULTS;
      return cached;
    }
    const parsed = JSON.parse(raw) as Partial<ScreenShareSettings>;
    cached = {
      preset: isPreset(parsed.preset) ? parsed.preset : DEFAULTS.preset,
    };
    return cached;
  } catch {
    cached = DEFAULTS;
    return cached;
  }
}

function write(s: ScreenShareSettings): void {
  cached = s;
  try {
    window.localStorage.setItem(STORAGE_KEY, JSON.stringify(s));
  } catch {
    /* quota / private mode */
  }
  for (const l of listeners) l(s);
}

export function getScreenShareSettings(): ScreenShareSettings {
  return read();
}

export function updateScreenShareSettings(
  patch: Partial<ScreenShareSettings>,
): ScreenShareSettings {
  const next = { ...read(), ...patch };
  write(next);
  return next;
}

export function subscribeScreenShareSettings(listener: Listener): () => void {
  listeners.add(listener);
  return () => listeners.delete(listener);
}