ruSTLa 0.38.0

/*!
A submodule that contains the line cursor type and its associated function definitions.

Copyright © 2020 Santtu Söderholm
*/

/// ### LineCursor
/// A line cursor type of a parser that holds the start line and offset from it.
/// The relative offset cursor is used to actually access
/// the source lines' contents, whereas the sum of relative and absolute cursors is
/// used mainly for debug prints and|or error messages.
#[derive(Debug)]
pub struct LineCursor {

    /// This is used to access the contents of the source lines vector held by the parser.
    /// It should generally be initialized to `0`.
    offset: Line,

    /// The line of text that a parser started working on.
    baseline: Line,
}

impl LineCursor {

    /// A `LineCursor` constructor.
    pub fn new(relative: Line, absolute: Line) -> Self {
        Self {
            offset: relative,
            baseline: absolute,
        }
    }

    /// Retrieves the line relative to the baseline that a (nested) parser is on.
    pub fn relative_offset(&self) -> Line {
        self.offset
    }

    /// Retrieves a mutable reference to the line that the (nested) parser is on.
    pub fn relative_offset_mut_ref(&mut self) -> &mut Line {
        &mut self.offset
    }

    /// Increments relative offset by given `amount`.
    pub fn increment_by(&mut self, amount: Line) {
        self.offset = match self.offset.checked_add(amount) {
            Some(line) => line,
            None => {
                eprintln!("Tried incrementing relative line offset by {} on line {} but overflowed.\nComputer says no...\n", amount, self.sum_total());
                panic!()
            }
        };
    }

    /// Returns the sum total of `self.relative_offset` and `*self.baseline`.
    pub fn sum_total(&self) -> Line {
        self.offset + self.baseline
    }
}

/// A type alias for a line vector index.
pub type Line = usize;