//! This file defines the behaviour of the Atomic languages, and
//! provides a default implementation.
//!
//! Here I do not to substitute external packages' implementations in
//! the future, so why define a trait for the atomic languages?
//! Because this way I can easily substitute other implementations if
//! I have better ideas in the future.

use grammar::{Error as GrammarError, Grammar, TNT};
use nfa::{DOption, LabelType, Nfa};

use std::ops::Deref;

/// The expected behaviours of an atomic language.
pub trait Atom: Nfa<LabelType<TNT>> + Deref<Target = Grammar> {
    /// Return the index of a node representing the derivative of the
    /// left-linear null closure of `nt` with respect to `t`.
    fn atom(&self, nt: usize, t: usize) -> Result<Option<usize>, GrammarError>;

    /// A type that iterates through the rule positions.
    type Iter<'a>: Iterator<Item = usize> + 'a
    where
        Self: 'a;

    /// Return an iterator of rule positions responsible for an edge
    /// from the virtual node corresponding to the non-terminal `nt`
    /// and terminal `t` to `target`.
    fn trace(&self, nt: usize, t: usize, target: usize) -> Option<<Self as Atom>::Iter<'_>>;

    /// Return the index of the empty state.
    fn empty(&self) -> usize;

    /// Tell whether a node is accepting.
    fn is_accepting(&self, node_id: usize) -> Result<bool, GrammarError>;

    /// Return the bound for `is_accepting`.
    fn accepting_len(&self) -> usize;
}

pub mod default;

pub use default::DefaultAtom;

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

    #[cfg(feature = "test-print-viz")]
    use graph::Graph;

    #[test]
    fn atom() -> Result<(), Box<dyn std::error::Error>> {
        let grammar = new_notes_grammar()?;

        let atom = DefaultAtom::from_grammar(grammar)?;

        println!("atom = {atom}");

        #[cfg(feature = "test-print-viz")]
        {
            println!("virtual frag for 1, 3: ");

            for (index, frag) in atom
                .generate_virtual_frags(1, 3, None)
                .iter()
                .flatten()
                .enumerate()
            {
                crate::item::default::print_labels(&atom, *frag)?;
                frag.print_viz(&format!("frag {index}.gv"))?;
            }
        }

        Ok(())
    }
}