use syntax::ast::{AstNode, BinExpr, BinOp};

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

// Assist: flip_binexpr
//
// Flips operands of a binary expression.
//
// ```
// fn main() {
//     let _ = 90 +$0 2;
// }
// ```
// ->
// ```
// fn main() {
//     let _ = 2 + 90;
// }
// ```
pub(crate) fn flip_binexpr(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
    let expr = ctx.find_node_at_offset::<BinExpr>()?;
    let lhs = expr.lhs()?.syntax().clone();
    let rhs = expr.rhs()?.syntax().clone();
    let op_range = expr.op_token()?.text_range();
    // The assist should be applied only if the cursor is on the operator
    let cursor_in_range = op_range.contains_range(ctx.frange.range);
    if !cursor_in_range {
        return None;
    }
    let action: FlipAction = expr.op_kind()?.into();
    // The assist should not be applied for certain operators
    if let FlipAction::DontFlip = action {
        return None;
    }

    acc.add(
        AssistId("flip_binexpr", AssistKind::RefactorRewrite),
        "Flip binary expression",
        op_range,
        |edit| {
            if let FlipAction::FlipAndReplaceOp(new_op) = action {
                edit.replace(op_range, new_op);
            }
            edit.replace(lhs.text_range(), rhs.text());
            edit.replace(rhs.text_range(), lhs.text());
        },
    )
}

enum FlipAction {
    // Flip the expression
    Flip,
    // Flip the expression and replace the operator with this string
    FlipAndReplaceOp(&'static str),
    // Do not flip the expression
    DontFlip,
}

impl From<BinOp> for FlipAction {
    fn from(op_kind: BinOp) -> Self {
        match op_kind {
            kind if kind.is_assignment() => FlipAction::DontFlip,
            BinOp::GreaterTest => FlipAction::FlipAndReplaceOp("<"),
            BinOp::GreaterEqualTest => FlipAction::FlipAndReplaceOp("<="),
            BinOp::LesserTest => FlipAction::FlipAndReplaceOp(">"),
            BinOp::LesserEqualTest => FlipAction::FlipAndReplaceOp(">="),
            _ => FlipAction::Flip,
        }
    }
}

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

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

    #[test]
    fn flip_binexpr_target_is_the_op() {
        check_assist_target(flip_binexpr, "fn f() { let res = 1 ==$0 2; }", "==")
    }

    #[test]
    fn flip_binexpr_not_applicable_for_assignment() {
        check_assist_not_applicable(flip_binexpr, "fn f() { let mut _x = 1; _x +=$0 2 }")
    }

    #[test]
    fn flip_binexpr_works_for_eq() {
        check_assist(flip_binexpr, "fn f() { let res = 1 ==$0 2; }", "fn f() { let res = 2 == 1; }")
    }

    #[test]
    fn flip_binexpr_works_for_gt() {
        check_assist(flip_binexpr, "fn f() { let res = 1 >$0 2; }", "fn f() { let res = 2 < 1; }")
    }

    #[test]
    fn flip_binexpr_works_for_lteq() {
        check_assist(flip_binexpr, "fn f() { let res = 1 <=$0 2; }", "fn f() { let res = 2 >= 1; }")
    }

    #[test]
    fn flip_binexpr_works_for_complex_expr() {
        check_assist(
            flip_binexpr,
            "fn f() { let res = (1 + 1) ==$0 (2 + 2); }",
            "fn f() { let res = (2 + 2) == (1 + 1); }",
        )
    }

    #[test]
    fn flip_binexpr_works_inside_match() {
        check_assist(
            flip_binexpr,
            r#"
            fn dyn_eq(&self, other: &dyn Diagnostic) -> bool {
                match other.downcast_ref::<Self>() {
                    None => false,
                    Some(it) => it ==$0 self,
                }
            }
            "#,
            r#"
            fn dyn_eq(&self, other: &dyn Diagnostic) -> bool {
                match other.downcast_ref::<Self>() {
                    None => false,
                    Some(it) => self == it,
                }
            }
            "#,
        )
    }
}