import { mulberry32, type IsotypeCell } from './patterns';

/** Row-major 3x3 grid (9 cells) — a tuple so every pattern is guaranteed complete at compile time. */
export type IsotypeMiniPattern = readonly [
  IsotypeCell,
  IsotypeCell,
  IsotypeCell,
  IsotypeCell,
  IsotypeCell,
  IsotypeCell,
  IsotypeCell,
  IsotypeCell,
  IsotypeCell,
];

/** Widen this union as new 3x3 isotypes join the series. */
export type IsotypeMiniPatternId = 'core';

export const ISOTYPE_MINI_PATTERNS: Record<IsotypeMiniPatternId, IsotypeMiniPattern> = {
  core: [
    'purple', 'blue', 'blue',
    'magenta', 'yellow', 'green',
    'magenta', 'red', 'brown',
  ],
};

export const ISOTYPE_MINI_PATTERN_IDS = Object.keys(
  ISOTYPE_MINI_PATTERNS
) as IsotypeMiniPatternId[];

/**
 * Returns a copy of the given pattern with exactly one cell (chosen
 * deterministically from `seed`) swapped to `'blank'`. Pure — the same
 * `(patternId, seed)` pair always returns the same result. Unlike
 * `getIsotypeVariant`, the mini patterns have no inherent blank cell, so
 * every cell is a candidate.
 */
export function getIsotypeMiniVariant(
  patternId: IsotypeMiniPatternId,
  seed: number
): IsotypeMiniPattern {
  const base = ISOTYPE_MINI_PATTERNS[patternId];
  const candidateIndices = base.reduce<number[]>(
    (acc, cell, i) => (cell === 'blank' ? acc : [...acc, i]),
    []
  );
  const rng = mulberry32(seed);
  const chosen = candidateIndices[Math.floor(rng() * candidateIndices.length)];
  return base.map((cell, i) => (i === chosen ? 'blank' : cell)) as unknown as IsotypeMiniPattern;
}