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use crate::ThudError;

/// Checked container for a coordinate to address into a [`Board`](enum.Board.html)
#[derive(Debug, PartialEq, Copy, Clone)]
pub struct Coord {
    x: usize,
    y: usize,
}

impl Coord {
    fn check_coords(x: usize, y: usize) -> Result<(), ThudError> {
        let sum = x + y;

        // Check flat bounds first
        let invalid = (x > 14)
            || (y > 14)
            // Extreme corners
            || (sum < 5)
            || (sum > 23)
            // Outer corners
            || (9 + y < x)
            || (9 + x < y);

        if invalid {
            Err(ThudError::InvalidPosition)
        } else {
            Ok(())
        }
    }

    /// Make a new `Coord` using 0-based axes values.
    ///
    /// The squares are addressed as if the board were a 15x15 square with the bottom-left square
    /// being (0, 0); confusingly, this is out of bounds. See the official Thud rules for the
    /// shape of the board.
    ///
    /// Will return [`Err(ThudError::InvalidPosition)`](enum.ThudError.html) if the coordinates supplied are out of bounds
    /// of the board.
    pub fn zero_based(x: usize, y: usize) -> Result<Self, ThudError> {
        Coord::check_coords(x, y)?;
        Ok(Coord { x, y })
    }

    pub fn one_based(x: usize, y: usize) -> Result<Self, ThudError> {
        let (x, y) = (x - 1, y - 1);
        Self::zero_based(x, y)
    }

    /// Get the values inside the coordinate, zero-based.
    ///
    /// Since `Coord` is bound-checked on creation, the values returned here are guaranteed to be
    /// valid coordinates on the board.
    pub fn value(&self) -> (usize, usize) {
        (self.x, self.y)
    }

    /// Return the larger of the two coordinates.
    ///
    /// Useful for use with [`.diff()`](#method.diff) to get the orthogonal/diagonal distance between two squares:
    /// ```
    /// use thud::Coord;
    ///
    /// let source = Coord::zero_based(7,7).unwrap();
    /// let destination1 = Coord::zero_based(10, 10).unwrap();
    /// let destination2 = Coord::zero_based(12, 7).unwrap();
    ///
    /// assert_eq!(source.diff(destination1).max(), 3);
    /// assert_eq!(source.diff(destination2).max(), 5);
    /// ```
    pub fn max(&self) -> usize {
        if self.x > self.y {
            self.x
        } else {
            self.y
        }
    }

    /// Return the *absolute* difference between two `Coord`s.
    ///
    /// Example:
    /// ```
    /// use thud::Coord;
    ///
    /// let source = Coord::zero_based(7,7).unwrap();
    /// let destination1 = Coord::zero_based(10, 10).unwrap();
    /// let destination2 = Coord::zero_based(12, 7).unwrap();
    ///
    /// assert_eq!(source.diff(destination1), (3, 3).into());
    /// assert_eq!(source.diff(destination2), (5, 0).into());
    /// ```
    pub fn diff(self, rhs: Self) -> Self {
        let new_x = if self.x > rhs.x {
            self.x - rhs.x
        } else {
            rhs.x - self.x
        };
        let new_y = if self.y > rhs.y {
            self.y - rhs.y
        } else {
            rhs.y - self.y
        };

        Coord { x: new_x, y: new_y }
    }
}

impl From<(usize, usize)> for Coord {
    fn from((x, y): (usize, usize)) -> Self {
        Coord::zero_based(x, y).unwrap()
    }
}

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

    #[test_case(6, 9)]
    #[test_case(2, 3)]
    #[test_case(5, 0)]
    #[test_case(9, 0)]
    #[test_case(10, 2)]
    #[test_case(13, 5)]
    #[test_case(14, 6)]
    #[test_case(14, 8)]
    #[test_case(0, 0 => panics "no")]
    #[test_case(4, 0 => panics "no")]
    #[test_case(10, 0 => panics "no")]
    #[test_case(14, 4 => panics "no")]
    #[test_case(14, 10 => panics "no")]
    fn valid_coordinates(x: usize, y: usize) {
        Coord::zero_based(x, y).expect("no");
    }

    #[test_case(0, 9)]
    #[test_case(2, 3)]
    #[test_case(5, 0)]
    #[test_case(9, 0)]
    #[test_case(10, 2)]
    #[test_case(13, 5)]
    #[test_case(14, 6)]
    fn into(x: usize, y: usize) {
        let _coord: Coord = (x, y).into();
    }

    #[test_case((7,7), (8,8) => 1)]
    #[test_case((8,8), (7,7) => 1)]
    #[test_case((7,8), (8,8) => 1)]
    #[test_case((7,7), (9,8) => 2)]
    #[test_case((7,7), (10,7) => 3)]
    #[test_case((8,7), (9,7) => 1)]
    fn diff_then_max(lhs: (usize, usize), rhs: (usize, usize)) -> usize {
        Coord::zero_based(lhs.0, lhs.1)
            .unwrap()
            .diff(Coord::zero_based(rhs.0, rhs.1).unwrap())
            .max()
    }
}