use ra_db::SourceDatabase;
use ra_syntax::{
    AstNode, SyntaxNode, TreeArc, ast::{self, NameOwner, VisibilityOwner, TypeAscriptionOwner},
    algo::{find_covering_node, find_node_at_offset, find_leaf_at_offset, visit::{visitor, Visitor}},
};

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

/// Contains the results when hovering over an item
#[derive(Debug, Clone)]
pub struct HoverResult {
    results: Vec<String>,
    exact: bool,
}

impl HoverResult {
    pub fn new() -> HoverResult {
        HoverResult {
            results: Vec::new(),
            // We assume exact by default
            exact: true,
        }
    }

    pub fn extend(&mut self, item: Option<String>) {
        self.results.extend(item);
    }

    pub fn is_exact(&self) -> bool {
        self.exact
    }

    pub fn is_empty(&self) -> bool {
        self.results.is_empty()
    }

    pub fn len(&self) -> usize {
        self.results.len()
    }

    pub fn first(&self) -> Option<&str> {
        self.results.first().map(String::as_str)
    }

    pub fn results(&self) -> &[String] {
        &self.results
    }

    /// Returns the results converted into markup
    /// for displaying in a UI
    pub fn to_markup(&self) -> String {
        let mut markup = if !self.exact {
            let mut msg = String::from("Failed to exactly resolve the symbol. This is probably because rust_analyzer does not yet support traits.");
            if !self.results.is_empty() {
                msg.push_str("  \nThese items were found instead:");
            }
            msg.push_str("\n\n---\n");
            msg
        } else {
            String::new()
        };

        markup.push_str(&self.results.join("\n\n---\n"));

        markup
    }
}

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

    let mut range = None;
    if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(file.syntax(), position.offset) {
        use crate::goto_definition::{ReferenceResult::*, reference_definition};
        let ref_result = reference_definition(db, position.file_id, name_ref);
        match ref_result {
            Exact(nav) => res.extend(doc_text_for(db, nav)),
            Approximate(navs) => {
                // We are no longer exact
                res.exact = false;

                for nav in navs {
                    res.extend(doc_text_for(db, nav))
                }
            }
        }
        if !res.is_empty() {
            range = Some(name_ref.syntax().range())
        }
    } else if let Some(name) = find_node_at_offset::<ast::Name>(file.syntax(), position.offset) {
        let navs = crate::goto_definition::name_definition(db, position.file_id, name);

        if let Some(navs) = navs {
            for nav in navs {
                res.extend(doc_text_for(db, nav))
            }
        }

        if !res.is_empty() && range.is_none() {
            range = Some(name.syntax().range());
        }
    }

    if range.is_none() {
        let node = find_leaf_at_offset(file.syntax(), position.offset).find_map(|leaf| {
            leaf.ancestors().find(|n| ast::Expr::cast(*n).is_some() || ast::Pat::cast(*n).is_some())
        })?;
        let frange = FileRange { file_id: position.file_id, range: node.range() };
        res.extend(type_of(db, frange).map(Into::into));
        range = Some(node.range());
    }

    let range = range?;
    if res.is_empty() {
        return None;
    }
    let res = RangeInfo::new(range, res);
    Some(res)
}

pub(crate) fn type_of(db: &RootDatabase, frange: FileRange) -> Option<String> {
    let file = db.parse(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 = node.ancestors().find_map(ast::FnDef::cast)?;
    let function = hir::source_binder::function_from_source(db, frange.file_id, parent_fn)?;
    let infer = function.infer(db);
    let syntax_mapping = function.body_source_map(db);
    if let Some(expr) = ast::Expr::cast(node).and_then(|e| syntax_mapping.node_expr(e)) {
        Some(infer[expr].to_string())
    } else if let Some(pat) = ast::Pat::cast(node).and_then(|p| syntax_mapping.node_pat(p)) {
        Some(infer[pat].to_string())
    } else {
        None
    }
}

// FIXME: this should not really use navigation target. Rather, approximately
// resolved symbol should return a `DefId`.
fn doc_text_for(db: &RootDatabase, nav: NavigationTarget) -> Option<String> {
    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,
    }
}

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

    fn docs(&self, db: &RootDatabase) -> Option<String> {
        let node = self.node(db)?;
        fn doc_comments<N: ast::DocCommentsOwner>(node: &N) -> Option<String> {
            node.doc_comment_text()
        }

        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::TypeAliasDef>)
            .visit(doc_comments::<ast::ConstDef>)
            .visit(doc_comments::<ast::StaticDef>)
            .visit(doc_comments::<ast::NamedFieldDef>)
            .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)?;

        fn visit_ascribed_node<T>(node: &T, prefix: &str) -> Option<String>
        where
            T: NameOwner + VisibilityOwner + TypeAscriptionOwner,
        {
            let mut string = visit_node(node, prefix)?;

            if let Some(type_ref) = node.ascribed_type() {
                string.push_str(": ");
                type_ref.syntax().text().push_to(&mut string);
            }

            Some(string)
        }

        fn visit_node<T>(node: &T, label: &str) -> Option<String>
        where
            T: NameOwner + VisibilityOwner,
        {
            let mut string =
                node.visibility().map(|v| format!("{} ", v.syntax().text())).unwrap_or_default();
            string.push_str(label);
            node.name()?.syntax().text().push_to(&mut string);
            Some(string)
        }

        visitor()
            .visit(crate::completion::function_label)
            .visit(|node: &ast::StructDef| visit_node(node, "struct "))
            .visit(|node: &ast::EnumDef| visit_node(node, "enum "))
            .visit(|node: &ast::TraitDef| visit_node(node, "trait "))
            .visit(|node: &ast::Module| visit_node(node, "mod "))
            .visit(|node: &ast::TypeAliasDef| visit_node(node, "type "))
            .visit(|node: &ast::ConstDef| visit_ascribed_node(node, "const "))
            .visit(|node: &ast::StaticDef| visit_ascribed_node(node, "static "))
            .visit(|node: &ast::NamedFieldDef| visit_ascribed_node(node, ""))
            .accept(&node)?
    }
}

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

    fn trim_markup(s: &str) -> &str {
        s.trim_start_matches("```rust\n").trim_end_matches("\n```")
    }

    fn check_hover_result(fixture: &str, expected: &[&str]) {
        let (analysis, position) = analysis_and_position(fixture);
        let hover = analysis.hover(position).unwrap().unwrap();

        for (markup, expected) in
            hover.info.results().iter().zip(expected.iter().chain(std::iter::repeat(&"<missing>")))
        {
            assert_eq!(trim_markup(&markup), *expected);
        }

        assert_eq!(hover.info.len(), expected.len());
    }

    #[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.first(), Some("u32"));
    }

    #[test]
    fn hover_shows_fn_signature() {
        // Single file with result
        check_hover_result(
            r#"
            //- /main.rs
            pub fn foo() -> u32 { 1 }

            fn main() {
                let foo_test = fo<|>o();
            }
        "#,
            &["pub fn foo() -> u32"],
        );

        // Multiple results
        check_hover_result(
            r#"
            //- /a.rs
            pub fn foo() -> u32 { 1 }

            //- /b.rs
            pub fn foo() -> &str { "" }

            //- /c.rs
            pub fn foo(a: u32, b: u32) {}

            //- /main.rs
            mod a;
            mod b;
            mod c;

            fn main() {
                let foo_test = fo<|>o();
            }
        "#,
            &["pub fn foo() -> &str", "pub fn foo() -> u32", "pub fn foo(a: u32, b: u32)"],
        );
    }

    #[test]
    fn hover_shows_fn_signature_with_type_params() {
        check_hover_result(
            r#"
            //- /main.rs
            pub fn foo<'a, T: AsRef<str>>(b: &'a T) -> &'a str { }

            fn main() {
                let foo_test = fo<|>o();
            }
        "#,
            &["pub fn foo<'a, T: AsRef<str>>(b: &'a T) -> &'a str"],
        );
    }

    #[test]
    fn hover_shows_fn_signature_on_fn_name() {
        check_hover_result(
            r#"
            //- /main.rs
            pub fn foo<|>(a: u32, b: u32) -> u32 {}

            fn main() {
            }
        "#,
            &["pub fn foo(a: u32, b: u32) -> u32"],
        );
    }

    #[test]
    fn hover_shows_struct_field_info() {
        // Hovering over the field when instantiating
        check_hover_result(
            r#"
            //- /main.rs
            struct Foo {
                field_a: u32,
            }

            fn main() {
                let foo = Foo {
                    field_a<|>: 0,
                };
            }
        "#,
            &["field_a: u32"],
        );

        // Hovering over the field in the definition
        check_hover_result(
            r#"
            //- /main.rs
            struct Foo {
                field_a<|>: u32,
            }

            fn main() {
                let foo = Foo {
                    field_a: 0,
                };
            }
        "#,
            &["field_a: u32"],
        );
    }

    #[test]
    fn hover_const_static() {
        check_hover_result(
            r#"
            //- /main.rs
            fn main() {
                const foo<|>: u32 = 0;
            }
        "#,
            &["const foo: u32"],
        );

        check_hover_result(
            r#"
            //- /main.rs
            fn main() {
                static foo<|>: u32 = 0;
            }
        "#,
            &["static foo: u32"],
        );
    }

    #[test]
    fn hover_some() {
        let (analysis, position) = single_file_with_position(
            "
            enum Option<T> { Some(T) }
            use Option::Some;

            fn main() {
                So<|>me(12);
            }
            ",
        );
        let hover = analysis.hover(position).unwrap().unwrap();
        // not the nicest way to show it currently
        assert_eq!(hover.info.first(), Some("Some<i32>(T) -> Option<T>"));
    }

    #[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.first(), Some("i32"));
    }

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

    #[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<|>;
            }
            ",
        );

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

    #[test]
    fn test_hover_infer_associated_method_result() {
        let (analysis, position) = single_file_with_position(
            "
            struct Thing { x: u32 };

            impl Thing {
                fn new() -> Thing {
                    Thing { x: 0 }
                }
            }

            fn main() {
                let foo_<|>test = Thing::new();
            }
            ",
        );
        let hover = analysis.hover(position).unwrap().unwrap();
        assert_eq!(hover.info.first(), Some("Thing"));
    }
}