#[derive(Clone, Copy, PartialEq)]
pub enum Cell {
    Empty,
    X,
    O,
}

impl std::fmt::Display for Cell {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        let s: &str;
        match *self {
            Cell::X => s = "X",
            Cell::O => s = "O",
            Cell::Empty => s = " ",
        }

        write!(f, "{}", s)
    }
}

pub struct Move {
    pub x: usize,
    pub y: usize,
    pub piece: Cell,
}

pub struct Board {
    cells: Vec<Cell>,
    next: Cell,
}

impl Board {
    pub fn new() -> Board {
        Board {
            cells: vec![Cell::Empty; 9],
            next: Cell::X,
        }
    }

    pub fn reset(&mut self) {
        self.cells = vec![Cell::Empty; 9];
        self.next = Cell::X;
    }

    pub fn apply(&mut self, m: Move) -> Result<(), &str> {
        let i = m.x * 1 + m.y * 3;

        if !self.is_valid_move(&m) {
            return Err("invalid move");
        }

        self.cells[i] = m.piece;

        match self.next {
            Cell::X => self.next = Cell::O,
            Cell::O => self.next = Cell::X,
            _ => {}
        }

        Ok(())
    }

    pub fn is_valid_move(&self, m: &Move) -> bool {
        let i = m.x * 1 + m.y * 3;

        m.piece == self.next && self.cells[i] == Cell::Empty
    }

    pub fn valid_moves_available(&self) -> bool {
        // check for draw condition
        let mut empty: usize = 0;
        for i in 0..self.cells.len() {
            if self.cells[i] == Cell::Empty {
                empty += 1;
            }
        }

        empty > 0
    }

    pub fn has_winner(&self) -> Option<Cell> {
        // rows and cols
        for i in 0..3 {
            if (self.cells[i] != Cell::Empty)
                && (self.cells[i] == self.cells[i + 3] && self.cells[i] == self.cells[i + 6])
            {
                return Some(self.cells[i]);
            } else if (self.cells[i * 3] != Cell::Empty)
                && (self.cells[i * 3] == self.cells[i * 3 + 1]
                    && self.cells[i * 3] == self.cells[i * 3 + 2])
            {
                return Some(self.cells[i * 3]);
            }
        }

        // diagonals
        if (self.cells[0] != Cell::Empty)
            && (self.cells[0] == self.cells[4] && self.cells[0] == self.cells[8])
        {
            return Some(self.cells[0]);
        }

        if (self.cells[2] != Cell::Empty)
            && (self.cells[2] == self.cells[4] && self.cells[2] == self.cells[6])
        {
            return Some(self.cells[2]);
        }

        // no winner
        return None;
    }
}

impl std::fmt::Display for Board {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        let mut s = String::new();

        s.push_str("    1   2   3 \n");

        s.push_str("  ┌───┬───┬───┐\n");
        for i in 0..3 {
            match i {
                0 => s.push_str("a "),
                1 => s.push_str("b "),
                2 => s.push_str("c "),
                _ => {}
            }
            s.push_str(&format!(
                "│ {} │ {} │ {} │\n",
                self.cells[i * 3],
                self.cells[i * 3 + 1],
                self.cells[i * 3 + 2]
            ));
            if i < 2 {
                s.push_str("  ├───┼───┼───┤\n");
            }
        }
        s.push_str("  └───┴───┴───┘\n");

        match self.has_winner() {
            Some(w) => s.push_str(&format!("The winner is {w}")),
            None => match self.valid_moves_available() {
                true => s.push_str(&format!("Next: {}", self.next)),
                false => s.push_str("DRAW!"),
            },
        }

        write!(f, "{s}")
    }
}