use ra_db::{Cancelable, SyntaxDatabase};
use ra_editor::find_node_at_offset;
use ra_syntax::{
    AstNode, SyntaxNode,
    ast::{self, NameOwner},
    algo::{find_covering_node, visit::{visitor, Visitor}},
};

use crate::{db::RootDatabase, RangeInfo, FilePosition, FileRange, NavigationTarget};

pub(crate) fn hover(
    db: &RootDatabase,
    position: FilePosition,
) -> Cancelable<Option<RangeInfo<String>>> {
    let file = db.source_file(position.file_id);
    let mut res = Vec::new();

    let mut range = None;
    if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(file.syntax(), position.offset) {
        let navs = crate::goto_defenition::reference_defenition(db, position.file_id, name_ref)?;
        for nav in navs {
            res.extend(doc_text_for(db, nav)?)
        }
        if !res.is_empty() {
            range = Some(name_ref.syntax().range())
        }
    }
    if range.is_none() {
        let expr: ast::Expr = ctry!(find_node_at_offset(file.syntax(), position.offset));
        let frange = FileRange {
            file_id: position.file_id,
            range: expr.syntax().range(),
        };
        res.extend(type_of(db, frange)?);
        range = Some(expr.syntax().range());
    };

    let range = ctry!(range);
    if res.is_empty() {
        return Ok(None);
    }
    let res = RangeInfo::new(range, res.join("\n\n---\n"));
    Ok(Some(res))
}

pub(crate) fn type_of(db: &RootDatabase, frange: FileRange) -> Cancelable<Option<String>> {
    let file = db.source_file(frange.file_id);
    let syntax = file.syntax();
    let leaf_node = find_covering_node(syntax, frange.range);
    // if we picked identifier, expand to pattern/expression
    let node = leaf_node
        .ancestors()
        .take_while(|it| it.range() == leaf_node.range())
        .find(|&it| ast::Expr::cast(it).is_some() || ast::Pat::cast(it).is_some())
        .unwrap_or(leaf_node);
    let parent_fn = ctry!(node.ancestors().find_map(ast::FnDef::cast));
    let function = ctry!(hir::source_binder::function_from_source(
        db,
        frange.file_id,
        parent_fn
    )?);
    let infer = function.infer(db)?;
    Ok(infer.type_of_node(node).map(|t| t.to_string()))
}

// FIXME: this should not really use navigation target. Rather, approximatelly
// resovled symbol should return a `DefId`.
fn doc_text_for(db: &RootDatabase, nav: NavigationTarget) -> Cancelable<Option<String>> {
    let result = match (nav.description(db), nav.docs(db)) {
        (Some(desc), Some(docs)) => Some("```rust\n".to_string() + &*desc + "\n```\n\n" + &*docs),
        (Some(desc), None) => Some("```rust\n".to_string() + &*desc + "\n```"),
        (None, Some(docs)) => Some(docs),
        _ => None,
    };

    Ok(result)
}

impl NavigationTarget {
    fn node(&self, db: &RootDatabase) -> Option<SyntaxNode> {
        let source_file = db.source_file(self.file_id);
        let source_file = source_file.syntax();
        let node = source_file
            .descendants()
            .find(|node| node.kind() == self.kind && node.range() == self.range)?
            .owned();
        Some(node)
    }

    fn docs(&self, db: &RootDatabase) -> Option<String> {
        let node = self.node(db)?;
        let node = node.borrowed();
        fn doc_comments<'a, N: ast::DocCommentsOwner<'a>>(node: N) -> Option<String> {
            let comments = node.doc_comment_text();
            if comments.is_empty() {
                None
            } else {
                Some(comments)
            }
        }

        visitor()
            .visit(doc_comments::<ast::FnDef>)
            .visit(doc_comments::<ast::StructDef>)
            .visit(doc_comments::<ast::EnumDef>)
            .visit(doc_comments::<ast::TraitDef>)
            .visit(doc_comments::<ast::Module>)
            .visit(doc_comments::<ast::TypeDef>)
            .visit(doc_comments::<ast::ConstDef>)
            .visit(doc_comments::<ast::StaticDef>)
            .accept(node)?
    }

    /// Get a description of this node.
    ///
    /// e.g. `struct Name`, `enum Name`, `fn Name`
    fn description(&self, db: &RootDatabase) -> Option<String> {
        // TODO: After type inference is done, add type information to improve the output
        let node = self.node(db)?;
        let node = node.borrowed();
        // TODO: Refactor to be have less repetition
        visitor()
            .visit(|node: ast::FnDef| {
                let mut string = "fn ".to_string();
                node.name()?.syntax().text().push_to(&mut string);
                Some(string)
            })
            .visit(|node: ast::StructDef| {
                let mut string = "struct ".to_string();
                node.name()?.syntax().text().push_to(&mut string);
                Some(string)
            })
            .visit(|node: ast::EnumDef| {
                let mut string = "enum ".to_string();
                node.name()?.syntax().text().push_to(&mut string);
                Some(string)
            })
            .visit(|node: ast::TraitDef| {
                let mut string = "trait ".to_string();
                node.name()?.syntax().text().push_to(&mut string);
                Some(string)
            })
            .visit(|node: ast::Module| {
                let mut string = "mod ".to_string();
                node.name()?.syntax().text().push_to(&mut string);
                Some(string)
            })
            .visit(|node: ast::TypeDef| {
                let mut string = "type ".to_string();
                node.name()?.syntax().text().push_to(&mut string);
                Some(string)
            })
            .visit(|node: ast::ConstDef| {
                let mut string = "const ".to_string();
                node.name()?.syntax().text().push_to(&mut string);
                Some(string)
            })
            .visit(|node: ast::StaticDef| {
                let mut string = "static ".to_string();
                node.name()?.syntax().text().push_to(&mut string);
                Some(string)
            })
            .accept(node)?
    }
}

#[cfg(test)]
mod tests {
    use ra_syntax::TextRange;
    use crate::mock_analysis::{single_file_with_position, single_file_with_range};

    #[test]
    fn hover_shows_type_of_an_expression() {
        let (analysis, position) = single_file_with_position(
            "
            pub fn foo() -> u32 { 1 }

            fn main() {
                let foo_test = foo()<|>;
            }
            ",
        );
        let hover = analysis.hover(position).unwrap().unwrap();
        assert_eq!(hover.range, TextRange::from_to(95.into(), 100.into()));
        assert_eq!(hover.info, "u32");
    }

    #[test]
    fn hover_for_local_variable() {
        let (analysis, position) = single_file_with_position("fn func(foo: i32) { fo<|>o; }");
        let hover = analysis.hover(position).unwrap().unwrap();
        assert_eq!(hover.info, "i32");
    }

    #[test]
    fn test_type_of_for_function() {
        let (analysis, range) = single_file_with_range(
            "
            pub fn foo() -> u32 { 1 };

            fn main() {
                let foo_test = <|>foo()<|>;
            }
            ",
        );

        let type_name = analysis.type_of(range).unwrap().unwrap();
        assert_eq!("u32", &type_name);
    }

    // FIXME: improve type_of to make this work
    #[test]
    fn test_type_of_for_expr_1() {
        let (analysis, range) = single_file_with_range(
            "
            fn main() {
                let foo = <|>1 + foo_test<|>;
            }
            ",
        );

        let type_name = analysis.type_of(range).unwrap().unwrap();
        assert_eq!("[unknown]", &type_name);
    }

    // FIXME: improve type_of to make this work
    #[test]
    fn test_type_of_for_expr_2() {
        let (analysis, range) = single_file_with_range(
            "
            fn main() {
                let foo: usize = 1;
                let bar = <|>1 + foo_test<|>;
            }
            ",
        );

        let type_name = analysis.type_of(range).unwrap().unwrap();
        assert_eq!("[unknown]", &type_name);
    }

}