// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use super::probe;

use check::{FnCtxt, callee};
use hir::def_id::DefId;
use rustc::ty::subst::Substs;
use rustc::traits;
use rustc::ty::{self, LvaluePreference, NoPreference, PreferMutLvalue, Ty};
use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow};
use rustc::ty::fold::TypeFoldable;
use rustc::infer::{self, InferOk, TypeOrigin};
use syntax_pos::Span;
use rustc::hir;

use std::ops::Deref;

struct ConfirmContext<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
    fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
    span: Span,
    self_expr: &'gcx hir::Expr,
    call_expr: &'gcx hir::Expr,
}

impl<'a, 'gcx, 'tcx> Deref for ConfirmContext<'a, 'gcx, 'tcx> {
    type Target = FnCtxt<'a, 'gcx, 'tcx>;
    fn deref(&self) -> &Self::Target {
        &self.fcx
    }
}

struct InstantiatedMethodSig<'tcx> {
    /// Function signature of the method being invoked. The 0th
    /// argument is the receiver.
    method_sig: ty::FnSig<'tcx>,

    /// Generic bounds on the method's parameters which must be added
    /// as pending obligations.
    method_predicates: ty::InstantiatedPredicates<'tcx>,
}

impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
    pub fn confirm_method(&self,
                          span: Span,
                          self_expr: &'gcx hir::Expr,
                          call_expr: &'gcx hir::Expr,
                          unadjusted_self_ty: Ty<'tcx>,
                          pick: probe::Pick<'tcx>,
                          supplied_method_types: Vec<Ty<'tcx>>)
                          -> ty::MethodCallee<'tcx> {
        debug!("confirm(unadjusted_self_ty={:?}, pick={:?}, supplied_method_types={:?})",
               unadjusted_self_ty,
               pick,
               supplied_method_types);

        let mut confirm_cx = ConfirmContext::new(self, span, self_expr, call_expr);
        confirm_cx.confirm(unadjusted_self_ty, pick, supplied_method_types)
    }
}

impl<'a, 'gcx, 'tcx> ConfirmContext<'a, 'gcx, 'tcx> {
    fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
           span: Span,
           self_expr: &'gcx hir::Expr,
           call_expr: &'gcx hir::Expr)
           -> ConfirmContext<'a, 'gcx, 'tcx> {
        ConfirmContext {
            fcx: fcx,
            span: span,
            self_expr: self_expr,
            call_expr: call_expr,
        }
    }

    fn confirm(&mut self,
               unadjusted_self_ty: Ty<'tcx>,
               pick: probe::Pick<'tcx>,
               supplied_method_types: Vec<Ty<'tcx>>)
               -> ty::MethodCallee<'tcx> {
        // Adjust the self expression the user provided and obtain the adjusted type.
        let self_ty = self.adjust_self_ty(unadjusted_self_ty, &pick);

        // Make sure nobody calls `drop()` explicitly.
        self.enforce_illegal_method_limitations(&pick);

        // Create substitutions for the method's type parameters.
        let rcvr_substs = self.fresh_receiver_substs(self_ty, &pick);
        let all_substs = self.instantiate_method_substs(&pick, supplied_method_types, rcvr_substs);

        debug!("all_substs={:?}", all_substs);

        // Create the final signature for the method, replacing late-bound regions.
        let InstantiatedMethodSig { method_sig, method_predicates } =
            self.instantiate_method_sig(&pick, all_substs);
        let method_self_ty = method_sig.inputs[0];

        // Unify the (adjusted) self type with what the method expects.
        self.unify_receivers(self_ty, method_self_ty);

        // Create the method type
        let def_id = pick.item.def_id();
        let method_ty = pick.item.as_opt_method().unwrap();
        let fty = self.tcx.mk_fn_def(def_id,
                                     all_substs,
                                     self.tcx.mk_bare_fn(ty::BareFnTy {
                                         sig: ty::Binder(method_sig),
                                         unsafety: method_ty.fty.unsafety,
                                         abi: method_ty.fty.abi.clone(),
                                     }));

        // Add any trait/regions obligations specified on the method's type parameters.
        self.add_obligations(fty, all_substs, &method_predicates);

        // Create the final `MethodCallee`.
        let callee = ty::MethodCallee {
            def_id: def_id,
            ty: fty,
            substs: all_substs,
        };

        if let Some(hir::MutMutable) = pick.autoref {
            self.convert_lvalue_derefs_to_mutable();
        }

        callee
    }

    ///////////////////////////////////////////////////////////////////////////
    // ADJUSTMENTS

    fn adjust_self_ty(&mut self,
                      unadjusted_self_ty: Ty<'tcx>,
                      pick: &probe::Pick<'tcx>)
                      -> Ty<'tcx> {
        let autoref = if let Some(mutbl) = pick.autoref {
            let region = self.next_region_var(infer::Autoref(self.span));
            Some(AutoBorrow::Ref(region, mutbl))
        } else {
            // No unsizing should be performed without autoref (at
            // least during method dispach). This is because we
            // currently only unsize `[T;N]` to `[T]`, and naturally
            // that must occur being a reference.
            assert!(pick.unsize.is_none());
            None
        };


        // Commit the autoderefs by calling `autoderef` again, but this
        // time writing the results into the various tables.
        let mut autoderef = self.autoderef(self.span, unadjusted_self_ty);
        let (autoderefd_ty, n) = autoderef.nth(pick.autoderefs).unwrap();
        assert_eq!(n, pick.autoderefs);

        autoderef.unambiguous_final_ty();
        autoderef.finalize(LvaluePreference::NoPreference, Some(self.self_expr));

        let target = pick.unsize.unwrap_or(autoderefd_ty);
        let target = target.adjust_for_autoref(self.tcx, autoref);

        // Write out the final adjustment.
        self.write_adjustment(self.self_expr.id, Adjustment {
            kind: Adjust::DerefRef {
                autoderefs: pick.autoderefs,
                autoref: autoref,
                unsize: pick.unsize.is_some(),
            },
            target: target
        });

        target
    }

    ///////////////////////////////////////////////////////////////////////////
    //

    /// Returns a set of substitutions for the method *receiver* where all type and region
    /// parameters are instantiated with fresh variables. This substitution does not include any
    /// parameters declared on the method itself.
    ///
    /// Note that this substitution may include late-bound regions from the impl level. If so,
    /// these are instantiated later in the `instantiate_method_sig` routine.
    fn fresh_receiver_substs(&mut self,
                             self_ty: Ty<'tcx>,
                             pick: &probe::Pick<'tcx>)
                             -> &'tcx Substs<'tcx> {
        match pick.kind {
            probe::InherentImplPick => {
                let impl_def_id = pick.item.container().id();
                assert!(self.tcx.impl_trait_ref(impl_def_id).is_none(),
                        "impl {:?} is not an inherent impl",
                        impl_def_id);
                self.impl_self_ty(self.span, impl_def_id).substs
            }

            probe::ObjectPick => {
                let trait_def_id = pick.item.container().id();
                self.extract_existential_trait_ref(self_ty, |this, object_ty, principal| {
                    // The object data has no entry for the Self
                    // Type. For the purposes of this method call, we
                    // substitute the object type itself. This
                    // wouldn't be a sound substitution in all cases,
                    // since each instance of the object type is a
                    // different existential and hence could match
                    // distinct types (e.g., if `Self` appeared as an
                    // argument type), but those cases have already
                    // been ruled out when we deemed the trait to be
                    // "object safe".
                    let original_poly_trait_ref = principal.with_self_ty(this.tcx, object_ty);
                    let upcast_poly_trait_ref = this.upcast(original_poly_trait_ref, trait_def_id);
                    let upcast_trait_ref =
                        this.replace_late_bound_regions_with_fresh_var(&upcast_poly_trait_ref);
                    debug!("original_poly_trait_ref={:?} upcast_trait_ref={:?} target_trait={:?}",
                           original_poly_trait_ref,
                           upcast_trait_ref,
                           trait_def_id);
                    upcast_trait_ref.substs
                })
            }

            probe::ExtensionImplPick(impl_def_id) => {
                // The method being invoked is the method as defined on the trait,
                // so return the substitutions from the trait. Consider:
                //
                //     impl<A,B,C> Trait<A,B> for Foo<C> { ... }
                //
                // If we instantiate A, B, and C with $A, $B, and $C
                // respectively, then we want to return the type
                // parameters from the trait ([$A,$B]), not those from
                // the impl ([$A,$B,$C]) not the receiver type ([$C]).
                let impl_polytype = self.impl_self_ty(self.span, impl_def_id);
                let impl_trait_ref =
                    self.instantiate_type_scheme(self.span,
                                                 impl_polytype.substs,
                                                 &self.tcx.impl_trait_ref(impl_def_id).unwrap());
                impl_trait_ref.substs
            }

            probe::TraitPick => {
                let trait_def_id = pick.item.container().id();

                // Make a trait reference `$0 : Trait<$1...$n>`
                // consisting entirely of type variables. Later on in
                // the process we will unify the transformed-self-type
                // of the method with the actual type in order to
                // unify some of these variables.
                self.fresh_substs_for_item(self.span, trait_def_id)
            }

            probe::WhereClausePick(ref poly_trait_ref) => {
                // Where clauses can have bound regions in them. We need to instantiate
                // those to convert from a poly-trait-ref to a trait-ref.
                self.replace_late_bound_regions_with_fresh_var(&poly_trait_ref).substs
            }
        }
    }

    fn extract_existential_trait_ref<R, F>(&mut self, self_ty: Ty<'tcx>, mut closure: F) -> R
        where F: FnMut(&mut ConfirmContext<'a, 'gcx, 'tcx>,
                       Ty<'tcx>,
                       ty::PolyExistentialTraitRef<'tcx>)
                       -> R
    {
        // If we specified that this is an object method, then the
        // self-type ought to be something that can be dereferenced to
        // yield an object-type (e.g., `&Object` or `Box<Object>`
        // etc).

        // FIXME: this feels, like, super dubious
        self.fcx
            .autoderef(self.span, self_ty)
            .filter_map(|(ty, _)| {
                match ty.sty {
                    ty::TyTrait(ref data) => Some(closure(self, ty, data.principal)),
                    _ => None,
                }
            })
            .next()
            .unwrap_or_else(|| {
                span_bug!(self.span,
                          "self-type `{}` for ObjectPick never dereferenced to an object",
                          self_ty)
            })
    }

    fn instantiate_method_substs(&mut self,
                                 pick: &probe::Pick<'tcx>,
                                 mut supplied_method_types: Vec<Ty<'tcx>>,
                                 substs: &Substs<'tcx>)
                                 -> &'tcx Substs<'tcx> {
        // Determine the values for the generic parameters of the method.
        // If they were not explicitly supplied, just construct fresh
        // variables.
        let num_supplied_types = supplied_method_types.len();
        let method = pick.item.as_opt_method().unwrap();
        let num_method_types = method.generics.types.len();

        if num_supplied_types > 0 && num_supplied_types != num_method_types {
            if num_method_types == 0 {
                struct_span_err!(self.tcx.sess,
                                 self.span,
                                 E0035,
                                 "does not take type parameters")
                    .span_label(self.span, &"called with unneeded type parameters")
                    .emit();
            } else {
                struct_span_err!(self.tcx.sess,
                                 self.span,
                                 E0036,
                                 "incorrect number of type parameters given for this method: \
                                  expected {}, found {}",
                                 num_method_types,
                                 num_supplied_types)
                    .span_label(self.span,
                                &format!("Passed {} type argument{}, expected {}",
                                         num_supplied_types,
                                         if num_supplied_types != 1 { "s" } else { "" },
                                         num_method_types))
                    .emit();
            }
            supplied_method_types = vec![self.tcx.types.err; num_method_types];
        }

        // Create subst for early-bound lifetime parameters, combining
        // parameters from the type and those from the method.
        //
        // FIXME -- permit users to manually specify lifetimes
        let supplied_start = substs.params().len() + method.generics.regions.len();
        Substs::for_item(self.tcx,
                         method.def_id,
                         |def, _| {
            let i = def.index as usize;
            if i < substs.params().len() {
                substs.region_at(i)
            } else {
                self.region_var_for_def(self.span, def)
            }
        },
                         |def, cur_substs| {
            let i = def.index as usize;
            if i < substs.params().len() {
                substs.type_at(i)
            } else if supplied_method_types.is_empty() {
                self.type_var_for_def(self.span, def, cur_substs)
            } else {
                supplied_method_types[i - supplied_start]
            }
        })
    }

    fn unify_receivers(&mut self, self_ty: Ty<'tcx>, method_self_ty: Ty<'tcx>) {
        match self.sub_types(false, TypeOrigin::Misc(self.span), self_ty, method_self_ty) {
            Ok(InferOk { obligations, .. }) => {
                // FIXME(#32730) propagate obligations
                assert!(obligations.is_empty());
            }
            Err(_) => {
                span_bug!(self.span,
                          "{} was a subtype of {} but now is not?",
                          self_ty,
                          method_self_ty);
            }
        }
    }

    ///////////////////////////////////////////////////////////////////////////
    //

    fn instantiate_method_sig(&mut self,
                              pick: &probe::Pick<'tcx>,
                              all_substs: &'tcx Substs<'tcx>)
                              -> InstantiatedMethodSig<'tcx> {
        debug!("instantiate_method_sig(pick={:?}, all_substs={:?})",
               pick,
               all_substs);

        // Instantiate the bounds on the method with the
        // type/early-bound-regions substitutions performed. There can
        // be no late-bound regions appearing here.
        let method_predicates = pick.item
            .as_opt_method()
            .unwrap()
            .predicates
            .instantiate(self.tcx, all_substs);
        let method_predicates = self.normalize_associated_types_in(self.span, &method_predicates);

        debug!("method_predicates after subst = {:?}", method_predicates);

        // Instantiate late-bound regions and substitute the trait
        // parameters into the method type to get the actual method type.
        //
        // NB: Instantiate late-bound regions first so that
        // `instantiate_type_scheme` can normalize associated types that
        // may reference those regions.
        let method_sig = self.replace_late_bound_regions_with_fresh_var(&pick.item
            .as_opt_method()
            .unwrap()
            .fty
            .sig);
        debug!("late-bound lifetimes from method instantiated, method_sig={:?}",
               method_sig);

        let method_sig = self.instantiate_type_scheme(self.span, all_substs, &method_sig);
        debug!("type scheme substituted, method_sig={:?}", method_sig);

        InstantiatedMethodSig {
            method_sig: method_sig,
            method_predicates: method_predicates,
        }
    }

    fn add_obligations(&mut self,
                       fty: Ty<'tcx>,
                       all_substs: &Substs<'tcx>,
                       method_predicates: &ty::InstantiatedPredicates<'tcx>) {
        debug!("add_obligations: fty={:?} all_substs={:?} method_predicates={:?}",
               fty,
               all_substs,
               method_predicates);

        self.add_obligations_for_parameters(traits::ObligationCause::misc(self.span, self.body_id),
                                            method_predicates);

        // this is a projection from a trait reference, so we have to
        // make sure that the trait reference inputs are well-formed.
        self.add_wf_bounds(all_substs, self.call_expr);

        // the function type must also be well-formed (this is not
        // implied by the substs being well-formed because of inherent
        // impls and late-bound regions - see issue #28609).
        self.register_wf_obligation(fty, self.span, traits::MiscObligation);
    }

    ///////////////////////////////////////////////////////////////////////////
    // RECONCILIATION

    /// When we select a method with a mutable autoref, we have to go convert any
    /// auto-derefs, indices, etc from `Deref` and `Index` into `DerefMut` and `IndexMut`
    /// respectively.
    fn convert_lvalue_derefs_to_mutable(&self) {
        // Gather up expressions we want to munge.
        let mut exprs = Vec::new();
        exprs.push(self.self_expr);
        loop {
            let last = exprs[exprs.len() - 1];
            match last.node {
                hir::ExprField(ref expr, _) |
                hir::ExprTupField(ref expr, _) |
                hir::ExprIndex(ref expr, _) |
                hir::ExprUnary(hir::UnDeref, ref expr) => exprs.push(&expr),
                _ => break,
            }
        }

        debug!("convert_lvalue_derefs_to_mutable: exprs={:?}", exprs);

        // Fix up autoderefs and derefs.
        for (i, &expr) in exprs.iter().rev().enumerate() {
            debug!("convert_lvalue_derefs_to_mutable: i={} expr={:?}", i, expr);

            // Count autoderefs.
            let adjustment = self.tables.borrow().adjustments.get(&expr.id).cloned();
            match adjustment {
                Some(Adjustment { kind: Adjust::DerefRef { autoderefs, .. }, .. }) => {
                    if autoderefs > 0 {
                        let mut autoderef = self.autoderef(expr.span, self.node_ty(expr.id));
                        autoderef.nth(autoderefs).unwrap_or_else(|| {
                            span_bug!(expr.span,
                                      "expr was deref-able {} times but now isn't?",
                                      autoderefs);
                        });
                        autoderef.finalize(PreferMutLvalue, Some(expr));
                    }
                }
                Some(_) | None => {}
            }

            // Don't retry the first one or we might infinite loop!
            if i == 0 {
                continue;
            }
            match expr.node {
                hir::ExprIndex(ref base_expr, ref index_expr) => {
                    // If this is an overloaded index, the
                    // adjustment will include an extra layer of
                    // autoref because the method is an &self/&mut
                    // self method. We have to peel it off to get
                    // the raw adjustment that `try_index_step`
                    // expects. This is annoying and horrible. We
                    // ought to recode this routine so it doesn't
                    // (ab)use the normal type checking paths.
                    let adj = self.tables.borrow().adjustments.get(&base_expr.id).cloned();
                    let (autoderefs, unsize, adjusted_base_ty) = match adj {
                        Some(Adjustment {
                            kind: Adjust::DerefRef { autoderefs, autoref, unsize },
                            target
                        }) => {
                            match autoref {
                                None => {
                                    assert!(!unsize);
                                }
                                Some(AutoBorrow::Ref(..)) => {}
                                Some(_) => {
                                    span_bug!(base_expr.span,
                                              "unexpected adjustment autoref {:?}",
                                              adj);
                                }
                            }

                            (autoderefs, unsize, if unsize {
                                target.builtin_deref(false, NoPreference)
                                      .expect("fixup: AutoBorrow::Ref is not &T")
                                      .ty
                            } else {
                                let ty = self.node_ty(base_expr.id);
                                let mut ty = self.shallow_resolve(ty);
                                let mut method_type = |method_call: ty::MethodCall| {
                                    self.tables.borrow().method_map.get(&method_call).map(|m| {
                                        self.resolve_type_vars_if_possible(&m.ty)
                                    })
                                };

                                if !ty.references_error() {
                                    for i in 0..autoderefs {
                                        ty = ty.adjust_for_autoderef(self.tcx,
                                                                     base_expr.id,
                                                                     base_expr.span,
                                                                     i as u32,
                                                                     &mut method_type);
                                    }
                                }

                                ty
                            })
                        }
                        None => (0, false, self.node_ty(base_expr.id)),
                        Some(_) => {
                            span_bug!(base_expr.span, "unexpected adjustment type");
                        }
                    };

                    let index_expr_ty = self.node_ty(index_expr.id);

                    let result = self.try_index_step(ty::MethodCall::expr(expr.id),
                                                     expr,
                                                     &base_expr,
                                                     adjusted_base_ty,
                                                     autoderefs,
                                                     unsize,
                                                     PreferMutLvalue,
                                                     index_expr_ty);

                    if let Some((input_ty, return_ty)) = result {
                        self.demand_suptype(index_expr.span, input_ty, index_expr_ty);

                        let expr_ty = self.node_ty(expr.id);
                        self.demand_suptype(expr.span, expr_ty, return_ty);
                    }
                }
                hir::ExprUnary(hir::UnDeref, ref base_expr) => {
                    // if this is an overloaded deref, then re-evaluate with
                    // a preference for mut
                    let method_call = ty::MethodCall::expr(expr.id);
                    if self.tables.borrow().method_map.contains_key(&method_call) {
                        let method = self.try_overloaded_deref(expr.span,
                                                               Some(&base_expr),
                                                               self.node_ty(base_expr.id),
                                                               PreferMutLvalue);
                        let method = method.expect("re-trying deref failed");
                        self.tables.borrow_mut().method_map.insert(method_call, method);
                    }
                }
                _ => {}
            }
        }
    }

    ///////////////////////////////////////////////////////////////////////////
    // MISCELLANY

    fn enforce_illegal_method_limitations(&self, pick: &probe::Pick) {
        // Disallow calls to the method `drop` defined in the `Drop` trait.
        match pick.item.container() {
            ty::TraitContainer(trait_def_id) => {
                callee::check_legal_trait_for_method_call(self.ccx, self.span, trait_def_id)
            }
            ty::ImplContainer(..) => {}
        }
    }

    fn upcast(&mut self,
              source_trait_ref: ty::PolyTraitRef<'tcx>,
              target_trait_def_id: DefId)
              -> ty::PolyTraitRef<'tcx> {
        let upcast_trait_refs = self.tcx
            .upcast_choices(source_trait_ref.clone(), target_trait_def_id);

        // must be exactly one trait ref or we'd get an ambig error etc
        if upcast_trait_refs.len() != 1 {
            span_bug!(self.span,
                      "cannot uniquely upcast `{:?}` to `{:?}`: `{:?}`",
                      source_trait_ref,
                      target_trait_def_id,
                      upcast_trait_refs);
        }

        upcast_trait_refs.into_iter().next().unwrap()
    }

    fn replace_late_bound_regions_with_fresh_var<T>(&self, value: &ty::Binder<T>) -> T
        where T: TypeFoldable<'tcx>
    {
        self.fcx
            .replace_late_bound_regions_with_fresh_var(self.span, infer::FnCall, value)
            .0
    }
}
