use hir::{AsAssocItem, HasVisibility, ModuleDef, Visibility};
use ide_db::assists::{AssistId, AssistKind};
use itertools::Itertools;
use stdx::to_lower_snake_case;
use syntax::{
    ast::{self, edit::IndentLevel, HasDocComments, HasName},
    AstNode,
};

use crate::assist_context::{AssistContext, Assists};

// Assist: generate_documentation_template
//
// Adds a documentation template above a function definition / declaration.
//
// ```
// pub fn my_$0func(a: i32, b: i32) -> Result<(), std::io::Error> {
//     unimplemented!()
// }
// ```
// ->
// ```
// /// .
// ///
// /// # Examples
// ///
// /// ```
// /// use test::my_func;
// ///
// /// assert_eq!(my_func(a, b), );
// /// ```
// ///
// /// # Errors
// ///
// /// This function will return an error if .
// pub fn my_func(a: i32, b: i32) -> Result<(), std::io::Error> {
//     unimplemented!()
// }
// ```
pub(crate) fn generate_documentation_template(
    acc: &mut Assists,
    ctx: &AssistContext,
) -> Option<()> {
    let name = ctx.find_node_at_offset::<ast::Name>()?;
    let ast_func = name.syntax().parent().and_then(ast::Fn::cast)?;
    if is_in_trait_impl(&ast_func, ctx)
        || !is_public(&ast_func, ctx)?
        || ast_func.doc_comments().next().is_some()
    {
        return None;
    }

    let parent_syntax = ast_func.syntax();
    let text_range = parent_syntax.text_range();
    let indent_level = IndentLevel::from_node(&parent_syntax);

    acc.add(
        AssistId("generate_documentation_template", AssistKind::Generate),
        "Generate a documentation template",
        text_range,
        |builder| {
            // Introduction / short function description before the sections
            let mut doc_lines = vec![introduction_builder(&ast_func, ctx)];
            // Then come the sections
            if let Some(mut lines) = examples_builder(&ast_func, ctx) {
                doc_lines.push("".into());
                doc_lines.append(&mut lines);
            }
            for section_builder in [panics_builder, errors_builder, safety_builder] {
                if let Some(mut lines) = section_builder(&ast_func) {
                    doc_lines.push("".into());
                    doc_lines.append(&mut lines);
                }
            }
            builder.insert(text_range.start(), documentation_from_lines(doc_lines, indent_level));
        },
    )
}

/// Builds an introduction, trying to be smart if the function is `::new()`
fn introduction_builder(ast_func: &ast::Fn, ctx: &AssistContext) -> String {
    || -> Option<String> {
        let hir_func = ctx.sema.to_def(ast_func)?;
        let container = hir_func.as_assoc_item(ctx.db())?.container(ctx.db());
        if let hir::AssocItemContainer::Impl(implementation) = container {
            let ret_ty = hir_func.ret_type(ctx.db());
            let self_ty = implementation.self_ty(ctx.db());

            let is_new = ast_func.name()?.to_string() == "new";
            match is_new && ret_ty == self_ty {
                true => {
                    Some(format!("Creates a new [`{}`].", lifetimes_removed(&self_type(ast_func)?)))
                }
                false => None,
            }
        } else {
            None
        }
    }()
    .unwrap_or_else(|| ".".into())
}

/// Builds an `# Examples` section. An option is returned to be able to manage an error in the AST.
fn examples_builder(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<Vec<String>> {
    let mut lines = string_vec_from(&["# Examples", "", "```"]);
    if is_in_trait_def(ast_func, ctx) {
        lines.push("// Example template not implemented for trait functions".into());
    } else {
        lines.append(&mut gen_ex_template(ast_func, ctx)?)
    };

    lines.push("```".into());
    Some(lines)
}

/// Builds an optional `# Panics` section
fn panics_builder(ast_func: &ast::Fn) -> Option<Vec<String>> {
    match can_panic(ast_func) {
        Some(true) => Some(string_vec_from(&["# Panics", "", "Panics if ."])),
        _ => None,
    }
}

/// Builds an optional `# Errors` section
fn errors_builder(ast_func: &ast::Fn) -> Option<Vec<String>> {
    match return_type(ast_func)?.to_string().contains("Result") {
        true => Some(string_vec_from(&["# Errors", "", "This function will return an error if ."])),
        false => None,
    }
}

/// Builds an optional `# Safety` section
fn safety_builder(ast_func: &ast::Fn) -> Option<Vec<String>> {
    let is_unsafe = ast_func.unsafe_token().is_some();
    match is_unsafe {
        true => Some(string_vec_from(&["# Safety", "", "."])),
        false => None,
    }
}

/// Generates an example template
fn gen_ex_template(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<Vec<String>> {
    let mut lines = Vec::new();
    let is_unsafe = ast_func.unsafe_token().is_some();
    let param_list = ast_func.param_list()?;
    let ref_mut_params = ref_mut_params(&param_list);
    let self_name: Option<String> = self_name(ast_func);

    lines.push(format!("use {};", build_path(ast_func, ctx)?));
    lines.push("".into());
    if let Some(self_definition) = self_definition(ast_func, self_name.as_deref()) {
        lines.push(self_definition);
    }
    for param_name in &ref_mut_params {
        lines.push(format!("let mut {} = ;", param_name))
    }
    // Call the function, check result
    let function_call = function_call(ast_func, &param_list, self_name.as_deref(), is_unsafe)?;
    if returns_a_value(ast_func, ctx) {
        if count_parameters(&param_list) < 3 {
            lines.push(format!("assert_eq!({}, );", function_call));
        } else {
            lines.push(format!("let result = {};", function_call));
            lines.push("assert_eq!(result, );".into());
        }
    } else {
        lines.push(format!("{};", function_call));
    }
    // Check the mutated values
    if is_ref_mut_self(ast_func) == Some(true) {
        lines.push(format!("assert_eq!({}, );", self_name?));
    }
    for param_name in &ref_mut_params {
        lines.push(format!("assert_eq!({}, );", param_name));
    }
    Some(lines)
}

/// Checks if the function is public / exported
fn is_public(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<bool> {
    let hir_func = ctx.sema.to_def(ast_func)?;
    Some(
        hir_func.visibility(ctx.db()) == Visibility::Public
            && all_parent_mods_public(&hir_func, ctx),
    )
}

/// Checks that all parent modules of the function are public / exported
fn all_parent_mods_public(hir_func: &hir::Function, ctx: &AssistContext) -> bool {
    let mut module = hir_func.module(ctx.db());
    loop {
        if let Some(parent) = module.parent(ctx.db()) {
            match ModuleDef::from(module).visibility(ctx.db()) {
                Visibility::Public => module = parent,
                _ => break false,
            }
        } else {
            break true;
        }
    }
}

/// Returns the name of the current crate
fn crate_name(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<String> {
    let krate = ctx.sema.scope(&ast_func.syntax()).module()?.krate();
    Some(krate.display_name(ctx.db())?.to_string())
}

/// `None` if function without a body; some bool to guess if function can panic
fn can_panic(ast_func: &ast::Fn) -> Option<bool> {
    let body = ast_func.body()?.to_string();
    let can_panic = body.contains("panic!(")
        // FIXME it would be better to not match `debug_assert*!` macro invocations
        || body.contains("assert!(")
        || body.contains(".unwrap()")
        || body.contains(".expect(");
    Some(can_panic)
}

/// Helper function to get the name that should be given to `self` arguments
fn self_name(ast_func: &ast::Fn) -> Option<String> {
    self_partial_type(ast_func).map(|name| to_lower_snake_case(&name))
}

/// Heper function to get the name of the type of `self`
fn self_type(ast_func: &ast::Fn) -> Option<String> {
    ast_func
        .syntax()
        .ancestors()
        .find_map(ast::Impl::cast)
        .and_then(|i| i.self_ty())
        .map(|t| (t.to_string()))
}

/// Output the same string as the input, removing lifetimes.
///
/// Lifetimes are detected as starting with a `'` and ending with `,\s*` or before a `>`.
fn lifetimes_removed(with_lifetimes: &str) -> String {
    #[derive(Debug)]
    enum State {
        OutOfLifetime,
        AfterLifetime,
        InLifetime,
    }

    let mut state = State::OutOfLifetime;
    let mut without_lifetimes = String::new();
    for c in with_lifetimes.chars() {
        match state {
            State::OutOfLifetime => {
                if c == '\'' {
                    state = State::InLifetime;
                } else {
                    without_lifetimes.push(c);
                }
            }
            State::InLifetime => {
                if c == ',' {
                    state = State::AfterLifetime;
                } else if c == '>' {
                    without_lifetimes.push(c);
                    state = State::OutOfLifetime;
                }
            }
            State::AfterLifetime => {
                if c == '\'' {
                    state = State::InLifetime;
                } else if !c.is_whitespace() {
                    without_lifetimes.push(c);
                    state = State::OutOfLifetime;
                }
            }
        }
    }
    without_lifetimes
}

/// Heper function to get the name of the type of `self` without generic arguments
fn self_partial_type(ast_func: &ast::Fn) -> Option<String> {
    let mut self_type = self_type(ast_func)?;
    if let Some(idx) = self_type.find(|c| ['<', ' '].contains(&c)) {
        self_type.truncate(idx);
    }
    Some(self_type)
}

/// Helper function to determine if the function is in a trait implementation
fn is_in_trait_impl(ast_func: &ast::Fn, ctx: &AssistContext) -> bool {
    ctx.sema
        .to_def(ast_func)
        .and_then(|hir_func| hir_func.as_assoc_item(ctx.db()))
        .and_then(|assoc_item| assoc_item.containing_trait_impl(ctx.db()))
        .is_some()
}

/// Helper function to determine if the function definition is in a trait definition
fn is_in_trait_def(ast_func: &ast::Fn, ctx: &AssistContext) -> bool {
    ctx.sema
        .to_def(ast_func)
        .and_then(|hir_func| hir_func.as_assoc_item(ctx.db()))
        .and_then(|assoc_item| assoc_item.containing_trait(ctx.db()))
        .is_some()
}

/// Returns `None` if no `self` at all, `Some(true)` if there is `&mut self` else `Some(false)`
fn is_ref_mut_self(ast_func: &ast::Fn) -> Option<bool> {
    let self_param = ast_func.param_list()?.self_param()?;
    Some(self_param.mut_token().is_some() && self_param.amp_token().is_some())
}

/// Helper function to define an variable to be the `self` argument
fn self_definition(ast_func: &ast::Fn, self_name: Option<&str>) -> Option<String> {
    let definition = match is_ref_mut_self(ast_func)? {
        true => format!("let mut {} = ;", self_name?),
        false => format!("let {} = ;", self_name?),
    };
    Some(definition)
}

/// Helper function to determine if a parameter is `&mut`
fn is_a_ref_mut_param(param: &ast::Param) -> bool {
    match param.ty() {
        Some(ast::Type::RefType(param_ref)) => param_ref.mut_token().is_some(),
        _ => false,
    }
}

/// Helper function to build the list of `&mut` parameters
fn ref_mut_params(param_list: &ast::ParamList) -> Vec<String> {
    param_list
        .params()
        .filter_map(|param| match is_a_ref_mut_param(&param) {
            // Maybe better filter the param name (to do this maybe extract a function from
            // `arguments_from_params`?) in case of a `mut a: &mut T`. Anyway managing most (not
            // all) cases might be enough, the goal is just to produce a template.
            true => Some(param.pat()?.to_string()),
            false => None,
        })
        .collect()
}

/// Helper function to build the comma-separated list of arguments of the function
fn arguments_from_params(param_list: &ast::ParamList) -> String {
    let args_iter = param_list.params().map(|param| match param.pat() {
        // To avoid `mut` in the function call (which would be a nonsense), `Pat` should not be
        // written as is so its variants must be managed independently. Other variants (for
        // instance `TuplePat`) could be managed later.
        Some(ast::Pat::IdentPat(ident_pat)) => match ident_pat.name() {
            Some(name) => match is_a_ref_mut_param(&param) {
                true => format!("&mut {}", name),
                false => name.to_string(),
            },
            None => "_".to_string(),
        },
        _ => "_".to_string(),
    });
    Itertools::intersperse(args_iter, ", ".to_string()).collect()
}

/// Helper function to build a function call. `None` if expected `self_name` was not provided
fn function_call(
    ast_func: &ast::Fn,
    param_list: &ast::ParamList,
    self_name: Option<&str>,
    is_unsafe: bool,
) -> Option<String> {
    let name = ast_func.name()?;
    let arguments = arguments_from_params(&param_list);
    let function_call = if param_list.self_param().is_some() {
        format!("{}.{}({})", self_name?, name, arguments)
    } else if let Some(implementation) = self_partial_type(ast_func) {
        format!("{}::{}({})", implementation, name, arguments)
    } else {
        format!("{}({})", name, arguments)
    };
    match is_unsafe {
        true => Some(format!("unsafe {{ {} }}", function_call)),
        false => Some(function_call),
    }
}

/// Helper function to count the parameters including `self`
fn count_parameters(param_list: &ast::ParamList) -> usize {
    param_list.params().count() + if param_list.self_param().is_some() { 1 } else { 0 }
}

/// Helper function to transform lines of documentation into a Rust code documentation
fn documentation_from_lines(doc_lines: Vec<String>, indent_level: IndentLevel) -> String {
    let mut result = String::new();
    for doc_line in doc_lines {
        result.push_str("///");
        if !doc_line.is_empty() {
            result.push(' ');
            result.push_str(&doc_line);
        }
        result.push('\n');
        result.push_str(&indent_level.to_string());
    }
    result
}

/// Helper function to transform an array of borrowed strings to an owned `Vec<String>`
fn string_vec_from(string_array: &[&str]) -> Vec<String> {
    string_array.iter().map(|&s| s.to_owned()).collect()
}

/// Helper function to build the path of the module in the which is the node
fn build_path(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<String> {
    let crate_name = crate_name(ast_func, ctx)?;
    let leaf = self_partial_type(ast_func)
        .or_else(|| ast_func.name().map(|n| n.to_string()))
        .unwrap_or_else(|| "*".into());
    let module_def: ModuleDef = ctx.sema.to_def(ast_func)?.module(ctx.db()).into();
    match module_def.canonical_path(ctx.db()) {
        Some(path) => Some(format!("{}::{}::{}", crate_name, path, leaf)),
        None => Some(format!("{}::{}", crate_name, leaf)),
    }
}

/// Helper function to get the return type of a function
fn return_type(ast_func: &ast::Fn) -> Option<ast::Type> {
    ast_func.ret_type()?.ty()
}

/// Helper function to determine if the function returns some data
fn returns_a_value(ast_func: &ast::Fn, ctx: &AssistContext) -> bool {
    ctx.sema
        .to_def(ast_func)
        .map(|hir_func| hir_func.ret_type(ctx.db()))
        .map(|ret_ty| !ret_ty.is_unit() && !ret_ty.is_never())
        .unwrap_or(false)
}

#[cfg(test)]
mod tests {
    use crate::tests::{check_assist, check_assist_not_applicable};

    use super::*;

    #[test]
    fn not_applicable_on_function_calls() {
        check_assist_not_applicable(
            generate_documentation_template,
            r#"
fn hello_world() {}
fn calls_hello_world() {
    hello_world$0();
}
"#,
        )
    }

    #[test]
    fn not_applicable_in_trait_impl() {
        check_assist_not_applicable(
            generate_documentation_template,
            r#"
trait MyTrait {}
struct MyStruct;
impl MyTrait for MyStruct {
    fn hello_world$0();
}
"#,
        )
    }

    #[test]
    fn not_applicable_if_function_is_private() {
        check_assist_not_applicable(generate_documentation_template, r#"fn priv$0ate() {}"#);
    }

    #[test]
    fn not_applicable_if_function_is_pub_crate() {
        check_assist_not_applicable(
            generate_documentation_template,
            r#"pub(crate) fn pri$0vate() {}"#,
        );
    }

    #[test]
    fn not_applicable_if_function_is_in_private_mod() {
        check_assist_not_applicable(
            generate_documentation_template,
            r#"
mod PrivateModule {
    pub fn pri$0vate() {}
}"#,
        );
    }

    #[test]
    fn not_applicable_if_function_is_in_pub_crate_mod() {
        check_assist_not_applicable(
            generate_documentation_template,
            r#"
pub(crate) mod PrivateModule {
    pub fn pr$0ivate() {}
}"#,
        );
    }

    #[test]
    fn not_applicable_if_function_is_in_non_public_mod_is_recursive() {
        check_assist_not_applicable(
            generate_documentation_template,
            r#"
mod ParentPrivateModule {
    pub mod PrivateModule {
        pub fn pr$0ivate() {}
    }
}"#,
        );
    }

    #[test]
    fn not_applicable_if_function_already_documented() {
        check_assist_not_applicable(
            generate_documentation_template,
            r#"
/// Some documentation here
pub fn $0documented_function() {}
"#,
        );
    }

    #[test]
    fn supports_noop_function() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn no$0op() {}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::noop;
///
/// noop();
/// ```
pub fn noop() {}
"#,
        );
    }

    #[test]
    fn supports_a_parameter() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn no$0op_with_param(_a: i32) {}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::noop_with_param;
///
/// noop_with_param(_a);
/// ```
pub fn noop_with_param(_a: i32) {}
"#,
        );
    }

    #[test]
    fn detects_unsafe_function() {
        check_assist(
            generate_documentation_template,
            r#"
pub unsafe fn no$0op_unsafe() {}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::noop_unsafe;
///
/// unsafe { noop_unsafe() };
/// ```
///
/// # Safety
///
/// .
pub unsafe fn noop_unsafe() {}
"#,
        );
    }

    #[test]
    fn guesses_panic_macro_can_panic() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn panic$0s_if(a: bool) {
    if a {
        panic!();
    }
}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::panics_if;
///
/// panics_if(a);
/// ```
///
/// # Panics
///
/// Panics if .
pub fn panics_if(a: bool) {
    if a {
        panic!();
    }
}
"#,
        );
    }

    #[test]
    fn guesses_assert_macro_can_panic() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn $0panics_if_not(a: bool) {
    assert!(a == true);
}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::panics_if_not;
///
/// panics_if_not(a);
/// ```
///
/// # Panics
///
/// Panics if .
pub fn panics_if_not(a: bool) {
    assert!(a == true);
}
"#,
        );
    }

    #[test]
    fn guesses_unwrap_can_panic() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn $0panics_if_none(a: Option<()>) {
    a.unwrap();
}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::panics_if_none;
///
/// panics_if_none(a);
/// ```
///
/// # Panics
///
/// Panics if .
pub fn panics_if_none(a: Option<()>) {
    a.unwrap();
}
"#,
        );
    }

    #[test]
    fn guesses_expect_can_panic() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn $0panics_if_none2(a: Option<()>) {
    a.expect("Bouh!");
}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::panics_if_none2;
///
/// panics_if_none2(a);
/// ```
///
/// # Panics
///
/// Panics if .
pub fn panics_if_none2(a: Option<()>) {
    a.expect("Bouh!");
}
"#,
        );
    }

    #[test]
    fn checks_output_in_example() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn returns_a_value$0() -> i32 {
    0
}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::returns_a_value;
///
/// assert_eq!(returns_a_value(), );
/// ```
pub fn returns_a_value() -> i32 {
    0
}
"#,
        );
    }

    #[test]
    fn detects_result_output() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn returns_a_result$0() -> Result<i32, std::io::Error> {
    Ok(0)
}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::returns_a_result;
///
/// assert_eq!(returns_a_result(), );
/// ```
///
/// # Errors
///
/// This function will return an error if .
pub fn returns_a_result() -> Result<i32, std::io::Error> {
    Ok(0)
}
"#,
        );
    }

    #[test]
    fn checks_ref_mut_in_example() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn modifies_a_value$0(a: &mut i32) {
    *a = 0;
}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::modifies_a_value;
///
/// let mut a = ;
/// modifies_a_value(&mut a);
/// assert_eq!(a, );
/// ```
pub fn modifies_a_value(a: &mut i32) {
    *a = 0;
}
"#,
        );
    }

    #[test]
    fn stores_result_if_at_least_3_params() {
        check_assist(
            generate_documentation_template,
            r#"
pub fn sum3$0(a: i32, b: i32, c: i32) -> i32 {
    a + b + c
}
"#,
            r#"
/// .
///
/// # Examples
///
/// ```
/// use test::sum3;
///
/// let result = sum3(a, b, c);
/// assert_eq!(result, );
/// ```
pub fn sum3(a: i32, b: i32, c: i32) -> i32 {
    a + b + c
}
"#,
        );
    }

    #[test]
    fn supports_fn_in_mods() {
        check_assist(
            generate_documentation_template,
            r#"
pub mod a {
    pub mod b {
        pub fn no$0op() {}
    }
}
"#,
            r#"
pub mod a {
    pub mod b {
        /// .
        ///
        /// # Examples
        ///
        /// ```
        /// use test::a::b::noop;
        ///
        /// noop();
        /// ```
        pub fn noop() {}
    }
}
"#,
        );
    }

    #[test]
    fn supports_fn_in_impl() {
        check_assist(
            generate_documentation_template,
            r#"
pub struct MyStruct;
impl MyStruct {
    pub fn no$0op() {}
}
"#,
            r#"
pub struct MyStruct;
impl MyStruct {
    /// .
    ///
    /// # Examples
    ///
    /// ```
    /// use test::MyStruct;
    ///
    /// MyStruct::noop();
    /// ```
    pub fn noop() {}
}
"#,
        );
    }

    #[test]
    fn supports_fn_in_trait() {
        check_assist(
            generate_documentation_template,
            r#"
pub trait MyTrait {
    fn fun$0ction_trait();
}
"#,
            r#"
pub trait MyTrait {
    /// .
    ///
    /// # Examples
    ///
    /// ```
    /// // Example template not implemented for trait functions
    /// ```
    fn function_trait();
}
"#,
        );
    }

    #[test]
    fn supports_unsafe_fn_in_trait() {
        check_assist(
            generate_documentation_template,
            r#"
pub trait MyTrait {
    unsafe fn unsafe_funct$0ion_trait();
}
"#,
            r#"
pub trait MyTrait {
    /// .
    ///
    /// # Examples
    ///
    /// ```
    /// // Example template not implemented for trait functions
    /// ```
    ///
    /// # Safety
    ///
    /// .
    unsafe fn unsafe_function_trait();
}
"#,
        );
    }

    #[test]
    fn supports_fn_in_trait_with_default_panicking() {
        check_assist(
            generate_documentation_template,
            r#"
pub trait MyTrait {
    fn function_trait_with_$0default_panicking() {
        panic!()
    }
}
"#,
            r#"
pub trait MyTrait {
    /// .
    ///
    /// # Examples
    ///
    /// ```
    /// // Example template not implemented for trait functions
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if .
    fn function_trait_with_default_panicking() {
        panic!()
    }
}
"#,
        );
    }

    #[test]
    fn supports_fn_in_trait_returning_result() {
        check_assist(
            generate_documentation_template,
            r#"
pub trait MyTrait {
    fn function_tr$0ait_returning_result() -> Result<(), std::io::Error>;
}
"#,
            r#"
pub trait MyTrait {
    /// .
    ///
    /// # Examples
    ///
    /// ```
    /// // Example template not implemented for trait functions
    /// ```
    ///
    /// # Errors
    ///
    /// This function will return an error if .
    fn function_trait_returning_result() -> Result<(), std::io::Error>;
}
"#,
        );
    }

    #[test]
    fn detects_new() {
        check_assist(
            generate_documentation_template,
            r#"
#[derive(Debug, PartialEq)]
pub struct MyGenericStruct<T> {
    pub x: T,
}
impl<T> MyGenericStruct<T> {
    pub fn new$0(x: T) -> MyGenericStruct<T> {
        MyGenericStruct { x }
    }
}
"#,
            r#"
#[derive(Debug, PartialEq)]
pub struct MyGenericStruct<T> {
    pub x: T,
}
impl<T> MyGenericStruct<T> {
    /// Creates a new [`MyGenericStruct<T>`].
    ///
    /// # Examples
    ///
    /// ```
    /// use test::MyGenericStruct;
    ///
    /// assert_eq!(MyGenericStruct::new(x), );
    /// ```
    pub fn new(x: T) -> MyGenericStruct<T> {
        MyGenericStruct { x }
    }
}
"#,
        );
    }

    #[test]
    fn removes_one_lifetime_from_description() {
        check_assist(
            generate_documentation_template,
            r#"
#[derive(Debug, PartialEq)]
pub struct MyGenericStruct<'a, T> {
    pub x: &'a T,
}
impl<'a, T> MyGenericStruct<'a, T> {
    pub fn new$0(x: &'a T) -> Self {
        MyGenericStruct { x }
    }
}
"#,
            r#"
#[derive(Debug, PartialEq)]
pub struct MyGenericStruct<'a, T> {
    pub x: &'a T,
}
impl<'a, T> MyGenericStruct<'a, T> {
    /// Creates a new [`MyGenericStruct<T>`].
    ///
    /// # Examples
    ///
    /// ```
    /// use test::MyGenericStruct;
    ///
    /// assert_eq!(MyGenericStruct::new(x), );
    /// ```
    pub fn new(x: &'a T) -> Self {
        MyGenericStruct { x }
    }
}
"#,
        );
    }

    #[test]
    fn removes_all_lifetimes_from_description() {
        check_assist(
            generate_documentation_template,
            r#"
#[derive(Debug, PartialEq)]
pub struct MyGenericStruct<'a, 'b, T> {
    pub x: &'a T,
    pub y: &'b T,
}
impl<'a, 'b, T> MyGenericStruct<'a, 'b, T> {
    pub fn new$0(x: &'a T, y: &'b T) -> Self {
        MyGenericStruct { x, y }
    }
}
"#,
            r#"
#[derive(Debug, PartialEq)]
pub struct MyGenericStruct<'a, 'b, T> {
    pub x: &'a T,
    pub y: &'b T,
}
impl<'a, 'b, T> MyGenericStruct<'a, 'b, T> {
    /// Creates a new [`MyGenericStruct<T>`].
    ///
    /// # Examples
    ///
    /// ```
    /// use test::MyGenericStruct;
    ///
    /// assert_eq!(MyGenericStruct::new(x, y), );
    /// ```
    pub fn new(x: &'a T, y: &'b T) -> Self {
        MyGenericStruct { x, y }
    }
}
"#,
        );
    }

    #[test]
    fn detects_new_with_self() {
        check_assist(
            generate_documentation_template,
            r#"
#[derive(Debug, PartialEq)]
pub struct MyGenericStruct2<T> {
    pub x: T,
}
impl<T> MyGenericStruct2<T> {
    pub fn new$0(x: T) -> Self {
        MyGenericStruct2 { x }
    }
}
"#,
            r#"
#[derive(Debug, PartialEq)]
pub struct MyGenericStruct2<T> {
    pub x: T,
}
impl<T> MyGenericStruct2<T> {
    /// Creates a new [`MyGenericStruct2<T>`].
    ///
    /// # Examples
    ///
    /// ```
    /// use test::MyGenericStruct2;
    ///
    /// assert_eq!(MyGenericStruct2::new(x), );
    /// ```
    pub fn new(x: T) -> Self {
        MyGenericStruct2 { x }
    }
}
"#,
        );
    }

    #[test]
    fn supports_method_call() {
        check_assist(
            generate_documentation_template,
            r#"
impl<T> MyGenericStruct<T> {
    pub fn co$0nsume(self) {}
}
"#,
            r#"
impl<T> MyGenericStruct<T> {
    /// .
    ///
    /// # Examples
    ///
    /// ```
    /// use test::MyGenericStruct;
    ///
    /// let my_generic_struct = ;
    /// my_generic_struct.consume();
    /// ```
    pub fn consume(self) {}
}
"#,
        );
    }

    #[test]
    fn checks_modified_self_param() {
        check_assist(
            generate_documentation_template,
            r#"
impl<T> MyGenericStruct<T> {
    pub fn modi$0fy(&mut self, new_value: T) {
        self.x = new_value;
    }
}
"#,
            r#"
impl<T> MyGenericStruct<T> {
    /// .
    ///
    /// # Examples
    ///
    /// ```
    /// use test::MyGenericStruct;
    ///
    /// let mut my_generic_struct = ;
    /// my_generic_struct.modify(new_value);
    /// assert_eq!(my_generic_struct, );
    /// ```
    pub fn modify(&mut self, new_value: T) {
        self.x = new_value;
    }
}
"#,
        );
    }
}