//! Completes mod declarations.

use std::iter;

use hir::Module;
use ide_db::{
    FxHashSet, RootDatabase, SymbolKind,
    base_db::{SourceDatabase, VfsPath},
};
use syntax::{AstNode, SyntaxKind, ast};

use crate::{CompletionItem, Completions, context::CompletionContext};

/// Complete mod declaration, i.e. `mod $0;`
pub(crate) fn complete_mod(
    acc: &mut Completions,
    ctx: &CompletionContext<'_>,
    mod_under_caret: &ast::Module,
) -> Option<()> {
    if mod_under_caret.item_list().is_some() {
        return None;
    }

    let _p = tracing::info_span!("completion::complete_mod").entered();

    let mut current_module = ctx.module;
    // For `mod $0`, `ctx.module` is its parent, but for `mod f$0`, it's `mod f` itself, but we're
    // interested in its parent.
    if ctx.original_token.kind() == SyntaxKind::IDENT
        && let Some(module) =
            ctx.original_token.parent_ancestors().nth(1).and_then(ast::Module::cast)
    {
        match ctx.sema.to_def(&module) {
            Some(module) if module == current_module => {
                if let Some(parent) = current_module.parent(ctx.db) {
                    current_module = parent;
                }
            }
            _ => {}
        }
    }

    let module_definition_file =
        current_module.definition_source_file_id(ctx.db).original_file(ctx.db);
    let source_root_id =
        ctx.db.file_source_root(module_definition_file.file_id(ctx.db)).source_root_id(ctx.db);
    let source_root = ctx.db.source_root(source_root_id).source_root(ctx.db);

    let directory_to_look_for_submodules = directory_to_look_for_submodules(
        current_module,
        ctx.db,
        source_root.path_for_file(&module_definition_file.file_id(ctx.db))?,
    )?;

    let existing_mod_declarations = current_module
        .children(ctx.db)
        .filter_map(|module| Some(module.name(ctx.db)?.display(ctx.db, ctx.edition).to_string()))
        .filter(|module| module != ctx.original_token.text())
        .collect::<FxHashSet<_>>();

    let module_declaration_file =
        current_module.declaration_source_range(ctx.db).map(|module_declaration_source_file| {
            module_declaration_source_file.file_id.original_file(ctx.db)
        });

    source_root
        .iter()
        .filter(|&submodule_candidate_file| {
            submodule_candidate_file != module_definition_file.file_id(ctx.db)
        })
        .filter(|&submodule_candidate_file| {
            module_declaration_file.is_none_or(|it| it.file_id(ctx.db) != submodule_candidate_file)
        })
        .filter_map(|submodule_file| {
            let submodule_path = source_root.path_for_file(&submodule_file)?;
            let directory_with_submodule = submodule_path.parent()?;
            let (name, ext) = submodule_path.name_and_extension()?;
            if ext != Some("rs") {
                return None;
            }
            match name {
                "lib" | "main" => None,
                "mod" => {
                    if directory_with_submodule.parent()? == directory_to_look_for_submodules {
                        match directory_with_submodule.name_and_extension()? {
                            (directory_name, None) => Some(directory_name.to_owned()),
                            _ => None,
                        }
                    } else {
                        None
                    }
                }
                file_name if directory_with_submodule == directory_to_look_for_submodules => {
                    Some(file_name.to_owned())
                }
                _ => None,
            }
        })
        .filter(|name| !existing_mod_declarations.contains(name))
        .for_each(|submodule_name| {
            let mut label = submodule_name;
            if mod_under_caret.semicolon_token().is_none() {
                label.push(';');
            }
            let item =
                CompletionItem::new(SymbolKind::Module, ctx.source_range(), &label, ctx.edition);
            item.add_to(acc, ctx.db)
        });

    Some(())
}

fn directory_to_look_for_submodules(
    module: Module,
    db: &RootDatabase,
    module_file_path: &VfsPath,
) -> Option<VfsPath> {
    let directory_with_module_path = module_file_path.parent()?;
    let (name, ext) = module_file_path.name_and_extension()?;
    if ext != Some("rs") {
        return None;
    }
    let base_directory = match name {
        "mod" | "lib" | "main" => Some(directory_with_module_path),
        regular_rust_file_name => {
            if matches!(
                (
                    directory_with_module_path
                        .parent()
                        .as_ref()
                        .and_then(|path| path.name_and_extension()),
                    directory_with_module_path.name_and_extension(),
                ),
                (Some(("src", None)), Some(("bin", None)))
            ) {
                // files in /src/bin/ can import each other directly
                Some(directory_with_module_path)
            } else {
                directory_with_module_path.join(regular_rust_file_name)
            }
        }
    }?;

    module_chain_to_containing_module_file(module, db)
        .into_iter()
        .filter_map(|module| module.name(db))
        .try_fold(base_directory, |path, name| path.join(name.as_str()))
}

fn module_chain_to_containing_module_file(
    current_module: Module,
    db: &RootDatabase,
) -> Vec<Module> {
    let mut path =
        iter::successors(Some(current_module), |current_module| current_module.parent(db))
            .take_while(|current_module| current_module.is_inline(db))
            .collect::<Vec<_>>();
    path.reverse();
    path
}

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

    use crate::tests::check;

    #[test]
    fn lib_module_completion() {
        check(
            r#"
//- /lib.rs
mod $0
//- /foo.rs
fn foo() {}
//- /foo/ignored_foo.rs
fn ignored_foo() {}
//- /bar/mod.rs
fn bar() {}
//- /bar/ignored_bar.rs
fn ignored_bar() {}
"#,
            expect![[r#"
                md bar;
                md foo;
            "#]],
        );
    }

    #[test]
    fn no_module_completion_with_module_body() {
        check(
            r#"
//- /lib.rs
mod $0 {

}
//- /foo.rs
fn foo() {}
"#,
            expect![[r#""#]],
        );
    }

    #[test]
    fn main_module_completion() {
        check(
            r#"
//- /main.rs
mod $0
//- /foo.rs
fn foo() {}
//- /foo/ignored_foo.rs
fn ignored_foo() {}
//- /bar/mod.rs
fn bar() {}
//- /bar/ignored_bar.rs
fn ignored_bar() {}
"#,
            expect![[r#"
                md bar;
                md foo;
            "#]],
        );
    }

    #[test]
    fn main_test_module_completion() {
        check(
            r#"
//- /main.rs
mod tests {
    mod $0;
}
//- /tests/foo.rs
fn foo() {}
"#,
            expect![[r#"
                md foo
            "#]],
        );
    }

    #[test]
    fn directly_nested_module_completion() {
        check(
            r#"
//- /lib.rs
mod foo;
//- /foo.rs
mod $0;
//- /foo/bar.rs
fn bar() {}
//- /foo/bar/ignored_bar.rs
fn ignored_bar() {}
//- /foo/baz/mod.rs
fn baz() {}
//- /foo/moar/ignored_moar.rs
fn ignored_moar() {}
"#,
            expect![[r#"
                md bar
                md baz
            "#]],
        );
    }

    #[test]
    fn nested_in_source_module_completion() {
        check(
            r#"
//- /lib.rs
mod foo;
//- /foo.rs
mod bar {
    mod $0
}
//- /foo/bar/baz.rs
fn baz() {}
"#,
            expect![[r#"
                md baz;
            "#]],
        );
    }

    // FIXME binary modules are not supported in tests properly
    // Binary modules are a bit special, they allow importing the modules from `/src/bin`
    // and that's why are good to test two things:
    // * no cycles are allowed in mod declarations
    // * no modules from the parent directory are proposed
    // Unfortunately, binary modules support is in cargo not rustc,
    // hence the test does not work now
    //
    // #[test]
    // fn regular_bin_module_completion() {
    //     check(
    //         r#"
    //         //- /src/bin.rs
    //         fn main() {}
    //         //- /src/bin/foo.rs
    //         mod $0
    //         //- /src/bin/bar.rs
    //         fn bar() {}
    //         //- /src/bin/bar/bar_ignored.rs
    //         fn bar_ignored() {}
    //     "#,
    //         expect![[r#"
    //             md bar;
    //         "#]],foo
    //     );
    // }

    #[test]
    fn already_declared_bin_module_completion_omitted() {
        check(
            r#"
//- /src/bin.rs crate:main
fn main() {}
//- /src/bin/foo.rs
mod $0
//- /src/bin/bar.rs
mod foo;
fn bar() {}
//- /src/bin/bar/bar_ignored.rs
fn bar_ignored() {}
"#,
            expect![[r#""#]],
        );
    }

    #[test]
    fn name_partially_typed() {
        check(
            r#"
//- /lib.rs
mod f$0
//- /foo.rs
fn foo() {}
//- /foo/ignored_foo.rs
fn ignored_foo() {}
//- /bar/mod.rs
fn bar() {}
//- /bar/ignored_bar.rs
fn ignored_bar() {}
"#,
            expect![[r#"
                md bar;
                md foo;
            "#]],
        );
    }

    #[test]
    fn semi_colon_completion() {
        check(
            r#"
//- /lib.rs
mod foo;
//- /foo.rs
mod bar {
    mod baz$0
}
//- /foo/bar/baz.rs
fn baz() {}
"#,
            expect![[r#"
                md baz;
            "#]],
        );
    }
}