/**
 * hasselink/tiling/echo-pixels.ts
 * ------------------------------------------------------
 * Type-level constructors for Echo pixels.
 *
 * This mirrors `payload-pixels.ts` but assigns PixelRole="Echo".
 * Echo pixels are the intended carrier for "prev-in-prev" redundancy:
 * older history encoded at finer scales.
 */

import type { BlockAssignment, PixelAssignment, TypedTiledPixel } from "./tiling.ts";
import type { Grid4x4 } from "./grid.ts";

export type EchoPixel<
  B extends BlockAssignment<2>,
  P extends readonly [number, number]
> =
  PixelAssignment<2> & {
    owner: B["owner"];
    level: 2;
    block: B["block"];
    role: B["role"];
    pixel: TypedTiledPixel<2> & {
      block: B["block"];
      index: { ix: P[0]; iy: P[1] };
      role: "Echo";
      channel: "Prev";
    };
  };

type UnionToIntersection<U> =
  (U extends unknown ? (x: U) => void : never) extends
  (x: infer I) => void ? I : never;

type UnionToTuple<U, T extends unknown[] = []> =
  [U] extends [never]
    ? T
    : UnionToIntersection<U extends unknown ? (u: U) => void : never> extends
        (u: infer I) => void
      ? UnionToTuple<Exclude<U, I>, [...T, I]>
      : T;

export type EchoPixelsForBlock<
  B extends BlockAssignment<2>
> =
  UnionToTuple<
    Grid4x4 extends infer P
      ? P extends readonly [number, number]
        ? EchoPixel<B, P>
        : never
      : never
  >;