use crate::infer::InferCtxt;
use crate::ty::{self, Ty, TyCtxt, ToPredicate};
use crate::traits::Obligation;
use crate::hir::def_id::DefId;

use super::{ChalkFulfillmentContext, FulfillmentContext, FulfillmentError};
use super::{ObligationCause, PredicateObligation};

pub trait TraitEngine<'tcx>: 'tcx {
    fn normalize_projection_type(
        &mut self,
        infcx: &InferCtxt<'_, 'gcx, 'tcx>,
        param_env: ty::ParamEnv<'tcx>,
        projection_ty: ty::ProjectionTy<'tcx>,
        cause: ObligationCause<'tcx>,
    ) -> Ty<'tcx>;

    /// Requires that `ty` must implement the trait with `def_id` in
    /// the given environment. This trait must not have any type
    /// parameters (except for `Self`).
    fn register_bound(
        &mut self,
        infcx: &InferCtxt<'_, 'gcx, 'tcx>,
        param_env: ty::ParamEnv<'tcx>,
        ty: Ty<'tcx>,
        def_id: DefId,
        cause: ObligationCause<'tcx>,
    ) {
        let trait_ref = ty::TraitRef {
            def_id,
            substs: infcx.tcx.mk_substs_trait(ty, &[]),
        };
        self.register_predicate_obligation(infcx, Obligation {
            cause,
            recursion_depth: 0,
            param_env,
            predicate: trait_ref.to_predicate()
        });
    }

    fn register_predicate_obligation(
        &mut self,
        infcx: &InferCtxt<'_, 'gcx, 'tcx>,
        obligation: PredicateObligation<'tcx>,
    );

    fn select_all_or_error(
        &mut self,
        infcx: &InferCtxt<'_, 'gcx, 'tcx>,
    ) -> Result<(), Vec<FulfillmentError<'tcx>>>;

    fn select_where_possible(
        &mut self,
        infcx: &InferCtxt<'_, 'gcx, 'tcx>,
    ) -> Result<(), Vec<FulfillmentError<'tcx>>>;

    fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>>;
}

pub trait TraitEngineExt<'tcx> {
    fn register_predicate_obligations(
        &mut self,
        infcx: &InferCtxt<'_, 'gcx, 'tcx>,
        obligations: impl IntoIterator<Item = PredicateObligation<'tcx>>,
    );
}

impl<T: ?Sized + TraitEngine<'tcx>> TraitEngineExt<'tcx> for T {
    fn register_predicate_obligations(
        &mut self,
        infcx: &InferCtxt<'_, 'gcx, 'tcx>,
        obligations: impl IntoIterator<Item = PredicateObligation<'tcx>>,
    ) {
        for obligation in obligations {
            self.register_predicate_obligation(infcx, obligation);
        }
    }
}

impl dyn TraitEngine<'tcx> {
    pub fn new(tcx: TyCtxt<'_, '_, 'tcx>) -> Box<Self> {
        if tcx.sess.opts.debugging_opts.chalk {
            Box::new(ChalkFulfillmentContext::new())
        } else {
            Box::new(FulfillmentContext::new())
        }
    }
}