use std::iter;

use either::Either;
use ide_db::syntax_helpers::node_ext::is_pattern_cond;
use syntax::{
    ast::{
        self,
        edit::{AstNodeEdit, IndentLevel},
        make, HasLoopBody,
    },
    AstNode, T,
};

use crate::{
    assist_context::{AssistContext, Assists},
    utils::invert_boolean_expression,
    AssistId, AssistKind,
};

// Assist: convert_while_to_loop
//
// Replace a while with a loop.
//
// ```
// fn main() {
//     $0while cond {
//         foo();
//     }
// }
// ```
// ->
// ```
// fn main() {
//     loop {
//         if !cond {
//             break;
//         }
//         foo();
//     }
// }
// ```
pub(crate) fn convert_while_to_loop(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
    let while_kw = ctx.find_token_syntax_at_offset(T![while])?;
    let while_expr = while_kw.parent().and_then(ast::WhileExpr::cast)?;
    let while_body = while_expr.loop_body()?;
    let while_cond = while_expr.condition()?;

    let target = while_expr.syntax().text_range();
    acc.add(
        AssistId("convert_while_to_loop", AssistKind::RefactorRewrite),
        "Convert while to loop",
        target,
        |edit| {
            let while_indent_level = IndentLevel::from_node(while_expr.syntax());

            let break_block = make::block_expr(
                iter::once(make::expr_stmt(make::expr_break(None, None)).into()),
                None,
            )
            .indent(while_indent_level);
            let block_expr = if is_pattern_cond(while_cond.clone()) {
                let if_expr = make::expr_if(while_cond, while_body, Some(break_block.into()));
                let stmts = iter::once(make::expr_stmt(if_expr).into());
                make::block_expr(stmts, None)
            } else {
                let if_cond = invert_boolean_expression(while_cond);
                let if_expr = make::expr_if(if_cond, break_block, None).syntax().clone().into();
                let elements = while_body.stmt_list().map_or_else(
                    || Either::Left(iter::empty()),
                    |stmts| {
                        Either::Right(stmts.syntax().children_with_tokens().filter(|node_or_tok| {
                            // Filter out the trailing expr
                            !node_or_tok
                                .as_node()
                                .is_some_and(|node| ast::Expr::can_cast(node.kind()))
                        }))
                    },
                );
                make::hacky_block_expr(iter::once(if_expr).chain(elements), while_body.tail_expr())
            };

            let replacement = make::expr_loop(block_expr.indent(while_indent_level));
            edit.replace(target, replacement.syntax().text())
        },
    )
}

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

    use super::*;

    #[test]
    fn convert_inside_fn() {
        check_assist(
            convert_while_to_loop,
            r#"
fn main() {
    while$0 cond {
        foo();
    }
}
"#,
            r#"
fn main() {
    loop {
        if !cond {
            break;
        }
        foo();
    }
}
"#,
        );
    }

    #[test]
    fn convert_busy_wait() {
        check_assist(
            convert_while_to_loop,
            r#"
fn main() {
    while$0 cond() {}
}
"#,
            r#"
fn main() {
    loop {
        if !cond() {
            break;
        }
    }
}
"#,
        );
    }

    #[test]
    fn convert_trailing_expr() {
        check_assist(
            convert_while_to_loop,
            r#"
fn main() {
    while$0 cond() {
        bar()
    }
}
"#,
            r#"
fn main() {
    loop {
        if !cond() {
            break;
        }
        bar()
    }
}
"#,
        );
    }

    #[test]
    fn convert_while_let() {
        check_assist(
            convert_while_to_loop,
            r#"
fn main() {
    while$0 let Some(_) = foo() {
        bar();
    }
}
"#,
            r#"
fn main() {
    loop {
        if let Some(_) = foo() {
            bar();
        } else {
            break;
        }
    }
}
"#,
        );
    }

    #[test]
    fn ignore_cursor_in_body() {
        check_assist_not_applicable(
            convert_while_to_loop,
            r#"
fn main() {
    while cond {$0
        bar();
    }
}
"#,
        );
    }

    #[test]
    fn preserve_comments() {
        check_assist(
            convert_while_to_loop,
            r#"
fn main() {
    let mut i = 0;

    $0while i < 5 {
        // comment 1
        dbg!(i);
        // comment 2
        i += 1;
        // comment 3
    }
}
"#,
            r#"
fn main() {
    let mut i = 0;

    loop {
        if i >= 5 {
            break;
        }
        // comment 1
        dbg!(i);
        // comment 2
        i += 1;
        // comment 3
    }
}
"#,
        );

        check_assist(
            convert_while_to_loop,
            r#"
fn main() {
    let v = vec![1, 2, 3];
    let iter = v.iter();

    $0while let Some(i) = iter.next() {
        // comment 1
        dbg!(i);
        // comment 2
    }
}
"#,
            r#"
fn main() {
    let v = vec![1, 2, 3];
    let iter = v.iter();

    loop {
        if let Some(i) = iter.next() {
            // comment 1
            dbg!(i);
            // comment 2
        } else {
            break;
        }
    }
}
"#,
        );
    }
}
