use rustc_hir as hir;
use rustc_infer::infer::canonical::{Canonical, QueryResponse};
use rustc_infer::infer::{DefiningAnchor, TyCtxtInferExt};
use rustc_infer::traits::ObligationCauseCode;
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::{self, FnSig, Lift, PolyFnSig, Ty, TyCtxt, TypeFoldable};
use rustc_middle::ty::{ParamEnvAnd, Predicate, ToPredicate};
use rustc_middle::ty::{UserSelfTy, UserSubsts};
use rustc_span::{Span, DUMMY_SP};
use rustc_trait_selection::infer::InferCtxtBuilderExt;
use rustc_trait_selection::traits::query::normalize::QueryNormalizeExt;
use rustc_trait_selection::traits::query::type_op::ascribe_user_type::AscribeUserType;
use rustc_trait_selection::traits::query::type_op::eq::Eq;
use rustc_trait_selection::traits::query::type_op::normalize::Normalize;
use rustc_trait_selection::traits::query::type_op::prove_predicate::ProvePredicate;
use rustc_trait_selection::traits::query::type_op::subtype::Subtype;
use rustc_trait_selection::traits::query::{Fallible, NoSolution};
use rustc_trait_selection::traits::{Normalized, Obligation, ObligationCause, ObligationCtxt};
use std::fmt;
use std::iter::zip;

pub(crate) fn provide(p: &mut Providers) {
    *p = Providers {
        type_op_ascribe_user_type,
        type_op_eq,
        type_op_prove_predicate,
        type_op_subtype,
        type_op_normalize_ty,
        type_op_normalize_predicate,
        type_op_normalize_fn_sig,
        type_op_normalize_poly_fn_sig,
        ..*p
    };
}

fn type_op_ascribe_user_type<'tcx>(
    tcx: TyCtxt<'tcx>,
    canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, AscribeUserType<'tcx>>>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, ()>>, NoSolution> {
    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |ocx, key| {
        type_op_ascribe_user_type_with_span(ocx, key, None)
    })
}

/// The core of the `type_op_ascribe_user_type` query: for diagnostics purposes in NLL HRTB errors,
/// this query can be re-run to better track the span of the obligation cause, and improve the error
/// message. Do not call directly unless you're in that very specific context.
pub fn type_op_ascribe_user_type_with_span<'tcx>(
    ocx: &ObligationCtxt<'_, 'tcx>,
    key: ParamEnvAnd<'tcx, AscribeUserType<'tcx>>,
    span: Option<Span>,
) -> Result<(), NoSolution> {
    let (param_env, AscribeUserType { mir_ty, def_id, user_substs }) = key.into_parts();
    debug!(
        "type_op_ascribe_user_type: mir_ty={:?} def_id={:?} user_substs={:?}",
        mir_ty, def_id, user_substs
    );
    let span = span.unwrap_or(DUMMY_SP);

    let UserSubsts { user_self_ty, substs } = user_substs;
    let tcx = ocx.infcx.tcx;
    let cause = ObligationCause::dummy_with_span(span);

    let ty = tcx.bound_type_of(def_id).subst(tcx, substs);
    let ty = ocx.normalize(&cause, param_env, ty);
    debug!("relate_type_and_user_type: ty of def-id is {:?}", ty);

    ocx.eq(&cause, param_env, mir_ty, ty)?;

    // Prove the predicates coming along with `def_id`.
    //
    // Also, normalize the `instantiated_predicates`
    // because otherwise we wind up with duplicate "type
    // outlives" error messages.
    let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);

    debug!(?instantiated_predicates);
    for (instantiated_predicate, predicate_span) in
        zip(instantiated_predicates.predicates, instantiated_predicates.spans)
    {
        let span = if span == DUMMY_SP { predicate_span } else { span };
        let cause = ObligationCause::new(
            span,
            hir::CRATE_HIR_ID,
            ObligationCauseCode::AscribeUserTypeProvePredicate(predicate_span),
        );
        let instantiated_predicate =
            ocx.normalize(&cause.clone(), param_env, instantiated_predicate);

        ocx.register_obligation(Obligation::new(tcx, cause, param_env, instantiated_predicate));
    }

    if let Some(UserSelfTy { impl_def_id, self_ty }) = user_self_ty {
        let impl_self_ty = tcx.bound_type_of(impl_def_id).subst(tcx, substs);
        let impl_self_ty = ocx.normalize(&cause, param_env, impl_self_ty);

        ocx.eq(&cause, param_env, self_ty, impl_self_ty)?;

        let predicate: Predicate<'tcx> =
            ty::Binder::dummy(ty::PredicateKind::WellFormed(impl_self_ty.into())).to_predicate(tcx);
        ocx.register_obligation(Obligation::new(tcx, cause.clone(), param_env, predicate));
    }

    // In addition to proving the predicates, we have to
    // prove that `ty` is well-formed -- this is because
    // the WF of `ty` is predicated on the substs being
    // well-formed, and we haven't proven *that*. We don't
    // want to prove the WF of types from  `substs` directly because they
    // haven't been normalized.
    //
    // FIXME(nmatsakis): Well, perhaps we should normalize
    // them?  This would only be relevant if some input
    // type were ill-formed but did not appear in `ty`,
    // which...could happen with normalization...
    let predicate: Predicate<'tcx> =
        ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into())).to_predicate(tcx);
    ocx.register_obligation(Obligation::new(tcx, cause, param_env, predicate));
    Ok(())
}

fn type_op_eq<'tcx>(
    tcx: TyCtxt<'tcx>,
    canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, Eq<'tcx>>>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, ()>>, NoSolution> {
    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |ocx, key| {
        let (param_env, Eq { a, b }) = key.into_parts();
        Ok(ocx.eq(&ObligationCause::dummy(), param_env, a, b)?)
    })
}

fn type_op_normalize<'tcx, T>(
    ocx: &ObligationCtxt<'_, 'tcx>,
    key: ParamEnvAnd<'tcx, Normalize<T>>,
) -> Fallible<T>
where
    T: fmt::Debug + TypeFoldable<'tcx> + Lift<'tcx>,
{
    let (param_env, Normalize { value }) = key.into_parts();
    let Normalized { value, obligations } =
        ocx.infcx.at(&ObligationCause::dummy(), param_env).query_normalize(value)?;
    ocx.register_obligations(obligations);
    Ok(value)
}

fn type_op_normalize_ty<'tcx>(
    tcx: TyCtxt<'tcx>,
    canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, Normalize<Ty<'tcx>>>>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>, NoSolution> {
    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, type_op_normalize)
}

fn type_op_normalize_predicate<'tcx>(
    tcx: TyCtxt<'tcx>,
    canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, Normalize<Predicate<'tcx>>>>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, Predicate<'tcx>>>, NoSolution> {
    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, type_op_normalize)
}

fn type_op_normalize_fn_sig<'tcx>(
    tcx: TyCtxt<'tcx>,
    canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, Normalize<FnSig<'tcx>>>>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, FnSig<'tcx>>>, NoSolution> {
    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, type_op_normalize)
}

fn type_op_normalize_poly_fn_sig<'tcx>(
    tcx: TyCtxt<'tcx>,
    canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, Normalize<PolyFnSig<'tcx>>>>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, PolyFnSig<'tcx>>>, NoSolution> {
    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, type_op_normalize)
}

fn type_op_subtype<'tcx>(
    tcx: TyCtxt<'tcx>,
    canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, Subtype<'tcx>>>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, ()>>, NoSolution> {
    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |ocx, key| {
        let (param_env, Subtype { sub, sup }) = key.into_parts();
        Ok(ocx.sup(&ObligationCause::dummy(), param_env, sup, sub)?)
    })
}

fn type_op_prove_predicate<'tcx>(
    tcx: TyCtxt<'tcx>,
    canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, ProvePredicate<'tcx>>>,
) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, ()>>, NoSolution> {
    // HACK This bubble is required for this test to pass:
    // impl-trait/issue-99642.rs
    tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).enter_canonical_trait_query(
        &canonicalized,
        |ocx, key| {
            type_op_prove_predicate_with_cause(ocx, key, ObligationCause::dummy());
            Ok(())
        },
    )
}

/// The core of the `type_op_prove_predicate` query: for diagnostics purposes in NLL HRTB errors,
/// this query can be re-run to better track the span of the obligation cause, and improve the error
/// message. Do not call directly unless you're in that very specific context.
pub fn type_op_prove_predicate_with_cause<'tcx>(
    ocx: &ObligationCtxt<'_, 'tcx>,
    key: ParamEnvAnd<'tcx, ProvePredicate<'tcx>>,
    cause: ObligationCause<'tcx>,
) {
    let (param_env, ProvePredicate { predicate }) = key.into_parts();
    ocx.register_obligation(Obligation::new(ocx.infcx.tcx, cause, param_env, predicate));
}