package sudoku.solver;

import sudoku.io.SudokuPrinter;
import sudoku.structure.MultiDoku;
import sudoku.structure.Cell;
import sudoku.structure.Sudoku;

import java.util.List;
import java.util.Random;
import java.util.concurrent.CancellationException;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Solver {
    private static final Logger logger = Logger.getLogger("SolverLogger");

    /**
     * Résout le multidoku passé en paramètre si c'est possible.
     * En testant toutes les possibilités, de manière aléatoire, avec un algorithme
     * de backtracking.
     *
     * @param doku Multidoku, à résoudre
     * @param rand Random, pour tester aléatoirement les symboles
     * @return boolean, true s'il est résolu ou false s'il ne l'est pas.
     */
    public static boolean solveRandom(MultiDoku doku, Random rand) {
        if (Thread.interrupted())
            throw new CancellationException("User wants to stop the solver");

        Sudoku sudoku = doku.getSubGrid(0);
        logger.log(Level.INFO,
                '\n' + SudokuPrinter.toStringRectangleSudoku(sudoku,
                        sudoku.getBlockWidth() == 0 ? sudoku.getSize() : sudoku.getBlockWidth(),
                        sudoku.getBlockWidth() == 0 ? sudoku.getSize() : sudoku.getSize() / sudoku.getBlockWidth()));

        if (doku.isValid()) {
            return true;
        }

        Cell cellToFill = doku.getFirstEmptyCell();
        if (cellToFill == null) {
            return false;
        }

        List<Integer> possibleSymbols = doku.getPossibleSymbolsOfCell(cellToFill);

        while (!possibleSymbols.isEmpty()) {
            int nextPossibleSymbolIndex = rand.nextInt(possibleSymbols.size());
            int nextSymbol = possibleSymbols.get(nextPossibleSymbolIndex);

            cellToFill.setSymbolIndex(nextSymbol);
            if (Solver.solveRandom(doku, rand)) {
                return true;
            }
            cellToFill.setSymbolIndex(Cell.NOSYMBOL);
            possibleSymbols.remove(nextPossibleSymbolIndex);

        }
        return false;
    }

    public static int countSolution(MultiDoku doku) {
        int result = 0;

        if (doku.isValid()) {
            return 1;
        }

        Cell cellToFill = doku.getFirstEmptyCell();
        if (cellToFill == null) {
            return 0;
        }

        List<Integer> possibleSymbols = doku.getPossibleSymbolsOfCell(cellToFill);

        for (int symbol : possibleSymbols) {

            cellToFill.setSymbolIndex(symbol);
            if (Solver.solve(doku)) {
                result++;
            }
            cellToFill.setSymbolIndex(Cell.NOSYMBOL);
        }

        return result;
    }

    public static boolean solve(MultiDoku doku) {
        if (Thread.interrupted())
            throw new CancellationException("User wants to stop the solver");

        if (doku.isValid()) {
            return true;
        }

        Cell cellToFill = doku.getFirstEmptyCell();
        if (cellToFill == null) {
            return false;
        }

        List<Integer> possibleSymbols = doku.getPossibleSymbolsOfCell(cellToFill);
        if (possibleSymbols.isEmpty()) {
            return false;
        }

        for (int symbol : possibleSymbols) {

            cellToFill.setSymbolIndex(symbol);
            if (Solver.solve(doku)) {
                return true;
            } else {
                cellToFill.setSymbolIndex(Cell.NOSYMBOL);
            }

        }
        return false;
    }
}