use hir::db::HirDatabase;
use ra_syntax::{
    ast::{self, AstNode},
    SmolStr,
    SyntaxKind::USE_ITEM,
    SyntaxNode,
};

use crate::{
    assist_ctx::{ActionBuilder, Assist, AssistCtx},
    auto_import_text_edit, AssistId, ImportsLocator,
};

// Assist: auto_import
//
// If the name is unresolved, provides all possible imports for it.
//
// ```
// fn main() {
//     let map = HashMap<|>::new();
// }
// ```
// ->
// ```
// use std::collections::HashMap;
//
// fn main() {
//     let map = HashMap<|>::new();
// }
// ```
pub(crate) fn auto_import<F: ImportsLocator>(
    ctx: AssistCtx<impl HirDatabase>,
    imports_locator: &mut F,
) -> Option<Assist> {
    let path_to_import: ast::Path = ctx.find_node_at_offset()?;
    let path_to_import_syntax = path_to_import.syntax();
    if path_to_import_syntax.ancestors().find(|ancestor| ancestor.kind() == USE_ITEM).is_some() {
        return None;
    }

    let module = path_to_import_syntax.ancestors().find_map(ast::Module::cast);
    let position = match module.and_then(|it| it.item_list()) {
        Some(item_list) => item_list.syntax().clone(),
        None => {
            let current_file = path_to_import_syntax.ancestors().find_map(ast::SourceFile::cast)?;
            current_file.syntax().clone()
        }
    };
    let source_analyzer = ctx.source_analyzer(&position, None);
    let module_with_name_to_import = source_analyzer.module()?;
    if source_analyzer.resolve_path(ctx.db, &path_to_import).is_some() {
        return None;
    }

    let proposed_imports = imports_locator
        .find_imports(&path_to_import_syntax.to_string())
        .into_iter()
        .filter_map(|module_def| module_with_name_to_import.find_use_path(ctx.db, module_def))
        .filter(|use_path| !use_path.segments.is_empty())
        .take(20)
        .map(|import| import.to_string())
        .collect::<std::collections::BTreeSet<_>>();
    if proposed_imports.is_empty() {
        return None;
    }

    ctx.add_assist_group(
        AssistId("auto_import"),
        format!("Import {}", path_to_import_syntax),
        || {
            proposed_imports
                .into_iter()
                .map(|import| import_to_action(import, &position, &path_to_import_syntax))
                .collect()
        },
    )
}

fn import_to_action(import: String, position: &SyntaxNode, anchor: &SyntaxNode) -> ActionBuilder {
    let mut action_builder = ActionBuilder::default();
    action_builder.label(format!("Import `{}`", &import));
    let import_segments = import.split("::").map(SmolStr::new).collect::<Vec<_>>();
    auto_import_text_edit(position, anchor, &import_segments, action_builder.text_edit_builder());
    action_builder
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::helpers::{
        check_assist_with_imports_locator, check_assist_with_imports_locator_not_applicable,
        TestImportsLocator,
    };

    #[test]
    fn applicable_when_found_an_import() {
        check_assist_with_imports_locator(
            auto_import,
            TestImportsLocator::new,
            r"
            <|>PubStruct

            pub mod PubMod {
                pub struct PubStruct;
            }
            ",
            r"
            <|>use PubMod::PubStruct;

            PubStruct

            pub mod PubMod {
                pub struct PubStruct;
            }
            ",
        );
    }

    #[test]
    fn auto_imports_are_merged() {
        check_assist_with_imports_locator(
            auto_import,
            TestImportsLocator::new,
            r"
            use PubMod::PubStruct1;

            PubStruct2<|>

            pub mod PubMod {
                pub struct PubStruct1;
                pub struct PubStruct2;
            }
            ",
            r"
            use PubMod::{PubStruct2, PubStruct1};

            PubStruct2<|>

            pub mod PubMod {
                pub struct PubStruct1;
                pub struct PubStruct2;
            }
            ",
        );
    }

    #[test]
    fn applicable_when_found_multiple_imports() {
        check_assist_with_imports_locator(
            auto_import,
            TestImportsLocator::new,
            r"
            PubSt<|>ruct

            pub mod PubMod1 {
                pub struct PubStruct;
            }
            pub mod PubMod2 {
                pub struct PubStruct;
            }
            pub mod PubMod3 {
                pub struct PubStruct;
            }
            ",
            r"
            use PubMod1::PubStruct;

            PubSt<|>ruct

            pub mod PubMod1 {
                pub struct PubStruct;
            }
            pub mod PubMod2 {
                pub struct PubStruct;
            }
            pub mod PubMod3 {
                pub struct PubStruct;
            }
            ",
        );
    }

    #[test]
    fn not_applicable_for_already_imported_types() {
        check_assist_with_imports_locator_not_applicable(
            auto_import,
            TestImportsLocator::new,
            r"
            use PubMod::PubStruct;

            PubStruct<|>

            pub mod PubMod {
                pub struct PubStruct;
            }
            ",
        );
    }

    #[test]
    fn not_applicable_for_types_with_private_paths() {
        check_assist_with_imports_locator_not_applicable(
            auto_import,
            TestImportsLocator::new,
            r"
            PrivateStruct<|>

            pub mod PubMod {
                struct PrivateStruct;
            }
            ",
        );
    }

    #[test]
    fn not_applicable_when_no_imports_found() {
        check_assist_with_imports_locator_not_applicable(
            auto_import,
            TestImportsLocator::new,
            "
            PubStruct<|>",
        );
    }

    #[test]
    fn not_applicable_in_import_statements() {
        check_assist_with_imports_locator_not_applicable(
            auto_import,
            TestImportsLocator::new,
            r"
            use PubStruct<|>;

            pub mod PubMod {
                pub struct PubStruct;
            }",
        );
    }
}