#![allow(dead_code)]

use std::rc::Rc;
use super::structure::{RSChoices, RSenvironment, RSprocess};

pub fn unfold<'a>(environment: &'a RSenvironment<'a>, context_process: &'a RSprocess<'a>) -> Result<RSChoices<'a>, String> {
    match context_process {
	RSprocess::Nill => Ok(RSChoices::new()),
	RSprocess::RecursiveIdentifier{identifier} => {
	    let newprocess = environment.get(identifier);
	    if let Some(newprocess) = newprocess {
		unfold(environment, newprocess)
	    } else {
		Err(format!("Recursive call to missing symbol: {identifier}"))
	    }
	},
	RSprocess::EntitySet{entities, next_process} => {
	    Ok(RSChoices::from(vec![(Rc::new(entities.clone()), Rc::clone(next_process))]))
	},
	RSprocess::WaitEntity{repeat, repeated_process: _, next_process} if *repeat <= 0 => {
	    unfold(environment, next_process)
	},
	RSprocess::WaitEntity{repeat, repeated_process, next_process} if *repeat == 1 => {
	    let mut choices1 = unfold(environment, repeated_process)?;
	    choices1.replace(Rc::clone(next_process));
	    Ok(choices1)
	},
	RSprocess::WaitEntity{repeat, repeated_process, next_process} => {
	    let mut choices1 = unfold(environment, repeated_process)?;
	    choices1.replace(
		Rc::new(
		    RSprocess::WaitEntity{ repeat: (*repeat - 1),
					   repeated_process: Rc::clone(repeated_process),
					   next_process: Rc::clone(next_process) }
		)
	    );
	    Ok(choices1)
	},
	RSprocess::Summation{children} => {
	    // short-circuits with try_fold.
	    children.iter().try_fold(RSChoices::new(), |mut acc, x| {
		match unfold(environment, x) {
		    Ok(mut choices) => {acc.append(&mut choices); Ok(acc)},
		    Err(e) => Err(e)
		}
	    })
	},
	RSprocess::NondeterministicChoice{children} => {
	    // short-circuits with try_fold.
	    children.iter().try_fold(RSChoices::new(), |mut acc, x| {
		match unfold(environment, x) {
		    Ok(choices) => {acc.shuffle(choices); Ok(acc)},
		    Err(e) => Err(e)
		}
	    })
	}
    }
}