//! FIXME: write short doc here
use either::Either;
use hir::{HasAttrs, HirDisplay, Semantics, Type};
use ide_db::RootDatabase;
use stdx::format_to;
use syntax::{
    ast::{self, ArgListOwner},
    match_ast, AstNode, SyntaxNode, SyntaxToken, TextRange, TextSize,
};
use test_utils::mark;

use crate::FilePosition;

/// Contains information about a call site. Specifically the
/// `FunctionSignature`and current parameter.
#[derive(Debug)]
pub struct CallInfo {
    pub doc: Option<String>,
    pub signature: String,
    pub active_parameter: Option<usize>,
    parameters: Vec<TextRange>,
}

impl CallInfo {
    pub fn parameter_labels(&self) -> impl Iterator<Item = &str> + '_ {
        self.parameters.iter().map(move |&it| &self.signature[it])
    }
    pub fn parameter_ranges(&self) -> &[TextRange] {
        &self.parameters
    }
    fn push_param(&mut self, param: &str) {
        if !self.signature.ends_with('(') {
            self.signature.push_str(", ");
        }
        let start = TextSize::of(&self.signature);
        self.signature.push_str(param);
        let end = TextSize::of(&self.signature);
        self.parameters.push(TextRange::new(start, end))
    }
}

/// Computes parameter information for the given call expression.
pub(crate) fn call_info(db: &RootDatabase, position: FilePosition) -> Option<CallInfo> {
    let sema = Semantics::new(db);
    let file = sema.parse(position.file_id);
    let file = file.syntax();
    let token = file.token_at_offset(position.offset).next()?;
    let token = sema.descend_into_macros(token);

    let (callable, active_parameter) = call_info_impl(&sema, token)?;

    let mut res =
        CallInfo { doc: None, signature: String::new(), parameters: vec![], active_parameter };

    match callable.kind() {
        hir::CallableKind::Function(func) => {
            res.doc = func.docs(db).map(|it| it.as_str().to_string());
            format_to!(res.signature, "fn {}", func.name(db));
        }
        hir::CallableKind::TupleStruct(strukt) => {
            res.doc = strukt.docs(db).map(|it| it.as_str().to_string());
            format_to!(res.signature, "struct {}", strukt.name(db));
        }
        hir::CallableKind::TupleEnumVariant(variant) => {
            res.doc = variant.docs(db).map(|it| it.as_str().to_string());
            format_to!(
                res.signature,
                "enum {}::{}",
                variant.parent_enum(db).name(db),
                variant.name(db)
            );
        }
        hir::CallableKind::Closure => (),
    }

    res.signature.push('(');
    {
        if let Some(self_param) = callable.receiver_param(db) {
            format_to!(res.signature, "{}", self_param)
        }
        let mut buf = String::new();
        for (pat, ty) in callable.params(db) {
            buf.clear();
            if let Some(pat) = pat {
                match pat {
                    Either::Left(_self) => format_to!(buf, "self: "),
                    Either::Right(pat) => format_to!(buf, "{}: ", pat),
                }
            }
            format_to!(buf, "{}", ty.display(db));
            res.push_param(&buf);
        }
    }
    res.signature.push(')');

    match callable.kind() {
        hir::CallableKind::Function(_) | hir::CallableKind::Closure => {
            let ret_type = callable.return_type();
            if !ret_type.is_unit() {
                format_to!(res.signature, " -> {}", ret_type.display(db));
            }
        }
        hir::CallableKind::TupleStruct(_) | hir::CallableKind::TupleEnumVariant(_) => {}
    }
    Some(res)
}

fn call_info_impl(
    sema: &Semantics<RootDatabase>,
    token: SyntaxToken,
) -> Option<(hir::Callable, Option<usize>)> {
    // Find the calling expression and it's NameRef
    let calling_node = FnCallNode::with_node(&token.parent())?;

    let callable = match &calling_node {
        FnCallNode::CallExpr(call) => sema.type_of_expr(&call.expr()?)?.as_callable(sema.db)?,
        FnCallNode::MethodCallExpr(call) => sema.resolve_method_call_as_callable(call)?,
    };
    let active_param = if let Some(arg_list) = calling_node.arg_list() {
        // Number of arguments specified at the call site
        let num_args_at_callsite = arg_list.args().count();

        let arg_list_range = arg_list.syntax().text_range();
        if !arg_list_range.contains_inclusive(token.text_range().start()) {
            mark::hit!(call_info_bad_offset);
            return None;
        }
        let param = std::cmp::min(
            num_args_at_callsite,
            arg_list
                .args()
                .take_while(|arg| arg.syntax().text_range().end() <= token.text_range().start())
                .count(),
        );

        Some(param)
    } else {
        None
    };
    Some((callable, active_param))
}

#[derive(Debug)]
pub(crate) struct ActiveParameter {
    pub(crate) ty: Type,
    pub(crate) name: String,
}

impl ActiveParameter {
    pub(crate) fn at(db: &RootDatabase, position: FilePosition) -> Option<Self> {
        let sema = Semantics::new(db);
        let file = sema.parse(position.file_id);
        let file = file.syntax();
        let token = file.token_at_offset(position.offset).next()?;
        let token = sema.descend_into_macros(token);
        Self::at_token(&sema, token)
    }

    pub(crate) fn at_token(sema: &Semantics<RootDatabase>, token: SyntaxToken) -> Option<Self> {
        let (signature, active_parameter) = call_info_impl(&sema, token)?;

        let idx = active_parameter?;
        let mut params = signature.params(sema.db);
        if !(idx < params.len()) {
            mark::hit!(too_many_arguments);
            return None;
        }
        let (pat, ty) = params.swap_remove(idx);
        let name = pat?.to_string();
        Some(ActiveParameter { ty, name })
    }
}

#[derive(Debug)]
pub(crate) enum FnCallNode {
    CallExpr(ast::CallExpr),
    MethodCallExpr(ast::MethodCallExpr),
}

impl FnCallNode {
    fn with_node(syntax: &SyntaxNode) -> Option<FnCallNode> {
        syntax.ancestors().find_map(|node| {
            match_ast! {
                match node {
                    ast::CallExpr(it) => Some(FnCallNode::CallExpr(it)),
                    ast::MethodCallExpr(it) => {
                        let arg_list = it.arg_list()?;
                        if !arg_list.syntax().text_range().contains_range(syntax.text_range()) {
                            return None;
                        }
                        Some(FnCallNode::MethodCallExpr(it))
                    },
                    _ => None,
                }
            }
        })
    }

    pub(crate) fn with_node_exact(node: &SyntaxNode) -> Option<FnCallNode> {
        match_ast! {
            match node {
                ast::CallExpr(it) => Some(FnCallNode::CallExpr(it)),
                ast::MethodCallExpr(it) => Some(FnCallNode::MethodCallExpr(it)),
                _ => None,
            }
        }
    }

    pub(crate) fn name_ref(&self) -> Option<ast::NameRef> {
        match self {
            FnCallNode::CallExpr(call_expr) => Some(match call_expr.expr()? {
                ast::Expr::PathExpr(path_expr) => path_expr.path()?.segment()?.name_ref()?,
                _ => return None,
            }),

            FnCallNode::MethodCallExpr(call_expr) => {
                call_expr.syntax().children().filter_map(ast::NameRef::cast).next()
            }
        }
    }

    fn arg_list(&self) -> Option<ast::ArgList> {
        match self {
            FnCallNode::CallExpr(expr) => expr.arg_list(),
            FnCallNode::MethodCallExpr(expr) => expr.arg_list(),
        }
    }
}

#[cfg(test)]
mod tests {
    use expect_test::{expect, Expect};
    use test_utils::mark;

    use crate::fixture;

    fn check(ra_fixture: &str, expect: Expect) {
        let (analysis, position) = fixture::position(ra_fixture);
        let call_info = analysis.call_info(position).unwrap();
        let actual = match call_info {
            Some(call_info) => {
                let docs = match &call_info.doc {
                    None => "".to_string(),
                    Some(docs) => format!("{}\n------\n", docs.as_str()),
                };
                let params = call_info
                    .parameter_labels()
                    .enumerate()
                    .map(|(i, param)| {
                        if Some(i) == call_info.active_parameter {
                            format!("<{}>", param)
                        } else {
                            param.to_string()
                        }
                    })
                    .collect::<Vec<_>>()
                    .join(", ");
                format!("{}{}\n({})\n", docs, call_info.signature, params)
            }
            None => String::new(),
        };
        expect.assert_eq(&actual);
    }

    #[test]
    fn test_fn_signature_two_args() {
        check(
            r#"
fn foo(x: u32, y: u32) -> u32 {x + y}
fn bar() { foo(<|>3, ); }
"#,
            expect![[r#"
                fn foo(x: u32, y: u32) -> u32
                (<x: u32>, y: u32)
            "#]],
        );
        check(
            r#"
fn foo(x: u32, y: u32) -> u32 {x + y}
fn bar() { foo(3<|>, ); }
"#,
            expect![[r#"
                fn foo(x: u32, y: u32) -> u32
                (<x: u32>, y: u32)
            "#]],
        );
        check(
            r#"
fn foo(x: u32, y: u32) -> u32 {x + y}
fn bar() { foo(3,<|> ); }
"#,
            expect![[r#"
                fn foo(x: u32, y: u32) -> u32
                (x: u32, <y: u32>)
            "#]],
        );
        check(
            r#"
fn foo(x: u32, y: u32) -> u32 {x + y}
fn bar() { foo(3, <|>); }
"#,
            expect![[r#"
                fn foo(x: u32, y: u32) -> u32
                (x: u32, <y: u32>)
            "#]],
        );
    }

    #[test]
    fn test_fn_signature_two_args_empty() {
        check(
            r#"
fn foo(x: u32, y: u32) -> u32 {x + y}
fn bar() { foo(<|>); }
"#,
            expect![[r#"
                fn foo(x: u32, y: u32) -> u32
                (<x: u32>, y: u32)
            "#]],
        );
    }

    #[test]
    fn test_fn_signature_two_args_first_generics() {
        check(
            r#"
fn foo<T, U: Copy + Display>(x: T, y: U) -> u32
    where T: Copy + Display, U: Debug
{ x + y }

fn bar() { foo(<|>3, ); }
"#,
            expect![[r#"
                fn foo(x: i32, y: {unknown}) -> u32
                (<x: i32>, y: {unknown})
            "#]],
        );
    }

    #[test]
    fn test_fn_signature_no_params() {
        check(
            r#"
fn foo<T>() -> T where T: Copy + Display {}
fn bar() { foo(<|>); }
"#,
            expect![[r#"
                fn foo() -> {unknown}
                ()
            "#]],
        );
    }

    #[test]
    fn test_fn_signature_for_impl() {
        check(
            r#"
struct F;
impl F { pub fn new() { } }
fn bar() {
    let _ : F = F::new(<|>);
}
"#,
            expect![[r#"
                fn new()
                ()
            "#]],
        );
    }

    #[test]
    fn test_fn_signature_for_method_self() {
        check(
            r#"
struct S;
impl S { pub fn do_it(&self) {} }

fn bar() {
    let s: S = S;
    s.do_it(<|>);
}
"#,
            expect![[r#"
                fn do_it(&self)
                ()
            "#]],
        );
    }

    #[test]
    fn test_fn_signature_for_method_with_arg() {
        check(
            r#"
struct S;
impl S {
    fn foo(&self, x: i32) {}
}

fn main() { S.foo(<|>); }
"#,
            expect![[r#"
                fn foo(&self, x: i32)
                (<x: i32>)
            "#]],
        );
    }

    #[test]
    fn test_fn_signature_for_method_with_arg_as_assoc_fn() {
        check(
            r#"
struct S;
impl S {
    fn foo(&self, x: i32) {}
}

fn main() { S::foo(<|>); }
"#,
            expect![[r#"
                fn foo(self: &S, x: i32)
                (<self: &S>, x: i32)
            "#]],
        );
    }

    #[test]
    fn test_fn_signature_with_docs_simple() {
        check(
            r#"
/// test
// non-doc-comment
fn foo(j: u32) -> u32 {
    j
}

fn bar() {
    let _ = foo(<|>);
}
"#,
            expect![[r#"
                test
                ------
                fn foo(j: u32) -> u32
                (<j: u32>)
            "#]],
        );
    }

    #[test]
    fn test_fn_signature_with_docs() {
        check(
            r#"
/// Adds one to the number given.
///
/// # Examples
///
/// ```
/// let five = 5;
///
/// assert_eq!(6, my_crate::add_one(5));
/// ```
pub fn add_one(x: i32) -> i32 {
    x + 1
}

pub fn do() {
    add_one(<|>
}"#,
            expect![[r##"
                Adds one to the number given.

                # Examples

                ```
                let five = 5;

                assert_eq!(6, my_crate::add_one(5));
                ```
                ------
                fn add_one(x: i32) -> i32
                (<x: i32>)
            "##]],
        );
    }

    #[test]
    fn test_fn_signature_with_docs_impl() {
        check(
            r#"
struct addr;
impl addr {
    /// Adds one to the number given.
    ///
    /// # Examples
    ///
    /// ```
    /// let five = 5;
    ///
    /// assert_eq!(6, my_crate::add_one(5));
    /// ```
    pub fn add_one(x: i32) -> i32 {
        x + 1
    }
}

pub fn do_it() {
    addr {};
    addr::add_one(<|>);
}
"#,
            expect![[r##"
                Adds one to the number given.

                # Examples

                ```
                let five = 5;

                assert_eq!(6, my_crate::add_one(5));
                ```
                ------
                fn add_one(x: i32) -> i32
                (<x: i32>)
            "##]],
        );
    }

    #[test]
    fn test_fn_signature_with_docs_from_actix() {
        check(
            r#"
struct WriteHandler<E>;

impl<E> WriteHandler<E> {
    /// Method is called when writer emits error.
    ///
    /// If this method returns `ErrorAction::Continue` writer processing
    /// continues otherwise stream processing stops.
    fn error(&mut self, err: E, ctx: &mut Self::Context) -> Running {
        Running::Stop
    }

    /// Method is called when writer finishes.
    ///
    /// By default this method stops actor's `Context`.
    fn finished(&mut self, ctx: &mut Self::Context) {
        ctx.stop()
    }
}

pub fn foo(mut r: WriteHandler<()>) {
    r.finished(<|>);
}
"#,
            expect![[r#"
                Method is called when writer finishes.

                By default this method stops actor's `Context`.
                ------
                fn finished(&mut self, ctx: &mut {unknown})
                (<ctx: &mut {unknown}>)
            "#]],
        );
    }

    #[test]
    fn call_info_bad_offset() {
        mark::check!(call_info_bad_offset);
        check(
            r#"
fn foo(x: u32, y: u32) -> u32 {x + y}
fn bar() { foo <|> (3, ); }
"#,
            expect![[""]],
        );
    }

    #[test]
    fn test_nested_method_in_lambda() {
        check(
            r#"
struct Foo;
impl Foo { fn bar(&self, _: u32) { } }

fn bar(_: u32) { }

fn main() {
    let foo = Foo;
    std::thread::spawn(move || foo.bar(<|>));
}
"#,
            expect![[r#"
                fn bar(&self, _: u32)
                (<_: u32>)
            "#]],
        );
    }

    #[test]
    fn works_for_tuple_structs() {
        check(
            r#"
/// A cool tuple struct
struct S(u32, i32);
fn main() {
    let s = S(0, <|>);
}
"#,
            expect![[r#"
                A cool tuple struct
                ------
                struct S(u32, i32)
                (u32, <i32>)
            "#]],
        );
    }

    #[test]
    fn generic_struct() {
        check(
            r#"
struct S<T>(T);
fn main() {
    let s = S(<|>);
}
"#,
            expect![[r#"
                struct S({unknown})
                (<{unknown}>)
            "#]],
        );
    }

    #[test]
    fn works_for_enum_variants() {
        check(
            r#"
enum E {
    /// A Variant
    A(i32),
    /// Another
    B,
    /// And C
    C { a: i32, b: i32 }
}

fn main() {
    let a = E::A(<|>);
}
"#,
            expect![[r#"
                A Variant
                ------
                enum E::A(i32)
                (<i32>)
            "#]],
        );
    }

    #[test]
    fn cant_call_struct_record() {
        check(
            r#"
struct S { x: u32, y: i32 }
fn main() {
    let s = S(<|>);
}
"#,
            expect![[""]],
        );
    }

    #[test]
    fn cant_call_enum_record() {
        check(
            r#"
enum E {
    /// A Variant
    A(i32),
    /// Another
    B,
    /// And C
    C { a: i32, b: i32 }
}

fn main() {
    let a = E::C(<|>);
}
"#,
            expect![[""]],
        );
    }

    #[test]
    fn fn_signature_for_call_in_macro() {
        check(
            r#"
macro_rules! id { ($($tt:tt)*) => { $($tt)* } }
fn foo() { }
id! {
    fn bar() { foo(<|>); }
}
"#,
            expect![[r#"
                fn foo()
                ()
            "#]],
        );
    }

    #[test]
    fn call_info_for_lambdas() {
        check(
            r#"
struct S;
fn foo(s: S) -> i32 { 92 }
fn main() {
    (|s| foo(s))(<|>)
}
        "#,
            expect![[r#"
                (S) -> i32
                (<S>)
            "#]],
        )
    }

    #[test]
    fn call_info_for_fn_ptr() {
        check(
            r#"
fn main(f: fn(i32, f64) -> char) {
    f(0, <|>)
}
        "#,
            expect![[r#"
                (i32, f64) -> char
                (i32, <f64>)
            "#]],
        )
    }
}