use prolog_parser::ast::*;

use crate::prolog::allocator::*;
use crate::prolog::arithmetic::*;
use crate::prolog::clause_types::*;
use crate::prolog::fixtures::*;
use crate::prolog::forms::*;
use crate::prolog::indexing::*;
use crate::prolog::instructions::*;
use crate::prolog::iterators::*;
use crate::prolog::machine::machine_indices::*;
use crate::prolog::targets::*;

use indexmap::{IndexMap, IndexSet};

use std::cell::Cell;
use std::rc::Rc;
use std::vec::Vec;

pub struct CodeGenerator<TermMarker> {
    marker: TermMarker,
    pub var_count: IndexMap<Rc<Var>, usize>,
    non_counted_bt: bool,
}

pub struct ConjunctInfo<'a> {
    pub perm_vs: VariableFixtures<'a>,
    pub num_of_chunks: usize,
    pub has_deep_cut: bool,
}

impl<'a> ConjunctInfo<'a> {
    fn new(perm_vs: VariableFixtures<'a>, num_of_chunks: usize, has_deep_cut: bool) -> Self {
        ConjunctInfo {
            perm_vs,
            num_of_chunks,
            has_deep_cut,
        }
    }

    fn allocates(&self) -> bool {
        self.perm_vs.size() > 0 || self.num_of_chunks > 1 || self.has_deep_cut
    }

    fn perm_vars(&self) -> usize {
        self.perm_vs.size() + self.perm_var_offset()
    }

    fn perm_var_offset(&self) -> usize {
        self.has_deep_cut as usize
    }

    fn mark_unsafe_vars(
        &self,
        mut unsafe_var_marker: UnsafeVarMarker,
        code: &mut Code,
    ) {
        if code.is_empty() {
            return;
        }

        let mut code_index = 0;

        for phase in 0 .. {
            while let Line::Query(ref query_instr) = &code[code_index] {
                if !unsafe_var_marker.mark_safe_vars(query_instr) {
                    unsafe_var_marker.mark_phase(query_instr, phase);
                }

                code_index += 1;
            }

            if code_index + 1 < code.len() {
                code_index += 1;
            } else {
                break;
            }
        }

        code_index = 0;

        for phase in 0 .. {
            while let Line::Query(ref mut query_instr) = &mut code[code_index] {
                unsafe_var_marker.mark_unsafe_vars(query_instr, phase);
                code_index += 1;
            }

            if code_index + 1 < code.len() {
                code_index += 1;
            } else {
                break;
            }
        }
    }
}

impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker> {
    pub fn new(non_counted_bt: bool) -> Self {
        CodeGenerator {
            marker: Allocator::new(),
            var_count: IndexMap::new(),
            non_counted_bt,
        }
    }

    pub fn take_vars(self) -> AllocVarDict {
        self.marker.take_bindings()
    }

    fn update_var_count<Iter: Iterator<Item = TermRef<'a>>>(&mut self, iter: Iter) {
        for term in iter {
            if let TermRef::Var(_, _, var) = term {
                let entry = self.var_count.entry(var).or_insert(0);
                *entry += 1;
            }
        }
    }

    fn get_var_count(&self, var: &'a Var) -> usize {
        *self.var_count.get(var).unwrap()
    }

    fn mark_non_callable(
        &mut self,
        name: Rc<Var>,
        arity: usize,
        term_loc: GenContext,
        vr: &'a Cell<VarReg>,
        code: &mut Code,
    ) -> RegType {
        match self.marker.bindings().get(&name) {
            Some(&VarData::Temp(_, t, _)) if t != 0 => RegType::Temp(t),
            Some(&VarData::Perm(p)) if p != 0 => RegType::Perm(p),
            _ => {
                let mut target = Vec::new();

                self.marker.reset_arg(arity);
                self.marker
                    .mark_var(name, Level::Shallow, vr, term_loc, &mut target);

                if !target.is_empty() {
                    for query_instr in target {
                        code.push(Line::Query(query_instr));
                    }
                }

                vr.get().norm()
            }
        }
    }

    fn add_or_increment_void_instr<Target>(target: &mut Vec<Target>)
    where
        Target: CompilationTarget<'a>,
    {
        if let Some(ref mut instr) = target.last_mut() {
            if Target::is_void_instr(&*instr) {
                Target::incr_void_instr(instr);
                return;
            }
        }

        target.push(Target::to_void(1));
    }

    fn deep_var_instr<Target: CompilationTarget<'a>>(
        &mut self,
        cell: &'a Cell<VarReg>,
        var: &'a Rc<Var>,
        term_loc: GenContext,
        is_exposed: bool,
        target: &mut Vec<Target>,
    ) {
        if is_exposed || self.get_var_count(var.as_ref()) > 1 {
            self.marker.mark_var(var.clone(), Level::Deep, cell, term_loc, target);
        } else {
            Self::add_or_increment_void_instr(target);
        }
    }

    fn subterm_to_instr<Target: CompilationTarget<'a>>(
        &mut self,
        subterm: &'a Term,
        term_loc: GenContext,
        is_exposed: bool,
        target: &mut Vec<Target>,
    ) {
        match subterm {
            &Term::AnonVar if is_exposed => {
                self.marker.mark_anon_var(Level::Deep, term_loc, target);
            }
            &Term::AnonVar => {
                Self::add_or_increment_void_instr(target);
            }
            &Term::Cons(ref cell, _, _) | &Term::Clause(ref cell, _, _, _) => {
                self.marker.mark_non_var(Level::Deep, term_loc, cell, target);
                target.push(Target::clause_arg_to_instr(cell.get()));
            }
            &Term::Constant(_, ref constant) => {
                target.push(Target::constant_subterm(constant.clone()));
            }
            &Term::Var(ref cell, ref var) => {
                self.deep_var_instr(cell, var, term_loc, is_exposed, target);
            }
        };
    }

     fn compile_target<Target, Iter>(
        &mut self,
        iter: Iter,
        term_loc: GenContext,
        is_exposed: bool,
    ) -> Vec<Target>
    where
        Target: CompilationTarget<'a>,
        Iter: Iterator<Item = TermRef<'a>>,
    {
        let mut target = Vec::new();

        for term in iter {
            match term {
                TermRef::AnonVar(lvl @ Level::Shallow) => {
                    if let GenContext::Head = term_loc {
                        self.marker.advance_arg();
                    } else {
                        self.marker.mark_anon_var(lvl, term_loc, &mut target);
                    }
                }
                TermRef::Clause(lvl, cell, ct, terms) => {
                    self.marker.mark_non_var(lvl, term_loc, cell, &mut target);
                    target.push(Target::to_structure(ct, terms.len(), cell.get()));

                    for subterm in terms {
                        self.subterm_to_instr(subterm.as_ref(), term_loc, is_exposed, &mut target);
                    }
                }
                TermRef::Cons(lvl, cell, head, tail) => {
                    self.marker.mark_non_var(lvl, term_loc, cell, &mut target);
                    target.push(Target::to_list(lvl, cell.get()));

                    self.subterm_to_instr(head, term_loc, is_exposed, &mut target);
                    self.subterm_to_instr(tail, term_loc, is_exposed, &mut target);
                }
                TermRef::Constant(lvl @ Level::Shallow, cell, Constant::String(ref string)) => {
                    self.marker.mark_non_var(lvl, term_loc, cell, &mut target);
                    target.push(Target::to_pstr(lvl, string.to_string(), cell.get(), false));
                }
                TermRef::Constant(lvl @ Level::Shallow, cell, constant) => {
                    self.marker.mark_non_var(lvl, term_loc, cell, &mut target);
                    target.push(Target::to_constant(lvl, constant.clone(), cell.get()));
                }
                TermRef::PartialString(lvl, cell, string, tail) => {
                    self.marker.mark_non_var(lvl, term_loc, cell, &mut target);

                    if let Some(tail) = tail {
                        target.push(Target::to_pstr(lvl, string, cell.get(), true));
                        self.subterm_to_instr(tail, term_loc, is_exposed, &mut target);
                    } else {
                        target.push(Target::to_pstr(lvl, string, cell.get(), false));
                    }
                }
                TermRef::Var(lvl @ Level::Shallow, cell, ref var) if var.as_str() == "!" => {
                    if self.marker.is_unbound(var.clone()) {
                        if term_loc != GenContext::Head {
                            self.marker.mark_reserved_var(
                                var.clone(),
                                lvl,
                                cell,
                                term_loc,
                                &mut target,
                                perm_v!(1),
                                false,
                            );
                            continue;
                        }
                    }

                    self.marker.mark_var(var.clone(), lvl, cell, term_loc, &mut target);
                }
                TermRef::Var(lvl @ Level::Shallow, cell, var) => {
                    self.marker.mark_var(var.clone(), lvl, cell, term_loc, &mut target);
                }
                _ => {
                }
            };
        }

        target
    }

    fn collect_var_data(&mut self, mut iter: ChunkedIterator<'a>) -> ConjunctInfo<'a> {
        let mut vs = VariableFixtures::new();

        while let Some((chunk_num, lt_arity, chunked_terms)) = iter.next() {
            for (i, chunked_term) in chunked_terms.iter().enumerate() {
                let term_loc = match chunked_term {
                    &ChunkedTerm::HeadClause(..) =>
                        GenContext::Head,
                    &ChunkedTerm::BodyTerm(_) => {
                        if i < chunked_terms.len() - 1 {
                            GenContext::Mid(chunk_num)
                        } else {
                            GenContext::Last(chunk_num)
                        }
                    }
                };

                self.update_var_count(chunked_term.post_order_iter());
                vs.mark_vars_in_chunk(chunked_term.post_order_iter(), lt_arity, term_loc);
            }
        }

        let num_of_chunks = iter.chunk_num;
        let has_deep_cut = iter.encountered_deep_cut();

        vs.populate_restricting_sets();
        vs.set_perm_vals(has_deep_cut);

        let vs = self.marker.drain_var_data(vs, num_of_chunks);
        ConjunctInfo::new(vs, num_of_chunks, has_deep_cut)
    }

    fn add_conditional_call(code: &mut Code, qt: &QueryTerm, pvs: usize) {
        match qt {
            &QueryTerm::Jump(ref vars) => code.push(jmp_call!(vars.len(), 0, pvs)),
            &QueryTerm::Clause(_, ref ct, ref terms, true) => {
                code.push(call_clause_by_default!(ct.clone(), terms.len(), pvs))
            }
            &QueryTerm::Clause(_, ref ct, ref terms, false) => {
                code.push(call_clause!(ct.clone(), terms.len(), pvs))
            }
            _ => {}
        }
    }

    fn lco(code: &mut Code) -> usize {
        let mut dealloc_index = code.len() - 1;

        match code.last_mut() {
            Some(&mut Line::Control(ref mut ctrl)) => match ctrl {
                &mut ControlInstruction::CallClause(_, _, _, ref mut last_call, _) => {
                    *last_call = true
                }
                &mut ControlInstruction::JmpBy(_, _, _, ref mut last_call) => *last_call = true,
                &mut ControlInstruction::Proceed => {}
                _ => dealloc_index += 1,
            },
            Some(&mut Line::Cut(CutInstruction::Cut(_))) => dealloc_index += 1,
            _ => {}
        };

        dealloc_index
    }

    fn compile_inlined(
        &mut self,
        ct: &InlinedClauseType,
        terms: &'a Vec<Box<Term>>,
        term_loc: GenContext,
        code: &mut Code,
    ) -> Result<(), ParserError> {
        match ct {
            &InlinedClauseType::CompareNumber(cmp, ..) => {
                if let &Term::Var(ref vr, ref name) = terms[0].as_ref() {
                    self.mark_non_callable(name.clone(), 2, term_loc, vr, code);
                }

                if let &Term::Var(ref vr, ref name) = terms[1].as_ref() {
                    self.mark_non_callable(name.clone(), 2, term_loc, vr, code);
                }

                let (mut lcode, at_1) = self.call_arith_eval(terms[0].as_ref(), 1)?;
                let (mut rcode, at_2) = self.call_arith_eval(terms[1].as_ref(), 2)?;

                code.append(&mut lcode);
                code.append(&mut rcode);

                code.push(compare_number_instr!(
                    cmp,
                    at_1.unwrap_or(interm!(1)),
                    at_2.unwrap_or(interm!(2))
                ));
            }
            &InlinedClauseType::IsAtom(..) => match terms[0].as_ref() {
                &Term::Constant(_, Constant::Char(_))
                | &Term::Constant(_, Constant::EmptyList)
                | &Term::Constant(_, Constant::Atom(..)) => {
                    code.push(succeed!());
                }
                &Term::Var(ref vr, ref name) => {
                    let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                    code.push(is_atom!(r));
                }
                _ => {
                    code.push(fail!());
                }
            },
            &InlinedClauseType::IsAtomic(..) => match terms[0].as_ref() {
                &Term::AnonVar | &Term::Clause(..) | &Term::Cons(..) => {
                    code.push(fail!());
                }
                &Term::Constant(..) => {
                    code.push(succeed!());
                }
                &Term::Var(ref vr, ref name) => {
                    let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                    code.push(is_atomic!(r));
                }
            },
            &InlinedClauseType::IsCompound(..) => match terms[0].as_ref() {
                &Term::Clause(..) | &Term::Cons(..) => {
                    code.push(succeed!());
                }
                &Term::Var(ref vr, ref name) => {
                    let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                    code.push(is_compound!(r));
                }
                _ => {
                    code.push(fail!());
                }
            },
            &InlinedClauseType::IsRational(..) => match terms[0].as_ref() {
                &Term::Constant(_, Constant::Rational(_)) => {
                    code.push(succeed!());
                }
                &Term::Var(ref vr, ref name) => {
                    let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                    code.push(is_rational!(r));
                }
                _ => {
                    code.push(fail!());
                }
            },
            &InlinedClauseType::IsFloat(..) => match terms[0].as_ref() {
                &Term::Constant(_, Constant::Float(_)) => {
                    code.push(succeed!());
                }
                &Term::Var(ref vr, ref name) => {
                    let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                    code.push(is_float!(r));
                }
                _ => {
                    code.push(fail!());
                }
            },
            &InlinedClauseType::IsNonVar(..) => match terms[0].as_ref() {
                &Term::AnonVar => {
                    code.push(fail!());
                }
                &Term::Var(ref vr, ref name) => {
                    let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                    code.push(is_nonvar!(r));
                }
                _ => {
                    code.push(succeed!());
                }
            },
            &InlinedClauseType::IsInteger(..) => match terms[0].as_ref() {
                &Term::Constant(_, Constant::Integer(_)) |
                &Term::Constant(_, Constant::Fixnum(_)) => {
                    code.push(succeed!());
                }
                &Term::Var(ref vr, ref name) => {
                    let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                    code.push(is_integer!(r));
                }
                _ => {
                    code.push(fail!());
                }
            },
            &InlinedClauseType::IsVar(..) => match terms[0].as_ref() {
                &Term::Constant(..) | &Term::Clause(..) | &Term::Cons(..) => {
                    code.push(fail!());
                }
                &Term::AnonVar => {
                    code.push(succeed!());
                }
                &Term::Var(ref vr, ref name) => {
                    let r = self.mark_non_callable(name.clone(), 1, term_loc, vr, code);
                    code.push(is_var!(r));
                }
            },
        }

        Ok(())
    }

    fn call_arith_eval(
        &self,
        term: &'a Term,
        target_int: usize,
    ) -> Result<ArithCont, ArithmeticError> {
        let mut evaluator = ArithmeticEvaluator::new(self.marker.bindings(), target_int);
        evaluator.eval(term)
    }

    fn compile_is_call(
        &mut self,
        terms: &'a Vec<Box<Term>>,
        code: &mut Code,
        term_loc: GenContext,
        use_default_call_policy: bool,
    ) -> Result<(), ParserError> {
        let (mut acode, at) = self.call_arith_eval(terms[1].as_ref(), 1)?;
        code.append(&mut acode);

        Ok(match terms[0].as_ref() {
            &Term::Var(ref vr, ref name) => {
                let mut target = vec![];

                self.marker.reset_arg(2);
                self.marker
                    .mark_var(name.clone(), Level::Shallow, vr, term_loc, &mut target);

                if !target.is_empty() {
                    code.extend(target.into_iter().map(Line::Query));
                }

                if use_default_call_policy {
                    code.push(is_call_by_default!(temp_v!(1), at.unwrap_or(interm!(1))))
                } else {
                    code.push(is_call!(temp_v!(1), at.unwrap_or(interm!(1))))
                }
            }
            &Term::Constant(_, ref c @ Constant::Integer(_)) |
            &Term::Constant(_, ref c @ Constant::Fixnum(_)) => {
                code.push(Line::Query(put_constant!(
                    Level::Shallow,
                    c.clone(),
                    temp_v!(1)
                )));

                if use_default_call_policy {
                    code.push(is_call_by_default!(temp_v!(1), at.unwrap_or(interm!(1))))
                } else {
                    code.push(is_call!(temp_v!(1), at.unwrap_or(interm!(1))))
                }
            }
            &Term::Constant(_, ref c @ Constant::Float(_)) => {
                code.push(Line::Query(put_constant!(
                    Level::Shallow,
                    c.clone(),
                    temp_v!(1)
                )));

                if use_default_call_policy {
                    code.push(is_call_by_default!(temp_v!(1), at.unwrap_or(interm!(1))))
                } else {
                    code.push(is_call!(temp_v!(1), at.unwrap_or(interm!(1))))
                }
            }
            &Term::Constant(_, ref c @ Constant::Rational(_)) => {
                code.push(Line::Query(put_constant!(
                    Level::Shallow,
                    c.clone(),
                    temp_v!(1)
                )));

                if use_default_call_policy {
                    code.push(is_call_by_default!(temp_v!(1), at.unwrap_or(interm!(1))))
                } else {
                    code.push(is_call!(temp_v!(1), at.unwrap_or(interm!(1))))
                }
            }
            _ => code.push(fail!()),
        })
    }

    #[inline]
    fn compile_unblocked_cut(&mut self, code: &mut Code, cell: &'a Cell<VarReg>) {
        let r = self.marker.get(Rc::new(String::from("!")));
        cell.set(VarReg::Norm(r));
        code.push(set_cp!(cell.get().norm()));
    }

    fn compile_get_level_and_unify(
        &mut self,
        code: &mut Code,
        cell: &'a Cell<VarReg>,
        var: Rc<Var>,
        term_loc: GenContext,
    ) {
        let mut target = Vec::new();

        self.marker.reset_arg(1);
        self.marker
            .mark_var(var, Level::Shallow, cell, term_loc, &mut target);

        if !target.is_empty() {
            code.extend(
                target
                    .into_iter()
                    .map(|query_instr| Line::Query(query_instr)),
            );
        }

        code.push(get_level_and_unify!(cell.get().norm()));
    }

    fn compile_seq(
        &mut self,
        iter: ChunkedIterator<'a>,
        conjunct_info: &ConjunctInfo<'a>,
        code: &mut Code,
        is_exposed: bool,
    ) -> Result<(), ParserError> {
        for (chunk_num, _, terms) in iter.rule_body_iter() {
            for (i, term) in terms.iter().enumerate() {
                let term_loc = if i + 1 < terms.len() {
                    GenContext::Mid(chunk_num)
                } else {
                    GenContext::Last(chunk_num)
                };

                match *term {
                    &QueryTerm::GetLevelAndUnify(ref cell, ref var) => {
                        self.compile_get_level_and_unify(code, cell, var.clone(), term_loc)
                    }
                    &QueryTerm::UnblockedCut(ref cell) => self.compile_unblocked_cut(code, cell),
                    &QueryTerm::BlockedCut => code.push(if chunk_num == 0 {
                        Line::Cut(CutInstruction::NeckCut)
                    } else {
                        Line::Cut(CutInstruction::Cut(perm_v!(1)))
                    }),
                    &QueryTerm::Clause(
                        _,
                        ClauseType::BuiltIn(BuiltInClauseType::Is(..)),
                        ref terms,
                        use_default_call_policy,
                    ) => self.compile_is_call(terms, code, term_loc, use_default_call_policy)?,
                    &QueryTerm::Clause(_, ClauseType::Inlined(ref ct), ref terms, _) => {
                        self.compile_inlined(ct, terms, term_loc, code)?
                    }
                    _ => {
                        let num_perm_vars = if chunk_num == 0 {
                            conjunct_info.perm_vars()
                        } else {
                            conjunct_info.perm_vs.vars_above_threshold(i + 1)
                        };

                        self.compile_query_line(term, term_loc, code, num_perm_vars, is_exposed);
                    }
                }
            }

            self.marker.reset_contents();
        }

        Ok(())
    }

    fn compile_seq_prelude(&mut self, conjunct_info: &ConjunctInfo, body: &mut Code) {
        if conjunct_info.allocates() {
            let perm_vars = conjunct_info.perm_vars();

            body.push(Line::Control(ControlInstruction::Allocate(perm_vars)));

            if conjunct_info.has_deep_cut {
                body.push(Line::Cut(CutInstruction::GetLevel(perm_v!(1))));
            }
        }
    }

    fn compile_cleanup(code: &mut Code, conjunct_info: &ConjunctInfo, toc: &'a QueryTerm) {
        // add a proceed to bookend any trailing cuts.
        match toc {
            &QueryTerm::BlockedCut | &QueryTerm::UnblockedCut(..) => code.push(proceed!()),
            &QueryTerm::Clause(_, ClauseType::Inlined(..), ..) => code.push(proceed!()),
            _ => {}
        };

        // perform lco.
        let dealloc_index = Self::lco(code);

        if conjunct_info.allocates() {
            code.insert(dealloc_index, Line::Control(ControlInstruction::Deallocate));
        }
    }

    pub fn compile_rule<'b: 'a>(&mut self, rule: &'b Rule) -> Result<Code, ParserError> {
        let iter = ChunkedIterator::from_rule(rule);
        let conjunct_info = self.collect_var_data(iter);

        let &Rule {
            head: (_, ref args, ref p1),
            ref clauses,
        } = rule;

        let mut code = Vec::new();

        self.marker.reset_at_head(args);
        self.compile_seq_prelude(&conjunct_info, &mut code);

        let iter = FactIterator::from_rule_head_clause(args);
        let mut fact = self.compile_target(iter, GenContext::Head, false);

        let mut unsafe_var_marker = UnsafeVarMarker::new();

        if !fact.is_empty() {
            unsafe_var_marker = self.mark_unsafe_fact_vars(&mut fact);

            for fact_instr in fact {
                code.push(Line::Fact(fact_instr));
            }
        }

        let iter = ChunkedIterator::from_rule_body(p1, clauses);
        self.compile_seq(iter, &conjunct_info, &mut code, false)?;

        conjunct_info.mark_unsafe_vars(unsafe_var_marker, &mut code);

        Self::compile_cleanup(&mut code, &conjunct_info, clauses.last().unwrap_or(p1));
        Ok(code)
    }

    fn mark_unsafe_fact_vars(&self, fact: &mut CompiledFact) -> UnsafeVarMarker {
        let mut safe_vars = IndexSet::new();

        for fact_instr in fact.iter_mut() {
            match fact_instr {
                &mut FactInstruction::UnifyValue(r) => {
                    if !safe_vars.contains(&r) {
                        *fact_instr = FactInstruction::UnifyLocalValue(r);
                        safe_vars.insert(r);
                    }
                }
                &mut FactInstruction::UnifyVariable(r) => {
                    safe_vars.insert(r);
                }
                _ => {}
            }
        }

        UnsafeVarMarker::from_safe_vars(safe_vars)
    }

    pub fn compile_fact<'b: 'a>(&mut self, term: &'b Term) -> Code {
        self.update_var_count(post_order_iter(term));

        let mut vs = VariableFixtures::new();
        vs.mark_vars_in_chunk(post_order_iter(term), term.arity(), GenContext::Head);

        vs.populate_restricting_sets();
        self.marker.drain_var_data(vs, 1);

        let mut code = Vec::new();

        if let &Term::Clause(_, _, ref args, _) = term {
            self.marker.reset_at_head(args);

            let iter = FactInstruction::iter(term);
            let mut compiled_fact = self.compile_target(iter, GenContext::Head, false);

            self.mark_unsafe_fact_vars(&mut compiled_fact);

            if !compiled_fact.is_empty() {
                for fact_instr in compiled_fact {
                    code.push(Line::Fact(fact_instr));
                }
            }
        }

        code.push(proceed!());
        code
    }

    fn compile_query_line(
        &mut self,
        term: &'a QueryTerm,
        term_loc: GenContext,
        code: &mut Code,
        num_perm_vars_left: usize,
        is_exposed: bool,
    ) {
        self.marker.reset_arg(term.arity());

        let iter = query_term_post_order_iter(term);
        let query = self.compile_target(iter, term_loc, is_exposed);

        if !query.is_empty() {
            for query_instr in query {
                code.push(Line::Query(query_instr));
            }
        }

        Self::add_conditional_call(code, term, num_perm_vars_left);
    }

    pub fn compile_query(&mut self, query: &'a Vec<QueryTerm>) -> Result<Code, ParserError> {
        let iter = ChunkedIterator::from_term_sequence(query);
        let conjunct_info = self.collect_var_data(iter);

        let mut code = Vec::new();
        self.compile_seq_prelude(&conjunct_info, &mut code);

        let iter = ChunkedIterator::from_term_sequence(query);
        self.compile_seq(iter, &conjunct_info, &mut code, true)?;

        conjunct_info.mark_unsafe_vars(UnsafeVarMarker::new(), &mut code);

        if let Some(query_term) = query.last() {
            Self::compile_cleanup(&mut code, &conjunct_info, query_term);
        }

        Ok(code)
    }

    fn split_predicate(clauses: &Vec<PredicateClause>) -> Vec<(usize, usize)> {
        let mut subseqs = Vec::new();
        let mut left_index = 0;

        for (right_index, clause) in clauses.iter().enumerate() {
            match clause.first_arg() {
                Some(&Term::Var(_, _)) | Some(&Term::AnonVar) => {
                    if left_index < right_index {
                        subseqs.push((left_index, right_index));
                    }

                    subseqs.push((right_index, right_index + 1));
                    left_index = right_index + 1;
                }
                _ => {}
            }
        }

        if left_index < clauses.len() {
            subseqs.push((left_index, clauses.len()));
        }

        subseqs
    }

    fn trust_me(&self) -> ChoiceInstruction {
        if self.non_counted_bt {
            ChoiceInstruction::DefaultTrustMe
        } else {
            ChoiceInstruction::TrustMe
        }
    }

    fn retry_me_else(&self, offset: usize) -> ChoiceInstruction {
        if self.non_counted_bt {
            ChoiceInstruction::DefaultRetryMeElse(offset)
        } else {
            ChoiceInstruction::RetryMeElse(offset)
        }
    }

    fn compile_pred_subseq<'b: 'a>(
        &mut self,
        clauses: &'b [PredicateClause],
    ) -> Result<Code, ParserError> {
        let mut code_body = Vec::new();
        let mut code_offsets = CodeOffsets::new();

        let num_clauses = clauses.len();

        for (i, clause) in clauses.iter().enumerate() {
            self.marker.reset();

            let mut clause_code = match clause {
                &PredicateClause::Fact(ref fact, ..) => self.compile_fact(fact),
                &PredicateClause::Rule(ref rule, ..) => self.compile_rule(rule)?,
            };

            if num_clauses > 1 {
                let choice = match i {
                    0 => ChoiceInstruction::TryMeElse(clause_code.len() + 1),
                    _ if i == num_clauses - 1 => self.trust_me(),
                    _ => self.retry_me_else(clause_code.len() + 1),
                };

                code_body.push(Line::Choice(choice));
            }

            clause.first_arg().map(|arg| {
                let index = code_body.len();
                code_offsets.index_term(arg, index);
            });

            code_body.append(&mut clause_code);
        }

        let mut code = Vec::new();

        code_offsets.add_indices(&mut code, code_body);
        Ok(code)
    }

    pub fn compile_predicate<'b: 'a>(
        &mut self,
        clauses: &'b Vec<PredicateClause>,
    ) -> Result<Code, ParserError> {
        let mut code = Vec::new();
        let split_pred = Self::split_predicate(&clauses);
        let multi_seq = split_pred.len() > 1;

        for (l, r) in split_pred {
            let mut code_segment = self.compile_pred_subseq(&clauses[l..r])?;

            if multi_seq {
                let choice = match l {
                    0 => ChoiceInstruction::TryMeElse(code_segment.len() + 1),
                    _ if r == clauses.len() => self.trust_me(),
                    _ => self.retry_me_else(code_segment.len() + 1),
                };

                code.push(Line::Choice(choice));
            }

            code.append(&mut code_segment);
        }

        Ok(code)
    }
}