use syntax::{
    ast::{self, AstNode, HasGenericParams, HasName, edit::AstNodeEdit, make},
    syntax_editor::{Position, SyntaxEditor},
};

use crate::{
    AssistContext, AssistId, Assists,
    utils::{self, DefaultMethods, IgnoreAssocItems},
};

fn insert_impl(
    editor: &mut SyntaxEditor,
    impl_: &ast::Impl,
    nominal: &impl AstNodeEdit,
) -> ast::Impl {
    let indent = nominal.indent_level();

    let impl_ = impl_.indent(indent);
    editor.insert_all(
        Position::after(nominal.syntax()),
        vec![
            // Add a blank line after the ADT, and indentation for the impl to match the ADT
            make::tokens::whitespace(&format!("\n\n{indent}")).into(),
            impl_.syntax().clone().into(),
        ],
    );

    impl_
}

// Assist: generate_impl
//
// Adds a new inherent impl for a type.
//
// ```
// struct Ctx$0<T: Clone> {
//     data: T,
// }
// ```
// ->
// ```
// struct Ctx<T: Clone> {
//     data: T,
// }
//
// impl<T: Clone> Ctx<T> {$0}
// ```
pub(crate) fn generate_impl(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
    let nominal = ctx.find_node_at_offset::<ast::Adt>()?;
    let name = nominal.name()?;
    let target = nominal.syntax().text_range();

    if ctx.find_node_at_offset::<ast::RecordFieldList>().is_some() {
        return None;
    }

    acc.add(
        AssistId::generate("generate_impl"),
        format!("Generate impl for `{name}`"),
        target,
        |edit| {
            // Generate the impl
            let impl_ = utils::generate_impl(&nominal);

            let mut editor = edit.make_editor(nominal.syntax());

            let impl_ = insert_impl(&mut editor, &impl_, &nominal);
            // Add a tabstop after the left curly brace
            if let Some(cap) = ctx.config.snippet_cap
                && let Some(l_curly) = impl_.assoc_item_list().and_then(|it| it.l_curly_token())
            {
                let tabstop = edit.make_tabstop_after(cap);
                editor.add_annotation(l_curly, tabstop);
            }

            edit.add_file_edits(ctx.vfs_file_id(), editor);
        },
    )
}

// Assist: generate_trait_impl
//
// Adds a new trait impl for a type.
//
// ```
// struct $0Ctx<T: Clone> {
//     data: T,
// }
// ```
// ->
// ```
// struct Ctx<T: Clone> {
//     data: T,
// }
//
// impl<T: Clone> ${1:_} for Ctx<T> {$0}
// ```
pub(crate) fn generate_trait_impl(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
    let nominal = ctx.find_node_at_offset::<ast::Adt>()?;
    let name = nominal.name()?;
    let target = nominal.syntax().text_range();

    if ctx.find_node_at_offset::<ast::RecordFieldList>().is_some() {
        return None;
    }

    acc.add(
        AssistId::generate("generate_trait_impl"),
        format!("Generate trait impl for `{name}`"),
        target,
        |edit| {
            // Generate the impl
            let impl_ = utils::generate_trait_impl_intransitive(&nominal, make::ty_placeholder());

            let mut editor = edit.make_editor(nominal.syntax());

            let impl_ = insert_impl(&mut editor, &impl_, &nominal);
            // Make the trait type a placeholder snippet
            if let Some(cap) = ctx.config.snippet_cap {
                if let Some(trait_) = impl_.trait_() {
                    let placeholder = edit.make_placeholder_snippet(cap);
                    editor.add_annotation(trait_.syntax(), placeholder);
                }

                if let Some(l_curly) = impl_.assoc_item_list().and_then(|it| it.l_curly_token()) {
                    let tabstop = edit.make_tabstop_after(cap);
                    editor.add_annotation(l_curly, tabstop);
                }
            }

            edit.add_file_edits(ctx.vfs_file_id(), editor);
        },
    )
}

// Assist: generate_impl_trait
//
// Adds this trait impl for a type.
//
// ```
// trait $0Foo {
//     fn foo(&self) -> i32;
// }
// ```
// ->
// ```
// trait Foo {
//     fn foo(&self) -> i32;
// }
//
// impl Foo for ${1:_} {
//     fn foo(&self) -> i32 {
//         $0todo!()
//     }
// }
// ```
pub(crate) fn generate_impl_trait(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
    let name = ctx.find_node_at_offset::<ast::Name>()?;
    let trait_ = ast::Trait::cast(name.syntax().parent()?)?;
    let target_scope = ctx.sema.scope(trait_.syntax())?;
    let hir_trait = ctx.sema.to_def(&trait_)?;

    let target = trait_.syntax().text_range();
    acc.add(
        AssistId::generate("generate_impl_trait"),
        format!("Generate `{name}` impl for type"),
        target,
        |edit| {
            let mut editor = edit.make_editor(trait_.syntax());

            let holder_arg = ast::GenericArg::TypeArg(make::type_arg(make::ty_placeholder()));
            let missing_items = utils::filter_assoc_items(
                &ctx.sema,
                &hir_trait.items(ctx.db()),
                DefaultMethods::No,
                IgnoreAssocItems::DocHiddenAttrPresent,
            );

            let trait_gen_args = trait_.generic_param_list().map(|list| {
                make::generic_arg_list(list.generic_params().map(|_| holder_arg.clone()))
            });

            let make_impl_ = |body| {
                make::impl_trait(
                    None,
                    trait_.unsafe_token().is_some(),
                    None,
                    trait_gen_args.clone(),
                    None,
                    None,
                    false,
                    make::ty(&name.text()),
                    make::ty_placeholder(),
                    None,
                    None,
                    body,
                )
                .clone_for_update()
            };

            let impl_ = if missing_items.is_empty() {
                make_impl_(None)
            } else {
                let impl_ = make_impl_(None);
                let assoc_items = utils::add_trait_assoc_items_to_impl(
                    &ctx.sema,
                    ctx.config,
                    &missing_items,
                    hir_trait,
                    &impl_,
                    &target_scope,
                );
                let assoc_item_list = make::assoc_item_list(Some(assoc_items));
                make_impl_(Some(assoc_item_list))
            };

            let impl_ = insert_impl(&mut editor, &impl_, &trait_);

            if let Some(cap) = ctx.config.snippet_cap {
                if let Some(generics) = impl_.trait_().and_then(|it| it.generic_arg_list()) {
                    for generic in generics.generic_args() {
                        let placeholder = edit.make_placeholder_snippet(cap);
                        editor.add_annotation(generic.syntax(), placeholder);
                    }
                }

                if let Some(ty) = impl_.self_ty() {
                    let placeholder = edit.make_placeholder_snippet(cap);
                    editor.add_annotation(ty.syntax(), placeholder);
                }

                if let Some(expr) =
                    impl_.assoc_item_list().and_then(|it| it.assoc_items().find_map(extract_expr))
                {
                    let tabstop = edit.make_tabstop_before(cap);
                    editor.add_annotation(expr.syntax(), tabstop);
                } else if let Some(l_curly) =
                    impl_.assoc_item_list().and_then(|it| it.l_curly_token())
                {
                    let tabstop = edit.make_tabstop_after(cap);
                    editor.add_annotation(l_curly, tabstop);
                }
            }

            edit.add_file_edits(ctx.vfs_file_id(), editor);
        },
    )
}

fn extract_expr(item: ast::AssocItem) -> Option<ast::Expr> {
    let ast::AssocItem::Fn(f) = item else {
        return None;
    };
    f.body()?.tail_expr()
}

#[cfg(test)]
mod tests {
    use crate::tests::{check_assist, check_assist_target};

    use super::*;

    #[test]
    fn test_add_impl() {
        check_assist(
            generate_impl,
            r#"
                struct Foo$0 {}
            "#,
            r#"
                struct Foo {}

                impl Foo {$0}
            "#,
        );
    }

    #[test]
    fn test_add_impl_with_generics() {
        check_assist(
            generate_impl,
            r#"
                struct Foo$0<T: Clone> {}
            "#,
            r#"
                struct Foo<T: Clone> {}

                impl<T: Clone> Foo<T> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_impl_with_generics_and_lifetime_parameters() {
        check_assist(
            generate_impl,
            r#"
                struct Foo<'a, T: Foo<'a>>$0 {}
            "#,
            r#"
                struct Foo<'a, T: Foo<'a>> {}

                impl<'a, T: Foo<'a>> Foo<'a, T> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_impl_with_attributes() {
        check_assist(
            generate_impl,
            r#"
                #[cfg(feature = "foo")]
                struct Foo<'a, T: Foo$0<'a>> {}
            "#,
            r#"
                #[cfg(feature = "foo")]
                struct Foo<'a, T: Foo<'a>> {}

                #[cfg(feature = "foo")]
                impl<'a, T: Foo<'a>> Foo<'a, T> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_impl_with_default_generic() {
        check_assist(
            generate_impl,
            r#"
                struct Defaulted$0<T = i32> {}
            "#,
            r#"
                struct Defaulted<T = i32> {}

                impl<T> Defaulted<T> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_impl_with_constrained_default_generic() {
        check_assist(
            generate_impl,
            r#"
                struct Defaulted$0<'a, 'b: 'a, T: Debug + Clone + 'a + 'b = String, const S: usize> {}
            "#,
            r#"
                struct Defaulted<'a, 'b: 'a, T: Debug + Clone + 'a + 'b = String, const S: usize> {}

                impl<'a, 'b: 'a, T: Debug + Clone + 'a + 'b, const S: usize> Defaulted<'a, 'b, T, S> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_impl_with_const_defaulted_generic() {
        check_assist(
            generate_impl,
            r#"
                struct Defaulted$0<const N: i32 = 0> {}
            "#,
            r#"
                struct Defaulted<const N: i32 = 0> {}

                impl<const N: i32> Defaulted<N> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_impl_with_trait_constraint() {
        check_assist(
            generate_impl,
            r#"
                pub trait Trait {}
                struct Struct$0<T>
                where
                    T: Trait,
                {
                    inner: T,
                }
            "#,
            r#"
                pub trait Trait {}
                struct Struct<T>
                where
                    T: Trait,
                {
                    inner: T,
                }

                impl<T> Struct<T>
                where
                    T: Trait,
                {$0
                }
            "#,
        );
    }

    #[test]
    fn add_impl_target() {
        check_assist_target(
            generate_impl,
            r#"
                struct SomeThingIrrelevant;
                /// Has a lifetime parameter
                struct Foo$0<'a, T: Foo<'a>> {}
                struct EvenMoreIrrelevant;
            "#,
            "/// Has a lifetime parameter\nstruct Foo<'a, T: Foo<'a>> {}",
        );
    }

    #[test]
    fn test_add_trait_impl() {
        check_assist(
            generate_trait_impl,
            r#"
                struct Foo$0 {}
            "#,
            r#"
                struct Foo {}

                impl ${1:_} for Foo {$0}
            "#,
        );
    }

    #[test]
    fn test_add_trait_impl_with_generics() {
        check_assist(
            generate_trait_impl,
            r#"
                struct Foo$0<T: Clone> {}
            "#,
            r#"
                struct Foo<T: Clone> {}

                impl<T: Clone> ${1:_} for Foo<T> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_trait_impl_with_generics_and_lifetime_parameters() {
        check_assist(
            generate_trait_impl,
            r#"
                struct Foo<'a, T: Foo<'a>>$0 {}
            "#,
            r#"
                struct Foo<'a, T: Foo<'a>> {}

                impl<'a, T: Foo<'a>> ${1:_} for Foo<'a, T> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_trait_impl_with_attributes() {
        check_assist(
            generate_trait_impl,
            r#"
                #[cfg(feature = "foo")]
                struct Foo<'a, T: Foo$0<'a>> {}
            "#,
            r#"
                #[cfg(feature = "foo")]
                struct Foo<'a, T: Foo<'a>> {}

                #[cfg(feature = "foo")]
                impl<'a, T: Foo<'a>> ${1:_} for Foo<'a, T> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_trait_impl_with_default_generic() {
        check_assist(
            generate_trait_impl,
            r#"
                struct Defaulted$0<T = i32> {}
            "#,
            r#"
                struct Defaulted<T = i32> {}

                impl<T> ${1:_} for Defaulted<T> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_trait_impl_with_constrained_default_generic() {
        check_assist(
            generate_trait_impl,
            r#"
                struct Defaulted$0<'a, 'b: 'a, T: Debug + Clone + 'a + 'b = String, const S: usize> {}
            "#,
            r#"
                struct Defaulted<'a, 'b: 'a, T: Debug + Clone + 'a + 'b = String, const S: usize> {}

                impl<'a, 'b: 'a, T: Debug + Clone + 'a + 'b, const S: usize> ${1:_} for Defaulted<'a, 'b, T, S> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_trait_impl_with_const_defaulted_generic() {
        check_assist(
            generate_trait_impl,
            r#"
                struct Defaulted$0<const N: i32 = 0> {}
            "#,
            r#"
                struct Defaulted<const N: i32 = 0> {}

                impl<const N: i32> ${1:_} for Defaulted<N> {$0}
            "#,
        );
    }

    #[test]
    fn test_add_trait_impl_with_trait_constraint() {
        check_assist(
            generate_trait_impl,
            r#"
                pub trait Trait {}
                struct Struct$0<T>
                where
                    T: Trait,
                {
                    inner: T,
                }
            "#,
            r#"
                pub trait Trait {}
                struct Struct<T>
                where
                    T: Trait,
                {
                    inner: T,
                }

                impl<T> ${1:_} for Struct<T>
                where
                    T: Trait,
                {$0
                }
            "#,
        );
    }

    #[test]
    fn add_trait_impl_target() {
        check_assist_target(
            generate_trait_impl,
            r#"
                struct SomeThingIrrelevant;
                /// Has a lifetime parameter
                struct Foo$0<'a, T: Foo<'a>> {}
                struct EvenMoreIrrelevant;
            "#,
            "/// Has a lifetime parameter\nstruct Foo<'a, T: Foo<'a>> {}",
        );
    }

    #[test]
    fn add_impl_with_indent() {
        check_assist(
            generate_impl,
            r#"
                mod foo {
                    struct Bar$0 {}
                }
            "#,
            r#"
                mod foo {
                    struct Bar {}

                    impl Bar {$0}
                }
            "#,
        );
    }

    #[test]
    fn add_impl_with_multiple_indent() {
        check_assist(
            generate_impl,
            r#"
                mod foo {
                    fn bar() {
                        struct Baz$0 {}
                    }
                }
            "#,
            r#"
                mod foo {
                    fn bar() {
                        struct Baz {}

                        impl Baz {$0}
                    }
                }
            "#,
        );
    }

    #[test]
    fn add_trait_impl_with_indent() {
        check_assist(
            generate_trait_impl,
            r#"
                mod foo {
                    struct Bar$0 {}
                }
            "#,
            r#"
                mod foo {
                    struct Bar {}

                    impl ${1:_} for Bar {$0}
                }
            "#,
        );
    }

    #[test]
    fn test_add_impl_trait() {
        check_assist(
            generate_impl_trait,
            r#"
                trait $0Foo {
                    fn foo(&self) -> i32;

                    fn bar(&self) -> i32 {
                        self.foo()
                    }
                }
            "#,
            r#"
                trait Foo {
                    fn foo(&self) -> i32;

                    fn bar(&self) -> i32 {
                        self.foo()
                    }
                }

                impl Foo for ${1:_} {
                    fn foo(&self) -> i32 {
                        $0todo!()
                    }
                }
            "#,
        );
    }

    #[test]
    fn test_add_impl_trait_use_generic() {
        check_assist(
            generate_impl_trait,
            r#"
                trait $0Foo<T> {
                    fn foo(&self) -> T;

                    fn bar(&self) -> T {
                        self.foo()
                    }
                }
            "#,
            r#"
                trait Foo<T> {
                    fn foo(&self) -> T;

                    fn bar(&self) -> T {
                        self.foo()
                    }
                }

                impl Foo<${1:_}> for ${2:_} {
                    fn foo(&self) -> _ {
                        $0todo!()
                    }
                }
            "#,
        );
        check_assist(
            generate_impl_trait,
            r#"
                trait $0Foo<T, U> {
                    fn foo(&self) -> T;

                    fn bar(&self) -> T {
                        self.foo()
                    }
                }
            "#,
            r#"
                trait Foo<T, U> {
                    fn foo(&self) -> T;

                    fn bar(&self) -> T {
                        self.foo()
                    }
                }

                impl Foo<${1:_}, ${2:_}> for ${3:_} {
                    fn foo(&self) -> _ {
                        $0todo!()
                    }
                }
            "#,
        );
    }

    #[test]
    fn test_add_impl_trait_docs() {
        check_assist(
            generate_impl_trait,
            r#"
                /// foo
                trait $0Foo {
                    /// foo method
                    fn foo(&self) -> i32;

                    fn bar(&self) -> i32 {
                        self.foo()
                    }
                }
            "#,
            r#"
                /// foo
                trait Foo {
                    /// foo method
                    fn foo(&self) -> i32;

                    fn bar(&self) -> i32 {
                        self.foo()
                    }
                }

                impl Foo for ${1:_} {
                    fn foo(&self) -> i32 {
                        $0todo!()
                    }
                }
            "#,
        );
    }

    #[test]
    fn test_add_impl_trait_assoc_types() {
        check_assist(
            generate_impl_trait,
            r#"
                trait $0Foo {
                    type Output;

                    fn foo(&self) -> Self::Output;
                }
            "#,
            r#"
                trait Foo {
                    type Output;

                    fn foo(&self) -> Self::Output;
                }

                impl Foo for ${1:_} {
                    type Output;

                    fn foo(&self) -> Self::Output {
                        $0todo!()
                    }
                }
            "#,
        );
    }

    #[test]
    fn test_add_impl_trait_indent() {
        check_assist(
            generate_impl_trait,
            r#"
                mod foo {
                    mod bar {
                        trait $0Foo {
                            type Output;

                            fn foo(&self) -> Self::Output;
                        }
                    }
                }
            "#,
            r#"
                mod foo {
                    mod bar {
                        trait Foo {
                            type Output;

                            fn foo(&self) -> Self::Output;
                        }

                        impl Foo for ${1:_} {
                            type Output;

                            fn foo(&self) -> Self::Output {
                                $0todo!()
                            }
                        }
                    }
                }
            "#,
        );
    }

    #[test]
    fn test_add_impl_trait_empty() {
        check_assist(
            generate_impl_trait,
            r#"
                trait $0Foo {}
            "#,
            r#"
                trait Foo {}

                impl Foo for ${1:_} {$0}
            "#,
        );
    }
}