use std::iter;

use ra_syntax::{
    ast::{self, edit::IndentLevel, make},
    AstNode,
};

use crate::{utils::TryEnum, Assist, AssistCtx, AssistId};

// Assist: replace_unwrap_with_match
//
// Replaces `unwrap` a `match` expression. Works for Result and Option.
//
// ```
// enum Result<T, E> { Ok(T), Err(E) }
// fn main() {
//     let x: Result<i32, i32> = Result::Ok(92);
//     let y = x.<|>unwrap();
// }
// ```
// ->
// ```
// enum Result<T, E> { Ok(T), Err(E) }
// fn main() {
//     let x: Result<i32, i32> = Result::Ok(92);
//     let y = match x {
//         Ok(a) => a,
//         _ => unreachable!(),
//     };
// }
// ```
pub(crate) fn replace_unwrap_with_match(ctx: AssistCtx) -> Option<Assist> {
    let method_call: ast::MethodCallExpr = ctx.find_node_at_offset()?;
    let name = method_call.name_ref()?;
    if name.text() != "unwrap" {
        return None;
    }
    let caller = method_call.expr()?;
    let ty = ctx.sema.type_of_expr(&caller)?;
    let happy_variant = TryEnum::from_ty(ctx.sema, &ty)?.happy_case();

    ctx.add_assist(AssistId("replace_unwrap_with_match"), "Replace unwrap with match", |edit| {
        let ok_path = make::path_unqualified(make::path_segment(make::name_ref(happy_variant)));
        let it = make::bind_pat(make::name("a")).into();
        let ok_tuple = make::tuple_struct_pat(ok_path, iter::once(it)).into();

        let bind_path = make::path_unqualified(make::path_segment(make::name_ref("a")));
        let ok_arm = make::match_arm(iter::once(ok_tuple), make::expr_path(bind_path));

        let unreachable_call = make::unreachable_macro_call().into();
        let err_arm = make::match_arm(iter::once(make::placeholder_pat().into()), unreachable_call);

        let match_arm_list = make::match_arm_list(vec![ok_arm, err_arm]);
        let match_expr = make::expr_match(caller.clone(), match_arm_list);
        let match_expr = IndentLevel::from_node(method_call.syntax()).increase_indent(match_expr);

        edit.target(method_call.syntax().text_range());
        edit.set_cursor(caller.syntax().text_range().start());
        edit.replace_ast::<ast::Expr>(method_call.into(), match_expr);
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::helpers::{check_assist, check_assist_target};

    #[test]
    fn test_replace_result_unwrap_with_match() {
        check_assist(
            replace_unwrap_with_match,
            r"
enum Result<T, E> { Ok(T), Err(E) }
fn i<T>(a: T) -> T { a }
fn main() {
    let x: Result<i32, i32> = Result::Ok(92);
    let y = i(x).<|>unwrap();
}
            ",
            r"
enum Result<T, E> { Ok(T), Err(E) }
fn i<T>(a: T) -> T { a }
fn main() {
    let x: Result<i32, i32> = Result::Ok(92);
    let y = <|>match i(x) {
        Ok(a) => a,
        _ => unreachable!(),
    };
}
            ",
        )
    }

    #[test]
    fn test_replace_option_unwrap_with_match() {
        check_assist(
            replace_unwrap_with_match,
            r"
enum Option<T> { Some(T), None }
fn i<T>(a: T) -> T { a }
fn main() {
    let x = Option::Some(92);
    let y = i(x).<|>unwrap();
}
            ",
            r"
enum Option<T> { Some(T), None }
fn i<T>(a: T) -> T { a }
fn main() {
    let x = Option::Some(92);
    let y = <|>match i(x) {
        Some(a) => a,
        _ => unreachable!(),
    };
}
            ",
        );
    }

    #[test]
    fn test_replace_result_unwrap_with_match_chaining() {
        check_assist(
            replace_unwrap_with_match,
            r"
enum Result<T, E> { Ok(T), Err(E) }
fn i<T>(a: T) -> T { a }
fn main() {
    let x: Result<i32, i32> = Result::Ok(92);
    let y = i(x).<|>unwrap().count_zeroes();
}
            ",
            r"
enum Result<T, E> { Ok(T), Err(E) }
fn i<T>(a: T) -> T { a }
fn main() {
    let x: Result<i32, i32> = Result::Ok(92);
    let y = <|>match i(x) {
        Ok(a) => a,
        _ => unreachable!(),
    }.count_zeroes();
}
            ",
        )
    }

    #[test]
    fn replace_unwrap_with_match_target() {
        check_assist_target(
            replace_unwrap_with_match,
            r"
enum Option<T> { Some(T), None }
fn i<T>(a: T) -> T { a }
fn main() {
    let x = Option::Some(92);
    let y = i(x).<|>unwrap();
}
            ",
            r"i(x).unwrap()",
        );
    }
}