//! Definitions for finding loops in simulation.

use super::classical::compute_all;
use super::structure::{RSenvironment, RSprocess, RSreaction, RSset, RSsystem};
use super::translator::IdType;

/// Returns the prefix and the loop from a trace.
fn split<'a>(
    set: &'a RSset,
    trace: &'a [RSset]
) -> Option<(&'a [RSset], &'a [RSset])> {
    let position = trace.iter().rposition(|x| x == set);
    position.map(|pos| trace.split_at(pos))
}

/// Finds the loops by simulating the system.
fn find_loop(
    rs: &[RSreaction],
    entities: RSset,
    q: &RSset
) -> (Vec<RSset>, Vec<RSset>) {
    let mut entities = entities;
    let mut trace = vec![];
    loop {
        if let Some((prefix, hoop)) = split(&entities, &trace) {
            return (prefix.to_vec(), hoop.to_vec());
        } else {
            let t = entities.union(q);
            let products = compute_all(&t, rs);
            trace.push(entities.clone());
            entities = products;
        }
    }
}

/// Finds the loops by simulating the system.
fn find_only_loop(
    rs: &[RSreaction],
    entities: RSset,
    q: &RSset
) -> Vec<RSset> {
    let mut entities = entities;
    let mut trace = vec![];
    loop {
        if let Some((_prefix, hoop)) = split(&entities, &trace) {
            return hoop.to_vec();
        } else {
            let t = entities.union(q);
            let products = compute_all(&t, rs);
            trace.push(entities.clone());
            entities = products;
        }
    }
}

/// Finds the loops and the length of the prefix by simulating the system.
fn find_prefix_len_loop(
    rs: &[RSreaction],
    entities: RSset,
    q: &RSset
) -> (usize, Vec<RSset>) {
    let mut entities = entities;
    let mut trace = vec![];
    loop {
        if let Some((prefix, hoop)) = split(&entities, &trace) {
            return (prefix.len(), hoop.to_vec());
        } else {
            let t = entities.union(q);
            let products = compute_all(&t, rs);
            trace.push(entities.clone());
            entities = products;
        }
    }
}

// -----------------------------------------------------------------------------

/// Finds only the rules X = pre(Q, rec(X)), but not only x = pre(Q, rec(x))
/// to use in filter_map.
fn filter_delta<'a>(x: (&IdType, &'a RSprocess)) -> Option<&'a RSset> {
    use super::structure::RSprocess::*;
    let (id, rest) = x;

    if let EntitySet { entities, next_process } = rest
	&& let RecursiveIdentifier { identifier } = &**next_process
        && identifier == id
    {
        return Some(entities);
    }

    None
}

/// A special case of systems is when the context recursively provides always
/// the same set of entities.  The corresponding computation is infinite.  It
/// consists of a finite sequence of states followed by a looping sequence.
/// IMPORTANT: We return all loops for all X = Q.X, by varing X.  The set of
/// reactions Rs and the context x are constant.  Each state of the computation
/// is distinguished by the current entities E.  Under these assumptions, the
/// predicate lollipop finds the Prefixes and the Loops sequences of entities.
/// see lollipop
pub fn lollipops_decomposed(
    delta: &RSenvironment,
    reaction_rules: &[RSreaction],
    available_entities: &RSset,
) -> Vec<(Vec<RSset>, Vec<RSset>)> {
    // FIXME: i think we are only interested in "x", not all symbols that
    // satisfy X = pre(Q, rec(X))
    let filtered = delta.iter().filter_map(filter_delta);

    let find_loop_fn = |q| find_loop(reaction_rules,
				     available_entities.clone(),
				     q);

    filtered.map(find_loop_fn).collect::<Vec<_>>()
}

/// A special case of systems is when the context recursively provides always
/// the same set of entities.  The corresponding computation is infinite.  It
/// consists of a finite sequence of states followed by a looping sequence.
/// IMPORTANT: We return all loops for all X = Q.X, by varing X.  The set of
/// reactions Rs and the context x are constant.  Each state of the computation
/// is distinguished by the current entities E.  Under these assumptions, the
/// predicate lollipop finds the Prefixes and the Loops sequences of entities.
/// see lollipop
pub fn lollipops(system: RSsystem) -> Vec<(Vec<RSset>, Vec<RSset>)> {
    lollipops_decomposed(
        &system.delta,
        &system.reaction_rules,
        &system.available_entities,
    )
}

/// Only returns the loop part of the lollipop, returns for all X, where X = Q.X
/// see loop
pub fn lollipops_only_loop(system: RSsystem) -> Vec<Vec<RSset>> {
    let filtered = system.delta.iter().filter_map(filter_delta);

    let find_loop_fn = |q| {
        find_only_loop(
            &system.reaction_rules,
            system.available_entities.clone(),
            q,
        )
    };

    filtered.map(find_loop_fn).collect::<Vec<_>>()
}

pub fn lollipops_prefix_len_loop_decomposed(
    delta: &RSenvironment,
    reaction_rules: &[RSreaction],
    available_entities: &RSset,
) -> Vec<(usize, Vec<RSset>)> {
    let filtered = delta.iter().filter_map(filter_delta);

    let find_loop_fn = |q| find_prefix_len_loop(reaction_rules,
						available_entities.clone(),
						q);

    filtered.map(find_loop_fn).collect::<Vec<_>>()
}

/// see loop
pub fn lollipops_only_loop_decomposed(
    delta: &RSenvironment,
    reaction_rules: &[RSreaction],
    available_entities: &RSset,
) -> Vec<Vec<RSset>> {
    let filtered = delta.iter().filter_map(filter_delta);

    let find_loop_fn = |q| find_only_loop(reaction_rules,
					  available_entities.clone(),
					  q);

    filtered.map(find_loop_fn).collect::<Vec<_>>()
}

// -----------------------------------------------------------------------------
// Named versions
// -----------------------------------------------------------------------------

/// Finds only the rules symb = pre(Q, rec(symb)), get symb from a translator
/// to use in filter_map.
fn filter_delta_named<'a>(
    x: (&IdType, &'a RSprocess),
    symb: &IdType
) -> Option<&'a RSset> {
    use super::structure::RSprocess::*;
    let (id, rest) = x;
    if id != symb {
        return None;
    }

    if let EntitySet { entities, next_process } = rest
	&& let RecursiveIdentifier { identifier } = &**next_process
	&& identifier == id
    {
        return Some(entities);
    }
    None
}

/// A special case of systems is when the context recursively provides always
/// the same set of entities.  The corresponding computation is infinite.  It
/// consists of a finite sequence of states followed by a looping sequence.
/// IMPORTANT: We return all loops for all X = Q.X, by varing X.  The set of
/// reactions Rs and the context x are constant.  Each state of the computation
/// is distinguished by the current entities E.  Under these assumptions, the
/// predicate lollipop finds the Prefixes and the Loops sequences of entities.
/// see lollipop
pub fn lollipops_decomposed_named(
    delta: &RSenvironment,
    reaction_rules: &[RSreaction],
    available_entities: &RSset,
    symb: IdType,
) -> Option<(Vec<RSset>, Vec<RSset>)> {
    let filtered = delta
        .iter()
        .filter_map(|x| filter_delta_named(x, &symb))
        .next();

    let find_loop_fn = |q| find_loop(reaction_rules,
				     available_entities.clone(),
				     q);

    filtered.map(find_loop_fn)
}

/// A special case of systems is when the context recursively provides always
/// the same set of entities.  The corresponding computation is infinite.  It
/// consists of a finite sequence of states followed by a looping sequence.
/// IMPORTANT: We return all loops for all X = Q.X, by varing X.  The set of
/// reactions Rs and the context x are constant.  Each state of the computation
/// is distinguished by the current entities E.  Under these assumptions, the
/// predicate lollipop finds the Prefixes and the Loops sequences of entities.
/// see lollipop
pub fn lollipops_named(
    system: &RSsystem,
    symb: IdType
) -> Option<(Vec<RSset>, Vec<RSset>)> {
    lollipops_decomposed_named(
        &system.delta,
        &system.reaction_rules,
        &system.available_entities,
        symb,
    )
}

/// Only returns the loop part of the lollipop, returns for all X, where X = Q.X
/// see loop
pub fn lollipops_only_loop_named(
    system: &RSsystem,
    symb: IdType
) -> Option<Vec<RSset>> {
    let filtered = system
        .delta
        .iter()
        .filter_map(|x| filter_delta_named(x, &symb))
        .next();

    let find_loop_fn = |q| {
        find_only_loop(
            &system.reaction_rules,
            system.available_entities.clone(),
            q,
        )
    };

    filtered.map(find_loop_fn)
}

pub fn lollipops_prefix_len_loop_decomposed_named(
    delta: &RSenvironment,
    reaction_rules: &[RSreaction],
    available_entities: &RSset,
    symb: IdType,
) -> Option<(usize, Vec<RSset>)> {
    let filtered = delta
        .iter()
        .filter_map(|x| filter_delta_named(x, &symb))
        .next();

    let find_loop_fn = |q| find_prefix_len_loop(reaction_rules,
						available_entities.clone(),
						q);

    filtered.map(find_loop_fn)
}

/// see loop
pub fn lollipops_only_loop_decomposed_named(
    delta: &RSenvironment,
    reaction_rules: &[RSreaction],
    available_entities: &RSset,
    symb: IdType,
) -> Option<Vec<RSset>> {
    let filtered = delta
        .iter()
        .filter_map(|x| filter_delta_named(x, &symb))
        .next();

    let find_loop_fn = |q| find_only_loop(reaction_rules,
					  available_entities.clone(),
					  q);

    filtered.map(find_loop_fn)
}

/// see loop/5
pub fn lollipops_only_loop_decomposed_q(
    q: &RSset,
    reaction_rules: &[RSreaction],
    available_entities: &RSset,
) -> Vec<RSset> {
    let find_loop_fn = |q| find_only_loop(reaction_rules,
					  available_entities.clone(),
					  q);

    find_loop_fn(q)
}