package sudoku.solver;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;

import sudoku.structure.Cell;
import sudoku.structure.MultiDoku;

public class HintHelper {

	public record Hint(Cell cell, int newValue) {}

	/**
	 * Si possible, donne un indice sur la résolution du doku passé en paramètre,
	 * selon la méthode de résolution rensaignée.
	 * @param doku MultiDoku, multidoku pour lequel on veut un indice
	 * @param solver Solver, méthode de résolution souhaitée
	 * @return Hint, indice sur une case à remplir, valant null si le doku n'a pas de solution.
	 */
	public static Hint getHint(MultiDoku doku, Solver solver) {
		doku.getStateManager().pushState();
		doku.clearMutableCells();
		if (!solver.solve(doku))
			return null;
		var stateSolved = doku.getStateManager().popAndGetState();
		// find differences
		Map<Cell, Integer> newValues = new HashMap<>();
		for (var entry : stateSolved.entrySet()) {
			Cell cell = entry.getKey();
			// we only want the cells that can be filled
			if (!cell.isMutable())
				continue;
			int oldValue = cell.getSymbolIndex();
			int newValue = stateSolved.get(cell);
			if (oldValue == newValue)
				continue;
			// we have to clear the cell
			if (newValue == Cell.NOSYMBOL)
				return new Hint(cell, newValue);
			// we have to change the cell value
			if (oldValue != Cell.NOSYMBOL)
				return new Hint(cell, newValue);

			// there is a valid move
			newValues.put(cell, newValue);
		}

		// this is too complex just for fetching a random entry, but whatever ...
		Random r = new Random();
		List<Cell> cells = new ArrayList<>(newValues.keySet());
		Cell randomCell = cells.get(r.nextInt(cells.size()));
		int randomCellValue = newValues.get(randomCell);
		return new Hint(randomCell, randomCellValue);
	}

}