/**
 * Validate a fully filled Sudoku board (81-char string)
 * Returns true if:
 *  - 81 characters long
 *  - all characters are digits 1–9
 *  - all rows, columns, and 3×3 boxes sum to 45
 */
export function validateFullBoard(board: string): boolean {
  // --- Basic sanity ---
  if (board.length !== 81) return false;
  if (!/^[1-9]+$/.test(board)) return false;

  const getCell = (r: number, c: number) => Number(board[r * 9 + c]);

  // --- Validate rows ---
  for (let r = 0; r < 9; r++) {
    const sum = Array.from({ length: 9 }, (_, c) => getCell(r, c))
      .reduce((a, b) => a + b, 0);
    if (sum !== 45) return false;
  }

  // --- Validate columns ---
  for (let c = 0; c < 9; c++) {
    const sum = Array.from({ length: 9 }, (_, r) => getCell(r, c))
      .reduce((a, b) => a + b, 0);
    if (sum !== 45) return false;
  }

  // --- Validate 3×3 boxes ---
  for (let br = 0; br < 3; br++) {
    for (let bc = 0; bc < 3; bc++) {
      const sum = Array.from({ length: 9 }, (_, i) => {
        const r = br * 3 + Math.floor(i / 3);
        const c = bc * 3 + (i % 3);
        return getCell(r, c);
      }).reduce((a, b) => a + b, 0);
      if (sum !== 45) return false;
    }
  }

  return true;
}
/**
 * 🔍 Assert that a Sudoku board string represents a valid, fully filled grid.
 *
 * Format:
 *  - 81 characters
 *  - Only digits 1–9
 *  - Each row, column, and 3×3 box contains unique digits that sum to 45
 *
 * Throws descriptive errors on failure.
 */

export function assertValidFullBoard(board: string): void {
  // --- Basic integrity checks ---
  console.assert(board.length === 81, `❌ Board length must be 81, got ${board.length}`);
  if (board.length !== 81) throw new Error(`Invalid board length: ${board.length}`);

  // All characters must be digits 1–9
  console.assert(/^[1-9]+$/.test(board), "❌ Board must contain only digits 1–9 (no 0s or dots)");
  if (!/^[1-9]+$/.test(board)) throw new Error("Board contains invalid characters");

  const get = (r: number, c: number) => Number(board[r * 9 + c]);

  // --- Helper to assert uniqueness and sum ---
  const assertGroup = (label: string, cells: number[]) => {
    const sum = cells.reduce((a, b) => a + b, 0);
    const unique = new Set(cells);
    console.assert(sum === 45, `❌ ${label} sum=${sum} (should be 45)`);
    console.assert(unique.size === 9, `❌ ${label} has duplicates: [${cells.join(",")}]`);

    if (sum !== 45) throw new Error(`${label} does not sum to 45`);
    if (unique.size !== 9) throw new Error(`${label} contains duplicates`);
  };

  // --- Validate rows ---
  for (let r = 0; r < 9; r++) {
    const row = Array.from({ length: 9 }, (_, c) => get(r, c));
    assertGroup(`Row ${r + 1}`, row);
  }

  // --- Validate columns ---
  for (let c = 0; c < 9; c++) {
    const col = Array.from({ length: 9 }, (_, r) => get(r, c));
    assertGroup(`Column ${c + 1}`, col);
  }

  // --- Validate 3×3 boxes ---
  for (let br = 0; br < 3; br++) {
    for (let bc = 0; bc < 3; bc++) {
      const box: number[] = [];
      for (let r = 0; r < 3; r++) {
        for (let c = 0; c < 3; c++) {
          box.push(get(br * 3 + r, bc * 3 + c));
        }
      }
      const idx = br * 3 + bc + 1;
      assertGroup(`Box ${idx}`, box);
    }
  }
}