use hir::{AsAssocItem, Impl, Semantics};
use ide_db::{
    defs::{Definition, NameClass, NameRefClass},
    helpers::pick_best_token,
    RootDatabase,
};
use itertools::Itertools;
use syntax::{ast, AstNode, SyntaxKind::*, T};

use crate::{display::TryToNav, FilePosition, NavigationTarget, RangeInfo};

// Feature: Go to Implementation
//
// Navigates to the impl block of structs, enums or traits. Also implemented as a code lens.
//
// |===
// | Editor  | Shortcut
//
// | VS Code | kbd:[Ctrl+F12]
// |===
//
// image::https://user-images.githubusercontent.com/48062697/113065566-02f85480-91b1-11eb-9288-aaad8abd8841.gif[]
pub(crate) fn goto_implementation(
    db: &RootDatabase,
    position: FilePosition,
) -> Option<RangeInfo<Vec<NavigationTarget>>> {
    let sema = Semantics::new(db);
    let source_file = sema.parse(position.file_id);
    let syntax = source_file.syntax().clone();

    let original_token =
        pick_best_token(syntax.token_at_offset(position.offset), |kind| match kind {
            IDENT | T![self] => 1,
            _ => 0,
        })?;
    let range = original_token.text_range();
    let navs =
        sema.descend_into_macros_many(original_token)
            .into_iter()
            .filter_map(|token| token.parent().and_then(ast::NameLike::cast))
            .filter_map(|node| {
                let def = match &node {
                    ast::NameLike::Name(name) => {
                        NameClass::classify(&sema, name).map(|class| match class {
                            NameClass::Definition(it) | NameClass::ConstReference(it) => it,
                            NameClass::PatFieldShorthand { local_def, field_ref: _ } => {
                                Definition::Local(local_def)
                            }
                        })
                    }
                    ast::NameLike::NameRef(name_ref) => NameRefClass::classify(&sema, name_ref)
                        .map(|class| match class {
                            NameRefClass::Definition(def) => def,
                            NameRefClass::FieldShorthand { local_ref, field_ref: _ } => {
                                Definition::Local(local_ref)
                            }
                        }),
                    ast::NameLike::Lifetime(_) => None,
                }?;

                match def {
                    Definition::ModuleDef(def) => Some(def),
                    _ => None,
                }
            })
            .unique()
            .filter_map(|def| {
                let navs = match def {
                    hir::ModuleDef::Trait(trait_) => impls_for_trait(&sema, trait_),
                    hir::ModuleDef::Adt(adt) => impls_for_ty(&sema, adt.ty(sema.db)),
                    hir::ModuleDef::TypeAlias(alias) => impls_for_ty(&sema, alias.ty(sema.db)),
                    hir::ModuleDef::BuiltinType(builtin) => {
                        let module = sema.to_module_def(position.file_id)?;
                        impls_for_ty(&sema, builtin.ty(sema.db, module))
                    }
                    hir::ModuleDef::Function(f) => {
                        let assoc = f.as_assoc_item(sema.db)?;
                        let name = assoc.name(sema.db)?;
                        let trait_ = assoc.containing_trait_or_trait_impl(sema.db)?;
                        impls_for_trait_item(&sema, trait_, name)
                    }
                    hir::ModuleDef::Const(c) => {
                        let assoc = c.as_assoc_item(sema.db)?;
                        let name = assoc.name(sema.db)?;
                        let trait_ = assoc.containing_trait_or_trait_impl(sema.db)?;
                        impls_for_trait_item(&sema, trait_, name)
                    }
                    _ => return None,
                };
                Some(navs)
            })
            .flatten()
            .collect();

    Some(RangeInfo { range, info: navs })
}

fn impls_for_ty(sema: &Semantics<RootDatabase>, ty: hir::Type) -> Vec<NavigationTarget> {
    Impl::all_for_type(sema.db, ty).into_iter().filter_map(|imp| imp.try_to_nav(sema.db)).collect()
}

fn impls_for_trait(sema: &Semantics<RootDatabase>, trait_: hir::Trait) -> Vec<NavigationTarget> {
    Impl::all_for_trait(sema.db, trait_)
        .into_iter()
        .filter_map(|imp| imp.try_to_nav(sema.db))
        .collect()
}

fn impls_for_trait_item(
    sema: &Semantics<RootDatabase>,
    trait_: hir::Trait,
    fun_name: hir::Name,
) -> Vec<NavigationTarget> {
    Impl::all_for_trait(sema.db, trait_)
        .into_iter()
        .filter_map(|imp| {
            let item = imp.items(sema.db).iter().find_map(|itm| {
                let itm_name = itm.name(sema.db)?;
                (itm_name == fun_name).then(|| *itm)
            })?;
            item.try_to_nav(sema.db)
        })
        .collect()
}

#[cfg(test)]
mod tests {
    use ide_db::base_db::FileRange;
    use itertools::Itertools;

    use crate::fixture;

    fn check(ra_fixture: &str) {
        let (analysis, position, expected) = fixture::annotations(ra_fixture);

        let navs = analysis.goto_implementation(position).unwrap().unwrap().info;

        let cmp = |frange: &FileRange| (frange.file_id, frange.range.start());

        let actual = navs
            .into_iter()
            .map(|nav| FileRange { file_id: nav.file_id, range: nav.focus_or_full_range() })
            .sorted_by_key(cmp)
            .collect::<Vec<_>>();
        let expected =
            expected.into_iter().map(|(range, _)| range).sorted_by_key(cmp).collect::<Vec<_>>();
        assert_eq!(expected, actual);
    }

    #[test]
    fn goto_implementation_works() {
        check(
            r#"
struct Foo$0;
impl Foo {}
   //^^^
"#,
        );
    }

    #[test]
    fn goto_implementation_works_multiple_blocks() {
        check(
            r#"
struct Foo$0;
impl Foo {}
   //^^^
impl Foo {}
   //^^^
"#,
        );
    }

    #[test]
    fn goto_implementation_works_multiple_mods() {
        check(
            r#"
struct Foo$0;
mod a {
    impl super::Foo {}
       //^^^^^^^^^^
}
mod b {
    impl super::Foo {}
       //^^^^^^^^^^
}
"#,
        );
    }

    #[test]
    fn goto_implementation_works_multiple_files() {
        check(
            r#"
//- /lib.rs
struct Foo$0;
mod a;
mod b;
//- /a.rs
impl crate::Foo {}
   //^^^^^^^^^^
//- /b.rs
impl crate::Foo {}
   //^^^^^^^^^^
"#,
        );
    }

    #[test]
    fn goto_implementation_for_trait() {
        check(
            r#"
trait T$0 {}
struct Foo;
impl T for Foo {}
         //^^^
"#,
        );
    }

    #[test]
    fn goto_implementation_for_trait_multiple_files() {
        check(
            r#"
//- /lib.rs
trait T$0 {};
struct Foo;
mod a;
mod b;
//- /a.rs
impl crate::T for crate::Foo {}
                //^^^^^^^^^^
//- /b.rs
impl crate::T for crate::Foo {}
                //^^^^^^^^^^
            "#,
        );
    }

    #[test]
    fn goto_implementation_all_impls() {
        check(
            r#"
//- /lib.rs
trait T {}
struct Foo$0;
impl Foo {}
   //^^^
impl T for Foo {}
         //^^^
impl T for &Foo {}
         //^^^^
"#,
        );
    }

    #[test]
    fn goto_implementation_to_builtin_derive() {
        check(
            r#"
//- minicore: copy, derive
  #[derive(Copy)]
//^^^^^^^^^^^^^^^
struct Foo$0;
"#,
        );
    }

    #[test]
    fn goto_implementation_type_alias() {
        check(
            r#"
struct Foo;

type Bar$0 = Foo;

impl Foo {}
   //^^^
impl Bar {}
   //^^^
"#,
        );
    }

    #[test]
    fn goto_implementation_adt_generic() {
        check(
            r#"
struct Foo$0<T>;

impl<T> Foo<T> {}
      //^^^^^^
impl Foo<str> {}
   //^^^^^^^^
"#,
        );
    }

    #[test]
    fn goto_implementation_builtin() {
        check(
            r#"
//- /lib.rs crate:main deps:core
fn foo(_: bool$0) {{}}
//- /libcore.rs crate:core
#[lang = "bool"]
impl bool {}
   //^^^^
"#,
        );
    }

    #[test]
    fn goto_implementation_trait_functions() {
        check(
            r#"
trait Tr {
    fn f$0();
}

struct S;

impl Tr for S {
    fn f() {
     //^
        println!("Hello, world!");
    }
}
"#,
        );
    }

    #[test]
    fn goto_implementation_trait_assoc_const() {
        check(
            r#"
trait Tr {
    const C$0: usize;
}

struct S;

impl Tr for S {
    const C: usize = 4;
        //^
}
"#,
        );
    }
}
