ROWS = 6
COLUMNS = 7

FOUR = 4

INDEX_FIRST_ROW = 0
INDEX_FIRST_COLUMN = 0

RED = "R"
YELLOW = "Y"
EMPTY = "."

FIRST_PLAYER = RED
PLAYER_NAMES = {RED: "red", YELLOW: "yellow"}

grid = [([EMPTY] * COLUMNS) for i in xrange(0, ROWS)]


class ColumnFullError(Exception):
    pass


def get_player_name(player):
    return PLAYER_NAMES[player]


def print_grid():
    print("".join(["{} ".format(i) for i in xrange(0, COLUMNS)]))
    for row in grid:
        print("".join(["{} ".format(cell) for cell in row]))


def insert(colour, column):
    if grid[INDEX_FIRST_ROW][column] != EMPTY:
        raise ColumnFullError()
    row = INDEX_FIRST_ROW

    row_try = INDEX_FIRST_ROW
    while (row_try < ROWS and grid[row_try][column] == EMPTY):
        row = row_try
        row_try += 1

    grid[row][column] = colour
    return (row, column)


def is_column_input_valid(input):
    try:
        column = int(input)
        return INDEX_FIRST_COLUMN <= column and column < COLUMNS
    except ValueError:
        return False


def get_column_input(player):
    column_str = raw_input("{} player, pick a column: ".format(get_player_name(player).title()))
    while not is_column_input_valid(column_str):
        print("That isn't a column number!")
        column_str = raw_input("{} player, pick a column between {} and {}: ".format(INDEX_FIRST_COLUMN, COLUMNS - 1, get_player_name(player).title()))
    return int(column_str)


def is_grid_full():
    for row in grid:
        for cell in row:
            if cell == EMPTY:
                return False
    return True


def check_four_vertical(player, row, column):
    # downwards
    count = 0
    while row < ROWS and grid[row][column] == player:
        count += 1
        if count >= 4:
            return True
        row += 1
    return False



def check_four_horizontal(player, row, column):
    count_left = 0
    column_l = column - 1
    while column_l >= INDEX_FIRST_COLUMN and grid[row][column_l] == player:
        count_left += 1
        column_l -= 1

    count_right = 0
    column_r = column + 1
    while column_r < COLUMNS and grid[row][column_r] == player:
        count_right += 1
        column_r += 1

    return count_left + count_right + 1 >= 4


def check_four_posdiag(player, row, column):
    count_left = 0
    column_l = column - 1
    row_l = row - 1
    while column_l >= INDEX_FIRST_COLUMN and row_l >= INDEX_FIRST_ROW and grid[row_l][column_l] == player:
        count_left += 1
        column_l -= 1
        row_l -= 1

    count_right = 0
    column_r = column + 1
    row_r = row + 1
    while column_r < COLUMNS and row_r < ROWS and grid[row][column_r] == player:
        count_right += 1
        column_r += 1
        row_r += 1

    return count_left + count_right + 1 >= 4


def check_four_negdiag(player, row, column):
    count_left = 0
    column_l = column - 1
    row_l = row + 1
    while column_l >= INDEX_FIRST_COLUMN and row_l < ROWS and grid[row_l][column_l] == player:
        count_left += 1
        column_l -= 1
        row_l += 1

    count_right = 0
    column_r = column + 1
    row_r = row - 1
    while column_r < COLUMNS and row_r >= INDEX_FIRST_ROW and grid[row][column_r] == player:
        count_right += 1
        column_r += 1
        row_r -= 1

    return count_left + count_right + 1 >= 4


def has_won(player, row, column):
    return check_four_vertical(player, row, column) or check_four_horizontal(player, row, column) or check_four_posdiag(player, row, column) or check_four_negdiag(player, row, column)


def main():
    player = FIRST_PLAYER

    while True:
        if is_grid_full():
            print("It's a draw!")
            return

        column = get_column_input(player)
        try:
            (row, column) = insert(player, column)
            print("")
            print_grid()
            print("")

            if has_won(player, row, column):
                print("{} has won!".format(get_player_name(player).title()))
                return


        except ColumnFullError:
            print("Column {} is full! Pick a different column.".format(column))
            continue
        player = RED if player == YELLOW else YELLOW


main()