// Board premium layout — the 15x15 premium-square geometry, ported from the engine source
// of truth, scrabble-solver/rules/rules.go (standardBoard / eruditBoard). The board is not
// transmitted on the wire (StateView has no board), so the client renders the premiums
// locally; only the centre differs by variant. A Vitest parity test pins the geometry.
// Tile values and the alphabet moved to the server-sent per-variant table in Stage 13 (see
// lib/alphabet.ts), so this file is geometry only.

import type { Variant } from './model';

export const BOARD_SIZE = 15;

export type Premium = '' | 'TW' | 'DW' | 'TL' | 'DL';

// Legend (rules.go): T=triple word, D=double word, t=triple letter, d=double
// letter, .=plain, *=centre (a double word), +=centre with no premium.
const standardBoard = [
  'T..d...T...d..T',
  '.D...t...t...D.',
  '..D...d.d...D..',
  'd..D...d...D..d',
  '....D.....D....',
  '.t...t...t...t.',
  '..d...d.d...d..',
  'T..d...*...d..T',
  '..d...d.d...d..',
  '.t...t...t...t.',
  '....D.....D....',
  'd..D...d...D..d',
  '..D...d.d...D..',
  '.D...t...t...D.',
  'T..d...T...d..T',
];

// Эрудит: the standard layout but a non-doubling centre ('+').
const eruditBoard = [
  'T..d...T...d..T',
  '.D...t...t...D.',
  '..D...d.d...D..',
  'd..D...d...D..d',
  '....D.....D....',
  '.t...t...t...t.',
  '..d...d.d...d..',
  'T..d...+...d..T',
  '..d...d.d...d..',
  '.t...t...t...t.',
  '....D.....D....',
  'd..D...d...D..d',
  '..D...d.d...D..',
  '.D...t...t...D.',
  'T..d...T...d..T',
];

function template(variant: Variant): string[] {
  return variant === 'erudit' ? eruditBoard : standardBoard;
}

function premiumOf(ch: string): Premium {
  switch (ch) {
    case 'T':
      return 'TW';
    case 'D':
    case '*':
      return 'DW';
    case 't':
      return 'TL';
    case 'd':
      return 'DL';
    default:
      return '';
  }
}

/** premiumGrid returns the 15x15 premium layout for a variant (row-major). */
export function premiumGrid(variant: Variant): Premium[][] {
  return template(variant).map((line) => Array.from(line, premiumOf));
}

/** centre returns the first-move anchor square (row, col). */
export function centre(variant: Variant): { row: number; col: number } {
  const lines = template(variant);
  for (let r = 0; r < lines.length; r++) {
    const c = lines[r].search(/[*+]/);
    if (c >= 0) return { row: r, col: c };
  }
  return { row: 7, col: 7 };
}

// Tile values and the per-variant alphabet now arrive from the server (lib/alphabet.ts,
// Stage 13); the board geometry above is all this module owns.