use stdx::{format_to, to_lower_snake_case};
use syntax::ast::VisibilityOwner;
use syntax::ast::{self, AstNode, NameOwner};
use test_utils::mark;

use crate::{
    utils::{find_impl_block, find_struct_impl},
    AssistContext, AssistId, AssistKind, Assists,
};

// Assist: generate_enum_match_method
//
// Generate an `is_` method for an enum variant.
//
// ```
// enum Version {
//  Undefined,
//  Minor$0,
//  Major,
// }
// ```
// ->
// ```
// enum Version {
//  Undefined,
//  Minor,
//  Major,
// }
//
// impl Version {
//     /// Returns `true` if the version is [`Minor`].
//     fn is_minor(&self) -> bool {
//         matches!(self, Self::Minor)
//     }
// }
// ```
pub(crate) fn generate_enum_match_method(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
    let variant = ctx.find_node_at_offset::<ast::Variant>()?;
    let variant_name = variant.name()?;
    let parent_enum = variant.parent_enum();
    if !matches!(variant.kind(), ast::StructKind::Unit) {
        mark::hit!(test_gen_enum_match_on_non_unit_variant_not_implemented);
        return None;
    }

    let enum_lowercase_name = to_lower_snake_case(&parent_enum.name()?.to_string());
    let fn_name = to_lower_snake_case(&variant_name.to_string());

    // Return early if we've found an existing new fn
    let impl_def = find_struct_impl(
        &ctx,
        &ast::Adt::Enum(parent_enum.clone()),
        format!("is_{}", fn_name).as_str(),
    )?;

    let target = variant.syntax().text_range();
    acc.add(
        AssistId("generate_enum_match_method", AssistKind::Generate),
        "Generate an `is_` method for an enum variant",
        target,
        |builder| {
            let mut buf = String::with_capacity(512);

            if impl_def.is_some() {
                buf.push('\n');
            }

            let vis = parent_enum.visibility().map_or(String::new(), |v| format!("{} ", v));
            format_to!(
                buf,
                "    /// Returns `true` if the {} is [`{}`].
    {}fn is_{}(&self) -> bool {{
        matches!(self, Self::{})
    }}",
                enum_lowercase_name,
                variant_name,
                vis,
                fn_name,
                variant_name
            );

            let start_offset = impl_def
                .and_then(|impl_def| find_impl_block(impl_def, &mut buf))
                .unwrap_or_else(|| {
                    buf = generate_impl_text(&parent_enum, &buf);
                    parent_enum.syntax().text_range().end()
                });

            builder.insert(start_offset, buf);
        },
    )
}

// Generates the surrounding `impl Type { <code> }` including type and lifetime
// parameters
fn generate_impl_text(strukt: &ast::Enum, code: &str) -> String {
    let mut buf = String::with_capacity(code.len());
    buf.push_str("\n\nimpl ");
    buf.push_str(strukt.name().unwrap().text());
    format_to!(buf, " {{\n{}\n}}", code);
    buf
}

#[cfg(test)]
mod tests {
    use test_utils::mark;

    use crate::tests::{check_assist, check_assist_not_applicable};

    use super::*;

    fn check_not_applicable(ra_fixture: &str) {
        check_assist_not_applicable(generate_enum_match_method, ra_fixture)
    }

    #[test]
    fn test_generate_enum_match_from_variant() {
        check_assist(
            generate_enum_match_method,
            r#"
enum Variant {
    Undefined,
    Minor$0,
    Major,
}"#,
            r#"enum Variant {
    Undefined,
    Minor,
    Major,
}

impl Variant {
    /// Returns `true` if the variant is [`Minor`].
    fn is_minor(&self) -> bool {
        matches!(self, Self::Minor)
    }
}"#,
        );
    }

    #[test]
    fn test_generate_enum_match_already_implemented() {
        check_not_applicable(
            r#"
enum Variant {
    Undefined,
    Minor$0,
    Major,
}

impl Variant {
    fn is_minor(&self) -> bool {
        matches!(self, Self::Minor)
    }
}"#,
        );
    }

    #[test]
    fn test_add_from_impl_no_element() {
        mark::check!(test_gen_enum_match_on_non_unit_variant_not_implemented);
        check_not_applicable(
            r#"
enum Variant {
    Undefined,
    Minor(u32)$0,
    Major,
}"#,
        );
    }

    #[test]
    fn test_generate_enum_match_from_variant_with_one_variant() {
        check_assist(
            generate_enum_match_method,
            r#"enum Variant { Undefi$0ned }"#,
            r#"
enum Variant { Undefined }

impl Variant {
    /// Returns `true` if the variant is [`Undefined`].
    fn is_undefined(&self) -> bool {
        matches!(self, Self::Undefined)
    }
}"#,
        );
    }

    #[test]
    fn test_generate_enum_match_from_variant_with_visibility_marker() {
        check_assist(
            generate_enum_match_method,
            r#"
pub(crate) enum Variant {
    Undefined,
    Minor$0,
    Major,
}"#,
            r#"pub(crate) enum Variant {
    Undefined,
    Minor,
    Major,
}

impl Variant {
    /// Returns `true` if the variant is [`Minor`].
    pub(crate) fn is_minor(&self) -> bool {
        matches!(self, Self::Minor)
    }
}"#,
        );
    }
}