//! Completion of paths, i.e. `some::prefix::$0`.

use hir::HasVisibility;
use rustc_hash::FxHashSet;
use syntax::AstNode;

use crate::{CompletionContext, Completions};

pub(crate) fn complete_qualified_path(acc: &mut Completions, ctx: &CompletionContext) {
    if ctx.is_path_disallowed() {
        return;
    }
    let path = match ctx.path_qual() {
        Some(path) => path,
        None => return,
    };

    let resolution = match ctx.sema.resolve_path(path) {
        Some(res) => res,
        None => return,
    };

    let context_module = ctx.scope.module();

    if ctx.expects_item() || ctx.expects_assoc_item() {
        if let hir::PathResolution::Def(hir::ModuleDef::Module(module)) = resolution {
            let module_scope = module.scope(ctx.db, context_module);
            for (name, def) in module_scope {
                if let hir::ScopeDef::MacroDef(macro_def) = def {
                    if macro_def.is_fn_like() {
                        acc.add_macro(ctx, Some(name.clone()), macro_def);
                    }
                }
                if let hir::ScopeDef::ModuleDef(hir::ModuleDef::Module(_)) = def {
                    acc.add_resolution(ctx, name, &def);
                }
            }
        }
        return;
    }

    // Add associated types on type parameters and `Self`.
    resolution.assoc_type_shorthand_candidates(ctx.db, |_, alias| {
        acc.add_type_alias(ctx, alias);
        None::<()>
    });

    match resolution {
        hir::PathResolution::Def(hir::ModuleDef::Module(module)) => {
            let module_scope = module.scope(ctx.db, context_module);
            for (name, def) in module_scope {
                if ctx.in_use_tree() {
                    if let hir::ScopeDef::Unknown = def {
                        if let Some(name_ref) = ctx.name_ref_syntax.as_ref() {
                            if name_ref.syntax().text() == name.to_string().as_str() {
                                // for `use self::foo$0`, don't suggest `foo` as a completion
                                cov_mark::hit!(dont_complete_current_use);
                                continue;
                            }
                        }
                    }
                }

                let add_resolution = match def {
                    // Don't suggest attribute macros and derives.
                    hir::ScopeDef::MacroDef(mac) => mac.is_fn_like(),
                    // no values in type places
                    hir::ScopeDef::ModuleDef(
                        hir::ModuleDef::Function(_)
                        | hir::ModuleDef::Variant(_)
                        | hir::ModuleDef::Static(_),
                    )
                    | hir::ScopeDef::Local(_) => !ctx.expects_type(),
                    // unless its a constant in a generic arg list position
                    hir::ScopeDef::ModuleDef(hir::ModuleDef::Const(_)) => {
                        !ctx.expects_type() || ctx.expects_generic_arg()
                    }
                    _ => true,
                };

                if add_resolution {
                    acc.add_resolution(ctx, name, &def);
                }
            }
        }
        hir::PathResolution::Def(
            def
            @
            (hir::ModuleDef::Adt(_)
            | hir::ModuleDef::TypeAlias(_)
            | hir::ModuleDef::BuiltinType(_)),
        ) => {
            if let hir::ModuleDef::Adt(hir::Adt::Enum(e)) = def {
                add_enum_variants(acc, ctx, e);
            }
            let ty = match def {
                hir::ModuleDef::Adt(adt) => adt.ty(ctx.db),
                hir::ModuleDef::TypeAlias(a) => {
                    let ty = a.ty(ctx.db);
                    if let Some(hir::Adt::Enum(e)) = ty.as_adt() {
                        cov_mark::hit!(completes_variant_through_alias);
                        add_enum_variants(acc, ctx, e);
                    }
                    ty
                }
                hir::ModuleDef::BuiltinType(builtin) => {
                    let module = match ctx.scope.module() {
                        Some(it) => it,
                        None => return,
                    };
                    cov_mark::hit!(completes_primitive_assoc_const);
                    builtin.ty(ctx.db, module)
                }
                _ => unreachable!(),
            };

            // XXX: For parity with Rust bug #22519, this does not complete Ty::AssocType.
            // (where AssocType is defined on a trait, not an inherent impl)

            let krate = ctx.krate;
            if let Some(krate) = krate {
                let traits_in_scope = ctx.scope.traits_in_scope();
                ty.iterate_path_candidates(ctx.db, krate, &traits_in_scope, None, |_ty, item| {
                    if context_module.map_or(false, |m| !item.is_visible_from(ctx.db, m)) {
                        return None;
                    }
                    add_assoc_item(acc, ctx, item);
                    None::<()>
                });

                // Iterate assoc types separately
                ty.iterate_assoc_items(ctx.db, krate, |item| {
                    if context_module.map_or(false, |m| !item.is_visible_from(ctx.db, m)) {
                        return None;
                    }
                    if let hir::AssocItem::TypeAlias(ty) = item {
                        acc.add_type_alias(ctx, ty)
                    }
                    None::<()>
                });
            }
        }
        hir::PathResolution::Def(hir::ModuleDef::Trait(t)) => {
            // Handles `Trait::assoc` as well as `<Ty as Trait>::assoc`.
            for item in t.items(ctx.db) {
                if context_module.map_or(false, |m| !item.is_visible_from(ctx.db, m)) {
                    continue;
                }
                add_assoc_item(acc, ctx, item);
            }
        }
        hir::PathResolution::TypeParam(_) | hir::PathResolution::SelfType(_) => {
            if let Some(krate) = ctx.krate {
                let ty = match resolution {
                    hir::PathResolution::TypeParam(param) => param.ty(ctx.db),
                    hir::PathResolution::SelfType(impl_def) => impl_def.self_ty(ctx.db),
                    _ => return,
                };

                if let Some(hir::Adt::Enum(e)) = ty.as_adt() {
                    add_enum_variants(acc, ctx, e);
                }

                let traits_in_scope = ctx.scope.traits_in_scope();
                let mut seen = FxHashSet::default();
                ty.iterate_path_candidates(ctx.db, krate, &traits_in_scope, None, |_ty, item| {
                    if context_module.map_or(false, |m| !item.is_visible_from(ctx.db, m)) {
                        return None;
                    }

                    // We might iterate candidates of a trait multiple times here, so deduplicate
                    // them.
                    if seen.insert(item) {
                        add_assoc_item(acc, ctx, item);
                    }
                    None::<()>
                });
            }
        }
        _ => {}
    }
}

fn add_assoc_item(acc: &mut Completions, ctx: &CompletionContext, item: hir::AssocItem) {
    match item {
        hir::AssocItem::Function(func) if !ctx.expects_type() => acc.add_function(ctx, func, None),
        hir::AssocItem::Const(ct) if !ctx.expects_type() || ctx.expects_generic_arg() => {
            acc.add_const(ctx, ct)
        }
        hir::AssocItem::TypeAlias(ty) => acc.add_type_alias(ctx, ty),
        _ => (),
    }
}

fn add_enum_variants(acc: &mut Completions, ctx: &CompletionContext, e: hir::Enum) {
    if ctx.expects_type() {
        return;
    }
    e.variants(ctx.db).into_iter().for_each(|variant| acc.add_enum_variant(ctx, variant, None));
}

#[cfg(test)]
mod tests {
    use expect_test::{expect, Expect};

    use crate::{
        tests::{check_edit, filtered_completion_list},
        CompletionKind,
    };

    fn check(ra_fixture: &str, expect: Expect) {
        let actual = filtered_completion_list(ra_fixture, CompletionKind::Reference);
        expect.assert_eq(&actual);
    }

    fn check_builtin(ra_fixture: &str, expect: Expect) {
        let actual = filtered_completion_list(ra_fixture, CompletionKind::BuiltinType);
        expect.assert_eq(&actual);
    }

    #[test]
    fn dont_complete_values_in_type_pos() {
        check(
            r#"
const FOO: () = ();
static BAR: () = ();
struct Baz;
fn foo() {
    let _: self::$0;
}
"#,
            expect![[r#"
                st Baz
            "#]],
        );
    }

    #[test]
    fn dont_complete_enum_variants_in_type_pos() {
        check(
            r#"
enum Foo { Bar }
fn foo() {
    let _: Foo::$0;
}
"#,
            expect![[r#""#]],
        );
    }

    #[test]
    fn dont_complete_primitive_in_use() {
        check_builtin(r#"use self::$0;"#, expect![[""]]);
    }

    #[test]
    fn dont_complete_primitive_in_module_scope() {
        check_builtin(r#"fn foo() { self::$0 }"#, expect![[""]]);
    }

    #[test]
    fn completes_primitives() {
        check_builtin(
            r#"fn main() { let _: $0 = 92; }"#,
            expect![[r#"
                bt u32
                bt bool
                bt u8
                bt isize
                bt u16
                bt u64
                bt u128
                bt f32
                bt i128
                bt i16
                bt str
                bt i64
                bt char
                bt f64
                bt i32
                bt i8
                bt usize
            "#]],
        );
    }

    #[test]
    fn completes_enum_variant() {
        check(
            r#"
enum E { Foo, Bar(i32) }
fn foo() { let _ = E::$0 }
"#,
            expect![[r#"
                ev Foo    ()
                ev Bar(…) (i32)
            "#]],
        );
    }

    #[test]
    fn completes_struct_associated_items() {
        check(
            r#"
//- /lib.rs
struct S;

impl S {
    fn a() {}
    fn b(&self) {}
    const C: i32 = 42;
    type T = i32;
}

fn foo() { let _ = S::$0 }
"#,
            expect![[r#"
                fn a()  fn()
                me b(…) fn(&self)
                ct C    const C: i32 = 42;
                ta T    type T = i32;
            "#]],
        );
    }

    #[test]
    fn associated_item_visibility() {
        check(
            r#"
struct S;

mod m {
    impl super::S {
        pub(crate) fn public_method() { }
        fn private_method() { }
        pub(crate) type PublicType = u32;
        type PrivateType = u32;
        pub(crate) const PUBLIC_CONST: u32 = 1;
        const PRIVATE_CONST: u32 = 1;
    }
}

fn foo() { let _ = S::$0 }
"#,
            expect![[r#"
                fn public_method() fn()
                ct PUBLIC_CONST    pub(crate) const PUBLIC_CONST: u32 = 1;
                ta PublicType      pub(crate) type PublicType = u32;
            "#]],
        );
    }

    #[test]
    fn completes_enum_associated_method() {
        check(
            r#"
enum E {};
impl E { fn m() { } }

fn foo() { let _ = E::$0 }
        "#,
            expect![[r#"
                fn m() fn()
            "#]],
        );
    }

    #[test]
    fn completes_union_associated_method() {
        check(
            r#"
union U {};
impl U { fn m() { } }

fn foo() { let _ = U::$0 }
"#,
            expect![[r#"
                fn m() fn()
            "#]],
        );
    }

    #[test]
    fn completes_trait_associated_method_1() {
        check(
            r#"
trait Trait { fn m(); }

fn foo() { let _ = Trait::$0 }
"#,
            expect![[r#"
                fn m() fn()
            "#]],
        );
    }

    #[test]
    fn completes_trait_associated_method_2() {
        check(
            r#"
trait Trait { fn m(); }

struct S;
impl Trait for S {}

fn foo() { let _ = S::$0 }
"#,
            expect![[r#"
                fn m() fn()
            "#]],
        );
    }

    #[test]
    fn completes_trait_associated_method_3() {
        check(
            r#"
trait Trait { fn m(); }

struct S;
impl Trait for S {}

fn foo() { let _ = <S as Trait>::$0 }
"#,
            expect![[r#"
                fn m() fn()
            "#]],
        );
    }

    #[test]
    fn completes_ty_param_assoc_ty() {
        check(
            r#"
trait Super {
    type Ty;
    const CONST: u8;
    fn func() {}
    fn method(&self) {}
}

trait Sub: Super {
    type SubTy;
    const C2: ();
    fn subfunc() {}
    fn submethod(&self) {}
}

fn foo<T: Sub>() { T::$0 }
"#,
            expect![[r#"
                ta SubTy        type SubTy;
                ta Ty           type Ty;
                ct C2           const C2: ();
                fn subfunc()    fn()
                me submethod(…) fn(&self)
                ct CONST        const CONST: u8;
                fn func()       fn()
                me method(…)    fn(&self)
            "#]],
        );
    }

    #[test]
    fn completes_self_param_assoc_ty() {
        check(
            r#"
trait Super {
    type Ty;
    const CONST: u8 = 0;
    fn func() {}
    fn method(&self) {}
}

trait Sub: Super {
    type SubTy;
    const C2: () = ();
    fn subfunc() {}
    fn submethod(&self) {}
}

struct Wrap<T>(T);
impl<T> Super for Wrap<T> {}
impl<T> Sub for Wrap<T> {
    fn subfunc() {
        // Should be able to assume `Self: Sub + Super`
        Self::$0
    }
}
"#,
            expect![[r#"
                ta SubTy        type SubTy;
                ta Ty           type Ty;
                ct CONST        const CONST: u8 = 0;
                fn func()       fn()
                me method(…)    fn(&self)
                ct C2           const C2: () = ();
                fn subfunc()    fn()
                me submethod(…) fn(&self)
            "#]],
        );
    }

    #[test]
    fn completes_type_alias() {
        check(
            r#"
struct S;
impl S { fn foo() {} }
type T = S;
impl T { fn bar() {} }

fn main() { T::$0; }
"#,
            expect![[r#"
                fn foo() fn()
                fn bar() fn()
            "#]],
        );
    }

    #[test]
    fn completes_qualified_macros() {
        check(
            r#"
#[macro_export]
macro_rules! foo { () => {} }

fn main() { let _ = crate::$0 }
"#,
            expect![[r##"
                fn main()  fn()
                ma foo!(…) #[macro_export] macro_rules! foo
            "##]],
        );
    }

    #[test]
    fn does_not_complete_non_fn_macros() {
        check(
            r#"
mod m {
    #[rustc_builtin_macro]
    pub macro Clone {}
}

fn f() {m::$0}
"#,
            expect![[r#""#]],
        );
        check(
            r#"
mod m {
    #[rustc_builtin_macro]
    pub macro bench {}
}

fn f() {m::$0}
"#,
            expect![[r#""#]],
        );
    }

    #[test]
    fn completes_reexported_items_under_correct_name() {
        check(
            r#"
fn foo() { self::m::$0 }

mod m {
    pub use super::p::wrong_fn as right_fn;
    pub use super::p::WRONG_CONST as RIGHT_CONST;
    pub use super::p::WrongType as RightType;
}
mod p {
    fn wrong_fn() {}
    const WRONG_CONST: u32 = 1;
    struct WrongType {};
}
"#,
            expect![[r#"
                ct RIGHT_CONST
                fn right_fn()  fn()
                st RightType
            "#]],
        );

        check_edit(
            "RightType",
            r#"
fn foo() { self::m::$0 }

mod m {
    pub use super::p::wrong_fn as right_fn;
    pub use super::p::WRONG_CONST as RIGHT_CONST;
    pub use super::p::WrongType as RightType;
}
mod p {
    fn wrong_fn() {}
    const WRONG_CONST: u32 = 1;
    struct WrongType {};
}
"#,
            r#"
fn foo() { self::m::RightType }

mod m {
    pub use super::p::wrong_fn as right_fn;
    pub use super::p::WRONG_CONST as RIGHT_CONST;
    pub use super::p::WrongType as RightType;
}
mod p {
    fn wrong_fn() {}
    const WRONG_CONST: u32 = 1;
    struct WrongType {};
}
"#,
        );
    }

    #[test]
    fn completes_in_simple_macro_call() {
        check(
            r#"
macro_rules! m { ($e:expr) => { $e } }
fn main() { m!(self::f$0); }
fn foo() {}
"#,
            expect![[r#"
                fn main() fn()
                fn foo()  fn()
            "#]],
        );
    }

    #[test]
    fn function_mod_share_name() {
        check(
            r#"
fn foo() { self::m::$0 }

mod m {
    pub mod z {}
    pub fn z() {}
}
"#,
            expect![[r#"
                md z
                fn z() fn()
            "#]],
        );
    }

    #[test]
    fn completes_hashmap_new() {
        check(
            r#"
struct RandomState;
struct HashMap<K, V, S = RandomState> {}

impl<K, V> HashMap<K, V, RandomState> {
    pub fn new() -> HashMap<K, V, RandomState> { }
}
fn foo() {
    HashMap::$0
}
"#,
            expect![[r#"
                fn new() fn() -> HashMap<K, V, RandomState>
            "#]],
        );
    }

    #[test]
    fn dont_complete_attr() {
        check(
            r#"
mod foo { pub struct Foo; }
#[foo::$0]
fn f() {}
"#,
            expect![[""]],
        );
    }

    #[test]
    fn completes_variant_through_self() {
        check(
            r#"
enum Foo {
    Bar,
    Baz,
}

impl Foo {
    fn foo(self) {
        Self::$0
    }
}
"#,
            expect![[r#"
                ev Bar    ()
                ev Baz    ()
                me foo(…) fn(self)
            "#]],
        );
    }

    #[test]
    fn completes_primitive_assoc_const() {
        cov_mark::check!(completes_primitive_assoc_const);
        check(
            r#"
//- /lib.rs crate:lib deps:core
fn f() {
    u8::$0
}

//- /core.rs crate:core
#[lang = "u8"]
impl u8 {
    pub const MAX: Self = 255;

    pub fn func(self) {}
}
"#,
            expect![[r#"
                ct MAX     pub const MAX: Self = 255;
                me func(…) fn(self)
            "#]],
        );
    }

    #[test]
    fn completes_variant_through_alias() {
        cov_mark::check!(completes_variant_through_alias);
        check(
            r#"
enum Foo {
    Bar
}
type Foo2 = Foo;
fn main() {
    Foo2::$0
}
"#,
            expect![[r#"
                ev Bar ()
            "#]],
        );
    }

    #[test]
    fn completes_types_and_const_in_arg_list() {
        check(
            r#"
mod foo {
    pub const CONST: () = ();
    pub type Type = ();
}

struct Foo<T>(t);

fn foo(_: Foo<foo::$0>) {}
"#,
            expect![[r#"
                ta Type
                ct CONST
            "#]],
        );
    }
}