use hir::db::HirDatabase;
use ra_syntax::ast::{self, AstNode};
use ra_syntax::{TextRange, TextUnit};

use crate::{Assist, AssistCtx, AssistId};
use super::apply_demorgan::undo_negation;

// Assist: invert_if
//
// Apply invert_if
// This transforms if expressions of the form `if !x {A} else {B}` into `if x {B} else {A}`
// This also works with `!=`. This assist can only be applied with the cursor
// on `if`.
//
// ```
// fn main() {
//     if<|> !y {A} else {B}
// }
// ```
// ->
// ```
// fn main() {
//     if y {B} else {A}
// }
// ```


pub(crate) fn invert_if(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
    let expr = ctx.find_node_at_offset::<ast::IfExpr>()?;
    let expr_range = expr.syntax().text_range();
    let if_range = TextRange::offset_len(expr_range.start(), TextUnit::from_usize(2));
    let cursor_in_range = ctx.frange.range.is_subrange(&if_range);
    if !cursor_in_range {
        return None;
    }

    let cond = expr.condition()?.expr()?.syntax().clone();
    let then_node = expr.then_branch()?.syntax().clone();

    if let ast::ElseBranch::Block(else_block) = expr.else_branch()? {
        let flip_cond = undo_negation(cond.clone())?;
        let cond_range = cond.text_range();
        let else_node = else_block.syntax();
        let else_range = else_node.text_range();
        let then_range = then_node.text_range();
        ctx.add_assist(AssistId("invert_if"), "invert if branches", |edit| {
            edit.target(if_range);
            edit.replace(cond_range, flip_cond);
            edit.replace(else_range, then_node.text());
            edit.replace(then_range, else_node.text());
        })

    } else {
        None
    }


}

#[cfg(test)]
mod tests {
    use super::*;

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

    #[test]
    fn invert_if_remove_inequality() {
        check_assist(invert_if, "fn f() { i<|>f x != 3 {1} else {3 + 2} }", "fn f() { i<|>f x == 3 {3 + 2} else {1} }")
    }

    #[test]
    fn invert_if_remove_not() {
        check_assist(invert_if, "fn f() { <|>if !cond {3 * 2} else {1} }", "fn f() { <|>if cond {1} else {3 * 2} }")
    }

    #[test]
    fn invert_if_doesnt_apply_with_cursor_not_on_if() {
        check_assist_not_applicable(invert_if, "fn f() { if !<|>cond {3 * 2} else {1} }")
    }

    #[test]
    fn invert_if_doesnt_apply_without_negated() {
        check_assist_not_applicable(invert_if, "fn f() { i<|>f cond {3 * 2} else {1} }")
    }
}