core/presets.ts

import type { PresetName, WatermarkConfig } from './types.js';

/** Mid-frequency DCT coefficients (zigzag positions 3–14, 12 coeffs) */
const MID_FREQ_ZIGZAG = [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14];

/** Low+mid frequency coefficients (zigzag 1–20, 20 coeffs) — survive heavy compression */
const LOW_MID_FREQ_ZIGZAG = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20];

/** Low frequency coefficients (zigzag 1–10, 10 coeffs) — survive extreme compression */
const LOW_FREQ_ZIGZAG = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

export const PRESETS: Record<PresetName, WatermarkConfig> = {
  light: {
    alpha: 0.10,
    delta: 50,
    tilePeriod: 256,
    bch: { n: 63, k: 36, t: 5, m: 6 },
    crc: { bits: 4 },
    dwtLevels: 2,
    zigzagPositions: MID_FREQ_ZIGZAG,
    perceptualMasking: true,
    temporalFrames: 1,
  },

  moderate: {
    alpha: 0.13,
    delta: 62,
    tilePeriod: 240,
    bch: { n: 63, k: 36, t: 5, m: 6 },
    crc: { bits: 4 },
    dwtLevels: 2,
    zigzagPositions: MID_FREQ_ZIGZAG,
    perceptualMasking: true,
    temporalFrames: 1,
  },

  strong: {
    alpha: 0.26,
    delta: 110,
    tilePeriod: 208,
    bch: { n: 63, k: 36, t: 5, m: 6 },
    crc: { bits: 4 },
    dwtLevels: 2,
    zigzagPositions: LOW_MID_FREQ_ZIGZAG,
    perceptualMasking: true,
    temporalFrames: 1,
  },

  fortress: {
    alpha: 0.35,
    delta: 150,
    tilePeriod: 192,
    bch: { n: 63, k: 36, t: 5, m: 6 },
    crc: { bits: 4 },
    dwtLevels: 2,
    zigzagPositions: LOW_MID_FREQ_ZIGZAG,
    perceptualMasking: true,
    temporalFrames: 1,
  },
};

/**
 * Get a preset configuration by name
 */
export function getPreset(name: PresetName): WatermarkConfig {
  return { ...PRESETS[name] };
}

/**
 * Preset descriptions for the UI
 */
export const PRESET_DESCRIPTIONS: Record<PresetName, string> = {
  light: '🌤️ Lightest touch. Near-invisible, survives mild compression.',
  moderate: '⚡ Near-invisible with perceptual masking. Slightly stronger than light.',
  strong: '🛡️ Stronger embedding across more frequencies. Handles rescaling well.',
  fortress: '🏰 Maximum robustness. Survives heavy compression and color adjustments.',
};