use core::ops::ControlFlow;

use rustc_errors::{Applicability, StashKey, Suggestions};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::intravisit::VisitorExt;
use rustc_hir::{self as hir, AmbigArg, HirId};
use rustc_middle::ty::print::{with_forced_trimmed_paths, with_types_for_suggestion};
use rustc_middle::ty::util::IntTypeExt;
use rustc_middle::ty::{self, DefiningScopeKind, IsSuggestable, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::{bug, span_bug};
use rustc_span::{DUMMY_SP, Ident, Span};
use tracing::instrument;

use super::{HirPlaceholderCollector, ItemCtxt, bad_placeholder};
use crate::check::wfcheck::check_static_item;
use crate::hir_ty_lowering::HirTyLowerer;

mod opaque;

#[instrument(level = "debug", skip(tcx), ret)]
pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, Ty<'_>> {
    use rustc_hir::*;
    use rustc_middle::ty::Ty;

    // If we are computing `type_of` the synthesized associated type for an RPITIT in the impl
    // side, use `collect_return_position_impl_trait_in_trait_tys` to infer the value of the
    // associated type in the impl.
    match tcx.opt_rpitit_info(def_id.to_def_id()) {
        Some(ty::ImplTraitInTraitData::Impl { fn_def_id }) => {
            match tcx.collect_return_position_impl_trait_in_trait_tys(fn_def_id) {
                Ok(map) => {
                    let trait_item_def_id = tcx.trait_item_of(def_id).unwrap();
                    return map[&trait_item_def_id];
                }
                Err(_) => {
                    return ty::EarlyBinder::bind(Ty::new_error_with_message(
                        tcx,
                        DUMMY_SP,
                        "Could not collect return position impl trait in trait tys",
                    ));
                }
            }
        }
        // For an RPITIT in a trait, just return the corresponding opaque.
        Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
            return ty::EarlyBinder::bind(Ty::new_opaque(
                tcx,
                opaque_def_id,
                ty::GenericArgs::identity_for_item(tcx, opaque_def_id),
            ));
        }
        None => {}
    }

    let hir_id = tcx.local_def_id_to_hir_id(def_id);

    let icx = ItemCtxt::new(tcx, def_id);

    let output = match tcx.hir_node(hir_id) {
        Node::TraitItem(item) => match item.kind {
            TraitItemKind::Fn(..) => {
                let args = ty::GenericArgs::identity_for_item(tcx, def_id);
                Ty::new_fn_def(tcx, def_id.to_def_id(), args)
            }
            TraitItemKind::Const(ty, rhs) => rhs
                .and_then(|rhs| {
                    ty.is_suggestable_infer_ty().then(|| {
                        infer_placeholder_type(
                            icx.lowerer(),
                            def_id,
                            rhs.hir_id(),
                            ty.span,
                            rhs.span(tcx),
                            item.ident,
                            "associated constant",
                        )
                    })
                })
                .unwrap_or_else(|| icx.lower_ty(ty)),
            TraitItemKind::Type(_, Some(ty)) => icx.lower_ty(ty),
            TraitItemKind::Type(_, None) => {
                span_bug!(item.span, "associated type missing default");
            }
        },

        Node::ImplItem(item) => match item.kind {
            ImplItemKind::Fn(..) => {
                let args = ty::GenericArgs::identity_for_item(tcx, def_id);
                Ty::new_fn_def(tcx, def_id.to_def_id(), args)
            }
            ImplItemKind::Const(ty, rhs) => {
                if ty.is_suggestable_infer_ty() {
                    infer_placeholder_type(
                        icx.lowerer(),
                        def_id,
                        rhs.hir_id(),
                        ty.span,
                        rhs.span(tcx),
                        item.ident,
                        "associated constant",
                    )
                } else {
                    icx.lower_ty(ty)
                }
            }
            ImplItemKind::Type(ty) => {
                if let ImplItemImplKind::Inherent { .. } = item.impl_kind {
                    check_feature_inherent_assoc_ty(tcx, item.span);
                }

                icx.lower_ty(ty)
            }
        },

        Node::Item(item) => match item.kind {
            ItemKind::Static(_, ident, ty, body_id) => {
                if ty.is_suggestable_infer_ty() {
                    infer_placeholder_type(
                        icx.lowerer(),
                        def_id,
                        body_id.hir_id,
                        ty.span,
                        tcx.hir_body(body_id).value.span,
                        ident,
                        "static variable",
                    )
                } else {
                    let ty = icx.lower_ty(ty);
                    // MIR relies on references to statics being scalars.
                    // Verify that here to avoid ill-formed MIR.
                    // We skip the `Sync` check to avoid cycles for type-alias-impl-trait,
                    // relying on the fact that non-Sync statics don't ICE the rest of the compiler.
                    match check_static_item(tcx, def_id, ty, /* should_check_for_sync */ false) {
                        Ok(()) => ty,
                        Err(guar) => Ty::new_error(tcx, guar),
                    }
                }
            }
            ItemKind::Const(ident, _, ty, rhs) => {
                if ty.is_suggestable_infer_ty() {
                    infer_placeholder_type(
                        icx.lowerer(),
                        def_id,
                        rhs.hir_id(),
                        ty.span,
                        rhs.span(tcx),
                        ident,
                        "constant",
                    )
                } else {
                    icx.lower_ty(ty)
                }
            }
            ItemKind::TyAlias(_, _, self_ty) => icx.lower_ty(self_ty),
            ItemKind::Impl(hir::Impl { self_ty, .. }) => match self_ty.find_self_aliases() {
                spans if spans.len() > 0 => {
                    let guar = tcx
                        .dcx()
                        .emit_err(crate::errors::SelfInImplSelf { span: spans.into(), note: () });
                    Ty::new_error(tcx, guar)
                }
                _ => icx.lower_ty(self_ty),
            },
            ItemKind::Fn { .. } => {
                let args = ty::GenericArgs::identity_for_item(tcx, def_id);
                Ty::new_fn_def(tcx, def_id.to_def_id(), args)
            }
            ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
                let def = tcx.adt_def(def_id);
                let args = ty::GenericArgs::identity_for_item(tcx, def_id);
                Ty::new_adt(tcx, def, args)
            }
            ItemKind::GlobalAsm { .. } => tcx.typeck(def_id).node_type(hir_id),
            ItemKind::Trait { .. }
            | ItemKind::TraitAlias(..)
            | ItemKind::Macro(..)
            | ItemKind::Mod(..)
            | ItemKind::ForeignMod { .. }
            | ItemKind::ExternCrate(..)
            | ItemKind::Use(..) => {
                span_bug!(item.span, "compute_type_of_item: unexpected item type: {:?}", item.kind);
            }
        },

        Node::OpaqueTy(..) => tcx.type_of_opaque(def_id).instantiate_identity().skip_norm_wip(),

        Node::ForeignItem(foreign_item) => match foreign_item.kind {
            ForeignItemKind::Fn(..) => {
                let args = ty::GenericArgs::identity_for_item(tcx, def_id);
                Ty::new_fn_def(tcx, def_id.to_def_id(), args)
            }
            ForeignItemKind::Static(ty, _, _) => {
                let ty = icx.lower_ty(ty);
                // MIR relies on references to statics being scalars.
                // Verify that here to avoid ill-formed MIR.
                // We skip the `Sync` check to avoid cycles for type-alias-impl-trait,
                // relying on the fact that non-Sync statics don't ICE the rest of the compiler.
                match check_static_item(tcx, def_id, ty, /* should_check_for_sync */ false) {
                    Ok(()) => ty,
                    Err(guar) => Ty::new_error(tcx, guar),
                }
            }
            ForeignItemKind::Type => Ty::new_foreign(tcx, def_id.to_def_id()),
        },

        Node::Ctor(def) | Node::Variant(Variant { data: def, .. }) => match def {
            VariantData::Unit(..) | VariantData::Struct { .. } => {
                tcx.type_of(tcx.hir_get_parent_item(hir_id)).instantiate_identity().skip_norm_wip()
            }
            VariantData::Tuple(_, _, ctor) => {
                let args = ty::GenericArgs::identity_for_item(tcx, def_id);
                Ty::new_fn_def(tcx, ctor.to_def_id(), args)
            }
        },

        Node::Field(field) => icx.lower_ty(field.ty),

        Node::Expr(&Expr { kind: ExprKind::Closure { .. }, .. }) => {
            tcx.typeck(def_id).node_type(hir_id)
        }

        Node::AnonConst(_) => anon_const_type_of(&icx, def_id),

        Node::ConstBlock(_) => {
            let args = ty::GenericArgs::identity_for_item(tcx, def_id.to_def_id());
            args.as_inline_const().ty()
        }

        Node::GenericParam(param) => match &param.kind {
            GenericParamKind::Type { default: Some(ty), .. }
            | GenericParamKind::Const { ty, .. } => icx.lower_ty(ty),
            x => bug!("unexpected non-type Node::GenericParam: {:?}", x),
        },

        x => {
            bug!("unexpected sort of node in type_of(): {:?}", x);
        }
    };
    if let Err(e) = icx.check_tainted_by_errors()
        && !output.references_error()
    {
        ty::EarlyBinder::bind(Ty::new_error(tcx, e))
    } else {
        ty::EarlyBinder::bind(output)
    }
}

pub(super) fn type_of_opaque(tcx: TyCtxt<'_>, def_id: DefId) -> ty::EarlyBinder<'_, Ty<'_>> {
    if let Some(def_id) = def_id.as_local() {
        match tcx.hir_node_by_def_id(def_id).expect_opaque_ty().origin {
            hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: false, .. } => {
                opaque::find_opaque_ty_constraints_for_tait(
                    tcx,
                    def_id,
                    DefiningScopeKind::MirBorrowck,
                )
            }
            hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: true, .. } => {
                opaque::find_opaque_ty_constraints_for_impl_trait_in_assoc_type(
                    tcx,
                    def_id,
                    DefiningScopeKind::MirBorrowck,
                )
            }
            // Opaque types desugared from `impl Trait`.
            hir::OpaqueTyOrigin::FnReturn { parent: owner, in_trait_or_impl }
            | hir::OpaqueTyOrigin::AsyncFn { parent: owner, in_trait_or_impl } => {
                if in_trait_or_impl == Some(hir::RpitContext::Trait)
                    && !tcx.defaultness(owner).has_value()
                {
                    span_bug!(
                        tcx.def_span(def_id),
                        "tried to get type of this RPITIT with no definition"
                    );
                }
                opaque::find_opaque_ty_constraints_for_rpit(
                    tcx,
                    def_id,
                    owner,
                    DefiningScopeKind::MirBorrowck,
                )
            }
        }
    } else {
        // Foreign opaque type will go through the foreign provider
        // and load the type from metadata.
        tcx.type_of(def_id)
    }
}

pub(super) fn type_of_opaque_hir_typeck(
    tcx: TyCtxt<'_>,
    def_id: LocalDefId,
) -> ty::EarlyBinder<'_, Ty<'_>> {
    match tcx.hir_node_by_def_id(def_id).expect_opaque_ty().origin {
        hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: false, .. } => {
            opaque::find_opaque_ty_constraints_for_tait(tcx, def_id, DefiningScopeKind::HirTypeck)
        }
        hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: true, .. } => {
            opaque::find_opaque_ty_constraints_for_impl_trait_in_assoc_type(
                tcx,
                def_id,
                DefiningScopeKind::HirTypeck,
            )
        }
        // Opaque types desugared from `impl Trait`.
        hir::OpaqueTyOrigin::FnReturn { parent: owner, in_trait_or_impl }
        | hir::OpaqueTyOrigin::AsyncFn { parent: owner, in_trait_or_impl } => {
            if in_trait_or_impl == Some(hir::RpitContext::Trait)
                && !tcx.defaultness(owner).has_value()
            {
                span_bug!(
                    tcx.def_span(def_id),
                    "tried to get type of this RPITIT with no definition"
                );
            }
            opaque::find_opaque_ty_constraints_for_rpit(
                tcx,
                def_id,
                owner,
                DefiningScopeKind::HirTypeck,
            )
        }
    }
}

fn anon_const_type_of<'tcx>(icx: &ItemCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
    use hir::*;
    use rustc_middle::ty::Ty;
    let tcx = icx.tcx;
    let hir_id = tcx.local_def_id_to_hir_id(def_id);

    let node = tcx.hir_node(hir_id);
    let Node::AnonConst(&AnonConst { span, .. }) = node else {
        span_bug!(
            tcx.def_span(def_id),
            "expected anon const in `anon_const_type_of`, got {node:?}"
        );
    };

    let parent_node_id = tcx.parent_hir_id(hir_id);
    let parent_node = tcx.hir_node(parent_node_id);

    match parent_node {
        // Anon consts "inside" the type system.
        Node::ConstArg(&ConstArg {
            hir_id: arg_hir_id,
            kind: ConstArgKind::Anon(&AnonConst { hir_id: anon_hir_id, .. }),
            ..
        }) if anon_hir_id == hir_id => const_arg_anon_type_of(icx, arg_hir_id, span),

        Node::Variant(Variant { disr_expr: Some(e), .. }) if e.hir_id == hir_id => {
            tcx.adt_def(tcx.hir_get_parent_item(hir_id)).repr().discr_type().to_ty(tcx)
        }

        Node::Field(&hir::FieldDef { default: Some(c), def_id: field_def_id, .. })
            if c.hir_id == hir_id =>
        {
            tcx.type_of(field_def_id).instantiate_identity().skip_norm_wip()
        }

        _ => Ty::new_error_with_message(
            tcx,
            span,
            format!("unexpected anon const parent in type_of(): {parent_node:?}"),
        ),
    }
}

fn const_arg_anon_type_of<'tcx>(icx: &ItemCtxt<'tcx>, arg_hir_id: HirId, span: Span) -> Ty<'tcx> {
    use hir::*;
    use rustc_middle::ty::Ty;

    let tcx = icx.tcx;

    match tcx.parent_hir_node(arg_hir_id) {
        // Array length const arguments do not have `type_of` fed as there is never a corresponding
        // generic parameter definition.
        Node::Ty(&hir::Ty { kind: TyKind::Array(_, ref constant), .. })
        | Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
            if constant.hir_id == arg_hir_id =>
        {
            tcx.types.usize
        }

        Node::TyPat(pat) => {
            let node = match tcx.parent_hir_node(pat.hir_id) {
                // Or patterns can be nested one level deep
                Node::TyPat(p) => tcx.parent_hir_node(p.hir_id),
                other => other,
            };
            let hir::TyKind::Pat(ty, _) = node.expect_ty().kind else { bug!() };
            icx.lower_ty(ty)
        }

        // This is not a `bug!` as const arguments in path segments that did not resolve to anything
        // will result in `type_of` never being fed.
        _ => Ty::new_error_with_message(
            tcx,
            span,
            "`type_of` called on const argument's anon const before the const argument was lowered",
        ),
    }
}

fn infer_placeholder_type<'tcx>(
    cx: &dyn HirTyLowerer<'tcx>,
    def_id: LocalDefId,
    hir_id: HirId,
    ty_span: Span,
    body_span: Span,
    item_ident: Ident,
    kind: &'static str,
) -> Ty<'tcx> {
    let tcx = cx.tcx();
    // If the type is omitted on a `type const` we can't run
    // type check on since that requires the const have a body
    // which `type const`s don't.
    let ty = if tcx.is_type_const(def_id.to_def_id()) {
        if let Some(trait_item_def_id) = tcx.trait_item_of(def_id.to_def_id()) {
            tcx.type_of(trait_item_def_id).instantiate_identity().skip_norm_wip()
        } else {
            Ty::new_error_with_message(
                tcx,
                ty_span,
                "constant with `type const` requires an explicit type",
            )
        }
    } else {
        tcx.typeck(def_id).node_type(hir_id)
    };

    // If this came from a free `const` or `static mut?` item,
    // then the user may have written e.g. `const A = 42;`.
    // In this case, the parser has stashed a diagnostic for
    // us to improve in typeck so we do that now.
    let guar = cx
        .dcx()
        .try_steal_modify_and_emit_err(ty_span, StashKey::ItemNoType, |err| {
            if !ty.references_error() {
                // Only suggest adding `:` if it was missing (and suggested by parsing diagnostic).
                let colon = if ty_span == item_ident.span.shrink_to_hi() { ":" } else { "" };

                // The parser provided a sub-optimal `HasPlaceholders` suggestion for the type.
                // We are typeck and have the real type, so remove that and suggest the actual type.
                if let Suggestions::Enabled(suggestions) = &mut err.suggestions {
                    suggestions.clear();
                }

                if let Some(ty) = ty.make_suggestable(tcx, false, None) {
                    err.span_suggestion(
                        ty_span,
                        format!("provide a type for the {kind}"),
                        with_types_for_suggestion!(format!("{colon} {ty}")),
                        Applicability::MachineApplicable,
                    );
                } else {
                    with_forced_trimmed_paths!(err.span_note(
                        body_span,
                        format!("however, the inferred type `{ty}` cannot be named"),
                    ));
                }
            }
        })
        .unwrap_or_else(|| {
            let mut visitor = HirPlaceholderCollector::default();
            let node = tcx.hir_node_by_def_id(def_id);
            if let Some(ty) = node.ty() {
                visitor.visit_ty_unambig(ty);
            }
            // If we didn't find any infer tys, then just fallback to `span`.
            if visitor.spans.is_empty() {
                visitor.spans.push(ty_span);
            }
            let mut diag = bad_placeholder(cx, visitor.spans, kind);

            // HACK(#69396): Stashing and stealing diagnostics does not interact
            // well with macros which may delay more than one diagnostic on the
            // same span. If this happens, we will fall through to this arm, so
            // we need to suppress the suggestion since it's invalid. Ideally we
            // would suppress the duplicated error too, but that's really hard.
            if ty_span.is_empty() && ty_span.from_expansion() {
                // An approximately better primary message + no suggestion...
                diag.primary_message("missing type for item");
            } else if !ty.references_error() {
                if let Some(ty) = ty.make_suggestable(tcx, false, None) {
                    diag.span_suggestion_verbose(
                        ty_span,
                        "replace this with a fully-specified type",
                        ty,
                        Applicability::MachineApplicable,
                    );
                } else {
                    with_forced_trimmed_paths!(diag.span_note(
                        body_span,
                        format!("however, the inferred type `{ty}` cannot be named"),
                    ));
                }
            }

            diag.emit()
        });
    Ty::new_error(tcx, guar)
}

fn check_feature_inherent_assoc_ty(tcx: TyCtxt<'_>, span: Span) {
    if !tcx.features().inherent_associated_types() {
        use rustc_session::errors::feature_err;
        use rustc_span::sym;
        feature_err(
            &tcx.sess,
            sym::inherent_associated_types,
            span,
            "inherent associated types are unstable",
        )
        .emit();
    }
}

pub(crate) fn type_alias_is_lazy<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> bool {
    use hir::intravisit::Visitor;
    if tcx.features().lazy_type_alias() {
        return true;
    }
    struct HasTait;
    impl<'tcx> Visitor<'tcx> for HasTait {
        type Result = ControlFlow<()>;
        fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx, AmbigArg>) -> Self::Result {
            if let hir::TyKind::OpaqueDef(..) = t.kind {
                ControlFlow::Break(())
            } else {
                hir::intravisit::walk_ty(self, t)
            }
        }
    }
    HasTait.visit_ty_unambig(tcx.hir_expect_item(def_id).expect_ty_alias().2).is_break()
}
