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/*
    Appellation: turing <module>
    Contrib: FL03 <jo3mccain@icloud.com>
    Description: ... summary ...
*/
pub use self::{instructions::*, machine::*, operator::*, programs::*, tapes::*};

pub(crate) mod instructions;
pub(crate) mod machine;
pub(crate) mod operator;
pub(crate) mod programs;
pub(crate) mod tapes;

use crate::{
    states::{Stateful, States},
    Scope, Symbolic,
};

/// [Turing] describes a programmable Turing machine
pub trait Turing<S: Symbolic> {
    type Error;
    type Scope: Clone + Scope<S>;

    /// [Turing::driver]
    fn driver(&mut self) -> &mut Self::Scope;
    /// [Turing::execute]
    fn execute(&mut self, program: Program<S>) -> Result<Self::Scope, Self::Error> {
        let until = |actor: &Self::Scope| actor.clone().state().state().clone() == States::Invalid;
        self.execute_until(program, until)
    }
    /// [Turing::execute_once]
    fn execute_once(&mut self, program: Program<S>) -> Result<Self::Scope, Self::Error> {
        let head = Head::new(
            self.driver().state().clone().into(),
            self.driver().scope().clone(),
        );
        let inst = program
            .get(head)
            .expect("Failed to fetch the instruction head...")
            .clone();
        self.driver().set_state(inst.tail().state().clone());
        self.driver().set_symbol(inst.tail().symbol().clone());
        self.driver()
            .shift(*inst.tail().action(), program.default_symbol().clone());
        Ok(self.driver().clone())
    }
    /// [Turing::execute_until]
    fn execute_until(
        &mut self,
        program: Program<S>,
        until: impl Fn(&Self::Scope) -> bool,
    ) -> Result<Self::Scope, Self::Error> {
        while !until(self.driver()) {
            let head = Head::new(
                self.driver().state().clone().into(),
                self.driver().scope().clone(),
            );
            let inst = program
                .get(head)
                .expect("Failed to fetch the instruction head...")
                .clone();
            self.driver().set_state(inst.tail().state().clone());
            self.driver().set_symbol(inst.tail().symbol().clone());
            self.driver()
                .shift(*inst.tail().action(), program.default_symbol().clone());
        }
        Ok(self.driver().clone())
    }
    /// [Turing::translate] returns the mutated [Tape] after updating the [Turing::Scope] and finally invoking [Turing::execute]
    fn translate(&mut self, program: Program<S>, tape: Tapes<S>) -> Result<Tape<S>, Self::Error> {
        self.update(tape);
        Ok(self.execute(program)?.tape().clone())
    }
    /// [Turing::update] updates the [Turing::Scope] based on the given [Tapes]
    fn update(&mut self, tape: Tapes<S>);
}