use ide_db::ty_filter::TryEnum;
use syntax::{
    AstNode, T,
    ast::{
        self,
        edit::{AstNodeEdit, IndentLevel},
        syntax_factory::SyntaxFactory,
    },
};

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

// Assist: replace_let_with_if_let
//
// Replaces `let` with an `if let`.
//
// ```
// # enum Option<T> { Some(T), None }
//
// fn main(action: Action) {
//     $0let x = compute();
// }
//
// fn compute() -> Option<i32> { None }
// ```
// ->
// ```
// # enum Option<T> { Some(T), None }
//
// fn main(action: Action) {
//     if let Some(x) = compute() {
//     }
// }
//
// fn compute() -> Option<i32> { None }
// ```
pub(crate) fn replace_let_with_if_let(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
    let let_kw = ctx.find_token_syntax_at_offset(T![let])?;
    let let_stmt = let_kw.parent().and_then(ast::LetStmt::cast)?;
    let init = let_stmt.initializer()?;
    let original_pat = let_stmt.pat()?;

    let target = let_kw.text_range();
    acc.add(
        AssistId::refactor_rewrite("replace_let_with_if_let"),
        "Replace let with if let",
        target,
        |builder| {
            let mut editor = builder.make_editor(let_stmt.syntax());
            let make = SyntaxFactory::with_mappings();
            let ty = ctx.sema.type_of_expr(&init);
            let pat = if let_stmt.let_else().is_some() {
                // Do not add the wrapper type that implements `Try`,
                // since the statement already wraps the pattern.
                original_pat
            } else {
                let happy_variant = ty
                    .and_then(|ty| TryEnum::from_ty(&ctx.sema, &ty.adjusted()))
                    .map(|it| it.happy_case());
                match happy_variant {
                    None => original_pat,
                    Some(var_name) => {
                        make.tuple_struct_pat(make.ident_path(var_name), [original_pat]).into()
                    }
                }
            };
            let init_expr =
                if let_expr_needs_paren(&init) { make.expr_paren(init).into() } else { init };

            let block = make.block_expr([], None);
            let block = block.indent(IndentLevel::from_node(let_stmt.syntax()));
            let if_expr = make.expr_if(
                make.expr_let(pat, init_expr).into(),
                block,
                let_stmt
                    .let_else()
                    .and_then(|let_else| let_else.block_expr().map(ast::ElseBranch::from)),
            );
            let if_stmt = make.expr_stmt(if_expr.into());

            editor.replace(let_stmt.syntax(), if_stmt.syntax());
            editor.add_mappings(make.finish_with_mappings());
            builder.add_file_edits(ctx.vfs_file_id(), editor);
        },
    )
}

fn let_expr_needs_paren(expr: &ast::Expr) -> bool {
    let fake_expr_let =
        ast::make::expr_let(ast::make::tuple_pat(None).into(), ast::make::ext::expr_unit());
    let Some(fake_expr) = fake_expr_let.expr() else {
        stdx::never!();
        return false;
    };
    expr.needs_parens_in_place_of(fake_expr_let.syntax(), fake_expr.syntax())
}

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

    use super::*;

    #[test]
    fn replace_let_try_enum_ref() {
        check_assist(
            replace_let_with_if_let,
            r"
//- minicore: option
fn main(action: Action) {
    $0let x = compute();
}

fn compute() -> &'static Option<i32> { &None }
            ",
            r"
fn main(action: Action) {
    if let Some(x) = compute() {
    }
}

fn compute() -> &'static Option<i32> { &None }
            ",
        )
    }

    #[test]
    fn replace_let_unknown_enum() {
        check_assist(
            replace_let_with_if_let,
            r"
enum E<T> { X(T), Y(T) }

fn main() {
    $0let x = E::X(92);
}
            ",
            r"
enum E<T> { X(T), Y(T) }

fn main() {
    if let x = E::X(92) {
    }
}
            ",
        )
    }

    #[test]
    fn replace_let_logic_and() {
        check_assist(
            replace_let_with_if_let,
            r"
fn main() {
    $0let x = true && false;
}
            ",
            r"
fn main() {
    if let x = (true && false) {
    }
}
            ",
        )
    }

    #[test]
    fn replace_let_logic_or() {
        check_assist(
            replace_let_with_if_let,
            r"
fn main() {
    $0let x = true || false;
}
            ",
            r"
fn main() {
    if let x = (true || false) {
    }
}
            ",
        )
    }

    #[test]
    fn replace_let_else() {
        check_assist(
            replace_let_with_if_let,
            r"
//- minicore: option
fn main() {
    let a = Some(1);
    $0let Some(_) = a else { unreachable!() };
}
            ",
            r"
fn main() {
    let a = Some(1);
    if let Some(_) = a {
    } else { unreachable!() }
}
            ",
        )
    }
}
