WordGrid/src/lib.rs

const GRID_LENGTH: u8 = 15;
const TRAY_LENGTH: u8 = 7;
const ALL_LETTERS_BONUS: u32 = 50;

#[derive(Debug)]
enum Letter {
    FixedLetter{text: char, points: u32},
    Blank(char)
}

#[derive(Debug)]
enum CellType {
    Normal,
    DoubleWord,
    DoubleLetter,
    TripleLetter,
    TripleWord,
    Start,
}

#[derive(Debug)]
struct Cell {
    value: Option<Letter>,
    cell_type: CellType,
}

#[derive(Debug)]
struct Board {
    cells: Vec<Cell>,
}


impl Board {
    fn new() -> Self {
        let mut cells = Vec::new();


        /// Since the board is symmetrical in both directions for the purposes of our logic we can keep our coordinates in one corner
        ///
        /// # Arguments
        ///
        /// * `x`: A coordinate
        ///
        /// returns: u8 The coordinate mapped onto the lower-half
        fn map_to_corner(x: u8) -> u8 {
            return if x > GRID_LENGTH / 2 {
                GRID_LENGTH - x - 1
            } else {
                x
            }
        }

        for i in 0..GRID_LENGTH {
            let i = map_to_corner(i);
            for j in 0..GRID_LENGTH {
                let j = map_to_corner(j);

                let mut typee = CellType::Normal;

                // double word scores are diagonals
                if i == j {
                    typee = CellType::DoubleWord;
                }

                // Triple letters
                if (i % 4 == 1) && j % 4 == 1 && !(i == 1 && j == 1) {
                    typee = CellType::TripleLetter;
                }

                // Double letters
                if (i % 4 == 2) && (j % 4 == 2) && !(
                    i == 2 && j == 2
                ) {
                    typee = CellType::DoubleLetter;
                }
                if (i.min(j) == 0 && i.max(j) == 3) || (i.min(j)==3 && i.max(j) == 7) {
                    typee = CellType::DoubleLetter;
                }

                // Triple word scores
                if (i % 7 == 0) && (j % 7 == 0) {
                    typee = CellType::TripleWord;
                }

                // Start
                if i == 7 && j == 7 {
                    typee = CellType::Start;
                }

                cells.push(Cell {
                    cell_type: typee,
                    value: None,
                })

            }
        }

        Board {cells}
    }

    fn get_cell(&self, x: u8, y: u8) -> Result<&Cell, &str> {
        if x >= GRID_LENGTH || y >= GRID_LENGTH {
            Err("x & y must be within the board's coordinates")
        } else {
            let coord = (x + GRID_LENGTH*y) as usize;
            Ok(self.cells.get(coord).unwrap())
        }
    }
}



#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_cell_types() {
        let board = Board::new();

        assert!(matches!(board.get_cell(0, 0).unwrap().cell_type, CellType::TripleWord));
        assert!(matches!(board.get_cell(1, 0).unwrap().cell_type, CellType::Normal));
        assert!(matches!(board.get_cell(0, 1).unwrap().cell_type, CellType::Normal));
        assert!(matches!(board.get_cell(1, 1).unwrap().cell_type, CellType::DoubleWord));

        assert!(matches!(board.get_cell(13, 13).unwrap().cell_type, CellType::DoubleWord));
        assert!(matches!(board.get_cell(14, 14).unwrap().cell_type, CellType::TripleWord));
        assert!(matches!(board.get_cell(11, 14).unwrap().cell_type, CellType::DoubleLetter));

        assert!(matches!(board.get_cell(7, 7).unwrap().cell_type, CellType::Start));
        assert!(matches!(board.get_cell(8, 6).unwrap().cell_type, CellType::DoubleLetter));
        assert!(matches!(board.get_cell(5, 9).unwrap().cell_type, CellType::TripleLetter));
    }
}