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use crate::def_use::{self, DefUse};
use crate::location::{LocationIndex, LocationTable};
use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::{Body, Local, Location, Place};
use rustc_middle::ty::GenericArg;
use rustc_mir_dataflow::move_paths::{LookupResult, MoveData, MovePathIndex};

use super::TypeChecker;

type VarPointRelation = Vec<(Local, LocationIndex)>;
type PathPointRelation = Vec<(MovePathIndex, LocationIndex)>;

struct UseFactsExtractor<'me, 'tcx> {
    var_defined_at: &'me mut VarPointRelation,
    var_used_at: &'me mut VarPointRelation,
    location_table: &'me LocationTable,
    var_dropped_at: &'me mut VarPointRelation,
    move_data: &'me MoveData<'tcx>,
    path_accessed_at_base: &'me mut PathPointRelation,
}

// A Visitor to walk through the MIR and extract point-wise facts
impl<'tcx> UseFactsExtractor<'_, 'tcx> {
    fn location_to_index(&self, location: Location) -> LocationIndex {
        self.location_table.mid_index(location)
    }

    fn insert_def(&mut self, local: Local, location: Location) {
        debug!("UseFactsExtractor::insert_def()");
        self.var_defined_at.push((local, self.location_to_index(location)));
    }

    fn insert_use(&mut self, local: Local, location: Location) {
        debug!("UseFactsExtractor::insert_use()");
        self.var_used_at.push((local, self.location_to_index(location)));
    }

    fn insert_drop_use(&mut self, local: Local, location: Location) {
        debug!("UseFactsExtractor::insert_drop_use()");
        self.var_dropped_at.push((local, self.location_to_index(location)));
    }

    fn insert_path_access(&mut self, path: MovePathIndex, location: Location) {
        debug!("UseFactsExtractor::insert_path_access({:?}, {:?})", path, location);
        self.path_accessed_at_base.push((path, self.location_to_index(location)));
    }

    fn place_to_mpi(&self, place: &Place<'tcx>) -> Option<MovePathIndex> {
        match self.move_data.rev_lookup.find(place.as_ref()) {
            LookupResult::Exact(mpi) => Some(mpi),
            LookupResult::Parent(mmpi) => mmpi,
        }
    }
}

impl<'a, 'tcx> Visitor<'tcx> for UseFactsExtractor<'a, 'tcx> {
    fn visit_local(&mut self, local: Local, context: PlaceContext, location: Location) {
        match def_use::categorize(context) {
            Some(DefUse::Def) => self.insert_def(local, location),
            Some(DefUse::Use) => self.insert_use(local, location),
            Some(DefUse::Drop) => self.insert_drop_use(local, location),
            _ => (),
        }
    }

    fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
        self.super_place(place, context, location);
        match context {
            PlaceContext::NonMutatingUse(_) => {
                if let Some(mpi) = self.place_to_mpi(place) {
                    self.insert_path_access(mpi, location);
                }
            }

            PlaceContext::MutatingUse(MutatingUseContext::Borrow) => {
                if let Some(mpi) = self.place_to_mpi(place) {
                    self.insert_path_access(mpi, location);
                }
            }
            _ => (),
        }
    }
}

pub(super) fn populate_access_facts<'a, 'tcx>(
    typeck: &mut TypeChecker<'a, 'tcx>,
    body: &Body<'tcx>,
    location_table: &LocationTable,
    move_data: &MoveData<'tcx>,
    //FIXME: this is not mutated, but expected to be modified as
    // out param, bug?
    dropped_at: &mut Vec<(Local, Location)>,
) {
    debug!("populate_access_facts()");

    if let Some(facts) = typeck.borrowck_context.all_facts.as_mut() {
        let mut extractor = UseFactsExtractor {
            var_defined_at: &mut facts.var_defined_at,
            var_used_at: &mut facts.var_used_at,
            var_dropped_at: &mut facts.var_dropped_at,
            path_accessed_at_base: &mut facts.path_accessed_at_base,
            location_table,
            move_data,
        };
        extractor.visit_body(body);

        facts.var_dropped_at.extend(
            dropped_at.iter().map(|&(local, location)| (local, location_table.mid_index(location))),
        );

        for (local, local_decl) in body.local_decls.iter_enumerated() {
            debug!(
                "add use_of_var_derefs_origin facts - local={:?}, type={:?}",
                local, local_decl.ty
            );
            let _prof_timer = typeck.infcx.tcx.prof.generic_activity("polonius_fact_generation");
            let universal_regions = &typeck.borrowck_context.universal_regions;
            typeck.infcx.tcx.for_each_free_region(&local_decl.ty, |region| {
                let region_vid = universal_regions.to_region_vid(region);
                facts.use_of_var_derefs_origin.push((local, region_vid));
            });
        }
    }
}

/// For every potentially drop()-touched region `region` in `local`'s type
/// (`kind`), emit a Polonius `use_of_var_derefs_origin(local, origin)` fact.
pub(super) fn add_drop_of_var_derefs_origin<'tcx>(
    typeck: &mut TypeChecker<'_, 'tcx>,
    local: Local,
    kind: &GenericArg<'tcx>,
) {
    debug!("add_drop_of_var_derefs_origin(local={:?}, kind={:?}", local, kind);
    if let Some(facts) = typeck.borrowck_context.all_facts.as_mut() {
        let _prof_timer = typeck.infcx.tcx.prof.generic_activity("polonius_fact_generation");
        let universal_regions = &typeck.borrowck_context.universal_regions;
        typeck.infcx.tcx.for_each_free_region(kind, |drop_live_region| {
            let region_vid = universal_regions.to_region_vid(drop_live_region);
            facts.drop_of_var_derefs_origin.push((local, region_vid));
        });
    }
}